Xeroderma pigmentosum genes: functions inside and outside DNA repair

Xeroderma pigmentosum (XP) is an autosomal recessive disease, which is characterized by susceptibility to ultraviolet light (UV)-induced skin cancer. Among eight genes so far identified as responsible for XP, XPA through XPG are involved in nucleotide excision repair of DNA damage induced by UV as well as various chemical carcinogens. Since this repair system removes a major UV photoproduct, the cyclobutane pyrimidine dimer, quite slowly from the global genome, this lesion must be accurately bypassed during replication by DNA polymerase eta, encoded by the XPV gene. Recent studies have revealed that each of these XP genes possesses additional functions, some of which are concerned with other DNA repair pathways and/or cellular DNA damage responses. Such differential functions not only explain clinical heterogeneity among different genetic complementation groups but also have implications for the promotion of carcinogenic processes in XP patients.