P73 regulates cisplatin-induced apoptosis in ovarian cancer cells via a calcium/calpain-dependent mechanism.

P73 is important in drug-induced apoptosis in some cancer cells, yet its role in the regulation of chemosensitivity in ovarian cancer (OVCA) is poorly understood. Furthermore, if and how the deregulation of p73-mediated apoptosis confers resistance to cisplatin (CDDP) treatment is unclear. Here we demonstrate that TAp73α over-expression enhanced CDDP-induced PARP cleavage and apoptosis in both chemosensitive (OV2008 and A2780s) and their resistant counterparts (C13* and A2780cp) and another chemoresistant OVCA cells (Hey); in contrast, the effect of ΔNp73α over-expression was variable. P73α downregulation attenuated CDDP-induced PUMA and NOXA upregulation and apoptosis in OV2008 cells. CDDP decreased p73α steady-state protein levels in OV2008, but not in C13*, although the mRNA expression was identical. CDDP-induced p73α downregulation was mediated by a calpain-dependent pathway. CDDP induced calpain activation and enhanced its cytoplasmic interaction and co-localization with p73α in OV2008, but not C13* cells. CDDP increased the intracellular calcium concentration ([Ca²⁺]_i) in OV2008 but not C13* whereas cyclopiazonic acid (CPA), a Ca²⁺-ATPase inhibitor, caused this response and calpain activation, p73α processing and apoptosis in both cell types. CDDP-induced [Ca²⁺]_i increase in OV2008 cells was not effected by the elimination of extracellular Ca²⁺, but this was attenuated by the depletion of internal Ca²⁺ store, indicating that mobilization of intracellular Ca^2+] stores was potentially involved. These findings demonstrate that p73α and its regulation by the Ca²⁺-mediated calpain pathway are involved in CDDP-induced apoptosis in OVCA cells and that dysregulation of Ca²⁺/calpain/p73 signaling may in part be the pathophysiology of CDDP resistance. Understanding the cellular and molecular mechanisms of chemoresistance will direct the development of effective strategies for the treatment of chemoresistant OVCA. [ABSTRACT FROM AUTHOR]