Infrequent p53 gene mutation but UV gradient-like p53 protein positivity in keloids.

Keloids are characterized by extreme fibroblastic overgrowth of unknown pathogenesis after skin injury. Previous studies, mostly in non-Caucasian populations, suggest that p53 mutations may be involved. To substantiate this, we performed DNA sequence analysis of exons 4-8 of the p53 gene and immunohistochemical staining of p53 protein in archived keloidal tissue samples from 23 Caucasian patients. In contrast to previous reports, we found mutated p53 in keloidal tissue in a minority of cases (2/23; 12%). The G allele frequency and C allele frequency at the p53 polymorphic codon 72 were 0.72 (33/46) and 0.28 (13/46), respectively, in our study, a finding that was similar to the 0.77 (184/240) vs. 0.23 (56/240) (P = 0.4580; chi-squared test) observed in the Hap Map data of a European population but statistically significantly different from the 0.43 (547/1258) vs. 0.57 (711/1258) (P = 0.0002; chi-squared test) observed in the 1000 Genome project [Database of Single Nucleotide Polymorphisms (dbSNP). Bethesda (MD): National Center for Biotechnology Information, National Library of Medicine. dbSNP accession:rs1042522, (dbSNP Build ID: 132). Available from: (http://www.ncbi.nlm.nih.gov/SNP/] a difference most likely due to the different genetic background of the populations enrolled. However, one-third of the keloidal samples showed lesional nuclear p53 staining with a UV penetration gradient-like positivity (P ≤ 0.0084). Staining with an anti-cyclobutane pyrimidine dimer antibody revealed the total absence of short-term photoproducts in the epidermis as well as keloidal tissue. Furthermore, all fibroblasts expressing p53 stained negative for Ki-67, indicating that these cells were in a quiescent stage and p53 upregulation did not contribute to keloidal proliferation. We conclude that p53 plays no major role in the pathogenesis of keloids in the Caucasian population.