Association of Genetic Variants at the CDKN1B and CCND2 Loci Encoding p27Kip1 and Cyclin D2 Cell Cycle Regulators with Susceptibility and Clinical Course of Chronic Lymphocytic Leukemia

Beyond the essential role of p27<i>^Kip1</i> and cyclin D2 in cell cycle progression, they are also shown to confer an anti-apoptotic function in peripheral blood (PB) lymphocytes. Although the aberrant longevity and expression of p27<i>^Kip1</i> and cyclin D2 in leukemic cells is well documented, the exact mechanisms responsible for this phenomenon have yet to be elucidated. This study was undertaken to determine the associations between polymorphisms in the <i>CDKN1B</i> and <i>CCND2</i> genes (encoding p27<i>^Kip1</i> and cyclin D2, respectively) and susceptibility to chronic lymphocytic leukemia (CLL), as well as their influence on the expression of both cell cycle regulators in PB leukemic B cells and non-malignant T cells from untreated CLL patients divided according to the genetic determinants studied. Three <i>CDKN1B</i> single-nucleotide polymorphisms (SNPs), rs36228499, rs34330, and rs2066827, and three <i>CCND2</i> SNPs, rs3217933, rs3217901, and rs3217810, were genotyped using a real-time PCR system. The expression of p27<i>^Kip1</i> and cyclin D2 proteins in both leukemic B cells and non-malignant T cells was determined using flow cytometry. We found that the rs36228499A and rs34330T alleles in <i>CDKN1B</i> and the rs3217810T allele in the <i>CCND2</i> gene were more frequent in patients and were associated with increased CLL risk. Moreover, we observed that patients possessing the <i>CCND2</i>rs3217901G allele had lower susceptibility to CLL (most pronounced in the AG genotype). We also noticed that the presence of the <i>CDKN1B</i>rs36228499CC, <i>CDKN1B</i>rs34330CC, <i>CDKN1B</i>rs2066827TT, and <i>CCND2</i>rs3217901AG genotypes shortened the time to CLL progression. Statistically significant functional relationships were limited to T cells and assigned to <i>CDKN1B</i> polymorphic variants; carriers of the polymorphisms rs34330CC and rs36228499CC (determining the aggressive course of CLL) expressed a decrease in p27<i>^Kip1</i> and cyclin D2 levels, respectively. We indicate for the first time that genetic variants at the <i>CDKN1B</i> and <i>CCND2</i> loci may be considered as a potentially low-penetrating risk factor for CLL and determining the clinical outcome.