Non-canonical unfolded protein response transcription factor CREB3L2 regulates survival of long-lived plasma cells

Abstract

Abstract Differentiation of activated B cells into antibody-secreting cells (ASCs) involves extensive endoplasmic reticulum (ER) & Golgi biogenesis and remodeling that enable increased antibody synthesis and secretion. These processes are mediated by the unfolded protein response (UPR). Canonical UPR pathway genes are regulated by the transcription factors (TFs) XBP-1 and ATFs, which are activated upon ER or Golgi stress. Using scRNA-seq to analyze the generation of splenic and bone marrow (BM) plasma cells (PCs), we discovered that the Creb3l2gene, encoding a non-canonical UPR TF, is specifically expressed in PCs, with highest levels in long-lived PCs (LLPCs). CREB3L2 has been shown to regulate transcription of genes encoding components critical to secretory cells of the pancreas and pituitary gland. To analyze the function of CREB3L2 in ASCs, we pursued a two-pronged strategy (i) using CRISPR/Cas9-RNP editing in the murine CH12 B lymphoma cell line to generate out-of-frame deletions in exon 2 of the Creb3l2gene (Creb3l2−/−) and (ii) generating Creb3l2B-cell conditional KO (cKO) mice carrying a floxed allele of the Creb3l2gene by inserting loxpsites flanking exon 7 with a CD19-cre driver (Creb3l2fl/flCD19 cre/+). RNA-seq of Creb3l2−/−CH12 cells shows CREB3L2 positively regulated genes including Cd93and Cd28& its signaling adapter SLP-76 (Lcp2), that are involved in plasma cell survival in the BM niche. Expression of CD28/SLP-76 and CD93 proteins were strongly diminished in Creb3l2−/−CH12 cells. Consistent with these findings, Creb3l2cKO mice had reduced NP-specific LLPCs (90 d.p.i) after NP-KLH immunization. Thus, CREB3L2 appears to selectively regulate the survival of LLPCs by controlling the expression of CD28/SLP-76 and CD93. Supported by grants from NIAID (U01 AI141990, R01 AI145064).