Sprouty2 inhibits the Ras/MAP kinase pathway by inhibiting the activation of Raf.
Several genetic studies in Drosophila have shown that the dSprouty (dSpry) protein inhibits the Ras/mitogen-activated protein (MAP) kinase pathway induced by various activated receptor tyrosine kinase receptors, most notably those of the epidermal growth factor receptor (EGFR) and fibroblast growth factor receptor (FGFR). Currently, the mode of action of dSpry is unknown, and the point of inhibition remains controversial. There are at least four mammalian Spry isoforms that have been shown to co-express preferentially with FGFRs as compared with EGFRs. In this study, we investigated the effects of the various mammalian Spry isoforms on the Ras/MAP kinase pathway in cells overexpressing constitutively active FGFR1. hSpry2 was significantly more potent than mSpry1 or mSpry4 in inhibiting the Ras/MAP kinase pathway. Additional experiments indicated that full-length hSpry2 was required for its full potency. hSpry2 had no inhibitory effect on either the JNK or the p38 pathway and displayed no inhibition of FRS2 phosphorylation, Akt activation, and Ras activation. Constitutively active mutants of Ras, Raf, and Mek were employed to locate the prospective point of inhibition of hSpry2 downstream of activated Ras. Results from this study indicated that hSpry2 exerted its inhibitory effect at the level of Raf, which was verified in a Raf activation assay in an FGF signaling context.
Yusoff
Permeen
P
Signal Transduction Laboratory, Institute of Molecular and Cell Biology, National University of Singapore, Singapore 117609, Singapore.
Lao
Dieu-Hung
DH
Ong
Siew Hwa
SH
Wong
Esther Sook Miin
ES
Lim
Jormay
J
Lo
Ting Ling
TL
Leong
Hwei Fen
HF
Fong
Chee Wai
CW
Guy
Graeme R
GR
D000818:Animals; D002460:Cell Line; D003001:Cloning, Molecular; D004330:Drosophila; D005346:Fibroblast Growth Factors / Q000037:antagonists & inhibitors*; D006801:Humans; D020935:MAP Kinase Signaling System / Q000502:physiology*; D020928:Mitogen-Activated Protein Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D010957:Plasmids; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D014162:Transfection
D009419:Nerve Tissue Proteins; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; C404992:Spry2 protein, rat; D005346:Fibroblast Growth Factors; D019908:Proto-Oncogene Proteins c-raf; D020928:Mitogen-Activated Protein Kinases