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Keywords:

  • farnesyl transferase inhibitor;
  • breast cancer dormancy;
  • RhoA GTPase;
  • RhoC GTPase

Abstract

  1. Top of page
  2. Abstract
  3. Material and Methods
  4. Results
  5. Discussion
  6. References
  7. Supporting Information

Farnesyl transferase inhibitors (FTIs) were shown to be effective in modulating tumor growth in Ras-transformed tumor cells. Recent studies have focused on Rho GTPases as putative targets of FTI action. Previously, we demonstrated that FTIs were effective in inhibiting the growth and invasiveness of RhoC GTPase-overexpressing inflammatory breast cancer (IBC) cells however, RhoC activity was increased. In this study, we examine the mechanisms of FTI action on breast cancer cells in culture through modulation of RhoC and RhoA GTPases. We found that FTI inhibition of breast cancer cell growth was reversible and resembled what has been described for an in vitro model of tumor cell dormancy. On FTI treatment, levels of active RhoA decreased significantly, whereas levels of active RhoC increased 3.8-fold. We studied the role of these two GTPases in a fibronectin and basic FGF-induced model of breast cancer cell dormancy. Hypoactivation of RhoA and hyperactivation of RhoC were seen to induce morphology and growth changes consistent with tumor cell dormancy in culture. In addition, the JNK/SAPK pathway was induced on FTI treatment. A pharmacologic inhibitor of the JNK/SAPK pathway significantly reduced the number of dormant cells. This study has implications for the use of FTIs as therapeutic agents as well as potential mechanisms for breast cancer cell dormancy.

Breast cancer is the leading cause of cancer deaths among women in the United States.1 Recent progress in understanding the molecular mechanisms of breast tumor development, coupled with improvements in multi-modality treatments have led to significant increases in the survival of breast cancer patients.1 Inflammatory breast cancer (IBC) is a particularly aggressive form of locally advanced breast cancer that carries 5- and 10-year disease-free survival rates of 38% and 20%, respectively.2 The dismal prognosis of IBC is due to its propensity to invade the dermal lymphatics,3 which is due to expression and activation of RhoC GTPase.3, 4

RhoC is a member of the Rho subfamily of monomeric GTP-binding proteins and is a metastatic switch for a number of cancers.3, 5, 6 In an attempt to develop new therapies to target IBC metastasis, we demonstrated that treatment of the SUM149 IBC cell line with the farnesyl transferase inhibitor (FTI) L-744,832, led to a reversion of the cells growth and invasive capabilities.7 However, we found that inhibition of the SUM149 cells was reversible on FTI withdrawal.

We observed that FTI-treated IBC cells had a distinct flattened morphology, which was accompanied by a dramatic increase in RhoC GTPase activity levels.7 The FTI-induced morphologic changes are reminiscent of what is described for a fibronectin and basic fibroblast growth factor (FGF)-induced in vitro model of breast tumor cell dormancy where a decrease in RhoA GTPase activity is observed.8–10 Although they are highly homologous to each other RhoA and RhoC have distinct functions and can antagonize one another.11, 12 Thus, the possibility of a hypoactive RhoA and a hyperactive RhoC leading to a dormant phenotype in breast cancer cells is viable.

In this study, we set out to determine if altered RhoA and RhoC activity drives dormancy in breast cancer cells, particularly with FTI treatment. We compared the MCF-7 and MDA-MB-231 cells and found that the low metastatic MCF-7 cell line readily entered into dormancy due to hypoactivated RhoA and hyperactivated RhoC. Manipulating Rho levels changed the cells ability to enter or exit dormancy.

Material and Methods

  1. Top of page
  2. Abstract
  3. Material and Methods
  4. Results
  5. Discussion
  6. References
  7. Supporting Information

Cell culture

All breast cancer cell lines were obtained from American Type Culture Collection (Manassas, VA) and maintained as previously described.13 Cell lines were validated for authenticity by the Johns Hopkins Genetics Resource Core Facility. FTI L-744,832 was kindly provided by Dr. George Prendergast (Lankenau Institute for Medical Research) and treatment was performed as previously described.7 For cells treated with the JNK inhibitor SP600125 (EMD Biosciences, Gibbstown, NJ): 1000 MCF-7 and MDA-MB-231 cells were plated at a clonogenic density of 1,000 cells per well in six well plates and treated with 25 μM of FTI for 2 days, 25 μM SP600125, pharmacological inhibitor of JNK, was added in each well in 2 ml of medium along with 0.25% sterile dimethyl sulphoxide (DMSO). As control, 0.25% DMSO in 2 ml of medium was added to the FTI-alone treated cells.

