PC4 Coactivator Mediates Sp1‐driven Luteinizing Hormone Receptor Transcription

Abstract

The luteinizing hormone receptor (LHR) has an essential role in sexual development and reproductive function by participating in gonadal maturation and regulation of steroidogenesis and gametogenesis. Transcription of the LHR gene is subject to several modes of regulation by multiple effectors through its core promoter, which contains two activating Sp1/Sp3 binding domains and an inhibitory motif recognized by EAR2 and EAR3/COUP‐TF1. The present studies demonstrate that PC4 acts as a coactivator of Sp1 to mediate Sp1‐dependent LHR expression. In MCF‐7 breast cancer cells and choriocarcinoma JAR cells, knockdown of PC4 expression with its specific siRNA significantly reduced LHR promoter activity. Co‐transfection of PC4 with an Sp1 or Sp3 expression plasmid showed that PC4 synergistically enhanced Sp1 but not Sp3‐activated LHR expression in reporter gene analyses, indicative of a functional interaction between PC4 and Sp1. In support of this, DNA affinity precipitation assay revealed the sequence‐specific association of PC4 with Sp1/Sp3 binding sites of the LHR gene promoter. Moreover, dephosphorylation of PC4 by calf intestinal phosphatase substantially increased its interaction with the Sp1 binding sites, suggesting a role of phosphorylation in modulation of the PC4/Sp1 interaction. Taken together, these studies have demonstrated that PC4 functions as a coactivator of Sp1 in LHR regulation.