Regulation of chicken protein tyrosine phosphatase 1 and human protein tyrosine phosphatase 1B activity by casein kinase II- and p56lck-mediated phosphorylation.

Kee Ryeon Kang,Choong Won Kim

doi:10.1038/emm.2000.9

Abstract

Protein tyrosine phosphorylation and dephosphorylation are important in the regulation of cell proliferation and signaling cascade. In order to examine whether phosphatase activity of CPTP1 and HPTP1B, typical nontransmembrane protein tyrosine phosphatase, could be controlled by phosphorylation, affinity-purified PTPs were phosphorylated by CKII and p56lck in vitro. Phosphoamino acid analysis revealed that CPTP1 was phosphorylated on both serine and threonine residues by CKII, and tyrosine residue by p56lck. Phosphatase activity of CPTP1 was gradually increased by three-fold concomitant with phosporylation by CKII. Phosphorylation of HPTP1B by CKII resulted in quick two-fold enhancement of its phosphatase activity within 5 min of incubation and remained in that state. In the presence of CKII inhibitor, heparin or poly(Glu.Tyr), both phosphorylation and enhancement of phosphatase activity of CPTP1 and HPTP1B were mostly blocked. p56lck catalyzed tyrosine phosphorylation of CPTP1 and HPTP1B was only observed by inhibiting the intrinsic tyrosine phosphatase activity. Taken together, these results indicate that CPTP1 or HPTP1B possesses a capability to regulate its phosphatase activity through phosphorylation processes and may participate in the cellular signal cascades.

Highlights

The reversible phosphorylation of proteins on tyrosine residues regulates many cellular processes (Hunter, 1995; Tonks, 1996; Tonks and Neel, 1996)
Rather chicken protein tyrosine phosphatase 1 (CPTP1) contains several potential phosphorylation motifs of casein kinase II (CKII) (S/T-X-X-D/E), p56lck [(I > E > V)-Y-(E > G)-(E > D > P > N)-(I/V > L)], and MAP kinase (P-E-S-P). We report that both CPTP1 and human protein tyrosine phosphatase 1B (HPTP1B) are phosphorylated by CKII or p56lck in vitro, and induced enhancement of the phosphatase activity in chicken and human
In order to examine whether such phosphorylation of protein tyrosine phosphatases (PTPs) could be utilized, affinity-purified CPTP1-2 and HPTP1B were phosphorylated by a typical Ser/Thr kinase, CKII and Tyr kinase, p56lck in vitro

Summary

Introduction

The reversible phosphorylation of proteins on tyrosine residues regulates many cellular processes (Hunter, 1995; Tonks, 1996; Tonks and Neel, 1996). PTP1B, the first isolated intracellular PTP from human placenta, has catalytic domain located at the N-terminal region (Tonks et al, 1988). This nonrecepter-type PTP is phosphorylated on serine residue(s) in growing HeLa cells (Frangioni et al, 1992). The HPTP1B is phosphorylated in vitro at Ser 386 by p34cdc and at Ser 378 by protein kinase C (PKC) (Flint et al, 1993). These findings implicated that PTPs may participate in regulatory roles in various cellular signaling pathways, and the activity of PTPs are regulated by phosphorylation

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Conclusion