Induction of in vitro dormancy and counting of dormant clones

MCF-7 and MDA-MB-231 breast cancer cells were cultured in DMEM/10% FBS ±10 ng/ml recombinant human (rh)FGF-2 (R&D Systems, Minneapolis, MN) on plastic or extracellular matrix (ECM)-coated plates (BioCoat, Becton Dickinson, Lincoln Park, NJ). Cells were seeded at a clonogenic density of 1,000 cells/well in 6-well plates, visualized at 5, 10 and 15 days by staining with 0.1% crystal violet in 2% ethanol/10 mM sodium borate (pH 9.0) and growing (≥8, 24 or 100 cells on days 5, 10 or 15, respectively) or dormant (≤10 cells) clones were counted. Data are represented as percent growing versus percent dormant colonies with 500 colonies being counted.

Rho activation assays

Active levels of RhoA were measured using the G-LISA™ RhoA Activation Assay Kit, which is based on luminescence (Cytoskeleton, Denver, CO) per the manufacturer's specifications. A RhoC activation assay was performed as previously described using a GST-C214, 14 and detecting with a chicken anti-RhoC developed by our laboratory.

shRNA transfections

Specific shRNAs for human RhoA and RhoC were designed using Ambion's shRNA target finder. Hairpins targeting specific sequences of each GTPase were synthesized and cloned into pSilencer2.1-U6 neo (Ambion, Austin, TX). Details of these hairpin sequences for scrambled control (shScr), RhoA and RhoC were previously described and validated.11 Specific and significant downregulation of RhoA and RhoC was demonstrated using qPCR and western blot analysis. For the shRhoC experiments, cells were plated onto human Fn-coated 22 mm round coverslips (BD Biocoat) and treated with ±10 ng/ml rhFGF-2 (R&D Systems, Minneapolis, MN). Numbers of growing and dormant clones were counted after 5 days in culture. After 5 days, shRhoC was introduced into these cells using FuGENE HD transfection reagent (Roche, Indianapolis, IN), the numbers of dormant and growing clones were counted at 7 days (5 days in culture + 2 days post-transfection) and 10 days (5 days in culture + 5 days post-transfection). For shRhoA experiments, the constructs were transfected into cells by using FuGENE HD transfection reagent (Roche, Indianapolis, IN).

Western blot analysis

Western blotting was performed as previously described.15 Briefly, protein was harvested from cells using RIPA buffer. Lysates were separated by SDS-PAGE on a 4-20% (w/v) gel (Biorad, Hercules, CA) transferred to nitrocellulose, blocked and probed with a monoclonal antibodies for phosphorylated and total JNK, p38, ERK 1/2 (Cell Signaling, Beverly, MA) and β-actin (Sigma, St. Louis, MO). After incubation with a goat anti-rabbit-horseradish peroxidase (HRP) or goat anti-mouse-HRP antibody (Santa Cruz), immunoblots were developed with ECL, exposed to Hyperfilm (Amersham, Piscataway, NJ) and images recorded on an Alpha Image 90 documentation system (Alpha Innotech, San Leandro, CA).

Immunofluorescence

Dormancy was induced for 5 days, the cells fixed with 4% paraformaldehyde and incubated with either Alexa-Fluor488 phalloidin (Cytoskeleton) or mouse anti-Ki67 (Lifespan Biosciences, Seattle, WA). For Ki-67 staining an AlexaFluor 555 goat anti-mouse IgG (Invitrogen Molecular Probes, Carlsbad, CA) secondary antibody was used. Immunoflourescence was performed on a Zeiss LSM5 High-speed Live confocal microscope housed in Delaware Biotechnology Institute. X–Z scans were performed on the same microscope using the same conditions as immunofluorescence.

Results

  1. Top of page
  2. Abstract
  3. Material and Methods
  4. Results
  5. Discussion
  6. References
  7. Supporting Information

FTI treatment induces a dormant phenotype in breast cancer cells

MCF-7 and MDA-MB-231 cells were treated with 25 μM FTI L-744,832. Only the MCF-7 cells had a marked reduction in growth and exhibited a spread-out morphology as shown in Figure 1a. A small number of MDA-MB-231 cells displayed a similar flattened morphology but growth was not significantly altered. Lack of response of the MDA-MB-231 to the FTI R115,777 has been reported.16 On withdrawal of FTI, the MCF-7 cells regained a normal morphology and proliferation pattern. RhoC activation (Figure 1b) was increased on average 3.8- and 1.7-fold in the MCF-7 and MDA-MB-231 cells after FTI treatment, respectively. The increase in MCF-7 active RhoC is similar to what was observed in the IBC cells.7 Figure 1c demonstrates that there is a 4.2- and 2.1-fold reduction in active RhoA in the MCF-7 and MDA-MB-231 cells after FTI treatment, respectively. FTI withdrawal resulted in resumption of MCF-7 cell growth within 48 hr, concurrently levels of active RhoA and RhoC returned to pre-treatment levels (Fig. 1d). These data suggest a reciprocal balance of RhoA and RhoC activation after FTI treatment. Both the altered morphology and drastic changes in RhoA activation are reminiscent of what is described for an in vitro model of breast cancer cell dormancy.8, 9, 17

