MADR2 maps to 18q21 and encodes a TGF beta-regulated MAD-related protein that is functionally mutated in colorectal carcinoma

The MAD-related (MADR) family of proteins are essential components in the signaling pathways of serine/threonine kinase receptors for the transforming growth factor beta (TGF beta) superfamily. We demonstrate that MADR2 is specifically regulated by TGF beta and not bone morphogenetic proteins. The gene for MADR2 was found to reside on chromosome 18q21, near DPC4, another MADR protein implicated in pancreatic cancer. Mutational analysis of MADR2 in sporadic tumors identified four missense mutations in colorectal carcinomas, two of which display a loss of heterozygosity. Biochemical and functional analysis of three of these demonstrates that the mutations are inactivating. These findings suggest that MADR2 is a tumor suppressor and that mutations acquired in colorectal carcinomas may function to disrupt TGF beta signaling.