Synergistic regulation of immunoreceptor signaling by SLP-76-related adaptor Clnk and serine/threonine protein kinase HPK-1.
Recently, the identification of Clnk, a third member of the SLP-76 family of adaptors expressed exclusively in cytokine-stimulated hemopoietic cells, has been reported by us and by others. Like SLP-76 and Blnk, Clnk was shown to act as a positive regulator of immunoreceptor signaling. Interestingly, however, it did not detectably associate with known binding partners of SLP-76, including Vav, Nck, and GADS. In contrast, it became complexed in activated T cells and myeloid cells with an as yet unknown tyrosine-phosphorylated polypeptide of approximately 92 kDa (p92). In order to understand better the function of Clnk, we sought to identify the Clnk-associated p92. Using a yeast two-hybrid screen and cotransfection experiments with Cos-1 cells, evidence was adduced that p92 is HPK-1, a serine/threonine-specific protein kinase expressed in hemopoietic cells. Further studies showed that Clnk and HPK-1 were also associated in hemopoietic cells and that their interaction was augmented by immunoreceptor stimulation. A much weaker association was detected between HPK-1 and SLP-76. Transient transfections in Jurkat T cells revealed that Clnk and HPK-1 cooperated to increase immunoreceptor-mediated activation of the interleukin 2 (IL-2) promoter. Moreover, the ability of Clnk to stimulate IL-2 promoter activity could be blocked by expression of a kinase-defective version of HPK-1. Lastly we found that in spite of the differential ability of Clnk and SLP-76 to bind cellular proteins, Clnk was apt at rescuing immunoreceptor signaling in a Jurkat T-cell variant lacking SLP-76. Taken together, these results show that Clnk physically and functionally interacts with HPK-1 in hemopoietic cells. Moreover, they suggest that Clnk is capable of functionally substituting for SLP-76 in immunoreceptor signaling, albeit by using a distinct set of intracellular effectors.
Yu
J
J
Laboratory of Molecular Oncology, IRCM, Montréal, Québec, Canada H2W 1R7.
Riou
C
C
Davidson
D
D
Minhas
R
R
Robson
J D
JD
Julius
M
M
Arnold
R
R
Kiefer
F
F
Veillette
A
A
D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins / Q000502:physiology*; D002999:Clone Cells; D006801:Humans; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D011971:Receptors, Immunologic / Q000502:physiology*; D015398:Signal Transduction; D013601:T-Lymphocytes / Q000502:physiology
D048868:Adaptor Proteins, Signal Transducing; C411024:CLNK protein, human; D002352:Carrier Proteins; D010750:Phosphoproteins; D011971:Receptors, Immunologic; C092947:SLP-76 signal Transducing adaptor proteins; C102102:hematopoietic progenitor kinase 1; D017346:Protein Serine-Threonine Kinases