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- Materials and Methods
The role of insulin-like growth factor binding protein 5 (IGFBP5) in tumorigenesis and development of cancer is not well-defined. IGFBP5 has been shown to either stimulate or inhibit cell proliferation via an IGF-dependent mechanism and to promote cell proliferation and migration in an IGF-independent manner. In the authors’ previous study, IGFBP5 was found to be significantly up-regulated in lymph node metastases compared with their paired primary breast cancers. To further determine the role of IGFBP5 in breast cancer development and to evaluate its clinical significance in breast cancer, the mRNA expression level was detected in 30 normal breast tissues, 108 primary tumors, and 30 lymph node metastases using real time reverse transcription–polymerase chain reaction. The expression levels were correlated with several clinical parameters, including clinical stage, pathologic tumor size, axillary lymph node status, nuclear grade, estrogen receptor status, Her2 status, and local relapse or distant metastasis of the patients. As a result, the expression of IGFBP5 mRNA correlated positively with the invasion of axillary lymph nodes and the status of hormonal receptor. Furthermore, overexpression of IGFBP5 was associated with poor outcome of breast cancer patients with positive lymph nodes and negative ER. Thus, the expression level of IGFBP5 may contribute to the development of breast cancer and is a prognostic factor for breast cancer. (Cancer Sci 2007; 98: 1592–1596)
The insulin-like growth factor binding protein 5 (IGFBP5) belongs to a protein family of at least six members that binds to insulin-like growth factor (IGF). In humans, the IGFBP5 gene spans 33 kb and is located on 2q33–q36. The mature IGFBP5 protein consists of 252 amino acids and has a molecular mass of approximately 29 kDa. IGFBP5 was initially recognized as a secreted protein that binds to IGF with high affinity by its N-terminal motif and modulates their mitogenic and anti-apoptotic effects by either inhibiting or augmenting the interaction of IGF with their cell-surface receptor (IGF-IR). IGFBP5 has been shown to inhibit the proliferative responses of skeletal muscle cells(1) and breast cancer cells(2) to IGF-I. In contrast, in bone,(3) fibroblast,(4) osteoblasts,(5) and vascular smooth muscle cells,(6) IGFBP5 has been found to potentiate the effect of IGF on cell growth. The complexity of the cellular function of IGFBP and its regulation is further revealed by recent studies that have shown that IGFBP5 also stimulates cell growth,(7,8) migration,(6,9,10) and cell attachment to extracellular matrix (ECM)(11,12) through IGF-independent mechanisms. Thus, the role of IGFBP5 in cancer is far from being clear.
In the authors’ previous study of breast cancer tissues,(13) it was found that IGFBP5 was significantly up-regulated in lymph node metastases relative to their paired primary cancers, suggesting that IGFBP5 may play an important role in the metastasis of breast cancer. Additional studies have supported the notion that IGFBP5 overexpression contributes to metastasis and poor prognosis of cancer. Wang et al. have demonstrated a strong correlation between overexpression of IGFBP5 and the histologic grade of ovarian cancer and glioblastoma.(14,15) And up-regulated IGFBP5 was included in the ‘poor prognosis signature’ in a study by van't Veer et al.(16) To explore the role of IGFBP5 in the development of breast cancer, and to evaluate the clinical significance of IGFBP5 in the diagnosis and prognosis of breast cancer, the IGFBP5 mRNA expression levels were measured in 30 normal breast tissues, 108 primary tumors, and 30 lymph node metastases using real-time reverse transcription–polymerase chain reaction (RT-PCR). The association between IGFBP5 expression and several clinicopathologic parameters, including clinical stage, pathologic tumor size, axillary lymph node status, nuclear grade, estrogen receptor (ER) status, Her2 status, and local relapse or distant metastasis, was analyzed.
