microRNA 21: response to hormonal therapies and regulatory function in leiomyoma, transformed leiomyoma and leiomyosarcoma cells

Aberrant expression of microRNAs (miRNAs), including miR-21, and alteration of their target genes stability have been associated with cellular transformation and tumorigenesis. We investigated the expression, regulation and function of miR-21 in leiomyomas which develop from myometrial cellular transformation. The results indicated that miR-21 is over-expressed in leiomyomas with specific elevation during the secretory phase of the menstrual cycle and in women who received Depo-Provera and oral contraceptives, but reduced due to GnRHa therapy (P < 0.05). Bioinformatic analysis of microarray gene expression profiles previously obtained from the above cohorts, and myometrial smooth muscle cells (MSMC) and leiomyoma smooth muscle cells (LSMC) treated with GnRHa, transforming growth factor (TGF)-β and TGF-β receptor type II (TGF-βRII) antisense oligomer, indicated that a number of miR-21-predicted target genes were co-expressed and differentially regulated in these cohorts. Gain- and loss-of-function of miR-21 in MSMC, LSMC, transformed LSMC and leiomyosarcoma cell line (SKLM-S1) resulted in differential expression of many genes, including some of the miR-21-predicted/validated target genes, PTEN, PDCD4 and E2F1, and TGF-βRII, in a cell-specific manner. Gain-of miR-21 function in MSMC and LSMC reduced TGF-β-induced expression of fibromodulin and TGF-β-induced factor (P < 0.05), and moderately altered the rate of cell growth and caspase-3/7 activity in these cells. We concluded that miR-21 is aberrantly expressed and hormonally regulated in leiomyomas where, through functional interaction with ovarian steroids and the TGF-β signaling pathway, either directly or indirectly regulates a number of genes whose products are critical in leiomyoma growth and regression as well as their potential cellular transformation.