The role of Grb2 in the growth and transformation of mouse embryo cells.
An overexpressed insulin-like growth factor I receptor (IGF-IR) allows cells to grow in IGF-I only and to form colonies in soft agar. Conversely, cells with a targeted disruption of the IGF-IR genes, R- cells, are refractory to transformation by several oncoproteins and growth factor receptors, that readily transform their wild type counterparts, W cells. Grb2 is an SH2-SH3 domains protein that links tyrosine kinase receptors to ras signalling. In order to determine its role in mitogenesis and transformation, we have transfected a plasmid expressing Grb2 into R- and W cells, and their derivatives already expressing the SV40 large T antigen. In addition, we have used loss-of-function mutants of Grb2 to inquire whether they would act as dominant negatives. Our results show that: (1) an overexpressed Grb2 cannot replace the IGF-IR in IGF-I-mediated mitogenesis; (2) Grb2 also fails to transform either W or R- cells; (3) Grb2 and SV40 T antigen, singly transfected, cannot transform R- cells, but can do so when combined; and (4) SH3 domain mutants of Grb2 act as dominant negatives, causing reversion of the transformed phenotype. We conclude that Grb2 is necessary but not sufficient for transformation.
D'Ambrosio
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C
Jefferson Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USA.
Hongo
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A
Li
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Baserga
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R
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000952:Antigens, Polyomavirus Transforming / Q000502:physiology; D001483:Base Sequence; D002455:Cell Division; D002460:Cell Line; D002471:Cell Transformation, Neoplastic; D004247:DNA / Q000096:biosynthesis; D004622:Embryo, Mammalian / Q000166:cytology; D051380:GRB2 Adaptor Protein; D007334:Insulin-Like Growth Factor I / Q000502:physiology; D051379:Mice; D008969:Molecular Sequence Data; D011506:Proteins / Q000502:physiology*; D017526:Receptor, IGF Type 1 / Q000235:genetics; D013539:Simian virus 40 / Q000276:immunology
D048868:Adaptor Proteins, Signal Transducing; D000952:Antigens, Polyomavirus Transforming; D051380:GRB2 Adaptor Protein; C495949:Grb2 protein, mouse; D011506:Proteins; D007334:Insulin-Like Growth Factor I; D004247:DNA; D017526:Receptor, IGF Type 1