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Molecular and Cellular Biology, September 2001, p. 6102-6112, Vol. 21, No. 18
Laboratory of Molecular Oncology, IRCM,
Montréal, Québec, Canada H2W 1R71;
Departments of Biochemistry,2
Medicine,6 and Microbiology and
Immunology,7 McGill University, Montréal,
Québec, Canada H3G 1Y6; Sunnybrook and Women's
College Health Sciences Centre3 and the
Departments of Immunology and Medical
Biophysics,4 University of Toronto, Toronto,
Ontario, Canada M4N 3M5; and the Max-Planck-Institute for
Physiological and Clinical Research, W. G. Kerckhoff-Institute,
D-61231 Bad Nauheim, Germany5
Received 20 March 2001/Returned for modification 26 April
2001/Accepted 18 June 2001
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 ~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.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.18.6102-6112.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Synergistic Regulation of Immunoreceptor Signaling
by SLP-76-Related Adaptor Clnk and Serine/Threonine Protein
Kinase HPK-1
*
Corresponding author. Mailing address: Laboratory of
Molecular Oncology, IRCM, 110 Pine Ave. West, Montréal,
Québec, Canada H2W 1R7. Phone: (514) 987-5561. Fax: (514)
987-5562. E-mail: veillea{at}ircm.qc.ca.
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