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Figure 1. (a) Representative images of MCF-7 and MDA-MB-231 cells grown at clonogenic density and treated with 25 μM L-744,832 FTI and stained with crystal violet. MDA-MB-231 cells did not show significant change in growth patterns with FTI treatment, except for a few cells indicated by arrows. (b) Representative RhoC pulldown activation assay of FTI-treated cells. Active and total RhoC were detected using anti-RhoC IgY. Densitometry determined the ratio of active to total RhoC. (c) Results of a G-LISA RhoA luminescence activation assay demonstrating a significant reduction (Students t test, #p < 0.001 and ∧p < 0.005) in active RhoA in FTI-treated cells. Y-axis is relative luminescence units (RLU). All analyses were performed in triplicate. (d) Activation of RhoA and RhoC 48 hr after FTI withdrawal. RhoA activity was measured using the G-LISA RhoA luminescence activation assay. The Y-axis is relative luminescence units (RLU). RhoC activity was measured using a RhoC pulldown activation assay. Densitometry determined the ratio of active and total RhoC.

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Establishing an in vitro model of dormancy

To determine whether altered Rho GTPase activity drives the dormant phenotype, we re-established an in vitro model of dormancy comparing the MCF-7 and MDA-MB-231 cell lines. Growth of MCF-7 cells on fibronectin (Fn) with recombinant human basic fibroblast growth factor (rhFGF-2) has been shown to induce dormancy.8, 9 We began by comparing the number of growing colonies on various substrates in the absence of rhFGF-2: plastic, type I collagen (col) and Fn. There was no significant difference in the number of growing MCF-7 or MDA-MB-231 colonies, defined as having >29 cells, on any of the substrates (data not shown). Figure 2a demonstrates that breast cancer cells grown on plastic in the presence of rhFGF-2 or on Fn alone, form few dormant colonies. However, when grown on Fn in the presence of rhFGF-2 (Fig. 2b) a significant number of MCF-7 cells become dormant. A significant number of MCF-7 cells also become dormant when grown on col in the presence of rhFGF-2; however, the level of significance is less than Fn. The dormant state of the MCF-7 cells was confirmed by the absence of Ki-67 expression, suggesting that the cells are in G0 (Supporting Information Figure S1). In contrast, fewer MDA-MB-231 cells entered dormancy on either Fn or col in the presence of rhFGF-2 and the majority of cells expressed Ki-67. The number of growing MDA-MB-231 cells on Fn was significantly higher than the number of dormant cells. Figure 2c are representative micrographs showing the morphology of MCF-7 cells grown on Fn in the presence and absence of rhFGF-2 over a 15-day period. In the presence of rhFGF-2, the cells have morphology similar to FTI treatment, suggesting involvement of the Rho proteins.7

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Figure 2. (a) Comparison of growing (>29 cells) versus dormant (≤10 cells) MCF-7 and MDA-MB-231 colonies plated on tissue culture plastic with the addition of 10 ng/ml rhFGF-2 or fibronectin alone. Data are represented as percent growing versus percent dormant colonies (n = 500 colonies). The number of growing colonies was significantly higher than the number of dormant colonies (Students t test, *p < 0.0001). (b) MCF-7 cells grown on fibronectin +rhFGF-2 for 5 days had more dormant than growing colonies (#p = 0.0062). MDA-MB-231 cells at the same conditions had significantly (*p = 0.0107) more growing compared with dormant colonies. MCF-7 cells grown on collagen +rhFGF-2 had significantly more dormant colonies compared with growing (∧p = 0.0352). Data are represented as percent growing versus percent dormant colonies (n = 500 colonies). (c) Representative photomicrograph of crystal violet staining of MCF-7 cells plated on fibronectin +rhFGF-2 for 5, 10 and 15 days exhibited a characteristic morphology compared with cells grown on fibronectin alone. (d) Representative confocal images, reflective interference contrast (RIC) and X-Z scans of MCF-7 cells plated on fibronectin ±rhFGF-2. Cells were stained with phalloidin AlexaFluor 488 and Draq5 to visualize the actin cytoskeleton and nucleus, respectively. Images are at the same magnification, the scale bar is 0.037 micron. Areas indicated by arrows in the RIC images are contact points of cellular lamina with the substrate. Z-stack images indicate the thickness of cells at a 90° angle. MCF-7 cells grown in the absence of rhFGF-2 were an average of 8.1 micron, whereas rhFGF-2 treated cells were 1.54-micron thick. All analyses were preformed in triplicate.

