CONTROL OF GENE EXPRESSION AND CELL CYCLE REGULATION BY ADENOVIRUS 5 E1A PROTEINS

Abstract

The primary goal of this study was to gain a better understanding of the roles of the adenovirus E1A gene in oncogenic transformation. The E1A gene encodes two related multifunctional proteins of 243R and 289R that influence a wide variety of cellular regulatory processes, including control of gene expression and regulation of DNA synthesis and mitosis. Our approach to the study of E1A was to use a series of E1A mutants - constructed by me and other researchers in Dr. Bayley's lab - to determine which of ElA's biological activities were likely to be responsible for oncogenic transformation. The mutants were also used to map the E1A binding sites for a number of cellular proteins to determine if these proteins were likely to play a role in the underlying molecular mechanisms of E1A action. The ability of E1A to regulate the cell cycle was found to be closely correlated with the ability of the E1A proteins to interact with two cellular polypeptides, p300 and pRb (the product of the retinoblastoma susceptibility gene). Binding to either pRb or p300, by the 243R product, appeared to be sufficient for E1A to induce cellular DNA synthesis. However, association with both p3 00 and pRb was required for efficient induction of cell division by 243R. In the course of these studies I found that two other E1A- associated proteins, pl07 and cyclin A, form a complex normally present in cells. Studies with ElA-mutant viruses suggested that this complex may be involved in regulation of DNA replication. Transcriptional activation of gene expression by the region unique to the 289R protein was not required for induction of DNA synthesis or stimulation of mitosis. However, repression of enhancers by 243R may play an important role in cell cycle regulation. The E1A regions required for the cell cycle effects of E1A corresponded exactly with regions of the E1A proteins which are necessary for oncogenic transformation. Therefore my results implied that the role of E1A in transformation is to interact with cellular proteins that control cell growth.