The requirement of specific membrane domains for Raf-1 phosphorylation and activation.
Activation of Raf-1 by Ras requires recruitment to the membrane as well as additional phosphorylations, including phosphorylation at serine 338 (Ser-338) and tyrosine 341 (Tyr-341). In this study we show that Tyr-341 participates in the recruitment of Raf-1 to specialized membrane domains called "rafts," which are required for Raf-1 to be phosphorylated on Ser-338. Raf-1 is also thought to be recruited to the small G protein Rap1 upon GTP loading of Rap1. However, this does not result in Raf-1 activation. We propose that this is because Raf-1 is not phosphorylated on Tyr-341 upon recruitment to Rap1. Redirecting Rap1 to Ras-containing membranes or mimicking Tyr-341 phosphorylation of Raf-1 by mutation converts Rap1 into an activator of Raf-1. In contrast to Raf-1, B-Raf is activated by Rap1. We suggest that this is because B-Raf activation is independent of tyrosine phosphorylation. Moreover, mutants that render B-Raf dependent on tyrosine phosphorylation are no longer activated by Rap1.
Carey
Kendall D
KD
Vollum Institute, Department of Cell and Developmental Biology, L474 Oregon Health Sciences University, Portland, Oregon 97201, USA.
Watson
Robert T
RT
Pessin
Jeffrey E
JE
Stork
Philip J S
PJ
D000595:Amino Acid Sequence; D000818:Animals; D001665:Binding Sites; D019556:COS Cells; D002522:Chlorocebus aethiops; D018076:DNA, Complementary / Q000235:genetics; D011905:Genes, ras; D021962:Membrane Microdomains / Q000737:chemistry / Q000378:metabolism*; D008969:Molecular Sequence Data; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D019000:Phosphotyrosine / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000737:chemistry / Q000378:metabolism; D015183:Restriction Mapping; D014162:Transfection
D018076:DNA, Complementary; D011994:Recombinant Proteins; D010768:Phosphoserine; D019000:Phosphotyrosine; D019908:Proto-Oncogene Proteins c-raf