Evidence that v-Src-induced phospholipase D activity is mediated by a G protein.

Abstract

v-Src-induced increases in diglyceride are derived from phosphatidylcholine via a type D phospholipase (PLD) and a phosphatidic acid phosphatase. v-Src-induced PLD activity, as measured by PLD-catalyzed transphosphatidylation of phosphatidylcholine to phosphatidylethanol, is inhibited by GDPIS, which inhibits G-protein-mediated intracellular signals. Similarly, v-Src-induced increases in diglyceride are also blocked by GDPISS. In contrast to the PLD activity induced by v-Src, PLD activity induced by the protein kinase C agonist, 12-0-tetradecanoylphorbol-13-acetate (TPA), was insensitive to GDPIIS. Consistent with the involvement of a G protein in the activation of PLD activity by v-Src, GTP-yS, a nonhydrolyzable analog of GTP that potentiates G-protein-mediated signals, strongly enhanced PLD activity in v-Src-transformed cells relative to that in parental BALB/c 3T3 cells. v-Src was dependent upon the presence of ATP but was unaffected by either cholera or pertussis toxin. These data suggest that v-Src induces PLD activity through a phosphorylation event and is mediated by a cholera and pertussis toxin-insensitive G protein.Cellular transformation involves the disruption of intracellular signaling mechanisms (see reference 12 for a review). Protein-tyrosine kinase activity is frequently an early event in the transduction of intracellular signals and has been extensively implicated in transformation tumorigenesis (12). The oncogenic protein-tyrosine kinase, v-Src, transforms cells because of a constitutively active kinase (22). As a result of this constitutively active kinase activity, v-Src activates multiple intracellular signaling mechanisms that lead to the induction of gene expression (17,41,43). Protein kinase C (PKC) is a serine/threonine-specific protein kinase that has been implicated in v-Src-induced intracellular signaling (20,38,43,45,51,53), although not all intracellular signals activated by v-Src involve PKC (41, 43). PKC is activated by the phospholipid metabolite diglyceride (DG) (37). DG is frequently generated by the phospholipase C-mediated hydrolysis of phosphatidylinositol 4,5-bisphosphate (see references 16 and 17 for a review); however, v-Src-induced increases in DG are derived from phosphatidylcholine (PC) via the action of a type D phospholipase (PLD) and a phosphatidic acid phosphatase (50). The activation of PLD by v-Src was found to be independent of PKC (48). Thus, it is likely that the DG produced by the PLD-phosphatidic acid phosphatase mechanism is responsible for the activation of PKC by v-Src. (18,31,33,34), epidermal growth factor (26, 27, 55), and colony-stimulating factor 1 (24, 25) receptors. G proteins have also been implicated in mediating the effects of c-Src on the ,-adrenergic response (11,36). We previously demonstrated that the activation of PKC-dependent gene expression and phosphorylation of the PKC substrate MARCKS by the related protein-tyrosine kinase v-Fps is dependent on a G protein (1). Since PKC is presumably the target of the PLDgenerated DG, these data su...

Transmodulation between Phospholipase D and c-Src Enhances Cell Proliferation

“…In this study, we demonstrate for the first did not affect PLD activity in rat mesangial cells (44) but is in contrast to observations with fibroblasts transformed by the viral counterpart and oncogenic PTK v-Src (20). A comparison of the effects of pp60 c-src and pp60 v-src would suggest that only the oncogenic tyrosine kinase is able to interfere with the Ras pathway.…”

“…Consistent with these findings, PLD can facilitate mitogenesis and oncogenic transformation (17,28,36), and protein tyrosine kinase (PTK) activity occurs widely in mitogenic signaling (12). Jiang et al (20)(21)(22) demonstrated that v-Src (pp60 v-src ), the viral counterpart of the nonreceptor tyrosine kinase c-Src (pp60 c-src ), stimulated PLD activity in fibroblasts and that small G proteins Ras and GTPase Ral were involved in PLD activation. The src oncogene encodes a membrane-localized tyrosine-specific protein kinase whose enzymatic activity is necessary to induce oncogenic transformation (7,24,42).…”

Activation of phospholipase D by 8‐Br‐cAMP occurs through novel pathway involving Src, Ras, and ERK in human endometrial stromal cells

“…In addition, Ras and Src have been reported to be regulators of PLD activity. v‐Src activated a PLD activity in BALB/c 3T3 cells, which can be distinguished from the PLD activity induced by phorbol esters that activate PKC [34]. Jiang et al [35] reported that Ras plays a role in PLD activation by v‐Src, but PLD is not a direct target of Ras.…”

G Protein Activation Stimulates Phospholipase D Signaling in Plants.

“…PLD is frequently activated together with or downstream from PLC (Liscovitch, 1992). Both tyrosine kinase receptors and G protein-coupled receptors have been shown to activate PLC and PLD (Billah and Anthes, 1990;Exton, 1990Exton, , 1994Exton et al, 1991;Xie and Dubyak, 1991;Bourgoin and Grinstein, 1992;Cano et al, 1992;Dings et al, 1992;Jiang et al, 1994).…”