The second domain of the CD45 protein tyrosine phosphatase is critical forinterleukin-2 secretion and substrate recruitment of TCR-zeta in vivo

The CD45 protein tyrosine phosphatase (PTPase) has been shown to regulate t he activity of Lck and Fyn protein tyrosine kinases in T cells. However, it is not clear that these constitute the only CD45 substrates. Moreover, the manner by which PTPase activity and substrate recruitment are regulated, i s poorly understood. Previous in vitro studies suggest that the first cytop lasmic PTPase domain (D1) of CD45 is the active PTPase, which may be regula ted by an enzymatically inactive second PTPase domain (D2), However, the fu nction of CD45 D2 in vivo is unknown. In this study, reconstitution of CD45 (-) T cells with specific CD45 PTPase mutants allowed demonstration of a cr itical role for D2 in TCR-mediated interleukin (IL)-2 production. Specifica lly, replacement of CD45 D2 with that of the LAR PTPase to form a CD45/LAR: D2 chimera, abrogates CD45-dependent IL-2 production. This effect cannot be accounted for by loss of PTPase activity per se. The expression of D1 subs trate-trapping mutants reveals an in vivo interaction between CD45 and TCR- zeta that is dependent on CD45 D2, Thus, cells expressing CD45 lacking D2 e xhibit abnormal TCR-mediated signaling characterized by hyperphosphorylatio n of zeta and deficient ZAP-70 phosphorylation, These data suggest an essen tial role for CD45 D2 in TCR-regulated IL-2 production through substrate re cruitment of the zeta chain.