A naturally occurring variant of HPV-16 E7 exerts increased transforming activity through acquisition of an additional phospho-acceptor site

Human Papillomavirus E6 and E7 play critical roles in cancer development, although not all isolates of the viral oncoproteins are identical. A common E7 variant encodes an amino acid change at N29S. We show that this change increases the levels of phosphorylation by CKII by creating an additional phospho-acceptor site at S29. This confers increased phospho-dependent interaction with a number of cellular targets, including TATA Box Binding Protein (TBP) and pRb. A further consequence is an increased ability to target pRb and p130 for degradation. Biologically, these biochemical differences are reflected in an increased ability of the N29S variant to transform primary rodent cells. This is the first study to demonstrate an important biochemical change in E7 function caused by a naturally occurring variation, and we suggest that the N29S variant merits further assessment to determine whether it has an increased association with the development of HPV-associated malignancies.