Role of microRNA-21 and programmed cell death 4 in the pathogenesis of human uterine leiomyomas

Objective: To determine whether programmed cell death 4 (PDCD-4) is altered in autologous leiomyoma and myometrial tissues and what microRNA-21's (miR-21) role is in PDCD-4 expression, apoptosis, and translation. Design: Laboratory research. Setting: Academic medical center. Patient(s): Myometrial and leiomyoma tissues from patients with symptomatic leiomyomata. Intervention(s): Tissue analysis and miR-21 knockdown in cultured immortalized myometrial (UtM) and leiomyoma (UtLM) cells. Main Outcome Measure(s): MiR-21 and PDCD-4 mRNA and protein expression. Result(s): Leiomyoma tissues robustly expressed the full-length 51 kd isoform of PDCD-4, but normal myometrial tissue had negligible expression. Consistent with autologous tissues, UtLM cells expressed elevated miR-21 and a similar pattern of PDCD-4 compared with UtM cells. Knockdown of miR-21 increased PDCD-4 levels in UtM cells and UtLM cells, indicating that it can regulate PDCD-4 expression. Loss of miR-21 also increased cleavage of caspase-3 (apoptosis marker) and increased phosphorylation of elongation factor-2 (marker of reduced translation) in both cell lines. Conclusion(s): Elevated leiomyoma miR-21 levels are predicted to decrease PDCD-4 levels, thus leiomyomas differ from other tumors where loss of PDCD-4 is associated with tumor progression. Our studies indicate regulation of PDCD-4 expression is not a primary miR-21 function in leiomyomas, but instead miR-21 is able to impact cellular apoptosis and translation, through unknown targets, in a manner consistent with its involvement in the pathophysiology of uterine fibroids.