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Altered Rho GTPase activity leads to a dormant phenotype

The Rho GTPases are intimately associated with the cytoskeleton; therefore, we visualized actin organization of the MCF-7 cells (Fig. 2d). Compared with the actively growing cells, the actin filaments in the dormant cells were short and disrupted. X–Z scans show that dormant MCF-7 cells have a diameter 10-fold greater than the actively growing cells. In addition, dormant cells are an average of 5.3-fold thinner than growing cells. Reflection interference contrast (RIC) imaging shows that the dormant cells have an increased number of contact points along the cell periphery suggesting that the cells are tightly bound to their substrate.

To determine whether the observed morphology and actin organization was due to altered Rho activity, we measured levels of active RhoA in the MCF-7 and MDA-MB-231 cells growing on Fn ± rhFGF-2. MCF-7 cells growing on Fn +rhFGF-2 had significantly lower levels of active RhoA GTPase as compared with those without rhFGF-2 (Fig. 3a). Under same conditions, the MDA-MB-231 cells did not display a reduction in RhoA activity. Next we measured RhoC activity. Because of technical limitations we were not able to directly perform a RhoC activation assay on the dormant tumor cells. Alternatively, we introduced a RhoC-specific shRNA into the cells and determined the number of dormant and growing colonies over a 5-day period post-transfection. Figure 3b demonstrates that the number of growing colonies significantly increased in shRhoC-transfected MCF-7 cells. Although there was a slight increase in the number of growing shRhoC-treated MDA-MB-231 colonies, it was not significant. These data suggest that active RhoC contributes to dormancy. The MDA-MB-231 cells are one of the few cell lines in which RhoA and RhoC function appears redundant.13, 18, 19 This may explain why these cells are resistant to FTI treatment and do not readily exhibit a dormant phenotype.

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Figure 3. (a) RhoA G-LISA showing a significant decrease (Students t test, #p = 0.0013) in RhoA activity when MCF-7 cells are grown on fibronectin +rhFGF-2. (b) Breast cancer cells grown on fibronectin +rhFGF-2 for 5 days until dormant, transfected with shRNA specific for RhoC and the number of growing versus dormant colonies counted 2 days (7 days total) and 5 days (10 days total) post-transfection. MCF-7 cells transfected with shRhoC had significantly more growing colonies at 5 days compared with controls (@ p = 0.0197). (c) MCF-7 cells transfected with either RhoCG14V or shRhoA had significantly more dormant as compared with growing colonies on fibronectin at 5 days. RhoCG14V and shRhoA together produced significantly more dormant colonies irrespective of substrate (Students t test, *p < 0.001). Data are represented as percent growing versus percent dormant colonies (n = 500 colonies). Analyses were preformed in triplicate. (d) Effectiveness of shRNAs in MCF-7 cells. For depletion of RhoC and RhoA, short hairpin RNAs specific for either RhoC or RhoA were introduced using FuGene HD. Protein was harvested 48 hr after introduction of the shRNA and protein levels detected with RhoC and RhoA-specific antibodies. Densitometry was performed and relative intensity of each GTPase represented as arbitrary units.

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To demonstrate the role of the Rho GTPases in dormancy, we transfected the MCF-7 cells with a constitutively active RhoC (RhoCG14V) and/or shRhoA and plated them on either glass or Fn (Fig. 3c). Because there are concerns that dnRhoA is not absolutely specific for RhoA and may have effects on RhoC, we decided to use shRhoA (unpublished observations). Similar problems in specificity were observed with dnRac1, which affected Rac3 activity.20 There was no significant difference between cells that were untreated and those that were treated with the scrambled control (shScr). A significant increase in dormant colonies was observed when cells were grown on Fn and had either forced increased RhoC activity or decreased RhoA expression. When RhoCG14V and shRhoA were introduced together, a significant increase in dormant colonies was observed regardless of substrate. This suggests that both increased RhoC and decreased RhoA activity are required for dormancy and that attachment to Fn impinges on both the RhoA and RhoC pathway. Figure 3d demonstrates the efficacy of the short hairpin RNAs used to deplete RhoC and RhoA GTPases. There was an 83% and 65% decrease in RhoC and RhoA protein levels, respectively, with the introduction of shRNAs.

Next, we transfected the MCF-7 cells with shRhoC and treated with FTI. Downregulation of RhoC expression led to a decreased number of cells responding to FTI treatment, suggesting a role for RhoC in FTI action (Fig. 4a). We then treated the MCF-7 and MDA-MB-231 cells with FTI to determine which signaling pathways were being activated. Since the mitogen activated protein kinases are common downstream effectors of Rho GTPases and have been implicated in tumor cell dormancy, we investigated the activation levels of p38MAPK, ERK1/2. No changes were observed in activation of the p38 or ERK 1/2 pathways (Supporting Information Figure S2) therefore we next examined the JNK stress-activated protein kinase pathway. As shown in Figure 4b, activation of the JNK/SAPK pathway in the MCF-7 was increased, whereas remaining relatively unchanged in the MDA-MB-231 cells.

