Fig. 4.

PCGEM1 functions as a c-Myc coactivator. (A) Association of ectopically expressed PCGEM1 with HA-tagged c-Myc, AR, p53, or HIF-1α was detected by RIP assay. The relative levels of coimmunoprecipitated PCGEM1 were calculated as fold difference compared with vector control (*P < 0.05, **P < 0.01). (B) RNA pull-down of the in vitro transcribed biotinylated PCGEM1 incubated with LNCaP cell lysate (Left) or purified recombinant c-Myc protein (Right). The biotinylated GFP mRNA served as a negative control. (C) Myc responsive luciferase was cotransfected with empty vector, c-Myc, PCGEM1, or both into PC3 cells for the reporter assay. Coexpression of PCGEM1 and c-Myc significantly enhanced the luciferase activity. (D) The luciferase activity (same as C) was measured in LNCaP/shPCGEM1 cell cultured with or without DOX treatment. Knockdown of the endogenous PCGEM1 significantly reduced c-Myc transactivity. The relative luciferase activity was calculated by normalization against Renilla-Luc activity (*P < 0.05, **P < 0.01).