Spotlight

• Truncated Receptor Halts 3T3 Morphological Transformation

Bjøndal et al., pp. 961–969

Ras proteins are known to be important for normal signal transduction and cell growth. Mutations in this gene family occur with high frequency in human tumors, although the explicit connection between Ras mutations and cancer is not fully understood.

In this paper, Bjøndal et al., used a retroviral suppressor screen to identify potential genes that can oppose Ki-ras induced morphological changes — such as cell rounding and foci formation — in 3T3 cells. One gene identified was a cDNA for murine receptor for activated kinase (RACK1) that contained a 150 nucleotide deletion at the 5′ end.

The authors found that the stable expression of this truncated RACK1 protein — known as RACK1ΔWD1 — inhibited Ki-Ras-induced morphological changes in 3T3 cells. Furthermore, RACK1ΔWD1 expression appeared to influence the Raf-MEK-ERK signaling pathway, as substantially reduced levels of activated ERK were found in RACK1ΔWD1/Ki-Ras cells compared to Ki-Ras cells.

Using immunoprecipitation, the truncated RACK1 protein appeared able to bind wtRACK1 and RACK1 interacting partners, such as PKC isoforms α, βI and δ. However, in RACK1ΔWD1-expressing cells, translocation of PKC isoforms were reduced in response to PKC-activating phorbol ester (TPA) treatment.

The authors cannot draw conclusions as to whether the effects of truncated RACK1 are physiologically functional or a dominant negative phenomenon. However, this study highlights the importance of RACK1 in Ki-ras-mediated morphological cell transformation and unravels a mechanism whereby this process can be inhibited.

• Do Vitamins Protect Against Oral Premalignant Lesions

Maserejian et al., pp. 970–977

Oxidative DNA damage, which is exacerbated by tobacco use, is known to trigger oral cancer. Potential antioxidant effects of vitamins A, C, E, and carotenoids—particularly through the dietary consumption of fruits and vegetables—have been observed. However, the evidence to prove that these substances have a protective effect in oral cancer has been inconsistent.

In this report Maserejian et al., evaluated vitamin A, C, E, α-carotene, β-carotene, β-cryptoxanthin, lycopene, lutein and tobacco consumption with respect to the risk of developing oral premalignant lesions (OPL). Using the Health Professionals Follow-up Study—a prospective study—over 42,000 men were monitored every 2 years with a detailed dietary, lifestyle and medical history questionnaire.

Some 207 confirmed OPL cases were identified. Dietary, but not supplemental vitamin C, was significantly associated with almost a 50% decreased risk of developing OPL. A decreased risk was also observed with α-carotene, and β-cryptoxanthin. Vitamin E, on the other hand, showed a statistically significant increased risk: relative risk (RR) = 1.84, 95% CI 1.06-3.19.

When the authors analyzed the risk associated with vitamin intake and tobacco use, they found that former smokers with high dietary vitamin C intake had a 50% lower risk of OPL. However, an increased risk of OPL was observed in individuals with a high intake of β-carotene and supplemental vitamin A. Most striking was the association between current smokers and vitamin E intake. Individuals taking 600 IU/ vitamin E per day had a 3-fold higher risk of developing OPL than smokers who did not use vitamin E supplements.

This prospective study confirms the protective effects of dietary vitamin C against developing OPL. Importantly, it highlights the potentially negative effects of vitamin E and β-carotene, particularly in the context of supplementation.

• Tracking of Dendritic Cells Using Magnetic Resonance

Verdijk et al., pp. 978–984

The use of dendritic cells (DC) to mount an anti-tumor response in patients has met with variable success. One current obstacle is ascertaining whether the DCs have arrived at the correct anatomical site.

Recently Verdijk et al., used magnetic resonance imaging (MRI) to successfully track superparamagnetic iron oxide (SPIO)-labeled DCs in melanoma patients. In the current study, the same authors investigated the detection threshold of MRI tracking of DCs in vitro and whether labeling cells affects DC function.

SPIO particles approved for clinical use were found to be efficiently endocytosed by DCs. Concentrations of up to 30pg Fe/cell did not appear to compromise cell viability. Using gelatin-embedded DCs loaded with 25pg Fe/cell, only 100 and 50 cells/mm³ were needed for imaging using magnetic field strengths of 3 and 7 T, respectively. Bearing in mind the likely decrease in signal intensity in vivo – due to tissue heterogenicity – the authors estimated that cell densities of 1000 and 500 cells/mm³, for 3 and 7 T imaging, respectively, would be required for detection in vivo. The authors then demonstrated that SPIO-DCS had similar surface marker expression to nontreated DCs and, importantly, retained antigen processing and presentation functions, as confirmed by mixed lymphocyte reaction and antigen-specific T-cell responses. Finally, DC migration apparently was not affected by SPIO labeling.

This thorough report shows that SPIO labeling of DCS is a sensitive technique that does not appear to affect DC function. The use of MRI allows excellent spatial resolution, and thus, together with its noninvasiveness, could be very useful in determining whether immunotherapeutic cells reach their correct anatomical destination.