p73 participates in male germ cells apoptosis induced by etoposide

Etoposide is a commonly used drug in testicular cancer chemotherapy. However, the molecular pathways that activate germ cell apoptosis in response to etoposide are poorly understood. The aim of this study was to evaluate the participation of p73, a member of the p53 family, in apoptosis induced by etoposide in male germ cells. First, we used GC2-spc cells-a male germ cell model-to evaluate apoptotic signaling after treatment of etoposide. We found an important increase in p73 protein levels, along with the c-Abl kinase, its physiological activator, in response to etoposide. This increase was accompanied by a decrease in cell viability and activation of caspase-3. Pifithrin (PFT) treatment prevented p73 increase and apoptosis induced by etoposide. Also, the in vitro knockdown of p73 or p53 by shRNA, significantly prevented the decrease in cell viability after etoposide treatment. In an in vivo model-21-day-old rat testes-we observed an up-regulation of the protein levels of p73 and phosphorylated p73-at c-Abl site Tyr99-in response to the etoposide injection. STI571 (a pharmacological inhibitor of c-Abl) or PFT co-injection prevented etoposide-induced up-regulation of phospho-p73 and pro-apoptotic TAp73 isoform levels. Moreover, caspases-3, -8, -9 activation and germ cell death induced by etoposide were significantly decreased by these drugs. These results support the notion that the c-Abl/p73 pathway is activated in germ cells after etoposide treatment, triggering apoptosis, possibly assisting p53.