PTP-S2, a nuclear tyrosine phosphatase, is phosphorylated and excluded from condensed chromosomes during mitosis.

PTP-S2 is a tyrosine specific protein phosphatase that binds to DNA and is localized to the nucleus in association with chromatin. It plays a role in the regulation of cell proliferation. Here we show that the subcellular distribution of this protein changes during cell division. While PTP-S2 was localized exclusively to the nucleus in interphase cells, during metaphase and anaphase it was distributed throughout the cytoplasm and excluded from condensed chromosomes. At telophase PTP-S2 began to associate with chromosomes and at cytokinesis it was associated with chromatin in the newly formed nucleus. It was hyperphosphorylated and showed retarded mobility in cells arrested in metaphase. In vitro experiments showed that it was phosphorylated by CK2 resulting in mobility shift. Using a deletion mutant we found that CK2 phosphorylated PTP-S2 in the C-terminal non-catalytic domain. A heparin sensitive kinase from mitotic cell extracts phosphorylated PTP-S2 resulting in mobility shift. These results are consistent with the suggestion that during metaphase PTP-S2 is phosphorylated (possibly by CK2 or a CK2-like enzyme), resulting in its dissociation from chromatin.

Nucleotide sequences of a cDNA coding for rat hck tyrosine kinase and characterization of its gene product.

The hck gene is member of src family of non-receptor type tyrosine kinases. Here we report the nucleotide sequence of the rat hck eDNA of 1.94 kb. The nuclcotide sequence shows an open reading frame coding for a polypeptide of 503 amino acids. A vector expressing a fusion protein of glutathione-S-transferase with 82 amino acids of the N-terminal region of hck (from amino acids 32 to 113) was constructed, Using this bacterially expressed fusion protein antibodies were prepared which recognize the cellular hck gene product. These antibodies identified, by immunoblotting, two polypeptides of 56 and 59 kDa in rat spleen where hck transcripts are present at high level. Immunoprecipitated hck polypeptides were enzymatically active and were autophosphorylated in the presence of ATP and Mg2+. 1mmunoprecipitated hck could phosphorylate exogenous substrates. Treatment of immunoprecipitated hck by a purified protein tyrosine phosphatase decreased its enzymatic acitivity. Our results suggest that the enzymatic activity of hck tyrosine kinase is regulated by phosphorylation and dephosphorylation.