Regulation of transforming growth factor-β1 expression by granulocyte macrophage-colony-stimulating factor in leiomyoma and myometrial smooth muscle cells

Human myometrium and leiomyomas express granulocyte macrophage-colony-stimulating factor (GM-CSF), transforming growth factor-beta (TGF beta), and their receptors. Overexpression of TGF beta and, to a limited extent, GM-CSF has been associated with tissue fibrosis throughout the body, including leiomyomas. The objective of the present study was to determine the action of GM-CSF on leiomyoma and myometrial smooth muscle cells (LSMC and MSMC) and examine whether the action of GM-CSF is mediated through the induction of TGF beta 1 expression. Using competitive quantitative RT-PCR and enzyme-linked immunosorbent assay, we found that LSMC express significantly higher GM-CSF messenger ribonucleic acid (mRNA; 0.6 +/- 0.1 x 10(3) copies of mRNA/mu g total RNA) and protein (0.75 +/- 0.2 ng/mL than MSMC (0.5 +/- 0.1 x 10(2) copies of mRNA and 0.45 +/- 0.07 ng/mL protein; P < 0.05). In addition, LSMC expressed significantly higher TGF beta 1 mRNA (1.6 +/- 0.3 x 10(4) copies of mRNA/mu g total RNA) than MSMC (2.4 +/- 0.4 x 103 copies) and synthesized and secreted more TGF beta 1 protein (1.7 +/- 0.2 vs. 0.5 +/- 0.02 ng/mL); whereas MSMC contained more cell-associated TGF beta 1 (56.2 +/- 1.2 ng/mL) than LSMC (35.2 +/- 1.2 ng/mL; P < 0.05). We found that GM-CSF (0.01-100 ng/mL) has limited mitogenic activity for LSMC but not for MSMC determined by the rate of [H-3]thymidine incorporation and cell proliferation assay. However, GM-CSF at 1 ng/mL increased its own production, the expression of TGF beta 1 mRNA, the cell-associated TGF beta 1 protein content in both cell types, and TGF beta 1 released into the culture-conditioned medium of LSMC (P < 0.05). TGF beta 1 also increased its own mRNA and protein expression, but had no effect on cell-associated TGF beta 1 in both cell types (P < 0.05). Cotreatment of LSMC and MSMC with GM-CSF and TGF beta 1 induced changes similar to those produced by GM-CSF in both cells. In conclusion, our data suggest that GM-CSF is not a mitogen for MSMC and LSMC, but it regulates its own expression and the expression of TGF beta 1 by these cells, a regulatory interaction that may account for the GM-CSF-induced tissue fibrosis that occurs in leiomyomas.