| Research Abstract |
Recently we have cloned a putative protein tyrosine phosphatase (PTP), PTP36, which possesses a domain homologous to the N-terminal half of band 4.1 protein. In mouse fibroblast adhered to substrate, PTP36 was phosphorylated on serine residues. PTP36 was found to make a complex with serine/threonine kinae (s), which phosphorylated PTP36 in vitro. Staurosporine but not ML-9, Calphostin C,KN-62, and W-7, inhibited the phosphorylation of PTP36 in vitro. Staurosporine also inhibited the in vivo phosphorylation.
Disruption of cell-substrate adhesion induced rapid dephosphorylation of PTP36 and translocation of PTP36 into cytoskeletal fraction containing actin. Both dephosphorylation and translocation of PTP36 was completely blocked by okadaic acid, an inhibitor of serine/threonine phosphatase. Thus, the phosphorylation level and intracellular localization of PTP36 is regulated by cell-substrate adhesion, suggesting that PTP36 may play roles in the signal transduction pathway of cell adhesion.
To gain insight into the biological function of PTP36, we established a stable transfectant (HtTA1-38) of HeLa cells in which the expression level of PTP36 was regulated by tetracycline or doxycycline (Dox). PTP36 protein was hardly detectable in wild type HeLa cells as well as in uninduced HtTA1-38. Any difference of Phenotype was found in these cells. Strong induction of PTP36 was observed only in HtTA1-38 when Dox was removed from the culture. Upon induction of PTP36 overexpression, changes in morphology, actin cytoskeleton, cell growth, and apoptosis by Fas antibody were induced. Our results suggest that PTP36 is involved in the regulatory processes of cell adhesion, cell growth and cell death.
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