The adaptor protein regulator for ubiquitous kinase/c-Cbl-interacting protein of 85kDa (Ruk/CIN85) was found to modulate HER1/EGFR signaling and processes like cell adhesion and apoptosis. Although these features imply a role in carcinogenesis, it is so far unknown how and by which molecular mechanisms Ruk/CIN85 could affect a certain tumor phenotype. By analyzing samples from breast cancer patients, we found high levels of Ruk(l)/CIN85 especially in lymph node metastases from patients with invasive breast adenocarcinomas, suggesting that Ruk(l)/CIN85 contributes to malignancy. Expression of Ruk(l)/CIN85 in weakly invasive breast adenocarcinoma cells deficient of Ruk(l)/CIN85 indeed converted them into more malignant cells. In particular, Ruk(l)/CIN85 reduced the growth rate, decreased cell adhesion, enhanced anchorage-independent growth, increased motility in both transwell migration and wound healing assays as well as affected the response to epidermal growth factor. Thereby, Ruk(l)/CIN85 led to a more rapid and prolonged epidermal growth factor-dependent activation of Src, Akt and ERK1/2 and treatment with the Src inhibitor PP2 and the PI3K inhibitor LY294002 abolished the Ruk(l)/CIN85-dependent changes in cell motility. Together, this study indicates that high levels of Ruk(l)/CIN85 contribute to the conversion of breast adenocarcinoma cells into a more malignant phenotype via modulation of the Src/Akt pathway.

Some types of tumor cells are unable to synthesize arginine from its precursors. They exhibit growth inhibition and decreased viability in vitro and in vivo under enzymatic arginine deprivation. However, prolonged arginine starvation in human may cause vasoconstriction and thrombosis due to the deficit of arginine derivative, nitric oxide (NO), as vasodilator and disaggregant. This problem can be overcome via supplementation with exogenous NO-donors in vivo, which, in turn, may produce either, pro-apoptotic or anti-apoptotic specific effects on cancer cells under arginine restriction. In this study we elucidated the effect of exogenous NO donor, sodium nitroprusside (SNP) on the viability of human Jurkat leukemic cells under arginine deprivation in vitro. We observed that arginine deprivation suppressed cell proliferation and led to a rapid decrease in cell viability concomitant with progression of apoptosis. According to SNP IC50 determination and apoptosis assays, NO-donor at physiological concentration did not promote survival of tumor cells in arginine-free medium. Moreover, SNP cytotoxicity for Jurkat cells was increased upon arginine withdrawal, suggesting that application of NO donor in vivo may potentially enhance the therapeutic effect of arginine deprivation.

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