Calpain system protein expression and activity in ovarian cancer

PurposeExpression of members of the calpain system are associated with clinical outcome of patients with, amongst others, breast and ovarian cancers, with calpain-2 expression in ovarian cancer being implicated in chemo-resistance and survival. This study aimed, using a large patient cohort and in vitro models, to verify its importance and further investigate the role in ovarian cancer chemoresponse.MethodsCalpain-1, calpain-2, calpain-4 and calpastatin expression were evaluated in primary ovarian carcinomas (n=575) by immunohistochemistry. Protein expression was assessed, via western blotting, in five ovarian cancer cell lines with various sensitivities towards cisplatin/carboplatin. In vitro calpain activity was inhibited by calpeptin treatment to assess changes in platinum sensitivity by proliferation assay, with expression of genes associated with epithelial-mesenchymal transition being examined by RT2 Profiler PCR Array.ResultsThe current study confirmed previous data that high calpain-2 expression is associated with poor overall survival (P=0.026) and that calpain-1 was not associated with overall survival or progression-free survival. Low expression of calpastatin (P=0.010) and calpain-4 (P=0.003) were also associated with adverse survival. Such prognostic associations do not seem to be linked with altered tumour sensitivity towards platinum-based chemotherapy. Interestingly, low calpain-1 expression was more frequent in patients with confined tumours (stage 1) ((2)=11.310, df=1, P=0.001). Calpain and calpastatin expression varied among ovarian cancer cell lines yet their expression levels were similar between chemo-sensitive cells and resistant counterparts. Moreover, calpeptin treatment did not alter cellular response to platinum-based chemotherapy or epithelial-mesenchymal transition-related gene expression.ConclusionsThe conventional calpains and calpastatin have been confirmed to play an important role in ovarian cancer; however, the precise mechanisms whereby they exert effects remain to be elucidated.