Regulation of E3 ubiquitin ligase Cbl-b expression by protein tyrosine phosphatase SHP-1 (IRM10P.753)

Abstract

Abstract Casitas B cell lymphoma protein-b (Cbl-b) is a RING finger family E3 ubiquitin ligase. It has been well documented that Cbl-b plays a crucial role in T cell activation and tolerance induction. Our recent study also indicates that Cbl-b regulates proallergic T cell development and allergic airway inflammation. Therefore, the regulation of Cbl-b expression in T cells is important for its biological functions. Our previous studies demonstrate that CD28 costimulation potentiates Cbl-b sel-ubiquitination, CTLA-4-B7 interaction induces Cbl-b expression. However, the molecular mechanism(s) of this regulation remains to be elucidated. In this study, we found that Cbl-b tyrosine phosphorylation in primary mouse T cells requires CD28 costimulation. The failure to detect Cbl-b tyrosine phosphorylation upon CD3 stimulation is not due to defective PTK activation, but rather interestingly SHP-1 is recruited to Cbl-b upon CD3 stimulation, while CD28 costimulation abrogates the interaction between Cbl-b and SHP-1. Furthermore, we identified Cbl-b N-terminal tyrosine residues within TKB domain and linker region (Y106, Y133, and Y363) are required for its E3 ubiquitin ligase activity. The aberrant Th2 phenotype observed in T cell-specific SHP-1-/- (tSHP-1-/-) mice is reminiscent of our recent observation that Th2 responses are heightened in Cbl-b-/- mice. In support of this notion, Cbl-b expression is down-regulated in naïve T cells of tSHP-1-/- mice.