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Figure 4. (a) Introduction of a shRhoC into MCF-7 cells led to significant increase (∧p < 0.005) in the number of growing cells when treated with 25 μM FTI L-744,832. Data are represented as percent growing versus percent dormant colonies (n = 500 colonies). (b) Representative western blot analysis for active phosphorylated and total JNK/SAPK in FTI treated MCF-7 and MDA-MB-231 cells. Protein lysates were harvested as described in the Material and Methods section, protein was separated by SDS-PAGE and transferred to nitrocellulose. The nitrocellulose membrane was probed with an antibody specific for phosphorylated JNK/SAPK. The membrane was then stripped and reprobed with an antibody for total JNK/SAPK. Actin was used as a loading control. (c) Treatment of MCF-7 and MDA-MB-231 cells with 25 μM JNK/SAPK inhibitor SB600125 (iJNK) or DMSO control in the presence of 25 μM FTI for 48 hr, followed by analysis for growing versus dormant cells. MCF-7 cells treated with iJNK and FTI had significantly fewer dormant cells (p = 0.0058) and significantly more growing cells (p = 0.0012) than cells treated with FTI alone. There were no significant changes in the MDA-MB-231 cells.

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Finally, to determine whether JNK/SAPK signaling is involved in FTI-induced dormancy, we treated cells with SP600125, a pharmacologic inhibitor of JNK and FTI. Figure 4c shows that pharmacologic inhibition of JNK/SAPK leads to a significant 50% decrease in nongrowing MCF-7 cells with a significant reciprocal increase in growing cells as compared with cells treated with FTI alone. In contrast, JNK inhibition did not change the ratio of nongrowing to grown MDA-MB-231 cells.

Discussion

  1. Top of page
  2. Abstract
  3. Material and Methods
  4. Results
  5. Discussion
  6. References
  7. Supporting Information

FTIs were designed to treat Ras-based tumors; however, their clinical application proved to be disappointing.21 The effect of FTI on Ras-induced transformation was later shown to be because of interference of Rho activity, specifically RhoB GTPase.22, 23 Our group demonstrated that IBC cells were susceptible to FTI treatment, with a reversion of the RhoC GTPase phenotype.7 FTI reversion of the RhoC-induced IBC phenotype could be phenocopied with the introduction of a RhoB GTPase that could only be geranylgeranylated.7 The morphology of the FTI-treated cells resemble that of cells induced in vitro to undergo dormancy.

Breast tumor cell dormancy is a significant clinical problem that faces every woman with breast cancer.24, 25 Many have hypothesized that the microenvironment influences whether a tumor cell will grow or become senescent over an indefinite period of time and that the Rho GTPases and cytoskeleton are involved.8, 17, 26 Here, we demonstrate that FTI treatment or induction of dormancy with Fn +rhFGF-2, reversibly perturbs RhoA and RhoC GTPase activation; specifically hypoactivating RhoA and hyperactivating RhoC. Recent reports from Wieder's group suggest that decreased RhoA GTPase activity is necessary but not sufficient to induce dormancy.9, 10 In these studies, general Rho inhibitors such as C3 exoenzyme and a dnRhoA were used, which could also drive down the activation of RhoC GTPase thereby supporting our observations. Interestingly, MDA-MB-231 cells are reported to be refractory to FTI R115,777 treatment.16 In this study, we saw that they have a limited response to FTI L-744,832. This may be due to an apparent redundancy in RhoA and RhoC function in these cells.13, 18, 19

RhoC GTPase is involved in conferring a metastatic phenotype to a number of cancers.27 Our laboratory has also shown that RhoC expression is a prognostic marker for metastatic spread of small breast cancers that are <1 cm in size.28, 29 Thus, a small breast cancer that may appear to have a good prognosis, may have already spread. RhoA GTPase is also suggested to play a role in progression to metastasis in a number of cancers.30, 31 However, overwhelming evidence suggests that increased activation of RhoA leads to stable stress-fiber formation and reduced motility.32–34 Therefore, to be effective in producing a motile cell the Rho GTPases must dynamically and transiently cycle from a “GDP-off” to a “GTP-on” back to a “GDP-off” state.34–36 This transient cycling can be influenced by the microenvironment of the cancer cell.36 Thus, the concept that Rho GTPases can control the senescent state of a cell is viable. Rho-induced cytoskeletal shape change could alter gene transcription, potentially activating cellular programs such as those for autophagy.37, 38 Indeed, it is shown that signaling via ECM or changes in tissue architecture alters gene transcription by rearranging the nuclear lamina (reviewed in Ref.39). This in turn leads to expression of autophagy genes.38 We are in the process of exploring this hypothesis in FTI treated and Fn + rhFGF-2 treated breast cancer cells.

