Coexpression of C-myc and transforming growth factor alfa in the liver promotes early replicative senescence and diminishes regenerative capacity after partial hepatectomy in transgenic mice

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Abstract

We have recently shown that overexpression of c-myc and transforming growth factor α (TGF-α) in the liver of double-transgenic mice results in severe DNA damage, aberrant hepatic growth, and development of tumors at a much younger age than that observed in c-myc single- transgenic mice. We now report that double-transgenic TGF-α/c-myc hepatocytes rapidly lose their ability to proliferate upon mitogenic stimulation following partial hepatectomy (PH). At 4 weeks of age, the overall rate of bromodeoxyuridine (BrdU) incorporation following PH was comparable in c-myc and TGF-α/c-myc livers and exceeded that seen in wild-type (WT) mice. However, by 10 weeks of age, c-myc single- transgenic hepatocytes showed proliferative advantages over the WT cells, whereas TGF-α/c-myc double-transgenic hepatocytes had a decreased capacity to proliferate upon mitogenic stimulation. This decreased proliferative response was accompanied by a reduction in the total fraction of proliferating hepatocytes, as well as by a decline in the induction of cyclin A, cyclin B, and cdc2 gene expression. These data show that constitutive coexpression of c-myc and TGF-α accelerates age-related loss in the regenerative potential following PH, and suggest that early replicative senescence of differentiated hepatocytes may have a role in providing a selective growth advantage to initiated cell populations in this model.

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