miR-1248 enhances bortezomib-induced autophagy by targeting MEF2C/p38-MAPK signaling in multiple myeloma

Multiple myeloma (MM) is incurable and many patients respond poorly to bortezomib. New strategies to improve bortezomib sensitivity are needed.

We screened bortezomib-responsive miRNAs by RNA-seq in RPMI8226 cells (fold change >4, P<0.05). miR-1248 was measured by qRT-PCR in MM cells and in plasma from 30 patients before/after VCD therapy. MEF2C was examined by qRT-PCR and Western blot. A dual-luciferase reporter assay was performed to test miR-1248 binding to the MEF2C 3'-UTR. After miR-1248 inhibitor transfection, we detected MEF2C, p38 and autophagy markers by qRT-PCR/Western blot and assessed autophagic activity by staining. Rescue experiments overexpressed MEF2C. In vivo, a xenograft model (n=6) was used to detect these markers after miR-1248 inhibition plus bortezomib(0.5 mg/kg).

Bortezomib increased miR-1248 by 2-fold (P<0.05) and reduced MEF2C mRNA by 62% and protein by 55% (both P<0.01). Plasma miR-1248 also rose after VCD therapy (median 2.1-fold, P<0.05). Luciferase assays confirmed direct targeting of the MEF2C 3'-UTR by miR-1248. Inhibiting miR-1248 reduced bortezomib-induced autophagy markers and staining, and partially restored MEF2C and p38 (P<0.05). MEF2C overexpression weakened bortezomib-induced apoptosis (cell viability rose from 42 ± 5% to 71 ± 6%, P<0.01) and suppressed those markers. In xenografts, miR-1248 knockdown cut tumor inhibition from 58 ± 7% to 23 ± 9% (P<0.01), with partial restoration of MEF2C/p38 and blunted autophagy marker elevation.

Our findings indicate that miR-1248 enhances bortezomib sensitivity in MM cells by directly targeting MEF2C, accompanied by reduced p38 expression and autophagic activity. The coordinated changes in MEF2C and p38 define a functional axis that may be targeted to improve bortezomib response.