The HPV-16 E5 protein represses expression of stress pathway genes XBP-1 and COX-2 in genital keratinocytes.
The HPV-16 E5 protein resides in membranes of the endoplasmic reticulum (ER) and modulates cell growth and viral replication. In order to help define its biological activities, we analyzed E5-induced changes in human keratinocyte gene expression. Our studies identified the downregulation of spliced XBP-1 transcripts, a key player in the ER stress response, as a biochemical marker of E5 expression. IRE1alpha, the endoribonuclease responsible for XBP-1 RNA splicing, was also downregulated. Furthermore, cDNA microarray analysis revealed the repression of COX-2, another member of the ER stress pathway. In contrast, these genes were not altered either by the low-risk HPV-6b E5, or a C-terminal HPV-16 E5 mutant, in which the histidine and alanine residues (conserved in high-risk HPVs) were replaced with tyrosine and isoleucine (conserved in low-risk HPVs). HPV-16 E5 was also able to lower COX-2 mRNA levels in cells co-expressing E6/E7, suggesting that it might exert similar activity during viral replication. Interestingly, the E6/E7 genes were independently able to lower COX-2 transcripts compared to vector cells, indicating that multiple pathways of COX-2 repression exist. COX-2 downregulation by E5 could be overcome by thapsigargin or tunicamycin treatments, which initiate ER stress via calcium fluxes and abnormal protein glycosylation respectively, making it unlikely that E5 specifically tempers these pathways. Overall, our data indicate that E5 represses the cellular ER stress response and suggest a potential role for E5 during productive HPV infection.
Sudarshan
Sawali R
SR
Department of Pathology, Georgetown University Medical School, 3900 Reservoir Road, NW, Washington, DC 20057, USA.
Schlegel
Richard
R
Liu
Xuefeng
X
D002478:Cells, Cultured; D002584:Cervix Uteri / Q000378:metabolism; D051546:Cyclooxygenase 2 / Q000235:genetics*; D004268:DNA-Binding Proteins / Q000235:genetics*; D015536:Down-Regulation; D005260:Female; D052816:Foreskin / Q000378:metabolism; D005786:Gene Expression Regulation; D052162:Human papillomavirus 16 / Q000378:metabolism / Q000502:physiology; D006801:Humans; D015603:Keratinocytes / Q000378:metabolism; D008297:Male; D009154:Mutation; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism*; D030361:Papillomavirus Infections / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D012326:RNA Splicing; D012333:RNA, Messenger / Q000378:metabolism; D000071701:Regulatory Factor X Transcription Factors; D013312:Stress, Physiological / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*; D002583:Uterine Cervical Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000821:virology; D014779:Virus Replication; D000071717:X-Box Binding Protein 1; D000086082:Viroporin Proteins
D051546:Cyclooxygenase 2; D004268:DNA-Binding Proteins; D009856:Oncogene Proteins, Viral; D012333:RNA, Messenger; D000071701:Regulatory Factor X Transcription Factors; D014157:Transcription Factors; D000071717:X-Box Binding Protein 1; C000605543:XBP1 protein, human; C054859:oncogene protein E5, Human papillomavirus type 16; D000086082:Viroporin Proteins; C496540:PTGS2 protein, human