Expression, menstrual cycle-dependent activation, and bimodal mitogenic effect of transforming growth factor-β1 in human myometrium and leiomyoma

OBJECTIVE: Transforming growth factor-beta1 is the prototype of a bimodal regulator of,cell growth, which can either inhibit or stimulate the proliferation of smooth muscle cells. Part of transforming growth factor-beta1-mediated stimulation of growth is associated with the increased production of platelet-derived growth factor. The conversion of latent-to-active transforming growth factor-beta provides a pivotal mechanism for the regulation of the biologic activity of transforming growth factor-beta. We investigated the differential expression and production of the active form of transforming growth factor-beta1 in the myometrium and leiomyoma throughout the menstrual cycle. We also studied the mitogenic effects of transforming growth factor-beta1 and platelet-derived growth factor on myometrial and leiomyoma cells in culture. STUDY DESIGN: Myometrium and leiomyoma tissue pairs were obtained from 28 women who underwent hysterectomy. Total RNA from,each tissue was extracted, and Northern blot analysis was performed for the detection of TGF-beta1 messenger RNA. Active and total transforming growth factor-beta1 protein was quantified with enzyme-linked immunosorbent assay. Cell proliferation of cultured human myometrial and leiomyoma cells that are treated with TGF-beta1 (0.01-1 ng/mL), anti-transforming growth factor-P antibody (0.01-10 ng/mL), or platelet-derived growth factor (10 ng/mL) was assessed by the [H-3]thymidine incorporation method. RESULTS: Overall, the transforming growth factor-beta1 messenger RNA level in myometrial samples was 1.2-fold higher than in the leiomyoma samples (P < .05). Active transforming growth factor-β1 protein levels in follicular and luteal phase myometrial and leiomyoma samples were significantly greater than the levels in samples from women with atrophic endometrium (P < 0.05). Transforming growth factor-beta1, at low concentrations (0.01 ng/mL), induced an increase in cell proliferation (2- to 3-fold; P < .05). When cells were treated with anti-transforming growth factor-β antibody, there was a larger magnitude of increase observed (7- to 20-fold; P < .05). Platelet-derived growth factor (10 ng/mL) consistently increased the rate of cell proliferation both in myometrium and leiomyoma cells (5- to 6-fold; P < .05). CONCLUSION: Levels of active transforming growth factor-β1 that were produced in follicular and luteal phases indicate a stimulatory role for ovarian hormones. The finding that transforming growth factor-β1, only at low concentrations, stimulates cell proliferation mainly in leiomyoma cells is in agreement with the bimodal and dose-dependent effects of transforming growth factor-β1 that is observed in smooth, muscle cells of other tissues. The persistent and high rate of cell proliferation with platelet-derived growth factor suggests that the growth stimulatory effect of transforming growth factor-β1 may be mediated through its up-regulatory effect on platelet-derived growth factor.