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A mutant alpha subunit of Gi2 induces neoplastic transformation of Rat-1 cells
A M Pace1, Y H Wong, H R Bourne
1Department of Pharmacology, University of California, San Francisco 94143.
Abstract:
In a recently discovered class of oncogenes, GTPase-inhibiting mutations constitutively activate alpha subunits of signal-transducing guanine nucleotide-binding proteins (G proteins). Somatic mutations in a subclass of endocrine tumors are found in the arginine-179 codon of the alpha subunit of Gi2 (alpha i2), creating the putative gip2 oncogene. We have tested the ability of gip2 to mediate neoplastic transformation of Rat-1 and NIH 3T3 fibroblasts in tissue culture. Expression of a mutant alpha i2 cDNA encoding cysteine in place of arginine-179 (alpha i2-R179C) caused Rat-1 cells to grow to a higher density in monolayer culture, to lose anchorage dependence, and to form tumors when injected subcutaneously into nude mice. In contrast, expression of alpha i2-R179C failed to alter growth or tumorigenicity of NIH 3T3 cells. We conclude that gip2 is an oncogene, by the criterion that it induces neoplastic transformation of Rat-1 cells. Failure of gip2 to transform NIH 3T3 cells is in keeping with clinical indications that gip2 is a tissue-selective oncogene.
Insights
The gip2 oncogene, a mutant alpha subunit of Gi2 (guanine nucleotide-binding protein), drives cancer development in Rat-1 cells. This tissue-selective oncogene promotes neoplastic transformation and tumor formation in specific cell types.
Area of Science:
- Molecular Biology
- Oncology
- Cell Biology
Background:
- Oncogenes can arise from GTPase-inhibiting mutations that constitutively activate alpha subunits of G proteins.
- Somatic mutations in endocrine tumors at the arginine-179 codon of the alpha subunit of Gi2 (alpha i2) create the gip2 oncogene.
Purpose of the Study:
- To investigate the oncogenic potential of gip2.
- To determine if gip2 can induce neoplastic transformation in fibroblasts.
Main Methods:
- Expression of a mutant alpha i2 cDNA (alpha i2-R179C) in Rat-1 and NIH 3T3 fibroblasts.
- Assessment of cellular growth, anchorage dependence, and tumor formation in nude mice.
Main Results:
- Expression of alpha i2-R179C induced higher cell density, loss of anchorage dependence, and subcutaneous tumor formation in Rat-1 cells.
- Alpha i2-R179C expression did not alter the growth or tumorigenicity of NIH 3T3 cells.
Conclusions:
- Gip2 functions as an oncogene by inducing neoplastic transformation in Rat-1 cells.
- The tissue-selective activity of gip2 is supported by its failure to transform NIH 3T3 cells, aligning with clinical observations.