MYSM1/miR-150/FLT3 inhibits B1a cell proliferation

The aberrant expansion of B1a cells has been observed in several murine autoimmune disease models; however, the mechanism of such proliferation of B1a cells is still limited. Here, we identify that Myb Like, SWIRM And MPN Domains 1 (MYSM1), a histone H2A deubiquitinase, plays an intrinsic role in the proliferation of B1a cells where MYSM1 deficiency results in the increased proliferation of B1a cells in mice. We demonstrate that MYSM1 recruits c-Myc to the promoter of miR-150 and stimulates the transcription of miR-150. Our further investigation shows that miR-150 decreases FMS-like tyrosine kinase 3 (FLT3) in B1a cells. In agreement with our animal studies, the percentage of FLT3+ B1 cells in Systemic Lupus Erythematosus (SLE) patients is significantly higher than healthy control. Thus, this study uncovers a novel pathway MYSM1/miR-150/FLT3 that inhibits proliferation of B1a, which may be involved in the pathogenesis of SLE.