Transcriptional regulation by transforming growth factor beta of the expression of retinoic acid and retinoid X receptor genes in osteoblastic cells is mediated through AP-1.
We now report that transforming growth factor beta1 (TGF-beta1), a potent regulatory cytokine of bone remodeling, is a powerful stimulator for gene expression of retinoic acid receptors (RARs) and retinoid X receptors (RXRs) in osteoblastic MC3T3-E1 cells. TGF-beta1 transcriptionally stimulated the expression of RARalpha, RARgamma, and RXRalpha genes, but did not do so for RARbeta, RXRbeta, and RXRgamma genes. We also observed that AP-1, a transcriptional factor, plays an important role in the signal pathway for expression of RARalpha, RARgamma, and RXRalpha genes stimulated by TGF-beta1 because stimulation of the expression of these genes in the cytokine-treated cells was markedly inhibited by a mixture of antisense c-fos and c-jun. A gel mobility shift assay demonstrated that TGF-beta1 is able to increase, in a dose-dependent manner, the binding of nuclear proteins to direct repeat 5, a consensus sequence with high affinity for RAR-RXR heterodimers. The mobility shift assay, using specific antibody for each receptor, showed that direct repeat 5-binding proteins may be RAR and RXR isoforms. The stimulated binding to direct repeat 5 was inhibited strongly by H-7, an inhibitor of serine/threonine kinase, and by curcumin, an inhibitor of AP-1. The present study suggests a novel pathway for TGF-beta1 action in osteoblastic cells via stimulation of RAR-RXR transcriptional activity in a ligand-dependent fashion.
Chen
Y
Y
Department of Oral Microbiology, Meikai University School of Dentistry, Keyakidai, Sakado City, Saitama 350-02, Japan.
Takeshita
A
A
Ozaki
K
K
Kitano
S
S
Hanazawa
S
S
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000494:pharmacology; D000818:Animals; D001667:Binding, Competitive; D015152:Blotting, Northern; D002460:Cell Line; D003474:Curcumin / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000235:genetics*; D004591:Electrophoresis, Polyacrylamide Gel; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005786:Gene Expression Regulation / Q000187:drug effects; D006801:Humans; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics*; D010006:Osteoblasts / Q000378:metabolism*; D018168:Receptors, Retinoic Acid / Q000235:genetics*; D047488:Retinoid X Receptors; D018808:Transcription Factor AP-1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics*; D014158:Transcription, Genetic; D016212:Transforming Growth Factor beta / Q000378:metabolism*
D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D018808:Transcription Factor AP-1; D014157:Transcription Factors; D016212:Transforming Growth Factor beta; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D003474:Curcumin