Abstract
The phosphorylation and dephosphorylation of proteins on tyrosyl residues are key regulatory mechanisms of cell growth and signal transduction and are controlled by opposing activities of protein tyrosine kinases and phosphotyrosyl phosphatases (PTPs). We have previously cloned and characterized a nontransmembrane chicken protein tyrosine phosphatase 1 (CPTP1) similar to human placental PTP1B (HPTP1B). CPTP1 contains several phosphorylation sequence motifs (S/T-X-X-D/E) for casein kinase II (CKII), [(I>E>V)-Y-(E>G)-(E>D>P>N)-(I/V>L)] for p56(lck), and (P-E-S-P) for MAP kinase. To examine whether phosphatase activity of CPTP1 could be controlled by phosphorylation, CPTP1 and HPTP1B fusion proteins purified from E. coli were subjected to the in vitro phosphorylation by CKII. Phosphoamino acid analysis revealed that CPTP1 was phosphorylated on both serine and threonine residues by CKII in vitro. In addition, the degree of the phosphorylation of CPTP1 by CKII was shown to be five times higher than that of HPTP1B. Phosphorylation on both serine and threonine residues of CPTP1 in vitro results in an inhibition of its phosphatase activity. This result suggests that phosphorylation of CPTP1 and HPTP1B by CKII might be implicated in the regulation of their catalytic activities in the cell.
Highlights
The phosphorylation of protein tyrosine residues is an early event in signal transduction initiated by binding of growth factors and hormones to their cognate receptors and it leads to regulation of cellular activities which include proliferation, differentiation, and malignant transformation of cells (Hunter, 1989; Ullirich and Schlessinger, 1990; Cantley et al, 1991)
In this study we demonstrated that chicken protein tyrosine phosphatase 1 (CPTP1) is phosphorylated by casein kinase II (CKII) in vitro and this phosphorylation causes a decrease in the CPTP1
CPTP1 contains multiple potential phosphorylation sequence motifs for CKII, p56lck, and MAP kinase. This suggests that CPTP1 and human placental PTP1B (HPTP1B) could be phosphorylated on serine and threonine as well as tyrosine by these kinases
Summary
The phosphorylation of protein tyrosine residues is an early event in signal transduction initiated by binding of growth factors and hormones to their cognate receptors and it leads to regulation of cellular activities which include proliferation, differentiation, and malignant transformation of cells (Hunter, 1989; Ullirich and Schlessinger, 1990; Cantley et al, 1991). Protein tyrosine phosphatase activity of CD45, a transmembrane PTP, is activated by sequential phosphorylation by v-abl and casein kinase II (CKII) in vitro (Stover and Walsh, 1994). CPTP1 contains five CKII phosphorylation sequence motifs (S/T-X-X-D/E), one p56lck site [(I>E>V)-Y-(E>G)-(E>D>P>N)-(I/V>L)], and one MAP kinase site (P-E-S-P) (Kim et al, 1996).
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