We found that the JNK/SAPK pathway was activated in the FTI treated cells and that inhibition of JNK decreased the number of dormant cells in vitro. It has been suggested that in the case of angiogenic dormancy, increased p38 relative to ERK 1/2 signaling is indicative of dormancy.40 Previous work from our laboratory suggests that RhoC GTPase signals for motility through p38 signaling in pancreatic and IBC cells.15, 41 Therefore, it is interesting that increased RhoC activity did not affect phospho-p38 levels in either the MCF-7 or MDA-MB-231 cells. Previous reports suggest that treatment of MCF-7 cells with rhFGF-2 induces apoptosis.42 Therefore, Fn may be acting as the main external signal to promote survival of the MCF-7 cells.43 Induction of the JNK/SAPK pathway is also shown to be required for the induction of autophagy through different pathways.44, 45 Much of the literature points to Rac1 GTPase in the activation of the JNK/SAPK pathway, particularly in ECM signaling in MCF-7 cells.46 However, there are reports that RhoC GTPase can induce JNK signaling in 293T cells.47 We have previously shown in PC-3 prostate cancer cells that RhoC activity negatively modulates Rac1 expression and activation.11, 48 A reciprocal relationship between RhoA and Rac1 was also previously reported by John Collards group.49 We therefore are beginning to determine whether there is a similar interplay between RhoC, RhoA and Rac1 in FTI treated or Fn + rhFGF-2 treated breast cancer cells.

Taken together our data suggests that FTI treatment of some breast cancer cells may work by placing the cells in a state of dormancy. In vitro, dormancy can be driven by perturbing RhoA and RhoC GTPase activation. These data may suggest new applications for FTI treatment of breast cancer, possibly identifying patients that would benefit from adjuvant FTI treatment.50 Potentially, FTI-induced dormancy could synchronize tumor cells; FTI withdrawal would allow growth making the cells more susceptible to chemotherapeutics. In addition, this study may shed light on the mechanisms of breast cancer dormancy.

