Loss of hnRNPLL‐dependent splicing of Ptprc has no impact on B‐cell development, activation and terminal differentiation into antibody‐secreting cells

Abstract

The RNA‐binding protein heterogeneous nuclear ribonucleoprotein L‐like (hnRNPLL) controls alternative splicing of protein tyrosine phosphatase receptor type C (Ptprc) which encodes CD45. hnRNPLL deficiency leads to a failure in silencing Ptprc exons 4–6 causing aberrant expression of the corresponding CD45 isoforms, namely, CD45RA, RB and RC. While an N‐ethyl‐N‐nitrosourea‐induced point mutation in murine Hnrnpll results in loss of peripheral naïve T cells, its role in B‐cell biology remains unclear. Here, we demonstrate that B‐cell development in the bone marrow of Hnrnpllthu/thu mice is normal and the number of mature B‐cell subsets in the spleen and peritoneal cavity is comparable to control littermates. In response to in vivo immunization, Hnrnpllthu/thu mice were deficient in generating germinal center (GC) B cells, and analysis of mixed bone marrow chimeras revealed that the GC B‐cell deficiency was a B‐cell extrinsic effect of the hnRNPLL mutation. Mature Hnrnpllthu/thu B cells proliferated normally in response to various B‐cell receptor‐ and Toll‐like receptor‐mediated stimuli. Similarly, in vitro stimulation of mutant B cells led to normal generation of plasmablasts, but mutant plasmablasts failed to downregulate B220 expression because of the inability of cells to undergo proper CD45 pre‐messenger RNA alternative splicing. These findings collectively suggest that, like in T and natural killer T cells, the mutation disrupts hnRNPLL‐mediated alternative splicing of the Ptprc gene in plasmablasts, but this dysregulation of Ptprc alternative splicing does not affect the development and function of B cells.

The RNA regulatory programs that govern lymphocyte development and function

“…Wu, Jia, et al, 2008). By contrast, hnRNPLL deletion has no impact on B-cell development and function (Yabas et al, 2020), which suggests that splicing regulatory programs are fundamentally different in T and B cells.…”

“…More recently, genome wide studies have revealed that both hnRNPL and hnRNPLL control global splicing programs that are required for T cell development and function (Cho et al, 2014; Z. Wu, Jia, et al, 2008). By contrast, hnRNPLL deletion has no impact on B‐cell development and function (Yabas et al, 2020), which suggests that splicing regulatory programs are fundamentally different in T and B cells.…”

GPR55 in B cells limits atherosclerosis development and regulates plasma cell maturation

“…In vitro stimulation of Ptprc mutant B cells led to normal differentiation into plasmablasts, but the cells failed to downregulate B220 expression, albeit it did not affect their functionality. 39 The altered mitochondrial and actin cytoskeleton structure in Gpr55 deficient PCs is in agreement with an enhanced activation state. Activated B cells exposed to high levels of BAFF increased glucose uptake and mitochondrial mass, resulting in increased glycolysis and oxidative phosphorylation.…”

“…Less is known regarding Ptprc/LPAP in B cells. In vitro stimulation of Ptprc mutant B cells led to normal differentiation into plasmablasts, but the cells failed to downregulate B220 expression, albeit it did not affect their functionality 39 .…”

GPR55 in B cells limits atherosclerosis development and regulates plasma cell maturation

“…In vitro stimulation of Ptprc mutant B cells led to normal differentiation to plasmablasts, but the cells failed to downregulate B220 expression, albeit it did not affect their functionality. 43 Whether GPR55 signaling directly regulates LPAP and underlying mechanisms still needs to be clarified.…”