VprBP Is Required for Efficient Editing and Selection of Igκ+ B Cells, but Is Dispensable for Igλ+ and Marginal Zone B Cell Maturation and Selection

Abstract

B cell development past the pro-B cell stage in mice requires the Cul4-DDB1-Roc1 E3 ubiquitin ligase substrate recognition subunit VprBP. Enforced Bcl2 expression overcomes defects in distal VH-DJH and secondary Vκ-Jκ rearrangement associated with VprBP-insufficiency in B cells, and substantially rescues maturation of marginal zone and Igλ+ B cells, but not Igκ+ B cells. In this background, expression of a site-directed Igκ light chain transgene increases Igκ+ B cell frequency, suggesting VprBP does not regulate light chain expression from a productively rearranged Igk allele. In site-directed anti-dsDNA heavy chain transgenic mice, loss of VprBP function in B cells impairs selection of Igκ “editor” light chains typically arising through secondary Igk rearrangement, but not selection of Igλ editor light chains. Both heavy and light chain site-directed transgenic mice show increased B cell anergy when VprBP is inactivated in B cells. Taken together, these data argue that VprBP is required for the efficient receptor editing and selection of Igκ+ B cells, but is largely dispensable for Igλ+ B cell development and selection, and that VprBP is necessary to rescue autoreactive B cells from anergy induction.

DCAF1 (VprBP): emerging physiological roles for a unique dual-service E3 ubiquitin ligase substrate receptor

“…The picture currently emerging is of DCAF1 as a multi-functional protein that regulates a wide variety of cellular processes through the CRL4 DCAF1 and EDVP complexes. These include some cell type-specific processes, such as V(D)J recombination (Kassmeier et al, 2012; Palmer et al, 2015; Schabla et al, 2018) and others common to all tissues, such as p53 activity (Hrecka et al, 2007; Kim et al, 2012; Guo et al, 2016) and cell division (Hrecka et al, 2007; Maddika and Chen, 2009; Hossain et al, 2017). A graphical summary of current knowledge of the physiological regulatory targets of DCAF1 and their associated biological processes is shown in Figure 3.…”

“…RAG1 and its cofactor RAG2 together form a site-specific endonuclease that catalyzes DNA cleavage during the assembly of immunoglobulin (Ig) and TCR genes from variable, diverse, and joining gene segments, a process termed V(D)J recombination (Schatz and Swanson, 2011). B cell-intrinsic deletion of DCAF1 caused a profound block in B cell development in vivo , but this defect could be partially rescued through expression of an E μ -Bcl2 transgene on the DCAF1-deficient background (Palmer et al, 2015). Interestingly, most peripheral B cells developing on this genetic background express the Igλ light chain, rather than the Igκ light chain, which normally predominates.…”

VprBP (DCAF1) Regulates RAG1 Expression Independently of Dicer by Mediating RAG1 Degradation

“…The generation of VprBP fl/fl Bcl2 + and VprBP del/del Bcl2 + mice has been described (23, 27). Mice bearing conditional Dicer alleles (28) (B6.Cg- Dicer1 tm1Bdh /J; Dicer fl/fl mice henceforth) were purchased from the Jackson Laboratory.…”

“…More recently, we reported that the developmental block in VprBP del/del mice could be partially bypassed by enforced expression of Bcl2 (henceforth called VprBP del/del Bcl2 + mice), which also restored distal V gene rearrangement at both the Igh and Igk loci (23). Interestingly, most B cells reaching the periphery in VprBP del/del Bcl2 + mice are Igλ + , reflecting a ~10-fold loss in the absolute number of splenic Igκ + B cells.…”

“…Interestingly, most B cells reaching the periphery in VprBP del/del Bcl2 + mice are Igλ + , reflecting a ~10-fold loss in the absolute number of splenic Igκ + B cells. This outcome is correlated with increased levels of secondary V(D)J rearrangements in the Igk locus, including κ-deletion and skewing of Vκ rearrangements to Jκ5, as well as elevated rearrangement of the Igl locus (23). These secondary V(D)J rearrangements are often associated with receptor editing, which can be initiated in response to ligation of the BCR by self-antigen at the immature B cell stage (24), raising the possibility that loss of VprBP in VprBP del/del Bcl2 + mice leads to excessive V(D)J recombination and receptor editing.…”