Polymorphic insertion of additional repeat within an area of direct 8 bp tandem repeats in the 5'-untranslated region of the p53R2 gene and cancer risk

ATM-mediated serine 72 phosphorylation stabilizes ribonucleotide reductase small subunit p53R2 protein against MDM2 to DNA damage

Ribonucleotide reductase small subunit p53R2 was identified as a p53 target gene that provides dNTP for DNA damage repair. However, the slow transcriptional induction of p53R2 in RNA may not be rapid enough for prompt DNA damage repair, which has to occur within a few hours of damage. Here, we demonstrate that p53R2 becomes rapidly phosphorylated at Ser(72) by ataxia telangiectasia mutated (ATM) within 30 min after genotoxic stress. p53R2, as well as its heterodimeric partner RRM1, are associated with ATM in vivo. Mutational studies further indicate that ATM-mediated Ser(72) phosphorylation is essential for maintaining p53R2 protein stability and conferring resistance to DNA damage. The mutation of Ser(72) on p53R2 to alanine results in the hyperubiquitination of p53R2 and reduces p53R2 stability. MDM2, a ubiquitin ligase for p53, interacts and facilitates ubiquitination of the S72A-p53R2 mutant more efficiently than WT-p53R2 after DNA damage in vivo. Our results strongly suggest a novel mechanism for the regulation of p53R2 activity via ATM-mediated phosphorylation at Ser(72) and MDM2-dependent turnover of p53R2 dephosphorylated at the same residue.

Reprimo 824 G>C and p53R2 4696 C>G single nucleotide polymorphisms and colorectal cancer: a case-control disease association study

BACKGROUND

Improved survival from colorectal cancer (CRC) may result from screening for inherited genetic risk factors. Reprimo and p53R2 are p53-inducible genes involved in cell cycle surveillance and DNA repair. Single nucleotide polymorphisms (SNPs) of these genes have been discovered, but their effects on the genes' function and association with CRC is not known.

METHODS

Ninety healthy controls, 52 diverticular disease controls and 96 CRC cases were genotyped. DNA was extracted from buccal brush biopsies. Genotyping was performed by polymerase chain reaction (PCR) or polymerase chain reaction/restriction fragment length polymorphism (PCR/RFLP) methods. Tests for Hardy-Weinberg equilibrium and allelic- and genotype-disease association were performed online using the Finetti program.

RESULTS

All three populations were in Hardy-Weinberg equilibrium with respect to p53R2 4696C>G SNP, and no CRC associations were demonstrated with this SNP. The healthy and CRC populations were in Hardy-Weinberg equilibrium with respect to the Reprimo 824G>C SNP, but the diverticular disease population was not (P=0.03). No CRC were demonstrated with Reprimo 824G>C.

CONCLUSION

No association between p53R2 4696C>G and Reprimo 824G>C with CRC was shown by this study. An association between the Reprimo 824G>C heterozygote and diverticular disease may exist on the basis of deviation from Hardy-Weinberg equilibrium.

Novel genetic variations of the p53R2 gene in patients with colorectal adenoma and controls

AIM: p53-Inducible ribonucleotide reductase small subunit 2 (p53R2) encodes a 351-amino-acid peptide, which catalyzes conversion of ribonucleoside diphosphates to the corresponding deoxyribonucleotides required for DNA replication and repair. A recent study reported that a point mutation (G/T) in the p53 binding sequence in a colon cancer cell line completely impaired p53R2 protein activity.

METHODS: We screened the p53R2 gene coding regions and a regulatory region which contains a p53 binding sequence in 100 patients with colorectal adenoma and 100 control subjects using PCR, cold SSCP, and direct DNA sequencing.

RESULTS: Although we did not identify genetic variation in all nine exons, four regulatory-region variants were found, of which three were single nucleotide polymorphisms (SNPs) (nt 1 789 C/G, nt 1 928 A/G, 1 933 T/C), and one was 20 bp insertion which replaced a ATTTT between nt 1 831 and 1 835. Additionally, we determined the frequency of these p53R2 variants in a recently concluded case-control study of incident sporadic colorectal adenomas (163 cases and 210 controls).

CONCLUSION: Although more detailed functional characterizations of these polymorphisms remain to be undertaken, these polymorphic sites may be useful for identifying alleles associated with mis-splicing, additional transcript factors and, more generally, in cancer-susceptibility association studies.