Two Splice Variants of a Tyrosine Phosphatase Differ in Substrate Specificity, DNA Binding, and Subcellular Location

Abstract

Four different forms of a non-receptor type protein-tyrosine phosphatase are generated by alternative splicing; two of these forms (PTP-S2 and PTP-S4) are major forms, which are expressed in rat as well as human cells. Here we report that PTP-S2 binds to nonspecific DNA in vitro and localizes in the nucleus upon transfection in HeLa cells. PTP-S4 does not bind to nonspecific DNA and shows perinuclear and cytoplasmic localization. Removal of the C-terminal 34 amino acids of PTP-S4 gives rise to a truncated protein, which binds to nonspecific DNA and localizes to the nucleus. PTP-S4, but not PTP-S2, interacts strongly with the isolated nuclear matrix. The two forms of this tyrosine phosphatase show different substrate specificity in vitro, a feature novel to splice variants of tyrosine phosphatases. Mitogenic stimulation induces mRNAs for PTP-S2 as well as for PTP-S4 in the G1 phase during liver regeneration. These results suggest that alternative splicing gives rise to two protein-tyrosine phosphatases with distinct substrate specificities and subcellular locations. The 34 amino acids at the C terminus of PTP-S4 play a critical role in determining substrate specificity, subcellular location, and interaction with nuclear matrix and DNA.