Ras induces chromosome instability and abrogation of the DNA damage response.
Ras mutations are frequent in thyroid tumors, the most common endocrine malignancy. The ability of Ras to transform thyroid cells is thought to rely on its mitogenic activity. Unexpectedly, acute expression of activated Ras in normal rat thyroid cells induced a DNA damage response, followed by apoptosis. Notably, a subpopulation of cells evaded apoptosis and emerged with features of transformation, including the loss of epithelial morphology, dedifferentiation, and the acquisition of hormone- and anchorage-independent proliferation. Strikingly, the surviving cells showed marked chromosomal instability. Acutely, Ras stimulated replication stress as evidenced by the induction of ataxia telangiectasia mutated and Rad3-related protein kinase (ATR) activity (Chk1 phosphorylation) and of gammaH2A.X, a marker of DNA damage. Despite the activation of a checkpoint, cells continued through mitosis in the face of DNA damage, resulting in an increase in cells harboring micronuclei, an indication of defects in chromosome segregation and other forms of chromosome damage. Cells that survived exposure to Ras continued to exhibit replication stress (ATR activation) but no longer exhibited gammaH2A.X or full activation of p53. When rechallenged with Ras or DNA-damaging agents, the surviving cells were more resistant to apoptosis than parental cells. These data show that acute expression of activated Ras is sufficient to induce chromosomal instability in the absence of other signals, and suggest that Ras-induced chromosomal instability arises as a consequence of defects in the processing of DNA damage. Hence, abrogation of the DNA damage response may constitute a novel mechanism for Ras transformation.
Abulaiti
Adili
A
Department of Pharmacology, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6061, USA.
Fikaris
Aphrothiti J
AJ
Tsygankova
Oxana M
OM
Meinkoth
Judy L
JL
D000818:Animals; D017209:Apoptosis; D064007:Ataxia Telangiectasia Mutated Proteins; D002453:Cell Cycle; D018797:Cell Cycle Proteins / Q000378:metabolism; D002471:Cell Transformation, Neoplastic; D043171:Chromosomal Instability; D004249:DNA Damage; D004260:DNA Repair; D011905:Genes, ras / Q000502:physiology*; D006657:Histones / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D013964:Thyroid Neoplasms / Q000235:genetics
D018797:Cell Cycle Proteins; C468783:H2AX protein, human; D006657:Histones; C576597:ATR protein, human; D064007:Ataxia Telangiectasia Mutated Proteins; D017346:Protein Serine-Threonine Kinases