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Cell Commun Signal. 2017 Aug 7;15(1):29. doi: 10.1186/s12964-017-0186-x.

Csk-homologous kinase (Chk) is an efficient inhibitor of Src-family kinases but a poor catalyst of phosphorylation of their C-terminal regulatory tyrosine.

Author information

1
Department of Biochemistry & Molecular Biology, University of Melbourne, Parkville, VIC, 3010, Australia.
2
Bio21 Biotechnology and Molecular Science Institute, University of Melbourne, Parkville, VIC, 3010, Australia.
3
Cell Signalling Research Laboratories, School of Biomedical Sciences, University of Melbourne, Parkville, VIC, 3010, Australia.
4
PAP Rashidah Sa'adatul Bolkiah Institute of Health Sciences, Universiti Brunei Darussalam, Gadong, Brunei Darussalam.
5
Walter and Eliza Hall Institute for Medical Research and Department of Medical Biology, University of Melbourne, Parkville, VIC, 3010, Australia.
6
Department of Surgery, University of Melbourne, Royal Melbourne Hospital, Parkville, VIC, 3052, Australia.
7
Department of Pharmacology, Yale University School of Medicine, New Haven, CT, USA.
8
Department of Microbiology and Molecular Genetics, University of Pittsburgh School of Medicine, Pittsburgh, PA, USA.
9
Department of Biochemistry & Molecular Biology, University of Melbourne, Parkville, VIC, 3010, Australia. heung@unimelb.edu.au.
10
Bio21 Biotechnology and Molecular Science Institute, University of Melbourne, Parkville, VIC, 3010, Australia. heung@unimelb.edu.au.
11
Cell Signalling Research Laboratories, School of Biomedical Sciences, University of Melbourne, Parkville, VIC, 3010, Australia. heung@unimelb.edu.au.

Abstract

BACKGROUND:

C-terminal Src kinase (Csk) and Csk-homologous kinase (Chk) are the major endogenous inhibitors of Src-family kinases (SFKs). They employ two mechanisms to inhibit SFKs. First, they phosphorylate the C-terminal tail tyrosine which stabilizes SFKs in a closed inactive conformation by engaging the SH2 domain in cis. Second, they employ a non-catalytic inhibitory mechanism involving direct binding of Csk and Chk to the active forms of SFKs that is independent of phosphorylation of their C-terminal tail. Csk and Chk are co-expressed in many cell types. Contributions of the two mechanisms towards the inhibitory activity of Csk and Chk are not fully clear. Furthermore, the determinants in Csk and Chk governing their inhibition of SFKs by the non-catalytic inhibitory mechanism are yet to be defined.

METHODS:

We determined the contributions of the two mechanisms towards the inhibitory activity of Csk and Chk both in vitro and in transduced colorectal cancer cells. Specifically, we assayed the catalytic activities of Csk and Chk in phosphorylating a specific peptide substrate and a recombinant SFK member Src. We employed surface plasmon resonance spectroscopy to measure the kinetic parameters of binding of Csk, Chk and their mutants to a constitutively active mutant of the SFK member Hck. Finally, we determined the effects of expression of recombinant Chk on anchorage-independent growth and SFK catalytic activity in Chk-deficient colorectal cancer cells.

RESULTS:

Our results revealed Csk as a robust enzyme catalysing phosphorylation of the C-terminal tail tyrosine of SFKs but a weak non-catalytic inhibitor of SFKs. In contrast, Chk is a poor catalyst of SFK tail phosphorylation but binds SFKs with high affinity, enabling it to efficiently inhibit SFKs with the non-catalytic inhibitory mechanism both in vitro and in transduced colorectal cancer cells. Further analyses mapped some of the determinants governing this non-catalytic inhibitory mechanism of Chk to its kinase domain.

CONCLUSIONS:

SFKs are activated by different upstream signals to adopt multiple active conformations in cells. SFKs adopting these conformations can effectively be constrained by the two complementary inhibitory mechanisms of Csk and Chk. Furthermore, the lack of this non-catalytic inhibitory mechanism accounts for SFK overactivation in the Chk-deficient colorectal cancer cells.

KEYWORDS:

C-terminal Src kinase; Catalysis, colon cancer; Chk; Csk; Src-family protein kinases; Tumor suppressor

PMID:
28784162
PMCID:
PMC5547543
DOI:
10.1186/s12964-017-0186-x
[Indexed for MEDLINE]
Free PMC Article

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