TR4 transcriptionally regulates osteocalcin expression. A: Overexpression of TR4 promotes OC-Luc activity. Increasing amounts of pCMX-TR4 (1 and 2 μg, marked as + and ++, respectively) and the positive control pCMX-cbfa were transfected into CV-1 cells, followed by luciferase reporter assay (OC-Luc/CV). B: Overexpressing TR4 mutants (TR4▽N or TR4▽C) diminishes osteocalcin promoter activity. C: Knockdown of TR4 by siTR4 reduces osteocalcin promoter activity. Retro-siTR4 was infected into OC-Luc transfected CV-1 cells, followed by a reporter gene assay. D: Mutation of osteocalcin promoter diminishes promoter activity. A mutation of TR4RE in osteocalcin (OCm-Luc/CV) was co-transfected with TR4, and followed by a reporter gene assay. All the experiments were repeated three times independently.