The miR-17~92 family miRNAs regulate non-canonical NFκB pathway by targeting Socs3 to control plasma cell differentiation

Germinal center (GC) reaction in the lymphoid organs is a pivotal process for humoral immune response. The miR-17~92 family miRNAs have been demonstrated that regulate TFH cell differentiation, GC reaction and antibody response. However, whether they may also have functions in B cell activation and differentiation in GC reaction remain largely unknown. Here we show that mice with deletion of miR-17~92 in B cells exhibited reduced GC B cell formation and profound impaired plasma cell (PC) differentiation as well as decreased antibody response upon protein antigen immunization or chronic LMCV infection. In an in vitro plasma cell differentiation (iGCB) system, we found that miR-17~92 deficiency results in markedly decreased in vitro plasma cell (iPC) differentiation and defective NFB activation. Moreover, we developed and performed a screen by CRISPR/small guide (sg) RNA-mediated gene editing among the target genes of miR-17~92 in iGCB culture system. Intriguingly, Socs3 deletion substantially restored iPC differentiation and NFB activation in miR-17~92 deficient B cells, suggesting that Socs3 acts as a negative regulator of NFκB pathway involved in the regulation of iPC differentiation by miR-17~92. However, IL-21-induced STAT3 activation was not affected by miR-17~92 deficiency during iPC differentiation. Mechanistically, Socs3 interacts with MAP3K14 (NIK) and that promotes the ubiquitination of NIK and subsequent proteasome-mediated degradation of NIK, thereby leading to inhibition of the processing of p100 in non-canonical NFκB pathway and PC differentiation. WT and TKO iGCB cells (namely, iPC 0h) or iGCB cells cultured with 40LB cells plus IL-21 for 24 hrs (iPC 24h), 48 hrs (iPC 48h) were collected after sorting. Total RNA from iPC 0 h, 24 h, 48h samples were isolated for deep sequecing in triplicate.