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Session II : Receptor signaling and G proteins Poster II, 51
PDGFRbetaY857F mutant mediates PDGF-BB-induced signalling and chemotaxis,
despite severely reduced kinase activity.
Piotr Wardega, Carl-Henrik Heldin, Johan Lennartsson.
Ludwig Institute for Cancer Research, Uppsala University, Box 595, SE-751 24 Uppsala,
Sweden
Piotr.Wardega(AT)LICR.uu.se,C-H.Heldin(AT)LICR.uu.se,
Johan.Lennartsson(AT)LICR.uu.se
Platelet-derived growth factor receptor (PDGFR) becomes dimerized and activated upon
ligand binding, which leads to receptor transphosphorylation and increases its enzymatic
activity. In the present study, we studied the effects of mutation of tyrosine residue 857 in the
activation loop of PDGFRbeta, to phenylalanine. In agreement with published work, our
studies show, that PDGFRbetaY857F has much lower kinase activity in vitro in comparison
to PDGFRbetaWT , both as measured as receptor autophosphorylation and as phosphorylation
of an exogenous substrate. Interestingly, PDGF-induced tyrosine phosphorylation of
PDGFRbeta, in a cellular context, is not affected by the Tyr857 mutation. There are, however
significant changes in ability of PDGFRbetaY857F to induce signal transduction compared to
the wild-type receptor. For example, we could show that Stat5 signalling differs dramatically
between PDGFRbetaWT and PDGFRbetaY857F. We observed almost complete loss of
PDGF-induced Stat5 phosphorylation by the mutant receptor. Surprisingly Stat3, which
belongs to the same group of transcription factors as Stat5, was phosphorylated to the same
extent by mutant and wild-type receptor. In addition, we have also found that the Akt and
JNK signalling pathways are not affected by the PDGFRbetaY857F mutation. Moreover, the
Erk pathway was activated by slower kinetics in the mutant receptor. Interestingly, in spite of
the defect in the PDGFRbetaY857F receptors kinase activity and the changes observed in
signal transudction it could still efficiently induce cell chemotaxis. It is known that many
cytoplasmic tyrosine kinases are capable of phosphorylating the PDGFR and it is possible that
these may compensate for the lowered enzymatic activity of PDGFRbetaY857F . In summary,
we have demonstrated that the PDGFRbetaY857F has defect kinase activity, but is
nevertheless phosphorylated in the cell, presumably by cytoplasmic kinases and can induce
signals sufficient for normal chemotaxis toward PDGF-BB.
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