The Q205LGo-alpha subunit expressed in NIH-3T3 cells induces transformation

J Biol Chem. 1992 Nov 15;267(32):23183-8.


The growth functions of the heterotrimeric G protein G(o) was studied by expression in heterologous systems. The alpha-subunit of G(o) was mutated to convert Gln-205 to Leu (Q205L). Mutation of this conserved glutamine residue in G protein alpha-subunits is thought to persistently activate G proteins by inhibiting their GTPase activity. The wild type and mutant G(o)-alpha subunits were expressed in NIH-3T3 fibroblasts. These cells do not contain any measurable amounts of G(o)-alpha mRNA or protein. Transfection of wild type or Q205LG(o)-alpha subunit cDNA under the control of a dexamethasone-inducible promoter results in dexamethasone-dependent transcription of the mRNA and expression of the protein. The Q205LG(o)-alpha, but not wild type G(o)-alpha, stimulates mitogenesis in NIH-3T3 fibroblasts without significantly stimulating phospholipase C activity. Continuous expression of mutant G(o)-alpha induces focus formation, whereas transfections with vector alone or vector containing the native G(o)-alpha cDNA were without significant transforming effect in NIH-3T3 cells. Q205L G(o)-alpha did not induce focus formation in RAT-1 fibroblasts. Q205LG(o)-alpha-transformed NIH-3T3 cells are capable of anchorage-independent growth, as assessed by colony formation in soft agar. Q205LG(o)-alpha transformed cells induced tumors when injected into Nu/Nu mice. These results indicate that mutant G(o)-alpha subunits whose GTPase activity is presumably inhibited can induce the neoplastic transformation of NIH-3T3 cells in a phospholipase C-independent manner.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3 Cells
  • Amino Acid Sequence
  • Animals
  • Base Sequence
  • Cell Division / drug effects
  • Cell Line
  • Cell Transformation, Neoplastic*
  • Cloning, Molecular
  • Dexamethasone / pharmacology
  • GTP-Binding Proteins / genetics*
  • GTP-Binding Proteins / metabolism*
  • Glutamine
  • Kinetics
  • Leucine
  • Macromolecular Substances
  • Mice
  • Mice, Nude
  • Molecular Sequence Data
  • Mutagenesis, Site-Directed
  • Myocardium / metabolism
  • Neoplasm Transplantation
  • Oligodeoxyribonucleotides
  • Rats
  • Transfection
  • Type C Phospholipases / metabolism*


  • Macromolecular Substances
  • Oligodeoxyribonucleotides
  • Glutamine
  • Dexamethasone
  • Type C Phospholipases
  • GTP-Binding Proteins
  • Leucine