TGF-beta1 stimulates expression of the aromatase (CYP19) gene in human osteoblast-like cells and THP-1 cells.
Recent evidence has shown that bone is not only a target of estrogen action but also a source of local estrogen production. Bone cells such as osteoblasts express aromatase (P450arom) and the expression of P450arom in osteoblasts is positively regulated in a tissue specific fashion, as in the case of other tissues which express P450arom. To clarify the physiological factors regulating expression of P450arom in bone, we tested TGF-beta1 using osteoblast-like cells obtained from human fetuses as well as THP-1 cells. TGF-beta1 increased IL-1beta+DEX- induced aromatase activity in osteoblast-like cells, while it inhibited activity in skin fibroblasts. Similar enhancement of aromatase activity by TGF-beta1 was found in DEX-stimulated THP-1 cells and this cell line was used for further experiments. In THP-1 cells, TGF-beta1 enhanced DEX-induced aromatase activity almost linearly by 12 h and thereafter. Increased levels of P450arom transcripts were also demonstrated by RT-PCR at 3 h of TGF-beta1 treatment and thereafter. Cyclohexamide abolished enhancement of activity but did not inhibit the accumulation of P450arom transcripts induced by TGF-beta1. Increase in P450arom expression by TGF-beta1 was attributable to expression driven by promoter I.4. TGF-beta1 did not change the half life of P450arom transcripts. To identify the cis-acting elements responsible for TGF-beta1 action on aromatase expression, transient transfection assays were performed using a series of deletion constructs for promoter I.4 (P450-I.4/Luc). Two constructs (-410/+14 and-340/+14) that contain a functional glucocorticoid response element (GRE) and downstream sequence showed significant increase of luciferase activity in response to TGF-beta1. Deletion and mutation of the GRE in P450-I.4/Luc (-340/+14) abolished the TGF-beta1. The luciferase activity of a (GRE)(1)-SV40/Luc construct was also stimulated by TGF-beta1. These results indicate that TGF-beta1 increases the expression of P450arom at the level of transcription through promoter I.4, at least in part via an enhancement of transactivation activity of the GR in THP-1 cells. TGF-beta1 is suggested to be one of the physiological up-regulatory factors of bone aromatase.
Shozu
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Cecil H. and Ida Green Center for Reproductive Biology Sciences, The University of Texas Southwestern Medical Center, Dallas, TX 75235-9050, USA.
Zhao
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Simpson
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ER
D001141:Aromatase / Q000235:genetics* / Q000378:metabolism; D001483:Base Sequence; D002460:Cell Line; D017931:DNA Primers / Q000235:genetics; D003907:Dexamethasone / Q000494:pharmacology; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D007700:Kinetics; D010006:Osteoblasts / Q000187:drug effects* / Q000201:enzymology*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014162:Transfection; D016212:Transforming Growth Factor beta / Q000494:pharmacology*
D017931:DNA Primers; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta; D003907:Dexamethasone; D001141:Aromatase