Therapy Analysis - Human papillomavirus
Life cycle of the virus
The HPV viral genome consists of 8 genes; E1, E2, E4, E5, E6, E7, L1 and L2. These genes are expressed at early (E) or late (L) stages in the life cycle of the virus. Having entered the epithelial tissues, the HPV virus enters the nucleus of a basal epithelial cell, where early genes E1 and E2 are expressed, replicating the viral genome and transcribing messenger RNA needed for viral replication. As the host cells differentiate, genes E4 and E5 assist in the production of the viral genome by controlling epidermal growth factor.
E6 and E7 are viral oncogenes which now become important. E6 causes degradation of the tumour suppressor gene p53, while E7 completes for retinoblastoma protein (Rb), allowing the transcription factor E2F to drive cell proliferation processes. Genes E6 and E7 therefore act to remove two principle mechanisms of cell defence, and drive the cell replication machinery towards production of new virus particles. E6 and E7 are also known to promote oncogenesis. Late genes L6 and L7 code for structural capsid proteins which encapsidate the viral genome.
Following invasion of host cells, a latent period occurs before intraepithelial lesions and other symptoms are detected. This latent period can range from months to years.
