Association of gene polymorphisms in the p53 pathway with chromosome alterations in chronic lymphocytic leukemia

MERCADO GUZMÁN V; FONTECHA MB; ANADÓN MR; GALVANO C; STANGANELLI C; TOSIN MF; BORDONE J; BEZARES R; ENRICO A; RODRÍGUEZ CM; HELLER V; FUNDIA AF; SLAVUTSKY I

Edimburgo

Workshop; XVIII International Workshop on CLL; 2019

International Workshop on CLL

Genetic factors like single nucleotide polymorphisms (SNPs) may play an important role in theetiology and the clinical evolution of chronic lymphocytic leukemia (CLL). Owing to its role ingenome stability maintenance, TP53 gene plays a central role in controlling DNA damage responseand apoptosis, which in turn are related to cancer risk and progression. Loss of TP53 function inCLL due to chromosome 17p deletion or gene mutations is associated to a more malignantphenotype and predicts adverse prognosis. The frequency of TP53 mutations is relatively low innewly diagnosed CLL patients, but increases sharply with disease progression (Buccheri, AnnHematol 2018, 97:2269). Besides mutations, change of p53 activity is seen in many human cancersdue to polymorphisms in genes of the p53 pathway. The 3 most commonly studied TP53polymorphisms that affect protein functions are: SNP213 G>C (rs1042522), IVS3 16 bp indel(rs17878362) and TP53 IVS6+62A>G (rs1625895) (Lajin B, Gene 2012, 504:268). In addition,several p53-regulators are also frequently altered in cancer and exhibit polymorphisms that impairtheir activity such as MDM2 309T>G (rs2279744), MDM2 indel1518 (rs3730485) and NQO1609C>T (rs1800566). Association of these markers with CLL is not well studied.The aim of the present study was to assess the association between gene polymorphisms in the p53signaling pathway with the susceptibility and the prognostic factors in Argentinean CLL patients.This study was based on a retrospective series of 89 CLL patients at diagnosis (37 females; mean age64.6 years, range: 36-90 years) derived to our Laboratory from whom DNA samples were available.Patients were diagnosed according to the NCI-Working Group CLL criteria. Rai stages wereavailable for 66 cases showing the following distribution: 0: 15 (22.7%); I-II: 27 (40.9%); andIII-IV: 24 (36.4%). In addition, 122 healthy controls without a medical history of cancer (54females; mean age: 41; range: 20-70 years) were analyzed. The study was approved by theInstitutional Ethics Committee and conducted in accordance with the Declaration of Helsinki.Cytogenetics and FISH (fluorescence in situ hybridization) studies as well as IGHV(immunoglobulin heavy chain variable region) mutation status were evaluated in every patient. Sixpolymorphisms: TP53 213 G>C, TP53 IVS3 16 bp indel, TP53 IVS6+62A>G, MDM2 309T>G,MDM2 indel1518 and NQO1 609C>T were genotyped by different PCR methods and genotypeswere confirmed by direct DNA sequencing. Hardy-Weinberg equilibrium was conducted using χ2test. Associations between gene polymorphisms with CLL risk were estimated by calculating oddsratio (OR) with 95% confidence intervals (CI). Standard genetic models (additive, recessive anddominant) for disease penetrance and the association with clinical data were assessed by Fisher´sexact test. Survival curves were done with Kaplan-Meier method and compared by the log-rank test.Statistical analyses were performed using SPSS statistical package (Version 24.0) (IBM, SPSS Inc.,Chicago, USA) and SNPstats (https://www.snpstats.net/start.htm), considering values of p≤0.05 asstatistically significant.Genotype distribution for each polymorphism locus did not deviate from the Hardy?Weinbergequilibrium (p > 0.05). Comparison of genotype and allele frequencies distributions among patientsand controls showed no significant differences. Moreover, the analysis of the genetic modelsdemonstrated that none of the polymorphisms under study were significantly associated with the riskof CLL. Analyses of genotype-based stratification revealed statistically significant associations withabnormal karyotype and 17p13 deletions according to the recessive model. An increased risk ofabnormal karyotypes was found for patients carrying TP53 213-CC (p=0.016; OR=6.98; CI:1.25-38.9) and MDM2 309-GG genotypes (p=0.007; OR=7.22; CI: 1.17-36.90) (Table 1). Inaddition, patients carrying TP53 213-CC, TP53 IVS3-ins/ins, MDM2 309-GG, NQO1 609-TTgenotypes have an increased risk to exhibit 17p13 abnormalities (Table 2). However, no significantcorrelations with clinical prognostic factors, IGHV mutational status as well as time to first treatmentwere observed.Taking together these data indicate that polymorphisms in p53 pathway do not modulate CLL risk,but are associated with abnormal karyotypes and particularly with 17p13 deletions. Attenuation ofthe p53 pathway due to variant genotypes probably leads to deficient DNA damage repair resultingin genomic instability, which in turn would contribute to the onset of CLL-specific chromosomalalterations.