INCREASED CYCLIN-A AND DECREASED CYCLIN-D LEVELS IN ADENOVIRUS-5 E1A-TRANSFORMED RODENT CELL-LINES

Adenovirus-(Ad)- E1A proteins carry two conserved domains (CR1 and CR2 ) required for transformation of primary rodent cells and essential fo r association with cellular proteins, including p105RB, p58cyclin A an d p33cdk 2. We show that in normal rat kidney 49F (NRK) cell lines exp ressing various mutant Ad5-E1A genes, CR2-, but not CR-1-, deletion mu tants induce a typical transformed phenotype as characterized by morph ology, absence of density arrest and loss of serum requirement. This i ndicates that induction of these transformed properties is a function of CR1. The fact that E1A proteins with deletions in CR2 show a greatl y reduced association with RB, cyclin A and p33cdk 2 suggests that the se associations are dispensable for E1A-mediated transformation of NRK cells. Induction of the transformed properties is accompanied by a CR 1-dependent increase in Proliferating Cell Nuclear Antigen and cyclin A gene expression. Elevated mRNA and protein levels of cyclin A were a lso found in Ad12-E1-transformed NRK cells but not in ras-transformed NRK cells. On the other hand, cyclin D expression is decreased in a CR 1-dependent manner. Although Ad5-E1A proteins are sufficient to transf orm NRK cells, further deregulation of growth is obtained when Ad5-E1B proteins are co-expressed. One of the Ad5-E1B effects is the sequestr ation of the p53 protein into a cytoplasmic body containing the p53/Ad 5-E1B-55 kD complex. Interestingly, in NRK cell lines expressing Ad5-E 1B-55 kD, cyclin A could be detected not only in the nucleus but also in the cytoplasmic bodies. These results indicate that the deregulatio n of cell cycle control by the Adenovirus-E1 region may be due to a CR 1-dependent alteration of the expression of cyclins A and D.