Effect of transmembrane and kinase domain mutations on fibroblast growth factor receptor 3 chimera signaling in PC12 cells - A model for the control of receptor tyrosine kinase activation
S. Raffioni et al., Effect of transmembrane and kinase domain mutations on fibroblast growth factor receptor 3 chimera signaling in PC12 cells - A model for the control of receptor tyrosine kinase activation, J BIOL CHEM, 273(52), 1998, pp. 35250-35259
The effect of six point mutations causing various human skeletal dysplasias
, occurring in the transmembrane (TM) and kinase domains (KD) of fibroblast
growth factor receptor 3, were introduced into a chimera composed of the e
xtracellular domain of human platelet-derived growth factor beta and the TM
and intracellular domains of hFGFR3, Stable transfectants in rat PC12 cell
s showed distinct differences in the two classes of mutations. The cells co
ntaining TM mutants displayed normal expression and activation but higher r
esponsiveness to lower doses of ligand, The KD mutants showed significantly
altered expression patterns. Normal amounts of a lower M-r receptor (p130)
reflecting incomplete glycosylation, but only greatly decreased amounts of
the mature (p170) form, were observed. However, the latter material showed
normal ligand-dependent activation. In contrast, the p130 form, which is r
egularly observed in the expression of both native and chimeric receptors,
exhibits strong ligand-independent tyrosine phosphorylation, particularly w
ith the K650E mutation. Expression of two of the KD mutants (K650M and K650
E), under control of an inducible metallothionein promoter, indicated that
this receptor was sufficiently autoactivated to produce at least partial di
fferentiation and, in the case of the K650E mutation, to induce ligand-inde
pendent neurite outgrowth. A model is presented that suggests that the low
IM, (p130) KD mutants can, under the right conditions, signal intracellular
ly, but when they are fully glycosylated and move to the cell surface they
adopt a normal, inhibited conformation, in the form of ligand-independent d
imers, that neutralizes the effects of the mutations. When ligands bind, th
ese dimeric receptors are activated in a normal manner. This model suggests
that unliganded dimers may be a common intermediate in receptor tyrosine k
inase signaling.