Tyrosine phosphatases as a superfamily of tumor suppressors in colorectal cancer

Phosphorylation and dephosphorylation processes catalyzed by numerous kinases and phosphorylases are essential for cell homeostasis and may lead to disturbances in a variety of vital cellular pathways, such as cell proliferation and differentiation, and thus to complex diseases including cancer. As over 80 % of all oncogenes encode protein tyrosine kinases (PTKs), protein tyrosine phosphatases (PTPs), which can reverse the effects of tyrosine kinases, are very important tumor suppressors. Alterations in tyrosine kinase and phosphatase genes including point mutations, changes in epigenetic regulation, as well as chromosomal aberrations involving regions critical to these genes, are frequently observed in a variety of cancers. Colorectal cancer (CRC) is one of the most common cancers in humans. CRCs occur in a familial (about 15 % of all cases), hereditary (about 5%) and sporadic (almost 75-80 %) form. As genetic-environmental interrelations play an important role in the susceptibility to sporadic forms of CRCs, many studies are focused on genetic alterations in such tumors. Mutational analysis of the tyrosine phosphatome in CRCs has identified somatic mutations in PTPRG, PTPRT, PTPN3, PTPN13 and PTPN14. The majority of these mutations result in a loss of protein function. Also, alterations in the expression of these genes, such as decreased expression of PTPRR, PTPRO, PTPRG and PTPRD, mediated by epigenetic mechanisms have been observed in a variety of tumors. Since cancer is a social and global problem, there will be a growing number of studies on alterations in the candidate cancer genes, including protein kinases and phosphatases, to determine the origin, biology and potential pathways for targeted anticancer therapy.