PMEPA1 Binds NEDD4L to Inhibit the Malignant Progression of Multiple Myeloma by Inactivating Wnt/β-Catenin Signaling

Multiple myeloma (MM) is an incurable hematological malignancy with increasing prevalence. Prostate transmembrane androgen inducible protein 1 (PMEPA1) is positively associated with overall survival in MM patients, but the exact functions and mechanisms of PMEPA1 in MM have yet to be elucidated. PMEPA1 and neural precursor cell-expressed developmentally downregulated gene 4L (NEDD4L) levels in MM cells were examined. In RPMI-8226 cells with PMEPA1 overexpression or/and NEDD4L knockdown, cell proliferation, cycle distribution and apoptosis were evaluated with the application of CCK-8, EDU staining and flow cytometry. The BioGrid website and HDOCK SERVER were applied for predicting the binding between PMEPA1 and NEDD4L, which was checked by co-immunoprecipitation. Besides, the levels of proteins associated with proliferation (Ki67 and PCNA), apoptosis (Bcl-2, Bax and cleaved caspase3) and Wnt/β-catenin signaling (β-catenin, c-Myc and cyclin D1) was detected with immunoblotting. Finally, LiCl, an activator of Wnt/β-catenin pathway, was employed to treat RPMI-8226 cells to analyze the proliferation, cycle distribution and apoptosis of MM cells. As a result, PMEPA1 and NEDD4L were expressed at low levels in MM cells. PMEPA1 upregulation repressed proliferation induced cycle arrest and facilitated apoptosis of MM cells. Moreover, PMEPA1 bound to NEDD4L and upregulated NEDD4L expression in RPMI-8226 cells. Functionally, NEDD4L knockdown attenuated the influences of PMEPA1 overexpression on the proliferation, cycle distribution and apoptosis of RPMI-8226 cells. Additionally, PMEPA1 notably downregulated β-catenin, c-Myc and cyclin D1 expression in RPMI-8226 cells, which was abrogated by NEDD4L silencing. Further adding LiCl in RPMI-8226 cells led to the enhanced malignant biological behaviors. Collectively, PMEPA1 damaged MM progression through binding NEDD4L to inactivate Wnt/β-catenin signaling, which may be helpful to develop promising targets for MM treatment.