Full-length MEK5 is highly expressed in MM and spliced by RBM39. (A) Venn diagram showing overlap of identified AS events and RBM39-bound RNA (left). The overlap of 4 data sets was defined as RBM39 targets. Venn diagram showing the overlap of defined RBM39 targets and genes of the MAPK signaling pathway from KEGG (hsa04010) (right). (B) MEK5 mRNA expression level in CD138⁻ and CD138⁺ cells from BM of patients with newly diagnosed MM. (C) Elevated MEK5 was significantly correlated with poor overall survival in MM. Data from GSE2658. (D) RIP with anti-RBM39 followed by reverse transcription (RT)-PCR with MEK5 primers in MM.1S cells. (E) Quantitative RT-PCR analysis of enriched MEK5 in RIP with anti-RBM39 in MM.1S cells. (F) RNA sequencing (RNA-seq) coverage plot of MEK5 in MM.1S cells treated with RBM39 shRNA or control. (G) RNA-seq coverage plot of MEK5 in MM.1S cells treated with indisulam or dimethyl sulfoxide. (H) PCR analysis of different MEK5 isoforms from MM.1S treated with shRBM39 or scr. PCR products were analyzed by 3% agarose gel electrophoresis. (I) Number of different isoforms in MEK5 PCR products in panel H. PCR products were extracted from the gel and ligated to the pMD-T19 vector. The ligation products were transformed into DH5α and 50 clones were sequenced and aligned to MEK5. (J) PCR analysis of different MEK5 isoforms from MM.1S treated with indisulam or dimethyl sulfoxide. PCR products were analyzed by 3% agarose gel electrophoresis. (K) Number of different isoforms in MEK5 PCR products in panel J. ∗∗P < .01, ∗∗∗P < .001. MEK5Δ17-18, MEK5 transcripts with exon 17-18 loss, MEK5Δ18, MEK5 transcript with exon 18 loss.