True XP group E patients have a defective UV-damaged DNA binding protein complex and mutations in DDB2 which reveal the functional domains of its p48 product.
Xeroderma pigmentosum (XP) is a skin cancer-prone autosomal recessive disease characterized by inability to repair UV-induced DNA damage. The major form of XP is defective in nucleotide excision repair (NER) and comprises seven complementation groups (A-G). The genes defective in all groups have been identified unambiguously with the exception of group E. The cells of some XP-E patients are deficient in a protein complex (consisting of two subunits: p127/DDBI and p48/DDB2) which binds to UV-damaged DNA (UV-DDB) and is specifically involved in the removal of photoproducts from the non-transcribed regions of the genome. However, other XP-E patients have been reported not to lack UV-damaged DNA binding activity (DDB(+)). Here we describe several genetically unrelated XP-E patients, not previously analyzed in depth, each carrying two mutated alleles for DDB2, causing either a single amino acid change or a protein truncation or internal deletion. These defects result in a severe decrease of detectable p48 protein, abolish interaction with the p127 subunit, and produce a deficiency in UV-DDB binding activity (DDB(-)). The role of p48 in the repair defect of these patients was demonstrated in vivo and in vitro. Investigation of four DDB(+) cell strains from patients previously assigned to XP-E, allowed us to reclassify all of them into other groups and to show that they do not share the molecular and biochemical features typical for XP-E. Besides confirming that the true XP-E phenotype is DDB(-), resulting from defects in a single gene, DDB2, our results identify the functional domains of the corresponding p48 protein.
Rapić-Otrin
Vesna
V
Department of Molecular Genetics and Biochemistry, University of Pittsburgh School of Medicine, Pittsburgh, PA 15213, USA.
Navazza
Valentina
V
Nardo
Tiziana
T
Botta
Elena
E
McLenigan
Mary
M
Bisi
Dawn C
DC
Levine
Arthur S
AS
Stefanini
Miria
M
D000328:Adult; D000483:Alleles; D002467:Cell Nucleus / Q000378:metabolism; D002478:Cells, Cultured; D004252:DNA Mutational Analysis; D004260:DNA Repair; D004268:DNA-Binding Proteins / Q000235:genetics*; D004307:Dose-Response Relationship, Radiation; D005091:Exons; D005260:Female; D017353:Gene Deletion; D016678:Genome; D005838:Genotype; D006801:Humans; D015151:Immunoblotting; D008297:Male; D008957:Models, Genetic; D009154:Mutation; D010641:Phenotype; D011233:Precipitin Tests; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D017422:Sequence Analysis, DNA; D014466:Ultraviolet Rays; D014983:Xeroderma Pigmentosum / Q000235:genetics* / Q000378:metabolism*
C117669:DDB2 protein, human; D004268:DNA-Binding Proteins