CHLAMYDIA TRACHOMATIS EXPRESSES PHYLOGENETICALLY HOMOLOGOUS PROTEINS TO HUMAN PAPILLOMA VIRUS TYPE 16: INFERENCES FOR ORAL AND OROPHARYNGEAL SQUAMOUS CELL CARCINOMA

Abstract

Background Oral and oropharyngeal squamous cell carcinoma have been linked to infection by human papilloma virus (HPV) types 16 and 18. They produce proteins E6 and E7 that interfere with p53 and pRb1 proteins and hence support oncogenesis. HPV infection is typically via oro-genital contact and other organisms cohabiting the genitalia may have had sufficient time for a genetic exchange with HPV oncoproteins and hence develop oncogenic potential also within the oral cavity. Objective Our aim was to search for organisms with homologous match for HPV 16 E6/E7 protein sequences. Methods HPV 16 sequences were obtained from the NCBI database. E6 and E7 homologous sequences with accession numbers >ACQ90217 and >ACQ90218 were retrieved through BLAST search. The SWISS-MODEL template library was searched with BLAST and HHBlits for evolutionary related structures matching the target sequence. Utilizing the MPI Bioinformatics remote homology detection method linked with the UniProt database, best matches of E6 and E7 protein sequences were retrieved. Multiple sequence alignment was done and ProMod3 was used to build a protein model for E7. Results HPV 16 E7 protein and Chlamydia trachomatis homologous protein sequences were the most closely related from our bioinformatic search. Conclusions This similarity between C. trachomatis proteins and HPV 16 E7 oncogenic proteins could be because both organisms inhabit similar mucosae and have had considerable time to exchange genes. We postulate that a possible co-infection of C. trachomatis may be implicated in the development of oral and oropharyngeal squamous cell carcinoma as documented with cervical cancers.