- Top of page
- Materials and Methods
In the present study, the mRNA level of IGFBP5 was found to be up-regulated in breast cancers relative to normal breast tissues, overexpressed in breast cancers with positive axillary lymph nodes compared to cancers with negative lymph nodes, and positively correlated with the status of hormonal receptors. No significant difference of IGFBP5 was found between the mRNA levels of IGFBP5 and tumor size, clinical stage and nuclear grade. Furthermore, overexpression of IGFBP5 was associated with poor outcome of breast cancer patients with positive lymph nodes and negative ER.
IGFBP5 has been shown to affect cell proliferation and apoptosis differently under different conditions and contexts. IGFBP5 has been shown to inhibit proliferation of breast cancer via IGF-dependent mechanism in vitro,(2) whereas other studies have shown that IGFBP5 also stimulates cell proliferation(8) of breast cancer in an IGF-independent manner in vitro. IGFBP5 has been shown to induce apoptosis by inhibition of IGF-signaling,(2) enhance tumor necrosis factor (TNF)-induced growth inhibition,(18) increase expression of the pro-apoptotic regulator BAX,(2) and decrease the expression of the anti-apoptotic BCL2.(2) On the other hand, IGFBP5 has been shown to promote cell proliferation by inhibiting ceramide-induced apoptosis,(8,19) and to inhibit cell death induced by arginine–glycine–aspartate peptide (RGD).(19) Moreover, IGFBP5 may facilitate metastasis by increasing cell attachment to the extracellular matrix (ECM) and base membrane,(12,19) and by enhancing cell migration.(11) These contrary molecular mechanisms suggest a potential balancing function of IGFBP5 in cell proliferation and apoptosis, and that the balance and functions cross-talk with other cellular pathways in the cells. The present results suggest that overexpression of IGFBP5 mRNA may play a positive role in breast tumorigenesis and development, indicating that the proliferation and metastasis stimulation effects of IGFBP5 may be predominant over the anti-proliferation effect in vivo.
Yee et al. showed a positive correlation between the expression of IGFBP5 protein and ER and PR expression status in axillary lymph node-negative breast cancers, but showed no relationship between IGFBP5 expression and the disease-free survival of lymph node-negative breast cancer patients.(20) Consistent with their report, the present results showed that the mRNA of IGFBP5 was down-regulated in cases with negative ER/PR compared to cases with positive ER/PR, and that overexpression of IGFBP5 could not predict the disease-free survival of node-negative breast cancer patients. However, it was found that IGFBP5 could be a powerful prognostic factor for patients with positive lymph nodes and negative ER. Although Wang et al. demonstrated a strong correlation between overexpression of IGFBP5 and high histologic grade of ovarian cancer and glioblastoma,(14,15) this correlation was not found in breast cancers for the first time in the present study.
IGFBP5 was up-regulated in breast cancer and could distinguish most of the normal breast and cancer tissues, indicating that it might be a potential adjuvant molecular marker for diagnosis of breast cancer. Although the mRNA levels of IGFBP5 were not able to accurately classify axillary lymph node status, high levels of IGFBP5 were associated with higher false-negative rates of clinical palpation in ‘group without palpable nodes,’ and low levels of IGFBP5 with higher false positive rate of clinical palpable nodes in the ‘group with palpable nodes.’ So if IGFBP5 mRNA in needle biopsy specimens could be examined preoperatively, it could serve as an adjuvant factor of clinical palpation to predict axillary lymph node status and to guide surgery and systemic therapy.
Breast cancer is a hormone-dependent disease. ER/PR status reflects the level of estrogen and progesterone in vivo, and is a predictor of clinical outcome of breast cancer patients. Hewitt et al. found that the expression of IGFBP5 could be up-regulated by estrogen, indicating that the signal regulation of estrogen and progesterone might be involved in the complex functions of IGFBP5 in the development of breast cancer.(21) Furthermore, overexpression of IGFBP5 was a powerful prognostic predictor for breast cancer patients with positive lymph nodes and negative ER. Thus, IGFBP5 may play an important role in the breast cancer biologic process and might serve as a molecular marker to guide patient-tailored therapy.