A novel Myc target gene, mina53, that is involved in cell proliferation

Myc is a ubiquitous mediator of cell proliferation and can transactivate the expression of various genes through E-box sites. Here we report a novel gene, mina53 ((M) under bar yc-induced (n) under bar uclear (a) under bar ntigen with a molecular mass of 53 kDa). The mina53 gene encodes a protein with a molecular weight of 53 kDa, which is localized in the nucleus and with part of the protein concentrated in the nucleolus. When serum-starved cells were activated by serum, the level of c-myc mRNA was elevated, an an increase in mina53 mRNA followed the elevation of c-myc mRNA. When expression of c-myc was reduced in human promyelocytic leukemia HL60 cells by phorbol 12-myristate 13-acetate, the expression of mina53 mRNA and protein was reduced. The expression of mina53 mRNA and Mina53 protein was induced by ectopic introduction of wild type c-Myc but not by a mutant c-Myc lacking the transactivation domain. When c-Myc in the c-MycER chimeric protein was activated, mina53 mRNA was increased, even in the presence of an inhibitor for protein synthesis. E-box sites are present in a region proximal to the transcription initiation sites of the mina53 gene. The gene expression from the mina53 promoter was elevated by c-Myc through E-box sites. c-Myc protein bound to the mina53 promoter region in vivo in HL60 cells in the proliferating phase but not after treatment of cells with phorbol 12-myristate 13-acetate. Specific inhibition of mina53 expression by an RNA interference method severely suppressed cell proliferation. Taken together, these results indicate that mina53 is a direct target gene of Myc, suggesting that mina53 is involved in mammalian cell proliferation.