E3 ubiquitin ligase casitas B-lineage lymphoma-b modulates T-cell anergic resistance via phosphoinositide 3-kinase 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 considered an important negative regulator of immune cells. CBLB is essential for establishing a threshold of T-cell activation and regulating peripheral T-cell tolerance through various mechanisms. However, the involvement of CBLB in the pathogenesis of immune thrombocytopenia (ITP) is unknown.

Objectives: We aimed to investigate the expression and role of CBLB in CD4⁺ T cells obtained from patients with ITP through quantitative proteomics analyses.

Methods: CD4⁺ T cells were transfected with adenoviral vectors overexpressing CBLB to clarify the effect of CBLB on anergic induction of T cells in patients with ITP. DNA methylation levels of the CBLB promoter and 5' untranslated region (UTR) in patient-derived CD4⁺ T cells were detected via MassARRAY EpiTYPER assay (Agena Bioscience).

Results: CD4⁺ T cells from patients with ITP showed resistance to anergic induction, highly activated phosphoinositide 3-kinase-protein kinase B (AKT) signaling, decreased CBLB expression, and 5' UTR hypermethylation of CBLB. CBLB overexpression in T cells effectively attenuated the elevated phosphorylated protein kinase B level and resistance to anergy. Low-dose decitabine treatment led to significantly elevated levels of CBLB expression in CD4⁺ T cells from 7 patients showing a partial or complete response.

Conclusion: These results indicate that the 5' UTR hypermethylation of CBLB in CD4⁺ T cells induces resistance to T-cell anergy in ITP. Thus, the upregulation of CBLB expression by low-dose decitabine treatment may represent a potential therapeutic approach to ITP.

Keywords: CBLB; T-cell tolerance; decitabine; immune thrombocytopenia; proteomics.