Domain mapping of the human cytomegalovirus IE1-72 and cellular p107 protein-protein interaction and the possible functional consequences

Our previous work demonstrated that following human cytomegalovirus (HCMV) infection of fibroblasts, there was a protein-protein interaction between t he HCMV IE1-72 immediate-early (IE) protein and the cellular p107 protein w hich resulted in the alleviation of p107-mediated transcriptional repressio n of E2F-responsive promoters. In a further characterization of this intera ction, we now show that IE1-72 binds to the N-terminal portion of p107, not the C-terminal 'pocket' region that binds E2F-4, and where a number of oth er viral gene products bind. Additionally, we show that exons 2 and 3 of IE 1-72 are required for binding to p107, After mapping the binding domains, w e next wanted to address the additional functional consequences of this int eraction. It is well known that p107 can negatively regulate cell growth. T o examine whether IE1-72 can also overcome this growth suppression, we tran sfected and infected or cotransfected various constructs into SAOS-2 cells, We showed that infection of SAOS-2 cells was capable of alleviating p107/- mediated growth suppression. Additionally, we showed that IE1-72 alone is c apable of overcoming p107-mediated growth arrest, Alleviation of th is repr ession by IE1-72 is dependent on the protein-protein interaction between p1 07 and IE1-72 as deletion mutants of either protein which lack the identifi ed binding domains fail to achieve this effect. These data indicate that th e IE1-72 protein is capable of overcoming p107-mediated blocks in cellular proliferation, events that occur in both productive and non-productive HCMV infections.