No evidence for restriction of Beta-HPV8 gene expression by epidermodysplasia verruciformis susceptibility genes CIB1, TMC6, or TMC8 in keratinocytes

Epidermodysplasia verruciformis (EV) is an autosomal recessive disorder characterized by an extraordinary susceptibility to infections with human papillomaviruses (HPV), mainly from the genus beta. EV patients carry biallelic loss-of-function mutations in TMC6 encoding Transmembrane channel-like protein 6 or EV protein 1 (EVER1), TMC8 encoding Transmembrane channel-like protein 8 or EV protein 2 (EVER2), or CIB1 encoding Calcium and integrin-binding protein 1. TMC6, TMC8 and CIB1 form a protein complex in the endoplasmic reticulum which has been hypothesized to act as a restriction factor for beta-HPV in keratinocytes. SiRNA-mediated knock-down of CIB1, TMC6, or TMC8 greatly reduces transcript and protein levels, but does not activate beta-HPV8 gene expression in normal keratinocytes. TMC6 and TMC8 transcript levels are much lower in normal and HPV-positive human keratinocytes than in CD4⁺ T-cells suggesting that the levels are too low for anti-viral activity. However, neither the activation of DNA sensing pathways by HPV genomes, supernatants from activated immune cells, nor activation of pathways important for the viral life cycle such as the DNA damage response or keratinocyte differentiation induce high levels of TMC6 or TMC8 in normal keratinocytes. This is consistent with findings that TMC6 and TMC8 do not restrict Mus musculus PV1 expression in keratinocytes. Taken together, we find no evidence for restriction factor activity of EV susceptibility genes for beta-HPV8 or conditions to induce high levels of TMC6 and TMC8 in keratinocytes. Thus, it is plausible that the EV phenotype in humans may be associated with an immune deficiency involving immune cells.