Multiple Myeloma-Derived Mir-27b-3p Facilitates Tumor Progression Via Promoting Tumor Cell Proliferation and Immunosuppressive Microenvironment

Introduction: Multiple myeloma (MM) is an incurable plasma cell malignancy. The crosstalk between immune cells and MM cell is an important determinant of MM progression, but the underlying mechanism has not been fully defined. Our study aimed to identify and screen the profiling of miRNAs in MM patient serum and tumor cells to better understand the roles of miRNAs in MM pathogenesis and myeloma cells driving immune escape.

Methods: A pairwise miRNA profiling in serum and tumor cells was performed via small RNA-seq in NDMM patients and compared with HDs. RT-qPCR detection was performed for a large cohort including 201 NDMM patients and 60 HDs to further confirm the DEmiRs in patient serum. Exosome coculture experiments, confocal microscopy detection and in vivo experiments were utilized to investigate the function of miR-27b-3p encapsulated in exosomes. To upregulate the level of miRNAs, miR-27b-3p mimics was transfected to Jurkat and MM cell lines by using Lipofectamine 3000.

Results: (1). ROC and Kaplan-Meier analysis showed that the decreasing levels of miR-27b-3p, miR-145-3p and miR-628-3p in serum of MM patients presented diagnostic and prognostic efficiency. (2). The level of miR-27b-3p decreased in serum but significantly enriched in serum exosomes of MM patients. A large amount of miR-27b-3p in MM cells could be encapsulated in exosomes and secreted by MM cells into circulation. Confocal microscopy analysis showed that the PKH67-stained exosomes isolated from MM cells were transferred to CD3⁺ T cells after the coculture. More interesting, we found that the low level of circulatory miR-27b-3p in peripheral blood serum of MM highly correlated with the decreased proportion of CD3⁺ T cells, but the increase of CD3⁺CD28^-CD57⁺ senescent T cells, especially after the coculture with serum exosomes from patient. (3). Deul luciferase assay confirmed that CD28 (the prominent costimulatory molecule on T cells) and FBXW7 (a component of E3 ubiquitin ligase) were target genes of miR-27b-3p in T and MM cells, respectively. In T cells, MiR-27b-3p down-regulated the expression level of CD28, which led to the senescence of CD3⁺T cells with decreasing level of cytokines IL-2 and IFN-γ. It was also found that miR-27b-3p could stabilize the expression of c-MYC protein in MM cell lines by targeting FBXW7, thus promoting the proliferation of MM cells. (4). The results in vivo further clarify the role of miR-27b-3p promoting T senescent phenotype and the proliferation of MM cells.

Conclusion: Circulatory serum miR-27b-3p decreased and act as an effective biomarker for MM diagnosis and prognosis evaluation. miR-27b-3p enriched in MM cells and secreted by exosome into circulation. High-level of miR-27b-3p promotes MM cell proliferation via targeting FBXW7/c-MYC axis in tumor cells. Moreover, miR-27b-3p encapsulated in exosomes communicated with surrounding cells and promotes T cell senescence. High level of miR-27b-3p plays pivotal roles in MM pathogenesis. That is one stone two birds.