Association of a 85-kDa Serine Kinase with Activated Fibroblast Growth Factor Receptor-4

doi:10.1074/jbc.271.3.1270

Association of a 85-kDa Serine Kinase with Activated Fibroblast Growth Factor Receptor-4 (*)

From the Molecular/Cancer Biology Laboratory, Haartman Institute, University of Helsinki, PL21 (Haartmaninkatu 3), 00014 Helsinki, Finland and
(1)Ludwig Institute for Cancer Research, Uppsala Branch, Box 595, S-751 24 Uppsala, Sweden

^§ To whom correspondence should be addressed. Fax: 358-0-434-6448.

Abstract

Fibroblast growth factors (FGFs) transduce a variety of biological signals via four distinct tyrosine kinase receptors. We have characterized the phosphorylation of FGF receptor 4 (FGFR-4) and its association with a putative substrate, p85, using transfected L6 myoblast and NIH3T3 fibroblast cell lines. FGFR-4 was phosphorylated in vivo and in vitro mainly on serine and threonine residues in several peptides and to a lower degree on tyrosine residues. When analyzed further by in-gel kinase assay, immunoprecipitates of ligand-activated FGFR-4 contained a serine autophosphorylated polypeptide doublet of 85 kDa. Analysis of the major autophosphorylation site Y754F mutant of FGFR-4 showed that binding of p85 and its serine phosphorylation were independent of receptor autophosphorylation at this site. Okadaic acid treatment increased the basal autophosphorylation activity of p85 but decreased FGFR-4 tyrosine phosphorylation. In contrast, orthovanadate treatment increased the tyrosine phosphorylation of FGFR-4. These data show that a serine kinase is associated with activated FGFR-4 and suggest a role for serine phosphorylation in FGFR-4 function.

Footnotes

↵* This work was supported by the Maud Kuistila Foundation, Research and Science Foundation of Farmos, Emil Aaltonen Foundation, Sigrid Juselius Foundation, Finnish Cancer Research Organizations, and Finnish Academy of Sciences. The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

FGFR

fibroblast growth factor receptor

FGF

fibroblast growth factor

PLC-

phospholipase C-

aFGF

acidic fibroblast growth factor

WT

wild type

PAGE

polyacrylamide gel electrophoresis.
↵²S. Vainikka, V. Joukov, P. Klint, and K. Alitalo, unpublished results.
- Received October 6, 1995.
- Revision received November 22, 1995.