Human papillomavirus molecular biology

Abstract

Human papillomaviruses are small DNA viruses with a tropism for squamous epithelia. A unique aspect of human papillomavirus molecular biology involves dependence on the differentiation status of the host epithelial cell to complete the viral lifecycle. A small group of these viruses are the etiologic agents of several types of human cancers, including oral and anogenital tract carcinomas. This review focuses on the basic molecular biology of human papillomaviruses.

Keywords: Cervical cancer; Epithelial differentiation; Human papillomavirus; Oncogene; Tumor suppressor; Vaccine.

Figure 1. HPV16 Genome Organization and Protein function

On the left, the HPV16 genomic map of 7906 base pairs is shown. Only the coding strand is included and transcription occurs in the clockwise direction. The early promoter (P₉₇) is indicated by an arrow at the approximate position of the RNA initiation site in the long control region LCR. The late promoter (P₆₇₀) is also indicated by an arrow at its initiation site in the E7 ORF. The early region is depicted in blue and contains proteins necessary for viral replication including E1, E2, E3, E4, E5, E6 and E7. The late region is shown in purple and contains the viral capsid proteins L1 and L2. The LCR is shown in green and contains sequences controlling viral replication & transcription. On the right, a table of the HPV16 ORFs and a brief description of their corresponding viral functions is shown. More details can be found in section 1.3 of the text.

Figure 2. The HPV Lifecycle in Differentiating Squamous Epithelium

An illustration of normal differentiating squamous epithelium is shown on the left with the layers of the differentiating epithelium noted. On the right, a brief description of the HPV life cycle stage occurring in the corresponding epithelial layer is shown. Greater detail on HPV productive infection and the viral life cycle is included in section 1.5. This figure was illustrated by M. E. Harden and adapted from a figure by C. L. Nguyen.