Different Isoforms of HPV-16 E7 Protein are Present in Cytoplasm and Nucleus

H Valdovinos-Torres1, M Orozco-Morales1, A Pedroza-Saavedra1, L Padilla-Noriega3, F Esquivel-Guadarrama2, L Gutierrez-Xicotencatl*, 1
1 Research Center of Infectious Diseases, National Institute of Public Health, Cuernavaca, Morelos, Mexico
2 Biomedical Research Institute, National Autonomous University of Mexico, Mexico City, Mexico
3 Faculty of Medicine, Autonomous University of Morelos State, Cuernavaca, Morelos, Mexico

2008 Bentham Science Publishers Ltd.

open-access license: This is an open access article distributed under the terms of the Creative Commons Attribution License (, which permits unrestrictive use, distribution, and reproduction in any medium, provided the original work is properly cited.

* Address correspondence to this author at the Research Center of Infectious Diseases, National Institute of Public Health, Av. Universidad 655, Santa Ma. Ahucatitlan, Cuernavaca, Mor, Mexico CP 62508; Tel: (52) 777-3-29-30-86; Fax: (52) 777-317-54-85; E-mail:


The E7 protein of high risk HPV types has been found with different molecular weights, mainly because of phosphorylation, an event that changes protein charge and mobility in SDS-PAGE. Distribution of E7 protein in the cellular compartments has also been subject of debate as some groups report the protein in nucleus and others in cytoplasm. The different subcellular distribution and molecular weights reported for the E7 protein suggest the presence of isoforms. We examined this possibility by using several antibodies that recognize different epitopes on the HPV-16 E7 protein. We showed that E7 is processed in 3 isoforms with different molecular weights and isoelectric points (IEP), and described as E7a1 (17.5 kDa, IEP 4.68), E7a (17 kDa, IEP 6.18) and E7b (16 kDa, IEP 6.96). The immunofluorescense results also showed that E7 is distributed into different compartments (ER, Golgi and nucleus), which suggest the presence of other posttranslational modifications, besides phosphorylation.