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

ZEMA VERÓNICA MERCADO GUZMÁN; MARÍA BELÉN FONTECHA; MARÍA DEL ROSARIO ANADÓN; CARMEN GRACIELA STANGANELLI ; RAIMUNDO BEZARES; CECILIA MARIA RODRIGUEZ; HELLER VB; SLAVUTSKY, IRMA

Workshop; INTERNATIONAL WORKSHOP ON CLL; 2019

Abstract Text : Genetic factors like single nucleotide polymorphisms (SNPs) may play an important role in the etiology and the clinical evolution of chronic lymphocytic leukemia (CLL). Owing to its role in genome stability maintenance, TP53 gene plays a central role in controlling DNA damage response and apoptosis, which in turn are related to cancer risk and progression. Loss of TP53 function in CLL due to chromosome 17p deletion or gene mutations is associated to a more malignant phenotype and predicts adverse prognosis. The frequency of TP53 mutations is relatively low in newly diagnosed CLL patients, but increases sharply with disease progression (Buccheri, Ann Hematol 2018, 97:2269). Besides mutations, change of p53 activity is seen in many human cancers due to polymorphisms in genes of the p53 pathway. The 3 most commonly studied TP53 polymorphisms 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 impair their activity such as MDM2 309T>G (rs2279744), MDM2 indel1518 (rs3730485) and NQO1 609C>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 p53 signaling 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 age 64.6 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 were available for 66 cases showing the following distribution: 0: 15 (22.7%); I-II: 27 (40.9%); and III-IV: 24 (36.4%). In addition, 122 healthy controls without a medical history of cancer (54 females; mean age: 41; range: 20-70 years) were analyzed. The study was approved by the Institutional 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. Six polymorphisms: 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 genotypes were confirmed by direct DNA sequencing. Hardy-Weinberg equilibrium was conducted using χ2 test. Associations between gene polymorphisms with CLL risk were estimated by calculating odds ratio (OR) with 95% confidence intervals (CI). Standard genetic models (additive, recessive and dominant) for disease penetrance and the association with clinical data were assessed by Fisher's exact 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 as statistically significant.Genotype distribution for each polymorphism locus did not deviate from the Hardy?Weinberg equilibrium (p > 0.05). Comparison of genotype and allele frequencies distributions among patients and controls showed no significant differences. Moreover, the analysis of the genetic models demonstrated that none of the polymorphisms under study were significantly associated with the risk of CLL. Analyses of genotype-based stratification revealed statistically significant associations with abnormal karyotype and 17p13 deletions according to the recessive model. An increased risk of abnormal 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). In addition, patients carrying TP53 213-CC, TP53 IVS3-ins/ins, MDM2 309-GG, NQO1 609-TT genotypes have an increased risk to exhibit 17p13 abnormalities (Table 2). However, no significant correlations with clinical prognostic factors, IGHV mutational status as well as time to first treatment were 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 of the p53 pathway due to variant genotypes probably leads to deficient DNA damage repair resulting in genomic instability, which in turn would contribute to the onset of CLL-specific chromosomal alterations.