Requirement of wild-type p53 protein for maintenance of chromosomal integrity

Chromosomal double-strand breaks (DSBs) occurring in mammalian cells can in itiate genomic instability, and their misrepairs result in chromosomal dele tion, amplification, and translocation, common findings in human tumors. Th e tumor-suppressor protein p53 is involved in maintaining genomic stability . in this study, we demonstrate that the deficiency of wild-type p53 protei n may allow unrepaired DSBs to initiate chromosomal instability. The human lymphoblastoid cell line TK6-E6 was established by transfection with human papilloma virus 16 (HPV16) E6 cDNA into parental TK6 cells via a retroviral vector. Abrogation of p53 function by E6 resulted in an increase in the sp ontaneous mutation frequencies at the heterozygous thymidine kinase (TK) lo cus but not at the hemizygous hypoxanthine phosphoribosyl transferase (HPRT ) locus. Almost all TK-deficient mutants from TK6-E6 cells exhibited loss o f heterozygosity (LOH) with the hemizygous TK allele. LOH analysis with mic rosatellite loci spanning the long arm of chromosome 17, which harbors the TK locus, showed that LOH extended over half of 17q toward the terminal end . Cytogenetic analysis of LOH mutants by chromosome painting indicated a mo saic of chromosomal aberrations involving chromosome 17, in which partial c hromosome deletions, amplifications, and multiple translocations appeared h eterogeneously in a single mutant. We speculate that spontaneous DSBs trigg er the breakage-fusion bridge cycle leading to such multiple chromosome abe rrations, in contrast, no chromosomal alterations were observed in TK-defic ient mutants from TK6-20C cells expressing wild-type p53. In wild-type p53 cells, spontaneous DSBs appear to be promptly repaired through recombinatio n between homologous chromosomes. These results support a model in which p5 3 protein contributes to the maintenance of genomic integrity through recom binational repair. (C) 2000 Wiley-Liss, Inc.