Ablation of Go alpha-subunit results in a transformed phenotype and constitutively active phosphatidylcholine-specific phospholipase C.
Modulation of the components involved in mitogenic signaling cascades is critical to the regulation of cell growth. GTP-binding proteins and the stimulation of phosphatidylcholine (PC) hydrolysis have been shown to play major roles in these cascades. One of the enzymes involved in PC hydrolysis, a PC-specific phospholipase C (PC-PLC) has received relatively little attention. In this paper we examined the role of a particular heterotrimeric GTP-binding protein, Go, in the regulation of cell growth and PC-PLC-mediated hydrolysis of PC in IIC9 fibroblasts. The Go alpha-subunit was ablated in IIC9 cells by stable expression of antisense RNA. These stably transfected cells acquired a transformed phenotype as indicated by: (a) the formation of multiple foci in monolayer cultures, (b) the acquisition of anchorage-independent growth in soft agar; and (c) an increased level of thymidine incorporation in the absence of added mitogens. These data implicate Goalpha as a novel tumor suppressor. Interestingly, PC-PLC activity was constitutively active in the Goalpha-ablated cells as evidenced by the chronically elevated levels of diacylglycerol and phosphorylcholine in the absence of growth factors. In contrast, basal activities of PC-phospholipase D, phospholipase A2, or phosphoinositol-PLC were not affected. These data demonstrate, for the first time, a role for Go in regulating cell growth and provide definitive evidence for the existence of a PC-PLC in eukaryotic cells. The data further indicate that a subunit of Go, is involved in regulating this enzyme.
Cheng
J
J
Department of Physiology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA.
Weber
J D
JD
Baldassare
J J
JJ
Raben
D M
DM
D000818:Animals; D002455:Cell Division; D002471:Cell Transformation, Neoplastic; D002797:Choline Kinase / Q000378:metabolism; D006224:Cricetinae; D003412:Cricetulus; D004075:Diglycerides / Q000378:metabolism; D004789:Enzyme Activation; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D019204:GTP-Binding Proteins / Q000235:genetics / Q000502:physiology*; D006801:Humans; D016376:Oligonucleotides, Antisense / Q000378:metabolism; D010641:Phenotype; D010711:Phosphatidate Phosphatase / Q000378:metabolism; D010713:Phosphatidylcholines / Q000378:metabolism; D010716:Phosphatidylinositols / Q000378:metabolism; D010739:Phospholipase D / Q000378:metabolism; D010741:Phospholipases A / Q000378:metabolism; D054467:Phospholipases A2; D051381:Rats; D015293:Transducin / Q000494:pharmacology; D010738:Type C Phospholipases / Q000378:metabolism*
D004075:Diglycerides; D016376:Oligonucleotides, Antisense; D010713:Phosphatidylcholines; D010716:Phosphatidylinositols; D002797:Choline Kinase; D010741:Phospholipases A; D054467:Phospholipases A2; D010711:Phosphatidate Phosphatase; D010738:Type C Phospholipases; C105598:phosphatidylcholine-specific phospholipase C; D010739:Phospholipase D; D019204:GTP-Binding Proteins; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D015293:Transducin