Regulation of HSH2 adaptor protein turnover via a novel NF-κB-dependent mechanism is involved in determining the nature of the class switched antibody response (IRM8P.715)

Abstract

Abstract The Hematopoietic Src Homology 2 (HSH2) adaptor protein is differentially expressed in mature, peripheral B cell subpopulations; exhibiting high-level expression in B1 and marginal zone B cells versus low-level expression in germinal center B cells, independent of gene transcription. HSH2 plays an important role in regulating the production of class switched antibodies through its effect on B cell class switching and terminal differentiation. Mouse models revealed that over expression of HSH2 in the B cell lineage attenuates the class switched antibody response, whereas reduced expression accelerates the class switched response. Thus, it is of significant interest to delineate the molecular mechanisms by which expression of HSH2 is controlled. Upregulation of HSH2 expression in response to TNF receptor family and TLR agonists occurs in an NF-κB-dependent manner, yet does not involve increased transcription of the HSH2 locus based on analysis of HSH2 mRNA levels. Additionally, maintenance of HSH2 expression is dependent on NF-κB signaling. Inhibition of NF-κB results in the rapid down regulation of HSH2 with a half-life of 1 hour, which is in contrast to the results obtained following treatment with cycloheximide or actinomycin D demonstrating that mRNA for HSH2 is stable and the protein itself has a half-life greater than 12 hours. These data support the conclusion that HSH2 protein stability is regulated post-transcriptionally via a novel NF-κB-dependent mechanism.