PubMed Journals: Mol Cell Biol
Source: PMID: 9111318
⇦ ⇨ Mol Cell Biol. 1997 May;17(5):2497-501.
Activation of Jak2 catalytic activity requires
phosphorylation of Y1007 in the kinase activation
Feng J(1), Witthuhn BA, Matsuda T, Kohlhuber
F, Kerr IM, Ihle JN.
(1) Department of Biochemistry,
St. Jude Children's Research Hospital,
Memphis, Tennessee 38105, USA.
The Janus protein tyrosine kinases (Jaks)
play critical roles in transducing growth
and differentiation signals emanating from
ligand-activated cytokine receptor complexes.
The activation of the Jaks is hypothesized
to occur as a consequence of auto- or
transphosphorylation on tyrosine residues
associated with ligand-induced aggregation
of the receptor chains and the associated
Jaks. In many kinases, regulation of catalytic
activity by phosphorylation occurs on residues
within the activation loop of the kinase
domain. Within the Jak2 kinase domain, there
is a region that has considerable sequence
homology to the regulatory region of the
insulin receptor and contains two tyrosines,
Y1007 and Y1008, that are potential regulatory
sites. In the studies presented here, we
demonstrate that among a variety of sites,
Y1007 and Y1008 are sites of trans- or
autophosphorylation in vivo and in in vitro
kinase reactions. Mutation of Y1007, or
both Y1007 and Y1008, to phenylalanine essentially
eliminated kinase activity, whereas mutation
of Y1008 to phenylalanine had no detectable
effect on kinase activity. The mutants were
also examined for the ability to reconstitute
erythropoietin signaling in gamma2 cells,
which lack Jak2. Consistent with the kinase
activity, mutation of Y1007 to phenylalanine
eliminated the ability to restore signaling.
Moreover, phosphorylation of a kinase-inactive
mutant (K882E) was not detected, indicating
that Jak2 activation during receptor aggregation
is dependent on Jak2 and not another
receptor-associated kinase. The results
demonstrate the critical role of phosphorylation
of Y1007 in Jak2 regulation and function.
PMCID: PMC232098 PMID: 9111318 [Indexed