The HPV-16 E5 protein represses expression of stress pathway genes XBP-1 and COX-2 in genital keratinocytes

Abstract

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. IRE1α, 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.

Endoplasmic reticulum stress pathway PERK‐eIF2α confers radioresistance in oropharyngeal carcinoma by activating NF‐κB

“…The regulation of ERS by HPV infection had tumor specificity. In addition, ERS was inhibited in HPV16 (+) genital epithelial keratinocytes . The results of the present study showed that PERK did not correlate with p16 expression in oropharyngeal carcinoma.…”

mRNA sequencing of novel cell lines from human papillomavirus type-16 related vulval intraepithelial neoplasia: Consequences of expression of HPV16 E4 and E5

“…Two previous studies have examined the effects of E5 expression using cDNA microarrays. In human foreskin keratinocytes transformed retrovirally with HPV16 E6 and E7, stable expression of plasmid encoded E5 appeared to effect primarily the endoplasmic reticulum stress response [Sudarshan et al, ]. By contrast, a study of inducible E5 expression in spontaneously transformed HaCat cells showed significant effects on cell adhesion, cell motility, and mitogenic signaling [Kivi et al, ].…”

Expression of CHOP in Squamous Tumor of the Uterine Cervix

“…HPV16 E5 represses the cellular ER stress response in genital keratinocytes 15. HPV 16 E5 is a HPV 16 transforming protein, which localizes predominantly in the ER, and can enhance cell immortalization by E6E7.…”

“…There are some reports regarding the role of ER stress in HPV infection. Accordingly, ER stress responses were repressed in HPV 16 infected genital keratinocytes 15. ER protein 57 (ERp57), one of the ER stress markers, was induced in HPV 16 positive squamous cell carcinoma (SqCC) of uterine cervix 16…”