Lipid signalling pathways in normal and ras-transfected NIH/3T3 cells.
The role of ras oncogenes in cellular signalling pathways involving phospholipid breakdown was studied in untransfected and proto-H-ras and mutated H-, K- and N-ras transfected NIH/3T3 cells. When the cells were grown at low cell densities, all of the ras transfected cells had 2-4 fold higher diacylglycerol (DAG) levels compared to growing NIH/3T3 cells. At high cell densities, DAG levels decreased in the former and increased in contact inhibited NIH/3T3 cells. In this regard, only cells transformed by mutated cellular and viral H-ras oncogenes (but not by the H-ras proto-oncogene) had elevated DAG levels compared to contact inhibited NIH/3T3 cells. The basal levels of inositol phosphates in ras transfected cells were not significantly different from NIH/3T3 cells and did not vary with cell density. Thus, the elevated DAG levels are not a consequence of increased phosphoinositide hydrolysis. The latter was stimulated by serum and bombesin only in normal and proto-H-ras transfected cells. In contrast, stimulation by bradykinin was observed only in cells transformed by mutated cellular ras oncogenes. Furthermore, aluminum fluoride stimulated phosphoinositide breakdown in the latter cells indicating that there was no uncoupling of the G protein from phospholipase C. Treatment of ras transfected cells with dibutyryl cyclic AMP (DB-cAMP), which causes an inhibition of growth and a reversal of the transformed morphology, did not alter the basal levels of inositol phosphates, DB-cAMP, however, did lower DAG levels in some of the transformed cell lines, but elevated DAG levels in low density NIH/3T3 cells. These findings indicate that the ras gene product p21 is not involved in phosphoinositide hydrolysis and that DAG levels do not correlate with cell growth in either normal or ras transfected NIH/3T3 cells. Thus, p21 appears to alter cell growth through mechanism(s) independent of lipid signalling pathways.
Matyas
G R
GR
Laboratory of Molecular and Cellular Neurobiology, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892.
Fishman
P H
PH
D000535:Aluminum / Q000494:pharmacology; D017607:Aluminum Compounds; D000818:Animals; D001839:Bombesin / Q000494:pharmacology; D001920:Bradykinin / Q000494:pharmacology; D002452:Cell Count; D002455:Cell Division / Q000187:drug effects; D002460:Cell Line; D002461:Cell Line, Transformed; D004075:Diglycerides / Q000378:metabolism; D005459:Fluorides / Q000494:pharmacology; D011905:Genes, ras; D051379:Mice; D009154:Mutation; D010716:Phosphatidylinositols / Q000378:metabolism*; D011519:Proto-Oncogenes; D015398:Signal Transduction; D013997:Time Factors; D014162:Transfection
D017607:Aluminum Compounds; D004075:Diglycerides; D010716:Phosphatidylinositols; D000535:Aluminum; D001839:Bombesin; D005459:Fluorides; D001920:Bradykinin; C032311:aluminum fluoride