ras-p21 activates phospholipase D and A2, but not phospholipase C or PKC, in Xenopus laevis oocytes.
Xenopus laevis oocytes are a powerful tool for the characterization of signal transduction pathways leading to the induction of DNA synthesis. Since activation of PLA2, PLC, or PLD has been postulated as a mediator of ras function, we have used the oocyte system to study the putative functional relationship between ras-p21 and these phospholipases. A rapid generation of PA and DAG was observed after ras-p21 microinjection, suggesting the activation of both PLC and PLD enzymes. However, production of DAG was sensitive to inhibition of the PA-hydrolase by propranolol, indicating that PLD is the enzyme responsible for the generation of both PA and DAG. Microinjection of PLD or ras-p21 induced the late production of lysophosphatidylcholine on a p42MAPK-dependent manner, an indication of the activation of a PLA2. Inhibition of this enzyme by quinacrine does not inhibit PLD- or ras-induced GVBD, suggesting that PLA2 activation is not needed for ras or PLD function. Contrary to 3T3 fibroblasts, where ras-p21 is functionally dependent for its mitogenic activity on TPA- and staurosporine-sensitive PKC isoforms, in Xenopus oocytes, induction of GVBD by ras-p21 was independent of PKC, while PLC-induced GVBD was sensitive to PKC inhibition. Thus, our results demonstrate the activation of PLD and PLA2 by ras-p21 proteins, while no effect on PLC was observed.
Instituto de Investigaciones Biomédicas, Madrid, Spain.
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Carnero
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Dolfi
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Lacal
D000595:Amino Acid Sequence; D000818:Animals; D004075:Diglycerides / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D005260:Female; D008845:Microinjections; D008969:Molecular Sequence Data; D009865:Oocytes / Q000378:metabolism*; D010712:Phosphatidic Acids / Q000378:metabolism; D010739:Phospholipase D / Q000378:metabolism*; D010741:Phospholipases A / Q000378:metabolism*; D054467:Phospholipases A2; D011433:Propranolol / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D016283:Proto-Oncogene Proteins p21(ras) / Q000008:administration & dosage / Q000494:pharmacology*; D010738:Type C Phospholipases / Q000378:metabolism*; D014982:Xenopus laevis
D004075:Diglycerides; D010712:Phosphatidic Acids; D011433:Propranolol; D011493:Protein Kinase C; D010741:Phospholipases A; D054467:Phospholipases A2; D010738:Type C Phospholipases; D010739:Phospholipase D; D016283:Proto-Oncogene Proteins p21(ras)