ADENOVIRAL DELIVERY OF E2F-1 DIRECTS CELL-CYCLE REENTRY AND P53-INDEPENDENT APOPTOSIS IN POSTMITOTIC ADULT MYOCARDIUM IN-VIVO

Irreversible exit from the cell cycle precludes the ability of cardiac muscle cells to increase cell number after infarction. Using adenovir al E1A, we previously demonstrated dual pocket: protein-and p300-depen dent pathways in neonatal rat cardiac myocytes, and have proven that E 2F-1, which occupies the Rb pocket, suffices for these actions of EIA. By contrast, the susceptibility of adult ventricular cells to viral d elivery of exogenous cell cycle regulators has not been tested, in vit ro or in vivo. In cultured adult ventricular myocytes, adenoviral gene transfer of E2F-1 induced expression of proliferating cell nuclear an tigen, cyclin-dependent protein kinase 4, cell division cycle 2 kinase , DNA synthesis, and apoptosis. In vivo, adenoviral delivery of E2F-1 by direct injection into myocardium induced DNA synthesis, shown by 5' -bromodeoxyuridine incorporation, and accumulation in G2/M, by image a nalysis of Feulgen-stained nuclei. In p53(-/-) mice, the prevalence of G1 exit was more than twofold greater; however, E2F-1 evoked apoptosi s and rapid mortality comparably in both backgrounds. Thus, the differ ential effects of E2F-1 on G1 exit in wild-type versus p53-deficient m ice illustrate the combinatorial power of viral gene delivery to genet ically defined recipients: E2F-1 can override the G1/S checkpoint in p ostmitotic ventricular myocytes in vitro and in vivo, but leads to apo ptosis even in p53(-/-) mice.