Change of the Antigenecity of Human Papillomavirus Type 16 E7 Oncoprotein according to Phosphorylation

Park, No Hyun; Kee, Sun Ho; Noh, Joo Won; Kim, Jae Weon; Song, Yong Sang; Kang, Soon Beom; Lee, Hyo Pyo

Abstract

PURPOSE
It was suggested that immunogenic region of E7 proteins of human papillo- mavirus (HPV) type 16 encompass casein kinase (CK) II phosphorylation site and the resulting negative charge may affect the various biologic function of E7 protein. This study was undertaken to analyze the change of antigenic characteristics of HPV type 16, E7 oncoprotein according to phosphorylation.
MATERIALS AND METHODS
We produced two monoclonal antibodies (VD6 and IB10) which showed different reactivities to E7 proteins expressed from bacteria or extracted from CaSki cell. These reaction were analyzed by Western blotting. Also the antigenic sites estimation of these antibodies using nested deletion sets was done. On the basis of above experiments, we performed in vitro phosphorylation assay using CK II and its specific inhibitor, DRB (5, 6-dichloro-l-beta-D-ribofuranosylbenzimidazole), to analyze the IB10 reactivity to E7 oncoproteins according to phosphorylation.
RESULTS
In Westem blot analysis, VD6 and IB10 antibodies reacted strongly to bacterially expressed E7 protein. But using E7 extracted from CaSki cell, VD6 reacted to 2.0 kDa E7 protein whereas IB10 showed weak reactivity. The antigenic sites estimation of these antibodies showed that antigenic site of VD6 was located in amino terminal region and that of IB10 in the middle portion in the range of approximate amino acid 25-45. The antigenic site of IB10 might contain the possible phosphorylation sites (Ser-31, 32) in E7. Considering this, the different reactivities of IB10 to E7 proteins expressed in bacteria and extracted from CaSki cell might be due to phosphorylation. In in vitro phosphorylation assay using CK II, the phosphorylation of E7 increased according to reaction time. And this phosphorylation reduced the reactivity of IB10 to E7 protein whereas the reactivity of VD6 did not change. Also the reactivity of IB10 to E7 protein increased in a dose dependent manner with CK II specific inhibitor, DRB treated CaSki cell extracts.
CONCLUSION
These result showed the antigenecity is affected by the degree of phosphorylation of E7 protein.