MiR-137's Tumor Suppression on Prolactinomas by Targeting MITF and Modulating Wnt Signaling Pathway

Context: Prolactinomas are the most common functional pituitary adenomas; the aggressive tumors still present challenge to clinicians. Aberrant expression of miRNAs has been functionally associated with prolactinomas. Objective: Here we explored the role of miR-137 on the proliferation, invasion, and apoptosis of prolactinomas and its possible mechanism. Results: Low expression of miR-137 was correlated with the invasive behavior of human prolactinomas and predicted high recurrence. MiR-137 inhibited cell proliferation, invasion, and survivals of MMQ and GH3 cells and reduced tumor volume in F344 rat prolactinomas. The luciferase reporter assay confirmed that microphthalmia-associated transcription factor (MITF) was the direct target of miR-137. In addition, miR-137 mimics could inhibit MITF expression in vivo and in vitro. Upregulation of MITF expression promoted cell proliferation, invasion, and survivals and reversed the antitumor effect of miR-137 in vivo and in vitro. Furthermore, miR-137 could also upregulate wnt-inhibitory factor-1 and inhibit nuclear translocation of beta-catenin. Upregulation of wnt-inhibitory factor-1 with decitabine can enhance the inhibition on cell proliferation of miR-137. A glycogen synthase kinase-3 inhibitor, SB 216763, promoted cell proliferation by upregulation of total/cytoplasmic/nuclear beta-catenin and reversed tumor suppression of miR-137 mimics. Conclusions: Our data suggest that miR-137 possesses a tumor invasive suppressor function with a prognostic value in prolactinomas by targeting MITF and modulating Wnt-beta-catenin signaling pathway.