Human papillomavirus oncogenesis

HPVs have evolved to accomplish the task of controlling host cell proliferation and differentiation to the end of producing more infectious virions. Coincident with the viral life cycle, however, is the risk that the viral genome will be disrupted and its DNA integrated into the host cell chromosomes. Integration of the viral genome is potentiated by host factors and extracellular effectors that alone may increase genetic instability. But it is consequent to viral integration that most HPV-associated malignancies develop. Investigations of the potential for HPV to immortalize primary cells or transform immortalized cells in vitro demonstrate two distinct classes of genital viral types: (1) oncogenic, exemplified by HPV 16 and 18; and (2) the nononcogenic types 6 and 11. Subsequently, localization of the HPV oncogene implicated that E6 and E7 act by uncoupling the checkpoint controls of the cell cycle principally by inhibiting the normal functioning of p53 and pRb, respectively. By in large, the nononcogenic viruses do not effect irreversible growth properties through these same viral genes and the same cellular counterparts.