HPV16 E2-mediated potentiation of NF-κB activation induced by TNF-α involves parallel activation of STAT3 with a reduction in E2-induced apoptosis.
Human papilloma virus is associated with cervical and other tumors, and several cellular conditions also play an important role in carcinogenesis. Human papilloma virus (HPV)-infected cells exhibit activation of NF-κB and STAT3 (mediators of inflammation), but little is known about their regulation by HPV. This study attempts to understand the role of HPV16 E2, an important early protein of HPV16, in the regulation of NF-κB and STAT3 by reporter assays, quantitative reverse transcriptase-polymerase chain reaction, and immunoblotting. We demonstrate that E2 enhances NF-κB activation induced by TNF-α, a proinflammatory cytokine, in both non-tumor- and tumor-derived epithelial cell lines besides potentiating STAT3 transcriptional activity induced by TNF-α in HEK293 cells. E2 increases the expression of RelA and its transcriptional activation, and retention of E2 was observed in the nucleus with significant interaction with RelA (immunoprecipitation) upon TNF-α treatment. Transfection with shRNA-RelA or pretreatment with a STAT3 inhibitor had a negative effect on the ability of E2 to enhance TNF-α-induced NF-κB activation. Experiments with co-expression of a mutant of STAT3 with E2 also suggested that the activation of STAT3 is indispensible for TNF-α-induced NF-κB activation. Inhibition of STAT3 activation enhanced E2-induced apoptosis, whereas parallel activation of NF-κB and STAT3 by the combined action of E2 and TNF-α increased the expression of their common targets, cyclin-D1, c-Myc, survivin, and Bcl-2, leading to a decrease in E2-induced apoptosis (viability and cell cycle). Our results reveal novel mechanisms by which E2 may regulate NF-κB and STAT3 activation in the presence of TNF-α with implications on the survival of HPV-infected cells.
Department of Biotechnology, Bhupat and Jyoti Mehta School of Biosciences, Indian Institute of Technology Madras, Chennai, 600 036, India.
Devan
D
Prabhavathy
Bandaru Niranjana
BN
Prabhakar
Devarajan
D
Karunagaran
D017209:Apoptosis / Q000187:drug effects*; D051017:Apoptosis Regulatory Proteins / Q000378:metabolism; D002470:Cell Survival / Q000187:drug effects; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004847:Epithelial Cells / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism / Q000821:virology*; D057809:HEK293 Cells; D006367:HeLa Cells; D052162:Human papillomavirus 16 / Q000235:genetics / Q000276:immunology / Q000378:metabolism* / Q000472:pathogenicity; D006801:Humans; D061986:MCF-7 Cells; D009856:Oncogene Proteins, Viral / Q000235:genetics / Q000378:metabolism*; D030361:Papillomavirus Infections / Q000235:genetics / Q000276:immunology / Q000378:metabolism* / Q000473:pathology; D034622:RNA Interference; D050796:STAT3 Transcription Factor / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D051996:Transcription Factor RelA / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*
D051017:Apoptosis Regulatory Proteins; D004268:DNA-Binding Proteins; C054855:E2 protein, Human papillomavirus type 16; D009856:Oncogene Proteins, Viral; C498143:RELA protein, human; D050796:STAT3 Transcription Factor; C494086:STAT3 protein, human; D051996:Transcription Factor RelA; D014409:Tumor Necrosis Factor-alpha