Sequential binding of UV DNA damage binding factor and degradation of the p48 subunit as early events after UV irradiation

The UV-damaged DNA binding protein complex (UV-DDB) is implicated in global genomic nucleotide excision repair (NER) in mammalian cells. The complex consists of a heterodimer of p127 and p48. UV-DDB is defective in one complementation group (XP-E) of the heritable, skin cancer-prone disorder xeroderma pigmentosum. Upon UV irradiation of primate cells, UV-DDB associates tightly with chromatin, concomitant with the loss of extractable binding activity. We report here that an early event after UV, but not ionizing, radiation is the transient dose-dependent degradation of the small subunit, p48. Treatment of human cells with the proteasomal inhibitor NIP-L3VS blocks this UV-induced degradation of p48. In XP-E cell lines with impaired UV-DDB binding, p48 is resistant to degradation. UV-mediated degradation of p48 occurs independently of the expression of p53 and the cell's proficiency for NER, but recovery of p48 levels at later times (12 h and thereafter) is dependent upon the capacity of the cell to repair non-transcribed DNA. In addition, we find that the p127 subunit of UV-DDB binds in vivo to p300, a histone acetyltransferase. The data support a functional connection between UV-DDB binding activity, proteasomal degradation of p48 and chromatin remodeling during early steps of NER.