Regulation of mitogen-activated protein kinase activation by protein kinases A and C in a cell-free system.
Previously pp60v-src, cyclin A, p39mos, and maturation-promoting factor (composed of Cdc2 and cyclin B) have been shown to activate mitogen-activated protein kinase (MAPK) and MAPK kinase (MEK) in cell-free extracts of Xenopus oocytes. The pp60v-src pathway is dependent on a functional Ras signal whereas the cyclin/maturation-promoting factor pathway is not. Here we show that protein kinase C (PKC) is also able to stimulate MAPK in a Ras-dependent manner, but PKC is not necessary for signaling by pp60v-src. In addition, preincubation of extracts with cAMP-dependent protein kinase (PKA) blocks stimulation of MAPK by cyclin, p21V12ras, PKC, or pp60v-src, by at least 50%, but stimulation by c-Mos is unaffected. Furthermore, inhibition of endogenous PKA by the heat-stable PKA inhibitor is sufficient to stimulate MAPK activity in these extracts in the absence of protein synthesis and without dependence on a functional Ras protein. These results suggest that independent pp60v-src and PKC pathways converge at Ras and that PKA acts to block MAPK activation by both Ras-dependent and -independent signals.
VanRenterghem
B
B
Department of Pharmacology, University of Colorado School of Medicine, Denver 80262.
Browning
M D
MD
Maller
J L
JL
D000595:Amino Acid Sequence; D000818:Animals; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D002474:Cell-Free System; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology*; D004789:Enzyme Activation; D005260:Female; D008969:Molecular Sequence Data; D015688:Oncogene Protein pp60(v-src) / Q000502:physiology; D011493:Protein Kinase C / Q000502:physiology*; D016283:Proto-Oncogene Proteins p21(ras) / Q000502:physiology; D014982:Xenopus laevis
D015688:Oncogene Protein pp60(v-src); D017868:Cyclic AMP-Dependent Protein Kinases; D011493:Protein Kinase C; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D016283:Proto-Oncogene Proteins p21(ras)