Functional cleavage of the common cytokine receptor γ chain (γ_c) by calpain

Abstract

The small subunit of calpain, a calcium-dependent cysteine protease, was found to interact with the cytoplasmic domain of the common cytokine receptor γ chain (γ _c) in a yeast two-hybrid interaction trap assay. This interaction was functional as demonstrated by the ability of calpain to cleave in vitro-translated wild-type γ_c, but not γ_c containing a mutation in the PEST (proline, glutamate, serine, and threonine) sequence in its cytoplasmic domain, as well as by the ability of endogenous calpain to mediate cleavage of γ_c in a calcium-dependent fashion. In T cell receptor-stimulated murine thymocytes, calpain inhibitors decreased cleavage of γ _c. Moreover, in single positive CD4⁺ thymocytes, not only did a calpain inhibitor augment CD3-induced proliferation, but antibodies to γ _c blocked this effect. Finally, treatment of cells with ionomycin could inhibit interleukin 2-induced STAT protein activation, but this inhibition could be reversed by calpain inhibitors. Together, these data suggest that calpain-mediated cleavage of γ_c represents a mechanism by which γ_c-dependent signaling can be controlled.