Calpains and cancer: friends or enemies?

Calpains are a complex family of ubiquitous or tissue-specific cysteine proteases that proteolyze a variety of substrates (leading to their degradation or functional modulation) and are implicated in several pathophysiological phenomena. In tumor cell biology, calpains are implicated in a triple way: they are involved in different processes crucial for tumor progression, including cell proliferation, apoptotic cell death, survival mechanisms, migration and invasiveness; they have aberrant expression in several human cancers; a variety of anticancer drugs induce cytotoxicity through activation of calpains or the latter can influence response to therapy. This review covers established and recent literature showing these diverse aspects in tumor cells.