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Molecular and Cellular Biology, September 2001, p. 6170-6180, Vol. 21, No. 18
Department of Molecular Genetics and
Biochemistry, University of Pittsburgh School of Medicine,
Pittsburgh, Pennsylvania 15261
Received 8 May 2001/Accepted 27 June 2001
The c-fes locus encodes a 93-kDa non-receptor protein
tyrosine kinase (Fes) that regulates the growth and differentiation of
hematopoietic and vascular endothelial cells. Unique to Fes is a long
N-terminal sequence with two regions of strong homology to coiled-coil
oligomerization domains. We introduced leucine-to-proline substitutions
into the coiled coils that were predicted to disrupt the coiled-coil
structure. The resulting mutant proteins, together with
wild-type Fes, were fused to green fluorescent protein and expressed in
Rat-2 fibroblasts. We observed that a point mutation in the first
coiled-coil domain (L145P) dramatically increased Fes tyrosine kinase
and transforming activities in this cell type. In contrast, a similar
point mutation in the second coiled-coil motif (L334P) was without
effect. However, combining the L334P and L145P mutations reduced
transforming and kinase activities by approximately 50% relative to
the levels of activity produced with the L145P mutation alone. To study
the effects of the coiled-coil mutations in a biologically relevant
context, we expressed the mutant proteins in the granulocyte-macrophage
colony-stimulating factor (GM-CSF)-dependent myeloid leukemia cell line
TF-1. In this cellular context, the L145P mutation induced GM-CSF
independence, cell attachment, and spreading. These effects correlated
with a marked increase in L145P protein autophosphorylation relative to
that of wild-type Fes. In contrast, the double coiled-coil mutant
protein showed greatly reduced kinase and biological activities in TF-1
cells. These data are consistent with a role for the first coiled coil
in the negative regulation of kinase activity and a requirement for the
second coiled coil in either oligomerization or recruitment of
signaling partners. Gel filtration experiments showed that the unique
N-terminal region interconverts between monomeric and oligomeric forms.
Single point mutations favored oligomerization, while the double point
mutant protein eluted essentially as the monomer. These data provide
new evidence for coiled-coil-mediated regulation of c-Fes tyrosine
kinase activity and signaling, a mechanism unique among tyrosine kinases.
0270-7306/01/$04.00+0 DOI: 10.1128/MCB.21.18.6170-6180.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
A Point Mutation in the N-Terminal Coiled-Coil
Domain Releases c-Fes Tyrosine Kinase Activity and Survival Signaling
in Myeloid Leukemia Cells
*
Corresponding author. Mailing address: Department of
Molecular Genetics and Biochemistry, University of Pittsburgh School of
Medicine, E1240 Biomedical Science Tower, Pittsburgh, PA 15261. Phone:
(412) 648-9495. Fax: (412) 624-1401. E-mail:
tsmithga{at}pitt.edu.
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