NEDD4-1 Modulates the Resistance of Multiple Myeloma to Bortezomib

Background: Multiple myeloma (MM) is among the most common hematologic malignancies. Proteasome inhibitor bortezomib (Bor) is one of the most effective drugs for treatment of MM. However, during long-term Bor treatment, MM cells may eventually develop acquired-resistance to Bor which results in recurrence and a poor prognosis of MM. Several researches show that E3 ubiquitin ligases (E3s) primarily determine the substrate specificity of ubiquitin proteasome system and play an essential role in Bor resistance of MM. NEDD4-1 E3s, a founding member of the Neural precursor cell-Expressed Developmentally Downregulated gene 4 (NEDD4) family, was proved to involve in the proliferation, migration, invasion of cancer cells and the sensitivity of anticancer therapies. Our current study aims to explore the role and underlying mechanism of NEDD4-1 in acquired resistance of Bor in MM.

Methods: The mRNA and protein levels of NEDD4-1 and its substrates in MM cell lines (H929, LP-1, RPMI8226, OPM-2 and ARP-1) and MM patients were detected by Quantitative Realtime PCR and Western Blotting. Lentiviral plasmids containing shRNA against NEDD4-1 were transfected into MM cells. Cell viability, proliferation and apoptosis of MM cells were measured by Cell Counting kit8 (CCK8) and flow cytometry. Gene array was used to compare the gene expression profiles of a panel of Bor treated MM cells vs vehicle-treated MM cells.

Results: Gene array showed NEDD4-1 was significantly increased in MM cells treated with Bor. MM cells (CD138+ plasma cells of the bone marrow) from refractory/recurrence patients expressed lower NEDD4-1 than primary patient myeloma cells. Also, MM cell lines H929, ARP-1, LP-1 highly expressed NEDD4-1 at mRNA and protein levels. RPMI8226 and OPM-2 were relatively low expressed. Cell growth assay displayed no significant difference in proliferation between the NEDD4-1 knockdown (KD) and the control group (P>0.05). After suppression of NEDD4-1 using shRNAs, the killing effect of Bor in MM was significantly weaker than the control group (P<0.05). We also found that PTEN was decreased in the NEDD4-1 KD H929 cell line. Otherwise, phospho-STAT3 (ser727) and oncoprotein c-Myc and Bcl-2 were upregulated.

Conclusion: Collectively, our study reveals that inhibition of NEDD4-1 can reduce MM sensitivity to Bor via regulating PTEN, c-Myc and Bcl-2, may be related to JAK/STAT signaling pathway, which suggests that NEDD4-1 probably acts as a novel drug target and therapeutic paradigm in the battle against multiple myeloma.