Anti-neoplastic drugs increase caveolin-1-dependent migration, invasion and metastasis of cancer cells.

Expression of the scaffolding protein Caveolin-1 (CAV1) enhances migration and invasion of metastatic cancer cells. Yet, CAV1 also functions as a tumor suppressor in early stages of cancer, where expression is suppressed by epigenetic mechanisms. Thus, we sought to identify stimuli/mechanisms that revert epigenetic CAV1 silencing in cancer cells and evaluate how this affects their metastatic potential. We reasoned that restricted tissue availability of anti-neoplastic drugs during chemotherapy might expose cancer cells to sub-therapeutic concentrations, which activate signaling pathways and the expression of CAV1 to favor the acquisition of more aggressive traits. Here, we used in vitro [2D, invasion] and in vivo (metastasis) assays, as well as genetic and biochemical approaches to address this question. Colon and breast cancer cells were identified where CAV1 levels were low due to epigenetic suppression and could be reverted by treatment with the methyltransferase inhibitor 5'-azacytidine. Exposure of these cells to anti-neoplastic drugs for short periods of time (24-48 h) increased CAV1 expression through ROS production and MEK/ERK activation. In colon cancer cells, increased CAV1 expression enhanced migration and invasion in vitro via pathways requiring Src-family kinases, as well as Rac-1 activity. Finally, elevated CAV1 expression in colon cancer cells following exposure in vitro to sub-cytotoxic drug concentrations increased their metastatic potential in vivo. Therefore exposure of cancer cells to anti-neoplastic drugs at non-lethal drug concentrations induces signaling events and changes in transcription that favor CAV1-dependent migration, invasion and metastasis. Importantly, this may occur in the absence of selection for drug-resistance.

Caveolin-1-enhanced motility and focal adhesion turnover require tyrosine-14 but not accumulation to the rear in metastatic cancer cells.

Caveolin-1 is known to promote cell migration, and increased caveolin-1 expression is associated with tumor progression and metastasis. In fibroblasts, caveolin-1 polarization and phosphorylation of tyrosine-14 are essential to promote migration. However, the role of caveolin-1 in migration of metastatic cells remains poorly defined. Here, caveolin-1 participation in metastatic cell migration was evaluated by shRNA targeting of endogenous caveolin-1 in MDA-MB-231 human breast cancer cells and ectopic expression in B16-F10 mouse melanoma cells. Depletion of caveolin-1 in MDA-MB-231 cells reduced, while expression in B16-F10 cells promoted migration, polarization and focal adhesion turnover in a sequence of events that involved phosphorylation of tyrosine-14 and Rac-1 activation. In B16-F10 cells, expression of a non-phosphorylatable tyrosine-14 to phenylalanine mutant failed to recapitulate the effects observed with wild-type caveolin-1. Alternatively, treatment of MDA-MB-231 cells with the Src family kinase inhibitor PP2 reduced caveolin-1 phosphorylation on tyrosine-14 and cell migration. Surprisingly, unlike for fibroblasts, caveolin-1 polarization and re-localization to the trailing edge were not observed in migrating metastatic cells. Thus, expression and phosphorylation, but not polarization of caveolin-1 favor the highly mobile phenotype of metastatic cells.

A molecular evaluation of germ cell death induced by etoposide in pubertal rat testes.

Etoposide is widely used in the treatment of patients with testicular cancer. The mechanism underlying apoptosis induction in cancer cells has been studied in different cell types, but it is not known whether the same factors participate in viable germ cells undergoing programmed cell death. Since testicular cancer primarily affects young males, we used pubertal rats (21 days old) as a model to determine different apoptotic parameters after etoposide treatment in healthy testes. We found that one intratesticular injection of etoposide (1.2 microg/testis) induced a significant increase in spermatocytes undergoing apoptosis, along with activation of caspase-9, -8 and -3 after 24 h of treatment. Spermatocyte apoptosis was inhibited when a general caspase inhibitor was added along with etoposide. Etoposide induces a significant stabilization/activation of p53, resulting in an increase level of this protein. The mRNA of Bcl-2 antagonist of cell death (BAD), a pro-apoptotic gene and a transcriptional target of p53, was significantly increased after etoposide treatment. Thus, our results suggest a single injection of etoposide induces apoptosis in healthy pachytene spermatocytes mediated by p53 and caspase activation. These findings will assist the search for new therapies to prevent the deleterious effect of cancer drugs upon normal cells.