title: Repression of tissue inhibitor of matrix metalloproteinase expression by all-trans-retinoic acid in rat bone cell populations: comparison with transforming growth factor-beta 1.
abstract: Retinoids and transforming growth factor-beta 1 (TGF-beta 1) reduce the transcriptional activation of matrix metalloproteinases (MMPs) and increase the expression of the specific tissue inhibitor of MMPs (TIMP-1) in fibroblasts. In contrast, all-trans-retinoic acid (retinoic acid) increases MMP expression in osteoblasts. Therefore, the mechanistic aspects of TIMP-1 regulation by retinoic acid in primary cultures of rat calvarial bone cell populations were studied and compared with those of TGF-beta 1 to determine if modulation of TIMP-1 would augment MMP expression. Retinoic acid was found to reduce TIMP-1 mRNA levels after 24 and 72 hr of culture by up to 60% in a dose-dependent manner. Maximal inhibition occurred at 10(-6) M retinoic acid with half maximal repression at approximately 5 x 10(-8) M. To determine the half life of TIMP-1 mRNA, the specific RNA polymerase II inhibitor DRB was added to cultures and the chase RNA analyzed by slot blots. TIMP-1 mRNA had a half life of approximately 14 hr and this was unaltered by retinoic acid treatment, suggesting that retinoic acid exerts its effects on TIMP-1 transcriptionally. When retinoic acid was added to cycloheximide-treated cultures TIMP-1 mRNA levels were reduced at 5 hr compared with controls. This showed that ongoing protein synthesis was not required to mediate the retinoic acid repression of TIMP-1 mRNA levels and supports the evidence that retinoic acid acts at the transcriptional level to reduce TIMP-1 expression. In contrast, TGF-beta 1 increased TIMP-1 mRNA levels by 3.5-fold at 24 hr to > 10-fold at 72 hr without alterations in mRNA stability indicating that transforming growth factor (TGF)-beta 1 also acts at the transcriptional level to upregulate TIMP-1 expression in bone cells. Thus, these studies have revealed that TIMP-1 regulation by retinoic acid is different in osteoblasts from other cells and that retinoic acid has the property of generating resorptive and formative cell phenotypes in a tissue-specific manner. In bone, reduced TIMP-1 expression would favor bone matrix degradation and bone resorption that is a characteristic action of retinoids.
authors.affiliation: Faculty of Dentistry, University of British Columbia, Vancouver, Canada.
authors.forename: C M
authors.initials: CM
authors.lastname: Overall
mesh_terms: D000818:Animals; D001842:Bone and Bones / Q000166:cytology / Q000187:drug effects / Q000201:enzymology*; D004355:Drug Stability; D006023:Glycoproteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D008666:Metalloendopeptidases / Q000037:antagonists & inhibitors; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D013237:Stereoisomerism; D019714:Tissue Inhibitor of Metalloproteinases; D016212:Transforming Growth Factor beta / Q000494:pharmacology*; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D006023:Glycoproteins; D012333:RNA, Messenger; D019714:Tissue Inhibitor of Metalloproteinases; D016212:Transforming Growth Factor beta; D014212:Tretinoin; D008666:Metalloendopeptidases