Human Leiomyoma Smooth Muscle Cells Show Increased Expression of Transforming Growth Factor-β3 (TGFβ3) and Altered Responses to the Antiproliferative Effects of TGFβ

Abstract

Transforming growth factor-βs (TGFβs) are multifunctional peptides that regulate growth and differentiation in a variety of cells. The goals of this study were to compare expression of the TGFβ isoforms in normal myometrium and benign leiomyoma tumors of the uterus and to examine the effects of TGFβs on cell proliferation and collagen production by these cells in vitro. Myometrium and leiomyoma tissues were obtained from patients undergoing elective hysterectomies. Tissues were processed for ribonucleic acid (RNA) and were also established as primary cell cultures. Northern blot analysis showed that the levels of TGFβ1 messenger RNAs (mRNAs) were similar between leiomyoma and myometrium, whereas leiomyoma showed 5-fold higher levels of expression of TGFβ3 mRNA than autologous myometrium. Expression of TGFβ3 protein detected by immunohistochemistry was much more intense in leiomyoma tissues than in corresponding myometrium. Levels of both TGFβ1 and TGFβ3 increased with increasing cell density for leiomyoma and myometrium smooth muscle cells cultured in vitro. Effects of TGFβ1 and TGFβ3 on cell proliferation were assessed by measuring changes in DNA synthesis with the tritiated thymidine incorporation assay. The doses of TGFβs tested were 0, 0.1, 1.0, and 10.0 ng/mL. All three doses of TGFβ1 and TGFβ3 inhibited DNA synthesis in myometrium smooth muscle cells by 31–54%. Concomitant treatment with an immunoneutralizing antibody to TGFβ1–3 reversed this inhibitory effect. In contrast, TGFβ1 had no effect on leiomyoma smooth muscle cells, whereas TGFβ3 increased DNA synthesis by leiomyoma cells. Combined treatment with the immunoneutralizing antibody prevented this increase. Treatment of leiomyoma and myometrial cells with the TGFβ immunoneutralizing antibody for 24 h caused a 45–60% reduction in collagen type I and type III mRNA levels, suggesting that endogenous TGFβs are important for collagen production. These results support the hypothesis that alterations in the TGFβ system produce loss of sensitivity to the antiproliferative effects of TGFβ, and increased expression of TGFβ3 may contribute to the growth of these tumors.