Corticotropin-releasing hormone or dexamethasone regulates rat proopiomelanocortin transcription through Tpit/Pitx-responsive element in its promoter.
Tpit/Pitx-responsive element (Tpit/PitxRE), which binds transcription factors Tpit and Pitx1, confers cell-type specific expression of proopiomelanocortin (POMC) gene in pituitary corticotrops where the gene expression is mainly regulated by corticotropin-releasing hormone (CRH) and glucocorticoids (Gcs). CRH stimulates POMC gene expression, which is mediated by the accumulation of intracellular cAMP and requires binding of Nur factors to Nur-responsive element (NurRE). Gcs antagonize NurRE-dependent POMC gene expression through direct interaction between glucocorticoid receptors and Nur factors. We examined whether Tpit/PitxRE and NurRE are involved in CRH/cAMP-induced activation and Gc-induced repression of POMC gene expression by reporter assay in AtT-20 corticotropic cells. Deletion and mutation of Tpit/PitxRE markedly reduced basal activity of the promoter, and those of NurRE decreased the levels of the CRH/cAMP-induced activation. Nifedipine, KN-62, and W-7, specific inhibitors of the L-type calcium channel, calmodulin-dependent protein kinase II, and calmodulin respectively, attenuated CRH/cAMP-induced activation of promoters with three copies of either Tpit/PitxRE or NurRE, indicating that both Tpit/PitxRE and NurRE mediate CRH-induced activation of POMC gene expression in a calcium-dependent manner. Deletion and mutation of Tpit/PitxRE abolished dexamethasone (DEX)-induced repression of POMC gene expression, while those of NurRE did not, indicating that Tpit/PitxRE predominantly mediates Gc-induced repression of POMC transcription. However, DEX treatment attenuated activities of promoters with three copies of either Tpit/PitxRE or NurRE, suggesting that Gcs act at NurRE as well as Tpit/PitxRE to repress POMC gene expression. We conclude that Tpit/PitxRE is an important element by which CRH and Gcs regulate the POMC gene expression.
Murakami
Itsuo
I
Department of Biology, Faculty of Science, Okayama University, 3-1-1, Tsusima-naka, Okayama, Japan.
Takeuchi
Sakae
S
Kudo
Toshiyuki
T
Sutou
Shizuyo
S
Takahashi
Sumio
S
D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002147:Calmodulin / Q000037:antagonists & inhibitors; D002460:Cell Line; D003346:Corticotropin-Releasing Hormone / Q000494:pharmacology*; D000242:Cyclic AMP / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology*; D017353:Gene Deletion; D005786:Gene Expression Regulation; D005938:Glucocorticoids / Q000494:pharmacology*; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D051761:Paired Box Transcription Factors / Q000235:genetics / Q000378:metabolism; D011333:Pro-Opiomelanocortin / Q000235:genetics*; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013449:Sulfonamides / Q000494:pharmacology; D020825:T-Box Domain Proteins / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D002121:Calcium Channel Blockers; D002147:Calmodulin; D005938:Glucocorticoids; D018398:Homeodomain Proteins; D051761:Paired Box Transcription Factors; D012333:RNA, Messenger; D013449:Sulfonamides; D020825:T-Box Domain Proteins; C486589:TBX19 protein, human; C101485:homeobox protein PITX1; C063302:KN 62; C017967:W 7; D011333:Pro-Opiomelanocortin; D003907:Dexamethasone; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D003346:Corticotropin-Releasing Hormone; D000242:Cyclic AMP; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D009543:Nifedipine