References

  1. Top of page
  2. Abstract
  3. Material and Methods
  4. Results
  5. Discussion
  6. References
  7. Supporting Information
  • 1
    American Cancer Society. Cancer Facts & Figures 2010 ed., 2010. pamphlet.
  • 2
    Woodward WA, Cristofanilli M. Inflammatory breast cancer. Semin Radiat Oncol 2009; 19: 25665.
  • 3
    Radunsky GS, van Golen KL. The current understanding of the molecular determinants of inflammatory breast cancer metastasis. Clin Exp Metastasis 2006; 66: 61520.
  • 4
    van Golen KL, Wu ZF, Qiao XT, Bao LW, Merajver SD. RhoC GTPase, a novel transforming oncogene for human mammary epithelial cells that partially recapitulates the inflammatory breast cancer phenotype. Cancer Res 2000; 60: 58328.
  • 5
    Wheeler AP, Ridley AJ. Why three Rho proteins? RhoA, RhoB, RhoC, and cell motility. Exp Cell Res 2004; 301: 439.
  • 6
    Hakem A, Sanchez-Sweatman O, You-Ten A, Duncan G, Wakeham A, Khokha R, Mak TW. RhoC is dispensable for embryogenesis and tumor initiation but essential for metastasis. Genes Dev 2005; 19: 19749.
  • 7
    van Golen KL, Bao L, DiVito MM, Wu Z, Prendergast GC, Merajver SD. Reversion of RhoC GTPase-induced inflammatory breast cancer phenotype by treatment with a farnesyl transferase inhibitor. Mol Cancer Ther 2002; 1: 57583.
  • 8
    Korah R, Boots M, Wieder R. Integrin alpha5beta1 promotes survival of growth-arrested breast cancer cells: an in vivo paradigm for breast cancer dormancy in bone marrow. Cancer Res 2004; 64 451422.
  • 9
    Barrios J, Wieder R. Dual FGF-2 and intergrin alpha5beta1 signaling mediate GRAF-induced RhoA inactivation in a model of breast cancer dormancy. Cancer Microenviron 2009; 2: 3347.
  • 10
    Barrios J, Wieder R. FGF-2-induced breast cancer dormancy in an in vitro model is maintained through integrin alpha5beta1 signaling. Am Assoc Cancer Res 2007; 100.
  • 11
    Sequeira L, Dubyk CW, Riesenberger TA, Cooper CR, van Golen KL. Rho GTPases in PC-3 prostate cancer cell morphology, invasion and tumor cell diapadesis. Clin Exp Metastasis 2008; 25: 56979.
  • 12
    Simpson KJ, Dugan AS, Mercurio AM. Functional analysis of the contribution of RhoA and RhoC GTPases to invasive breast carcinoma. Cancer Res 2004; 64: 8694701.
  • 13
    Zhang X, Lin M, van Golen KL, Itoh K, Yee D. Multiple signaling pathways are activated during insulin-like growth factor-I (IGF-1) stimulated breast cancer cell migration. Breast Cancer Res Treat 2005; 93: 15968.
  • 14
    Zondag GC, Evers EE, ten Klooster JP, Janssen L, van der Kammen RA, Collard JG. Oncogenic Ras downregulates Rac activity, which leads to increased Rho activity and epithelial-mesenchymal transition. J Cell Biol 2000; 149: 77582.
  • 15
    van Golen KL, Bao LW, Pan Q, Miller FR, Wu ZF, Merajver SD. Mitogen activated protein kinase pathway is involved in RhoC GTPase induced motility, invasion and angiogenesis in inflammatory breast cancer. Clin Exp Metastasis 2002; 19: 30111.
  • 16
    Warnberg F, White D, Anderson E, Knox F, Clarke RB, Morris J, Bundred NJ. Effect of a farnesyl transferase inhibitor (R115777) on ductal carcinoma in situ of the breast in a human xenograft model and on breast and ovarian cancer cell growth in vitro and in vivo. Breast Cancer Res 2006; 8: R21.
  • 17
    Barkan D, Kleinman H, Simmons JL, Asmussen H, Kamaraju AK, Hoenorhoff MJ, Liu ZY, Costes SV, Cho EH, Lockett S, Khanna C, Chambers AF, et al. Inhibition of metastatic outgrowth from single dormant tumor cells by targeting the cytoskeleton. Cancer Res 2008; 68: 624150.
  • 18
    Pille JY, Denoyelle C, Varet J, Bertrand JR, Soria J, Opolon P, Lu H, Pritchard LL, Vannier JP, Malvy C, Soria C, Li H. Anti-RhoA and anti-RhoC siRNAs inhibit the proliferation and invasiveness of MDA-MB-231 breast cancer cells in vitro and in vivo. Mol Ther 2005; 11: 26774.
  • 19
    Pille JY, Li H, Bertand JR, Pritchard LL, Opolon P, Maksimenko A, Lu H, Vannier JP, Soria J, Malvy C, Soria C. Intravenous delivery of anti-RhoA small interferring RNA loaded in nonoparticles of chitosan in mice: safety and efficacy in xenografted aggressive breast cancer. Hum Mol Genet 2008; 17: 101926.
  • 20
    Chan AY, Coniglio SJ, Chuang YY, Michaelson D, Knaus UG, Philips MR, Symons M. Roles of the Rac1 and Rac3 GTPases in human tumor cell invasion. Oncogene 2005; 24: 78219.
  • 21
    Gibbs JB, Oliff A, Kohl NE. Farnesyltransferase inhibitors: Ras research yields a potential cancer therapeutic. Cell 1994; 77: 1758.
  • 22
    Lebowitz PF, Davide JP, Prendergast GC. Evidence that farnesyltransferase inhibitors suppress Ras transformation by interfering with Rho activity. Mol Cell Biol 1995; 15: 661322.
  • 23
    Du W, Lebowitz PF, Prendergast GC. Cell growth inhibition by farnesyltransferase inhibitors is mediated by gain of geranylgeranylated RhoB. Mol Cell Biol 1999; 19: 183140.
  • 24
    Metzler A. Dormancy and breast cancer. J Surg Oncol 1990; 43: 1818.
  • 25
    Naumov GN, MacDonald IC, Weinmeister PM, Kerkvliet N, Nadkarni KV, Wilson SM, Morris VL, Groom AC, Chambers AF. Persistence of solitary mammary carcinoma cells in a secondary site: a possible contributor to dormancy. Cancer Res 2002; 62: 21628.
