Chk, a Csk Family Tyrosine Protein Kinase, Exhibits Csk-like Activity in Fibroblasts, but Not in an Antigen-specific T-cell Line

doi:10.1074/jbc.272.2.1355

Chk, a Csk Family Tyrosine Protein Kinase, Exhibits Csk-like Activity in Fibroblasts, but Not in an Antigen-specific T-cell Line*

From the ^‡ McGill Cancer Centre and Departments of
^§ Biochemistry, and
^∥ Medicine and ^∥ Oncology, McGill University, Montréal H3G 1Y6, Canada and the ^∥ Departments of Medicine and Oncology, Montreal General Hospital, Montréal H3G 1A4, Canada

** Scientist of the Medical Research Council of Canada. To whom correspondence should be addressed:
Rm. 715, McIntyre Medical Sciences Bldg., McGill University, 3655 Drummond St., Montréal, Canada H3G 1Y6.
Tel.: 514-398-8936; Fax: 514-398-4438; E-mail: VEILLETTE{at}MEDCOR.MCGILL.CA.

Abstract

The Csk family of tyrosine protein kinases comprises two members named Csk and Chk. These enzymes phosphorylate the carboxyl-terminal tyrosine of Src-related kinases in vitro, thereby repressing their activity. Csk has been found to be necessary for normal embryonic development, and to be a potent negative regulator of antigen receptor signaling in T-lymphocytes. As the functions of Chk in mammalian cells are not known, we examined its ability to carry out Csk-like functions in vivo. Like p50^csk, Chk reduced the elevated phosphotyrosine levels and the augmented activity of Src family kinases in Csk-deficient fibroblasts. Contrary to Csk, however, Chk was inefficient at repressing antigen receptor-induced signals in a T-cell line (BI-141). We also noted that Chk, but not Csk, failed to stably associate with cellular membranes following addition of a membrane targeting signal to its amino terminus. This observation suggested that Chk may contain dominant targeting sequences disallowing its recruitment to cellular membranes. Hence, these data demonstrate that Chk can mediate some, but not all, Csk-related functions in vivo. Moreover, they suggest that the “restricted” function of Chk may relate at least in part to its inability to be recruited to certain cellular locales.

Footnotes

↵^¶ Held a Steve Fonyo Studentship from the National Cancer Institute of Canada.
↵* This work was supported by grants from the National Cancer Institute of Canada and the Medical Research Council of Canada. The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

SH

Src homology

TCR

T-cell receptor

MEFs

mouse embryo fibroblasts

FCS

fetal calf serum

GAP

GTPase-activating protein

MAb

monoclonal antibody

MOPS

N-morpholinopropanesulfonic acid

IL-2

interleukin-2

RIPA

radioimmunoprecipitation assay.
↵²D. Davidson, L. M. L. Chow, and A. Veillette, unpublished results.
- Received August 23, 1996.
- Revision received October 15, 1996.