SERUM-STIMULATED ALPHA(1) TYPE-IV COLLAGEN GENE-TRANSCRIPTION IS MEDIATED BY TGF-BETA AND INHIBITED BY ESTRADIOL

We examined the hypothesis that fetal calf serum (FCS) stimulates muri ne mesangial cell alpha(1) type IV collagen (COL4A1) gene transcriptio n by increasing autocrine production of transforming growth factor-bet a (TGF-beta) through a platelet-derived growth factor (PDGF)-dependent mechanism. PDGF-stimulated COL4A1 gene transcription was inhibited by neutralizing antibody to TGF-beta (119.3 +/- 3.6 vs. 106.0 +/- 6.2 re lative luciferase units, expressed as a percentage of control untreate d cells, P < 0.003). FCS-stimulated gene transcription was inhibited b y neutralizing antibody to PDGF (145.3 +/- 4.1 vs. 136.7 +/- 0.3 relat ive luciferase units, P < 0.002) and by neutralizing antibody to TGF-b eta (148.3 +/- 4.1 vs. 127.1 +/- 3.4 relative luciferase units, P < 0. 036). The inhibitory effect of combined treatment with anti-PDGF and a nti-TGF-beta antibody on gene transcription was no greater than that o f anti-TGF-beta antibody alone [129.5 +/- 0.53 as, 127.1 +/- 3.4 relat ive luciferase units, P = not significant (NS)]. FCS-stimulated gene t ranscription was also inhibited by estradiol (10(-7) M) (148.4 +/- 3.1 vs. 119.4 +/- 8.1 relative luciferase units, P < 0.019). In the prese nce of estradiol, anti-TGF-beta antibody failed to further reduce seru m-stimulated gene transcription (119.4 +/- 8.1 vs. 115.6 +/- 9.8, P = NS), suggesting that estradiol reverses FCS-stimulated COL4A1 gene tra nscription by antagonizing the actions of TGF-beta. Measurement of typ e IV collagen synthesis by Western blotting confirmed that the intact gene responded in a manner analogous to the promoter construct.