Please use this identifier to cite or link to this item: http://scholarbank.nus.edu.sg/handle/10635/34372
Title: HUMAN PAPILLOMAVIRUS 18 E2 IS FOUND AT THE MITOCHONDRIAL MEMBRANES AND MODULATES MITOCHONDRIAL FUNCTIONS
Authors: LAI CHOOI MUN DEBORAH
Keywords: HPV, E2, mitochondria, apoptosis, metabolism, redox
Issue Date: 29-Sep-2010
Source: LAI CHOOI MUN DEBORAH (2010-09-29). HUMAN PAPILLOMAVIRUS 18 E2 IS FOUND AT THE MITOCHONDRIAL MEMBRANES AND MODULATES MITOCHONDRIAL FUNCTIONS. ScholarBank@NUS Repository.
Abstract: Human papillomavirus E1 and E2 proteins are viral replication factors, E2 being also involved in transcriptional repression of the two viral oncogenes E6 and E7. For HPV 16, the E4 protein is involved in late stages of the viral cycle, has no start codon and is known to be exclusively expressed as an E1^E4 fusion product resulting from alternative splicing linking the beginning of the E1 open reading frame (ORF) to E4. The E4 gene lies within the E2 ORF but in a different frame, and we show here that the HPV18 E2 ORF also encodes two new E2^E4 chimeric proteins produced by alternative splicing of the E2 transcripts between the N-terminal part of E2 and E4. Both E2^E4 proteins are cytoplasmic, one being localized at mitochondria where E1^E4 has been previously shown to localize. In order to study E2 functions independently of E2^E4, we constructed an HPV18 E2 expression vector lacking the splice acceptor site in front of E4 and thus defective in E2^E4 expression. We could then show using biochemistry and immunofluorescence experiments that besides their known nuclear localization, high-risk E2 proteins also localize at mitochondrial membranes. Mitochondrial localization can be detected at higher levels of E2 expression after an initial nuclear accumulation, suggesting that E2 biological activities are linked to its levels of expression. Association of E2 with mitochondrial correlates with changes in mitochondrial morphology, although cytochrome c release, characteristic of the intrinsic pathway of apoptosis, is not detected. However, E2 can induce caspase-3 and Parp cleavage when highly expressed, both of which are characteristic of apoptosis that has been discussed in previous work as occurring via the extrinsic pathway. Mass spectrometry analyses allowed us to establish an E2 interactome that helped us to conclude that E2 strongly interacts with mitochondrial proteins involved in 10 oxidative phosphorylation (OXPHOS), more specifically with complexes I and III. E2 was found to modify the metabolism of infected cells by enhancing ATP production, and inducing a robust increase in generation of mitochondrial reactive oxygen species (ROS). Altogether, these results suggest that high-risk E2 proteins share propertieswith other oncogenic viral proteins that also target mitochondria and modulate their functions, therefore suggesting a role for E1 in early oncogenic transformation of cells infected by the high risk HV18 and HPV16 viruses.
URI: http://scholarbank.nus.edu.sg/handle/10635/34372
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