  • 26
    Goodison S, Kawai K, Hihara J, Jiang P, Yang M, Urquidi V, Hoffman R, Tarin D. Prolonged dormancy and site-specific growth potenitial of cancer cells spontaneously disseminated from non-metastatic breast cancer tumors as revealed by labeling with green fluorescent proteins. Clin Cancer Res 2003; 9: 380814.
  • 27
    van Golen KL. RhoC GTPase in cancer progression and metastasis. In: van GolenKL, ed. The Rho GTPases in cancered. New York: Springer, 2010. 12334.
  • 28
    Kleer CG, van Golen KL, Zhang Y, Wu ZF, Rubin MA, Merajver SD. Characterization of RhoC expression in benign and malignant breast disease: a potential new marker for small breast carcinomas with metastatic ability. Am J Pathol 2002; 160: 57984.
  • 29
    Kleer CG, Griffith KA, Sabel MS, Gallagher G, van Golen KL, Wu ZF, Merajver SD. RhoC-GTPase is a novel tissue biomarker associated with biologically aggressive carcinomas of the breast. Breast Cancer Res Treat 2005; 93: 10110.
  • 30
    del Peso L, Hernandez-Alcoceba R, Embade N, Carnero A, Esteve P, Paje C, Lacal JC. Rho proteins induce metastatic properties in vivo. Oncogene 1997; 15: 304757.
  • 31
    Fritz G, Just I, Kaina B. Rho GTPases are over-expressed in human tumors. Int J Cancer 1999; 81: 6827.
  • 32
    Burbelo PD, Miyamoto S, Utani A, Brill S, Yamada KM, Hall A, Yamada Y. p190-B, a new member of the Rho GAP family, and Rho are induced to cluster after integrin cross-linking. J Biol Chem 1995; 270: 3091926.
  • 33
    Tatsis N, Lannigan DA, Macara IG. The function of the p190 Rho GTPase-activating protein is controlled by its N-terminal GTP binding domain. J Biol Chem 1998; 273: 346318.
  • 34
    Moorman JP, Luu D, Wickham J, Bobak DA, Hahn CS. A balance of signaling by Rho family small GTPases RhoA, Rac1 and Cdc42 coordinates cytoskeletal morphology but not cell survival. Oncogene 1999; 18: 4757.
  • 35
    Tang Y, Yu J, Field J. Signals from the Ras, Rac, and Rho GTPases converge on the Pak protein kinase in Rat-1 fibroblasts. Mol Cell Biol 1999; 19: 188191.
  • 36
    Lin M, van Golen KL. Rho-regulatory proteins in breast cancer cell motility and invasion. Breast Cancer Res Treat 2004; 84: 4960.
  • 37
    Gewirtz DA. Autophagy, senescence and tumor dormancy in cancer therapy. Autophagy 2009; 12324.
  • 38
    Lock R, Debnath J. Extracellular matrix regulation of autophagy. Curr Opin Cell Biol 2008; 20: 5838.
  • 39
    Lelievre SA. Contributions of extracellular matrix signaling and tissue architecture to nuclear mechanisms and spatial organization of gene expression control. Biochim Biophys Acta 2009; 1790: 92535.
  • 40
    Aguirro Ghiso J, Estrada Y, Liu D, Ossowski L. ERKmapk activity as a determinant of tumor growth and dormancy; regulation by p38sapk. Cancer Res 2003; 63: 168495.
  • 41
    Lin M, DiVito MM, Merajver SD, Boyanapalli M, van Golen KL. Regulation of pancreatic cancer cell migration and invasion by RhoC GTPase and caveolin-1. Mol Cancer 2005; 4: 21.
  • 42
    Maloof P, Wang Q, Wang H, Stein D, Denny TN, Yahalom J, Fenig E, Wieder R. Overexpression of basic fibroblast growth factor (FGF-2) downregulates Bcl-2 and promotes apoptosis in MCF-7 human breast cancer cells. Breast Cancer Res Treat 1999; 56: 15367.
  • 43
    Danen EH, Yamada KM. Fibronectin, integrins, and growth control. J Cell Physiol 2001; 189: 113.
  • 44
    Lorin S, Pierron G, Ryan KM, Codogno P, Djavaheri-Mergny M. Evidence for the interplay between JNK and p53-DRAM signalling pathways in the regulation of autophagy. Autophagy 2010; 6: 1534.
  • 45
    Zhang Y, Wu Y, Cheng Y, Zhao Z, Tashiro S, Onodera S, Ikejima T. Fas-mediated autophagy requires JNK activation in HeLa cells. Biochem Biophys Res Commun 2008; 377: 120510.
  • 46
    Xie JW, Haslam SZ. Extracellular matrix, Rac1 signaling, and estrogen-induced proliferation in MCF-7 breast cancer cells. Breast Cancer Res Treat 2008; 110: 25768.
  • 47
    Teramoto H, Crespo P, Coso OA, Igishi T, Xu N, Gutkind JS. The small GTP-binding protein rho activates c-Jun N-terminal kinases/stress-activated protein kinases in human kidney 293T cells. Evidence for a Pak-independent signaling pathway. J Biol Chem 1996; 271: 257314.
  • 48
    Yao H, Dashner EJ, van Golen CM, van Golen KL. RhoC GTPase is required for PC-3 prostate cancer cell invasion but not motility. Oncogene 2006; 25: 228596.
  • 49
    Sander EE, ten Klooster JP, van Delft S, van der Kammen RA, Collard JG. Rac downregulates Rho activity: reciprocal balance between both GTPases determines cellular morphology and migratory behavior. J Cell Biol 1999; 147: 100922.
  • 50
    Prendergast GC. Farnesyltransferase inhibitors: antineoplastic mechanism and clinical prospects. Curr Opin Cell Biol 2000; 12: 16673.

Supporting Information

  1. Top of page
  2. Abstract
  3. Material and Methods
  4. Results
  5. Discussion
  6. References
  7. Supporting Information

Additional supporting information may be found in the online version of this article.

FilenameFormatSizeDescription
IJC_25655_sm_suppfig-1.tif2704KSupporting Figure 1
IJC_25655_sm_suppfig-2.tif16906KSupporting Figure 2

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