Malignant transformation by ras and other oncogenes produces common alterations in inositol phospholipid signaling pathways.

Abstract

The role ofras proteins in signal transduction was assessed by studying inositol phospholipid metabolism and inositol phospholipid-mediated cellular responsiveness to agonists in cells transformed by ras and other oncogenes. Specific alterations were observed in the inositol phospholipid cycle of ras-transformed fibroblasts, but similar changes were also produced by spontaneous transformation or transformation mediated by either membrane-associated oncogenes, such as src, met, or trk, or cytoplasmic oncogenes, mos and raf; the nuclear oncogenesfos and myc did not produce these changes. The alterations included (i) stimulation of phospholipase A2 activity as indicated by elevated levels of glycerophosphoinositol and nonesterified arachidonic acid and (ii) specific uncoupling between surface receptor-mediated stimulation by platelet-derived growth factor, bombesin, or serum and activation of intracellular phospholipase C. These findings suggest the existence of common biochemical pathways for transformation by cytoplasmic and membrane-associated oncogenes and are not consistent with the hypothesis that 21-kDa ras proteins (p21) are direct or distinct regulatory elements of phospholipase C or phospholipase A2 in inositol phospholipid signal transduction pathways.ras genes belong to a multigene family with a high degree of conservation, suggesting that they have essential cellular functions. It has been suggested that ras proteins play a role in signal transduction (for a review, see ref. 1). A direct relation with the mammalian adenylate cyclase system has been rejected (2). Other studies have investigated a possible role of 21-kDa ras proteins (p21) in inositol phospholipid signaling pathways (3-8), but these reports appear to be at least partially inconsistent. Thus, although some reports suggested that p21 ras proteins mediate stimulation of phospholipase C (3-5), others pointed to stimulation of phospholipase A2 (6) and yet others described inhibition of both phospholipases C and A2 in ras-transformed cells (7,8).In view of the conflicting reports, we have assessed the specificity of ras action by analyzing the inositol phospholipid cycle in normal and malignant NIH 3T3 and Rat-1 cells transformed either spontaneously or by the action of oncogenes other than ras. When available, normal revertant cell lines were also compared to their transformed counterparts.Also, in an effort to distinguish transformation-specific from proliferation-specific events, quiescent and actively proliferating normal cells were compared. In this communication we report that specific alterations were observed in the inositol phospholipid pathway of ras-transformed cells, but similar changes were also found in cells transformed spontaneously or by the action of other cytoplasmic and membraneassociated oncogenes. The alterations of inositol phospholipid metabolism included specific stimulation of phospholipase A2-like activity and specific uncoupling of intracellular phospholipase C activity from extracellular signals. These find...

Alteration of the lipid profile in lymphomas induced by MYC overexpression

“…PIs, which are phosphoinositide metabolites, are catalyzed by phospholipase A2 and a lysophospholipase, which are known to be RASdependent (45). Lysophospholipase catalyzes the production of PI from phosphoinositides, a process which is greatly augmented by RAS transformation in both fibroblasts and other cells, indicating the importance of glycerophospholipid metabolism in RAS (46)(47)(48). Our results could reflect that generally specific oncogenes will be associated with unique lipid signatures.…”

Cells transformed by ODC, c-Ha-ras and v-src exhibit MAP kinase/Erk-independent constitutive phosphorylation of Sos, Raf and c-Jun activation domain, and reduced PDGF receptor expression

“…Controversial results also exist regarding the speci®city of these changes to ras transformation. In v-src-transformed cells PDGF has been documented to stimulate normally phosphoinositide hydrolysis (Parries et al, 1987) and c-fos expression (Lin et al, 1988), but a complete lack of the PDGFstimulated inositol phospholipid hydrolysis has been reported as well (Alonso et al, 1988).…”

“…Cells transformed by ras, the most commonly activated oncogene in human cancers, have been found to become refractory to PDGF stimulation and display loss or suppression of the PDGFstimulated phospholipase C activity (Alonso et al, 1988;Parries et al, 1987), Ca 2+ mobilization (Benjamin et al, 1988) and expression of growth regulatory genes, like c-myc, c-fos and ornithine decarboxylase (ODC) (HoÈ lttaÈ et al, 1988;Lin et al, 1988;Zullo and Faller, 1988). The ras-transformed cells have, however, been found to display relatively normal levels of PDGF receptors (Parries et al, 1987;Rake et al, 1991;Zullo and Faller, 1988).…”

Reorganization of Actin Cytoskeleton by the Phosphoinositide Metabolite Glycerophosphoinositol 4-Phosphate

“…These molecules have been associated with the expression of oncogenic Ras (Alonso et al, 1988;Alonso and Santos, 1990;Valitutti et al, 1991;Falasca et al, 1995) and are biologically active. Lysophosphatidylinositol acts as a mitogen in Rastransformed cells (Falasca and Corda, 1994;Falasca et al, 1995Falasca et al, , 1998, and among the glycerophosphoinositols, glycerophosphoinositol 4-phosphate (GroPIns-4P) has been shown to inhibit the heterotrimeric G protein Gs in thyroid cells, thereby decreasing the cellular levels of cAMP and inhibiting cAMPdependent functions, such as cell proliferation and iodide uptake (Iacovelli et al, 1993).…”