HPV38 impairs UV-induced transcriptional activation of the IL-18 pro-inflammatory cytokine

Increasing evidence suggests that the beta genus of human papillomavirus (beta-HPV) cooperates with ultraviolet B (UVB) radiation in inducing non-melanoma skin cancer (NMSC). For instance, expression of E6 and E7 oncoproteins from cutaneous human papillomavirus type 38 (HPV38) in a transgenic mouse model (Tg38) leads to the development of squamous cell carcinoma (SCC) after chronic UVB exposure. Transcriptomic analysis of the Tg38 SCC samples revealed a deregulation of inflammasome pathway-related genes such as IL-18, which is consistent with the well-known capability of several oncogenic viruses to modulate the immune response, in order to efficiently produce new progeny. However, the mechanism at the gene expression level by which UVB and HPV38 synergize and modulate the innate immune response has not been elucidated yet. Here, we propose a new molecular mechanism for the regulation of the IL-18 promoter that involves direct binding of p53 to specific response elements. This mechanism seems to be impaired in the presence of the beta-HPV38 oncoproteins. Instead, a newly described inhibitory complex formed by DNA methyltransferase 1 (DNMT1)/PKR/Delta Np73 alpha is recruited to the region formerly occupied by p53 in primary keratinocytes. Together, these results corroborate our hypothesis that beta-HPV38 plays an important role in the inhibition of the ultraviolet-induced inflammasome response. This downregulation is likely to impair the ability of keratinocytes to recruit the immune cell population at the UVB-exposed area, causing a defect in the clearance of cells harboring DNA damage and promoting a favorable environment for the progression of NMSC.