CD45 Phosphatase Domain Required For Regulation Of Galectin‐1 Induced T cell Death

Abstract

CD45, a T cell surface glycoprotein, regulates susceptibility to galectin‐1 (gal‐1) cell death. Differential glycosylation allows CD45 to positively or negatively regulate the gal‐1 death signal. Modification of CD45 with core 2 O‐glycans, by core 2 O‐GlcNAc transferase (C2GnT), enhances susceptibility to gal‐1, while absence of core 2 O‐glycans on CD45 reduces susceptibility to gal‐1. T cells expressing C2GnT, with core 2 O‐glycans on CD45, cluster CD45 on the cell surface and have reduced CD45 phosphatase activity after gal‐1 binding; gal‐1 resistance of T cells lacking core 2 O‐glycans can be overcome by inhibition of phosphatase activity. To understand how the CD45 phosphatase controls susceptibility to gal‐1, we expressed a series of CD45 constructs with various mutations in the intracellular domain in T cells with and without C2GnT. We find that enhancement of gal‐1 susceptibility by core 2 O‐glycans requires the CD45 intracellular domain. Thus, binding of gal‐1 to specific glycans on the CD45 extracellular domain regulates intracellular phosphatase activity. We have made a series of gal‐1 analogues that vary orientation and spacing of the carbohydrate recognition domains (CRDs) of gal‐1 and found that increasing spacing of the CRDs increases the potency of the gal‐1 death signal. The effect of gal‐1 CRD spacing on regulation of CD45 phosphatase activity will be discussed.