Axin, an important regulator of beta-catenin, is frequently mutated in human hepatocellular carcinomas (HCCs), and transduction of the wild-type Axin gene (AXIN1) induces apoptosis in HCC cells as well as in colon cancer cells. To investigate the detailed biological function of Axin, we searched on a cDNA microarray for genes whose expression was altered by transfer of wild-type AXIN1 into colon-cancer cell line LoVo. Among the genes showing altered expression, we focused on one, termed AXUD1 (AXIN1 up-regulated), that revealed enhanced expression in response to exogenously expressed AXIN1 but not to LacZ, a control gene. The AXUD1 gene consists of five exons and encodes a transcript with an open reading frame of 1767 bp. A 3.2-kb transcript of AXUD1 was expressed in all human tissues examined, most abundantly in lung, placenta, skeletal muscle, pancreas and leukocyte. By radiation-hybrid mapping we assigned its chromosomal location at 3p22, a region where frequent loss of heterozygosity has been reported in lung, renal, prostate, breast and cervical cancers. AXUD1 was frequently down-regulated in lung, kidney, liver and colon cancers compared with their corresponding normal tissues, suggesting that AXUD1 may have a tumor-suppressor function in those organs.