Ferroportin downregulation promotes cell proliferation by modulating the Nrf2-miR-17-5p axis in multiple myeloma

Recent findings demonstrate that aberrant downregulation of the iron-exporter protein, ferroportin (FPN1), is associated with poor prognosis and osteoclast differentiation in multiple myeloma (MM). Here, we show that FPN1 was downregulated in MM and that clustered regularly interspaced short palindromic repeat (CRISPR)-mediated FPN1 knockout promoted MM cell growth and survival. Using a microRNA target-scan algorithm, we identified miR-17-5p as an FPN1 regulator that promoted cell proliferation and cell cycle progression, and inhibited apoptosis both in vitro and in vivo. miR-17-5p inhibited retarded tumor growth in a MM xenograft model. Moreover, restoring FPN1 expression at least partially abrogated the biological effects of miR-17-5p in MM cells. The cellular iron concentration regulated the expression of the iron-regulatory protein (IRP) via the 5'-untranslated region of IRP messenger RNA and modulated the post-transcriptional stability of FPN1. Bioinformatics analysis with subsequent chromatin immunoprecipitation-polymerase chain reaction and luciferase activity experiments revealed that the transcription factor Nrf2 drove FPN1 transcription through promoter binding and suppressed miR-17-5p (which also increased FPN1 expression). Nrf2-mediated FPN1 downregulation promoted intracellular iron accumulation and reactive oxygen species. Our study links FPN1 transcriptional and post-transcriptional regulation with MM cell growth and survival, and validates the prognostic value of FPN1 and its utility as a novel therapeutic target in MM.