On integration into the host cervical keratinocyte genome, human papillomavirus (HPV) E7 protein binds pRB,releasing E2F from normally incompetent pRB-E2F complexes and allowing propagation of G1-S transition by the E2F. p16(INK4a), a tumour suppressor protein, increases in reflex response to counter this. 29 histologically re-confirmed low-grade squamous intraepithelial lesions (LSIL), 27 high-grade squamous intraepithelial lesions (HSIL) and 30 invasive cervical squamous carcinoma (SCC) were immunohistochemically stained for p16(INK4a) expression using the CINtec Histology Kit (REF 9511, mtm laboratories AG, Heidelberg, Germany) to re-affirm the notion that integration of HPV occurs predominantly in SCC and possibly HSIL and less in LSIL and normal squamous epithelium (NSqE). Implicit was also the attempt to understand the role of E2F, as indicated by p16(INK4a), in evolution of SCC from HSIL. No ethnic predilection was noted for LSIL, HSIL or SCC. Patients with SCC were significantly older by about 14-years compared with HSIL (p < 0.05) while there was no significant age difference between HSIL and LSIL. p16(INK4a) expression was significantly increased (p < 0.05) in both HSIL (88.9%) and SCC (83.3%) compared with LSIL (3.4%) and NSqE (0%); the NSqE being normal squamous epithelium noted in 17 of the LSIL, 19 HSIL and 5 SCC. From these findings there is suggestion that fundamental upstream events viz HPV integration, E7 upregulation followed by E2F activation occurs at point of transformation to HSIL and continues unrelentingly for another one to two decades before hitherto unclear factors convert a non-invasive lesion into an overtly invasive malignant counterpart. Interestingly, the occurrence of HSIL and LSIL in almost the same age group could mean that alteration from episomal to integrated form of HPV may not incur a prolonged incubation period, unlike from HSIL to SCC.
* Title and MeSH Headings from MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine.