Cleavage of -Catenin by Calpain in Prostate and Mammary Tumor Cells

Mutations in the NH2-terminal regulatory domain of the -catenin gene lead to aberrant stabilization and accumulation of the protein and increased TCF/LEF-dependent transcription. Although these mutations are common in some cancers, they are infrequent in prostate and breast cancer. We have found that metastatic prostate cancer specimens, obtained through a rapid autopsy tissue procurement program, expressed a novel Mr 75,000 proteolytic fragment of -catenin ( -cat ). -Cat was also expressed in multiple prostate and breast cancer cell lines and was closely associated with the activity of the calcium-dependent protease, calpain. In a prostate cancer cDNA microarray, m-calpain RNA levels were found to be significantly increased in metastatic disease compared with normal prostate. We showed calpain-dependent generation of -cat in cell culture and in vitro. Molecular mapping revealed that calpain cleavage removed the NH2-terminal regulatory domain of the -catenin protein. Treatment of MCF-7 cells with ionomycin led to increased accumulation of -cat in the nucleus and TCF-dependent transcriptional activity. Overexpression of a similar -catenin fragment that lacks the NH2-terminal 132 amino acids and has transforming potential activated TCF-dependent transcription. Given the low frequency of mutationinduced activation of -catenin in prostate and breast cancers, proteolytic cleavage of -catenin by calpain may represent a novel mechanism by which the protein is activated during tumorigenesis.