Host defenses against human papillomaviruses: lessons from epidermodysplasia verruciformis

Epidermodysplasia verruciformis (EV) is a rare, autosomal recessive genodermatosis associated with a high risk of skin carcinoma (MIM 226400). EV is characterized by the abnormal susceptibility of otherwise healthy patients to infection by specific, weakly virulent human papillomaviruses (HPVs), including the potentially oncogenic HPV-5. Inactivating mutations in either of the related EVER1/TMC6 and EVER2/TMC8 genes cause most EV cases. New insights in EV pathogenesis have been gained from the following recent observations: (1) EV-specific HPVs (betapapillomaviruses) are defective for an important growth-promoting function encoded by an E5/E8 gene present in other HPVs, and inactivation of EVER proteins may compensate for the missing viral function; (2) the transmembrane viral E5/E8 and cellular EVER proteins interact both with the zinc transporter ZnT1, and are likely to modulate zinc homeostasis. EV may thus represent a primary deficiency in intrinsic, constitutive immunity to betapapillomaviruses, or constitute a primary deficiency in innate immunity (or both). Keratinocytes, the home cells of HPVs, are likely to play a central role in both cases. An important issue is to establish which cellular genes involved in intrinsic and innate antiviral responses play a part in the outcome of infections with other HPV types, such as genital oncogenic HPVs.