Human leiomyoma smooth muscle cells show increased expression of transforming growth factor-beta 3 (TGF beta 3) and altered responses to the antiproliferative effects of TGF beta

Transforming growth factor-betas (TGF betas) are multifunctional peptides t hat regulate growth and differentiation in a variety of cells. The goals of this study were to compare expression of the TGF beta isoforms in normal m yometrium and benign leiomyoma tumors of the uterus and to examine the effe cts of TGF betas on cell proliferation and collagen production by these cel ls in vitro. Myometrium and leiomyoma tissues were obtained from patients u ndergoing elective hysterectomies. Tissues were processed for ribonucleic a cid (RNA) and were also established as primary cell cultures. Northern blot analysis showed that the levels of TGF beta1 messenger RNAs (mRNAs) were s imilar between leiomyoma and myometrium, whereas leiomyoma showed 5-fold hi gher levels of expression of TGF beta3 mRNA than autologous myometrium. Exp ression of TGF beta3 protein detected by immunohistochemistry was much more intense in leiomyoma tissues than in corresponding myometrium. Levels of b oth TGF beta1 and TGF beta3 increased with increasing cell density for leio myoma and myometrium smooth muscle cells cultured in vitro. Effects of TGF beta1 and TGF beta3 on cell proliferation were assessed by measuring change s in DNA synthesis with the tritiated thymidine incorporation assay. The do ses of TGF betas tested were 0, 0.1, 1.0, and 10.0 ng/mL. All three doses o f TGF beta1 and TGF beta3 inhibited DNA synthesis in myometrium smooth musc le cells by 31-54%. Concomitant treatment with an immunoneutralizing antibo dy to TGF beta1-3 reversed this inhibitory effect. In contrast, TGF beta1 h ad no effect on leiomyoma smooth muscle cells, whereas TGF beta3 increased DNA synthesis by leiomyoma cells. Combined treatment with the immunoneutral izing antibody prevented this increase. Treatment of leiomyoma and myometri al cells with the TGF beta immunoneutralizing antibody for 24 h caused a 45 -60% reduction in collagen type I and type III mRNA levels, suggesting that endogenous TGF betas are important for collagen production. These results support the hypothesis that alterations in the TGF beta system produce loss of sensitivity to the antiproliferative effects of TGF beta, and increased expression of TGF beta3 may contribute to the growth of these tumors.