E3 ligase casitas B-lineage lymphoma-b modulates peripheral T-cell tolerance via PI3K signaling in patients with immune thrombocytopenia

Abstract Background: The E3 ubiquitin ligase casitas B-lineage lymphoma-b (CBLB) is a newly identified component of the ubiquitin-dependent protein degradation system and is thought to be an important negative regulator of immune cells. CBLB is essential for establishing a threshold for T cell activation and for regulating peripheral T cell tolerance through various mechanisms. However, the role of CBLB in the pathogenesis of immune thrombocytopenia (ITP) remains unknown. Methods: We performed quantitative proteomics to showed reduced CBLB expression and increased PI3K expression in CD4+ T cells from ITP patients. The regulating effect of CBLB on anergy induction was evaluated after transfecting with adenoviridae. We detected DNA methylation levels of the CBLB gene promoter and 5′UTR in CD4+ T cells using MassARRAY EpiTYPER. Results: We found that CD4+ T cells from patients with ITP showed resistance to anergy. Furthermore, highly activated PI3K-AKT signaling, and decreased CBLB expression were found in these pathogenic T cells, indicating that they may be involved in anergy resistance in ITP. Further research revealed that CBLB overexpression effectively decreased p-AKT and reversed anergy resistance. Notably, 5′ untranslated regions (UTR) hypermethylation of CBLB was found in CD4+ T cells from patients with ITP, and low-dose decitabine significantly increased the expression of CBLB in patients with ITP in remission. Conclusions: These results indicate that 5′UTR hypermethylation of the CBLB gene is involved in T cell anergy resistance in ITP through inhibition of CBLB expression. Upregulation of CBLB expression might be a potential therapeutic approach for ITP.