Analysis of CSK Homologous Kinase (CHK/HYL) in Hematopoiesis by Utilizing Gene Knockout Mice

“…It is well documented that CHK can down-regulate the activity of SFKs in vivo (25)(26)(27)(28)(29). For example, CHK inactivation of Src and Lyn was associated with suppression of breast carcinoma cell growth (29).…”

Section: Discussionmentioning

confidence: 99%

A Novel Non-catalytic Mechanism Employed by the C-terminal Src-homologous Kinase to Inhibit Src-family Kinase Activity

Chong

Mulhern

Zhu

et al. 2004

Journal of Biological Chemistry

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Although C-terminal Src kinase (CSK)-homologous kinase (CHK) is generally believed to inactivate Src-family tyrosine kinases (SFKs) by phosphorylating their consensus C-terminal regulatory tyrosine (Tyr T ), exactly how CHK inactivates SFKs is not fully understood. Herein, we report that in addition to phosphorylating Tyr T , CHK can inhibit SFKs by a novel non-catalytic mechanism. First, CHK directly binds to the SFK members Hck, Lyn, and Src to form stable protein complexes. The complex formation is mediated by a non-catalytic Tyr T -independent mechanism because it occurs even in the absence of ATP or when Tyr T of Hck is replaced by phenylalanine. Second, the non-catalytic CHK-SFK interaction alone is sufficient to inactivate SFKs by inhibiting the catalytic activity of autophosphorylated SFKs. Third, CHK and Src co-localize to specific plasma membrane microdomains of rat brain cells, suggesting that CHK is in close proximity to Src such that it can effectively inactivate Src in vivo. Fourth, native CHK⅐Src complex exists in rat brain, and recombinant CHK⅐Hck complex exists in transfected HEK293T cells, implying that CHK forms stable complexes with SFKs in vivo. Taken together, our findings suggest that CHK inactivates SFKs (i) by phosphorylating their Tyr T and (ii) by this novel Tyr T -independent mechanism involving direct binding of CHK to SFKs. It has been documented that autophosphorylated SFKs can still be active, in some cases even when their Tyr T is phosphorylated. Thus, the ability of the Tyr T -independent mechanism to suppress the activity of both non-phosphorylated and autophosphorylated SFKs represents a fail-safe measure employed by CHK to down-regulate SFK signaling under all circumstances.Src-family kinases (SFKs) 1 are non-receptor protein-tyrosine kinases that participate in many cellular functions ranging from cell growth and proliferation to memory and learning (1). The kinase activity of SFKs is regulated by phosphorylation, as well as by their interaction with other cellular proteins. Among the various regulatory mechanisms, the most important are autophosphorylation of a consensus tyrosine (Tyr A ) 2 in the kinase domain and phosphorylation of a consensus regulatory tyrosine near the C terminus (Tyr T ) 2 (2, 3). Autophosphorylation of Tyr A leads to activation of SFKs (1, 4, 5). The crystal structure of the autophosphorylated kinase domain of the Srcfamily kinase Lck reveals that the phosphorylated Tyr A (Tyr(P) A ) stabilizes the active kinase domain configuration by forming ionic interactions with the conserved Arg in the catalytic loop (6). We previously reported that the Src-family member Hck could undergo autophosphorylation at a novel site (Tyr-29) 2 in the Unique domain and that autophosphorylation of Hck at Tyr-29 contributed to Hck activation (4). However, the structural basis of activation by Tyr-29 autophosphorylation is not yet known. In contrast to the activating effect of Tyr A and Hck Tyr-29 autophosphorylation, Tyr T phosphorylation results in inactivation (7). Cryst...

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“…CHK is related to CSK, but tends to be expressed primarily in brain and hematopoietic cells. In contrast to the rather dramatic phenotype exhibited by CSK 7/7 mice, CHK 7/7 mice exhibit no detectable phenotype, even in cells of hematopoietic lineage (Hamaguchi et al, 1996;Samokhvalov et al, 1997), suggesting that CHK probably has di erent cellular functions than CSK. The similarities and di erences in function between CSK and CHK have been highlighted in a paper by Davidson et al (Davidson et al, 1997b).…”

Section: Ptp1b and Other Ptps That Might Target C-srcmentioning

confidence: 99%

Selected glimpses into the activation and function of Src kinase

2000

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Since the discovery of the v-src and c-src genes and their products, much progress has been made in the elucidation of the structure, regulation, localization, and function of the Src protein. Src is a non-receptor protein tyrosine kinase that transduces signals that are involved in the control of a variety of cellular processes such as proliferation, di erentiation, motility, and adhesion. Src is normally maintained in an inactive state, but can be activated transiently during cellular events such as mitosis, or constitutively by abnormal events such as mutation (i.e. v-Src and some human cancers). Activation of Src occurs as a result of disruption of the negative regulatory processes that normally suppress Src activity, and understanding the various mechanisms behind Src activation has been a target of intense study. Src associates with cellular membranes, in particular the plasma membrane, and endosomal membranes. Studies indicate that the di erent subcellular localizations of Src could be important for the regulation of speci®c cellular processes such as mitogenesis, cytoskeletal organization, and/or membrane tra cking. This review will discuss the history behind the discovery and initial characterization of Src and the regulatory mechanisms of Src activation, in particular, regulation by modi®cation of the carboxyterminal regulatory tyrosine by phosphatases and kinases. Its focus will then turn to the di erent subcellular localizations of Src and the possible roles of nuclear and perinuclear targets of Src. Finally, a brief section will review some of our present knowledge regarding Src involvement in human cancers. Oncogene (2000) 19, 5620 ± 5635.

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Analysis of CSK Homologous Kinase (CHK/HYL) in Hematopoiesis by Utilizing Gene Knockout Mice

Cited by 47 publications

References 0 publications

Genomic structure and alternative splicing of the murine bhk/ctk/ntk gene

Genomic structure and alternative splicing of the murine bhk/ctk/ntk gene

A Novel Non-catalytic Mechanism Employed by the C-terminal Src-homologous Kinase to Inhibit Src-family Kinase Activity

Selected glimpses into the activation and function of Src kinase

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