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Mol. Cell. Biol., Feb 1997, 695-706, Vol 17, No. 2
F Kohlhuber, NC Rogers, D Watling, J Feng, D Guschin, J Briscoe, BA Witthuhn, SV Kotenko, S Pestka, GR Stark, JN Ihle and IM Kerr
Cell lines that are mutated in interferon (IFN) responses have been
critical in establishing an essential role for the JAK family of
nonreceptor tyrosine kinases in interferon signalling. Mutant gamma1A cells
have previously been shown to be complemented by overexpression of JAK2.
Here, it is shown that these cells carry a defect in, and can also be
complemented by, the beta-subunit of the IFN-gamma receptor, consistent
with the hypothesis that the mutation in these cells affects JAK2-receptor
association. In contrast, mutant gamma2A cells lack detectable JAK2 mRNA
and protein. By using gamma2A cells, the role of various domains and
conserved tyrosine residues of JAK2 in IFN-gamma signalling was examined.
Individual mutation of six conserved tyrosine residues, mutation of a
potential phosphatase binding site, or mutation of the arginine residue in
the proposed SH2-like domain had no apparent effect on signalling in
response to IFN-gamma. Results with deletion mutants, however, indicated
that association of JAK2 with the IFN- gammaR2 subunit requires the
amino-terminal region but not the pseudokinase domain. Consistent with
this, in chimeras with JAK1, the JAK2 amino-terminal region was required
for receptor association and STAT1 activation. Conversely, a JAK1-JAK2
chimera with the amino- terminal domains of JAK1 linked to the pseudokinase
and kinase domains of JAK2 is capable of reconstituting JAK-STAT signalling
in response to IFN-alpha and -gamma in mutant U4C cells lacking JAK1. The
specificity of the JAKs may therefore lie mainly in their structural
interaction with different receptor and signalling proteins rather than in
the substrate specificity of their kinase domains.
Copyright © 1997, American Society for Microbiology
A JAK1/JAK2 chimera can sustain alpha and gamma interferon responses
Imperial Cancer Research Fund, London, United Kingdom.
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