CD45 TYROSINE PHOSPHATASE-ACTIVITY AND MEMBRANE ANCHORING ARE REQUIRED FOR T-CELL ANTIGEN RECEPTOR SIGNALING

T cells that lack the CD45 transmembrane tyrosine phosphatase have a v ariety of T-cell receptor (TCR) signaling defects that are corrected b y reexpression of wild-type CD45 or its intracytoplasmic domains. In t his study, a chimeric molecule containing the myristylation sequence o f Src and the intracellular portion of CD45, previously shown to resto re function in CD45(-) T cells, was mutagenized to determine if membra ne-associated CD45 tyrosine phosphatase activity is required to restor e TCR-mediated signaling in CD45(-) T cells. Abolition of enzymatic ac tivity by substitution of a serine for a critical cysteine in the firs t catalytic domain resulted in failure of this molecule to restore TCR signaling. Another mutation, in which a single amino acid substitutio n destroyed the myristylation site, resulted in failure of the chimeri c molecule to partition to the plasma membrane. Although expressed at high levels and enzymatically active, this form of intracellular CD45 also failed to restore normal signaling in CD45(-) T cells. These find ings strongly suggest that CD45's function in TCR signaling requires i ts proximity to membrane-associated tyrosine phosphatase substrates.