Background：

This gene lies adjacent to the tumor suppressor gene CDKN2A in a region that is frequently mutated and deleted in a wide variety of tumors. This gene encodes a cyclin-dependent kinase inhibitor， which forms a complex with CDK4 or CDK6， and prevents the activation of the CDK kinases， thus the encoded protein functions as a cell growth regulator that controls cell cycle G1 progression. The expression of this gene was found to be dramatically induced by TGF beta， which suggested its role in the TGF beta induced growth inhibition. Two alternatively spliced transcript variants of this gene， which encode distinct proteins， have been reported.