Raf-1-associated protein phosphatase 2A as a positive regulator of kinase activation.
The Raf-1 kinase plays a key role in relaying proliferation signals elicited by mitogens or oncogenes. Raf-1 is regulated by complex and incompletely understood mechanisms including phosphorylation. A number of studies have indicated that phosphorylation of serines 259 and 621 can inhibit the Raf-1 kinase. We show that both serines are hypophosphorylated during early mitogenic stimulation and that hypophosphorylation correlates with peak Raf-1 activation. Concentrations of okadaic acid that selectively inhibit protein phosphatase 2A (PP2A) induce phosphorylation of these residues and prevent maximal activation of the Raf-1 kinase. This effect is mediated via phosphorylation of serine 259. The PP2A core heterodimer forms complexes with Raf-1 in vivo and in vitro. These data identify PP2A as a positive regulator of Raf-1 activation and are the first indication that PP2A may support the activation of an associated kinase.
Abraham
D
D
Vienna Biocenter, Institute of Microbiology and Genetics, Dr. Bohr Gasse 9, A 1030 Vienna, Austria.
Podar
K
K
Pacher
M
M
Kubicek
M
M
Welzel
N
N
Hemmings
B A
BA
Dilworth
S M
SM
Mischak
H
H
Kolch
W
W
Baccarini
M
M
D000818:Animals; D002478:Cells, Cultured; D004789:Enzyme Activation; D010749:Phosphoprotein Phosphatases / Q000378:metabolism*; D054648:Protein Phosphatase 2; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D015398:Signal Transduction
D019908:Proto-Oncogene Proteins c-raf; D010749:Phosphoprotein Phosphatases; D054648:Protein Phosphatase 2