Cancer-testis antigen HCA587/MAGEC2 interacts with the general transcription coactivator TAF9 in cancer cells

Hepatocellular carcinoma-associated antigen 587/melanoma antigen gene (HCA587/MAGEC2) is a cancer-testis antigen, which is highly expressed in various types of tumors, but not in normal tissues with the exception of male germ-line cells. HCA587/MAGEC2 has been previously recognized as a tumor-specific target for immunotherapy; however, its biological functions have been relatively understudied. To investigate the function of HCA587/MAGEC2, the amino acid sequence of HCA587/MAGEC2 was analyzed by bioinformatics and it was demonstrated that HCA587/MAGEC2 contains a 9-amino acid transactivation domain which may mediate the interaction of most transcription factors with TATA-box binding protein associated factor 9 (TAF9), a general transcription coactivator. Co-immunoprecipitation experiments revealed that HCA587/MAGEC2 interacted with TAF9 in transfected 293T and in A375 melanoma cells endogenously expressing HCA587/MAGEC2, and confirmed the endogenous interaction of HCA587/MAGEC2 and TAF9 within cells. Endogenous HCA587/MAGEC2 and TAF9 were demonstrated to be co-localized principally in the nucleus of tumor cells using immunofluorescence. Glutathione-S-transferase pull-down experiments demonstrated that HCA587/MAGEC2 interacts with TAF9 directly and the conserved region in the TAF9 may becrucial for HCA587/MAGEC2 binding. The present study demonstrated that the cancer-testis antigen HCA587/MAGEC2 directly interacted with TAF9, which may provide novel information for identifying the oncogenic functions of HCA587/MAGEC2 in tumor cells.