Objective
To determine the expression and functional roles of a long noncoding RNA (lncRNA) X-inactive specific transcript (XIST) in leiomyoma. Design: Experimental study. Setting: Academic research laboratory. Patient(s): Women undergoing hysterectomy for leiomyoma. Intervention(s): Overexpression and underexpression of XIST; blockade of specific protein 1 (SP1). Main outcome measure(s): Expression of XIST in leiomyoma and its effects on microRNA 29c (miR-29c), miR-200c, and their targets. Result(s): Leiomyoma expressed statistically significantly more XIST as compared with matched myometrium, independent of race/ethnicity and menstrual cycle phase. By use of a three-dimensional spheroid culture system, we found reduced XIST levels in leiomyoma smooth muscle cells (LSMC) after treatment with 17β-estradiol, progesterone, and their combination. The expression of XIST was down-regulated by treatment with the SP1-inhibitor mithramycin A and SP1 small interfering RNA. Knockdown of XIST resulted in inhibition of cell proliferation, up-regulation of miR-29c and miR-200c, and a concomitant inhibition of the target genes of these miRNAs, namely collagen type I (COL1A1), collagen type III (COL3A1), and fibronectin (FN1). By contrast, overexpression of XIST in myometrium smooth muscle cells repressed miR-29c and miR-200c, and induced COL1A1, COL3A1, and FN1 levels. By use of RNA immunoprecipitation analysis we confirmed XIST has sponge activity over miR-29c and miR-200c, which is more pronounced in leiomyoma as compared with myometrium.