Journal
ONCOGENE
Volume 23, Issue 35, Pages 5994-5999Publisher
NATURE PUBLISHING GROUP
DOI: 10.1038/sj.onc.1207798
Keywords
ras oncogene; cell cycle; human tumours; epithelial; fibroblast; senescence
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Using microinjection of recombinant protein to directly control 'expression' levels, we have compared the proliferative response to ras oncogene activation in two normal cell types - fibroblast and thyroid epithelial cell which give rise to human tumours with very low and high frequencies of ras mutation respectively. A concentration-dependent stimulation of DNA synthesis was observed in thyrocytes, matched by an almost perfectly reciprocal inhibition in fibroblasts. A concentration-dependent induction of the cyclin-dependent kinase (CDK) inhibitor p21(WAF1) was observed in both cell types, but p16(Ink4a) was induced by ras only in fibroblasts. This difference could not account for the fibroblast specificity of the growth-inhibitory response, however, since proliferation of p16-deficient fibroblasts was also inhibited by mutant ras. We conclude that the striking contrast in proliferative response to ras between fibroblasts and thyroid epithelial cells cannot readily be explained by differential induction of either of the two key CDK inhibitors, p16(Ink4a) and p21(WAF1), but is consistent with a differential ability of p21(WAF1) to antagonize ras-induced mitogenic signals in the two cell types. Such tissue-specific differences provide an attractive explanation for the observed specificity of ras mutation for particular human tumour types, and emphasize the inappropriateness of fibroblasts as a model for ras-induced tumorigenesis.
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