Melanoma antigen A12 regulates cell cycle via tumor suppressor p21 expression

// Teruki Yanagi 1, 2 , Ko Nagai 1 , Hiroshi Shimizu 2 and Shu-Ichi Matsuzawa 1, 3 1 Sanford Burnham Prebys Medical Discovery Institute, La Jolla, California, USA 2 Department of Dermatology, Hokkaido University Graduate School of Medicine, Sapporo, Japan 3 Department of Neurology, Kyoto University Graduate School of Medicine, Kyoto, Japan Correspondence to: Shu-Ichi Matsuzawa, email: smatsuza@kuhp.kyoto-u.ac.jp Keywords: MAGEA12, cell cycle, p21, cyclin dependent kinase, ubiquitination Received: May 09, 2017 Accepted: June 08, 2017 Published: July 22, 2017 ABSTRACT Melanoma-associated antigen family A (MAGE-A) is a family of cancer/testis antigens that are expressed in malignant tumors but not in normal tissues other than the testes. MAGE-A12 is a MAGE-A family gene whose tumorigenic function in cancer cells remains unclear. Searches of the Oncomine and NextBio databases revealed that malignant tumors show up-regulation of MAGE-A12 mRNA relative to corresponding normal tissue. In PPC1 primary prostatic carcinoma cells and in HCT116 colorectal cancer cells (wild type and p53-depleted), MAGE-A12 gene knockdown using siRNA or shRNA diminishes cancer cell proliferation as assessed by cellular ATP levels, cell counting, and clonogenic assays. FACS analyses of annexin V-PI staining and DNA content show that MAGE-A12 knockdown causes G2/M arrest and apoptosis. In tumor xenografts of HCT116 cells, conditional knockdown of MAGE-A12 suppresses tumor growth. The depletion of MAGE-A12 leads to the accumulation of tumor suppressor p21 in PPC1, HCT116, and p53-depleted HCT116 cells. Conversely, CDKN1A knockdown partially rescues the viability of PPC1 cells transfected with siRNA targeting MAGE-A12 , while p21 overexpression leads to proliferation arrest in PPC-1 cells. Furthermore, exogenous MAGE-A12 expression promotes the ubiquitination of p21. Our findings reveal that MAGE-A12 plays crucial roles in p21 stability and tumor growth, suggesting that MAGE-A12 could provide a novel target for cancer treatment.