Characterization of Cellular Proteins Found in Association with Early Region 1a Polypeptides of Human Adenovirus Type 5

Abstract

<p>Human adenoviruses are capable of oncogenic transformation of mammalian cells in culture and are a a valuable model system for use in studying the molecular basis of cancer. The Early Region 1A (E1A) gene of the virus is involved in transformation, and its protein products have been previously reported to associate with cellular polypeptides termed p300, p107, p105, p68 and p65. The objective of the present investigation was to characterize these cellular proteins and to determine something of their function or biological significance with respect to Ela-mediated transformation.</p> <p>It was found that p300, p68 and p65, as well as a number of other cellular proteins were able to bind with specificity to bacterially-produced Ela products covalently linked to Sepharose beads (Ela-Sepharose), suggesting that this would be suitable for affinity purification of Ela-binding proteins.</p> <p>The binding sites for p300, p107 and p105 on the Ela polypeptides were mapped in a collaborative study with Dr. Stan Bayley's lab. A region at the amino terminus of Ela proteins was involved in binding p300, and p107 and p105 bound overlapping regions in CR2. CR1 played some role in binding all three proteins, but probably not as a primary binding site. Ela proteins which failed to bind either p300 or p105 were transformation defective, which indicated a role for both proteins in Ela-mediated transformation. Ela proteins which failed to bind both p300 and p105 were incapable of inducing DNA synthesis in quiescent cells, suggesting these proteins were cooperatively involved in suppressing DNA synthesis. p105 was confirmed to be the product of the retinoblastoma tumour suppressor gene, p105-Rb. Comparison of the peptide digestion products of p107 and p105-Rb and examination of the expression of p107 in retinoblastoma cells suggested that p107 and p105-Rb are from different, but related genes.</p>