HUMAN-PAPILLOMAVIRUS TYPE-16 E5 PROTEIN (REVIEW)

The association of certain human papillomavirus (HPV) types with malig nancies of the anogenital tract is well established. The virus type mo st frequently associated with cellular transformation is HPV 16, as ha s been shown in epidemiological studies. Its transforming capacity has also been demonstrated in many in vitro cell transformation experimen ts. The most potent oncogenes of HPV 16 are the E6 and E7 proteins, bu t the E5 protein, whose homologue is the main oncogene of bovine papil lomavirus, has recently been identified as an oncogene also for HPV. O n the basis of epidemiological and clinical data from tumor material a s well as from in vitro data it has been suggested, that the HPV 16 E5 protein would have a function at the early stages of cervical carcino genesis. The E5 protein enhances growth factor-mediated signal transdu ction to the nucleus and consequently augments cellular proliferation. Expression of the E5 protein enables the infected cell to escape grow th control provided by surrounding cells by inhibiting gap junctional intercellular communication in epithelial cells. This viral oncogene s eems to interfere with the control mechanisms of cellular growth and p roliferation and thus facilitate the function of the E6 and E7 protein s and further steps towards epithelial cell transformation.