Aberrant activation of Src-family tyrosine kinases such as Src and Yes promote cell proliferation, survival and metastasis leading to the progression of colorectal cancer (CRC). C-terminal Src kinase (CSK) and its homolog (CHK) are the two major upstream inhibitors of Src family kinases. Our main objective is to define the roles of CSK and CHK in aberrant activation of Src-family kinases in colon cancer cell lines. Data from protein kinase activity assays in DLD-1, SW620 and HCT116 cell lines revealed over activation of Src kinase activity even in the presence of catalytically active CSK. This suggested the inability of CSK to sufficiently inhibit Src kinases in CRC cells. In contrast to CSK, qPCR data showed the down-regulation of CHK mRNA in these cell lines. We further investigated the mechanism employed to down-regulate CHK. Microarray analysis and MS-PCR indicated the epigenetic silencing of CHK promoter region by hyper methylation which co-related with its expression. We thus report that CHK constrains Src activity and is a potential tumour suppressor gene in CRC. The methylation status of CHK in CRC cells could possibly be a novel biomarker for the diagnosis of CRC at its earlier stages.

We acknowledge John M. Mariadason, Oliver Sieber, Harshal Nandurkar, Armadeep Dhillon, Bruno Catimel, Daisy Sio Seng Lio, Ya Chee Lim, Glen Scholz, Tony Burgess, Hong-Jian Zhu and Mike Griffin for their important contribution.