MNS16A tandem repeat minisatellite of human telomerase gene: functional studies in colorectal, lung and prostate cancer

Abstract

MNS16A, a functional polymorphic tandem repeat minisatellite, is located in the promoter region of an antisense transcript of the human telomerase reverse transcriptase gene. MNS16A promoter activity depends on the variable number of tandem repeats (VNTR) presenting varying numbers of transcription factor binding sites for GATA binding protein 1. Although MNS16A has been investigated in multiple cancer epidemiology studies with incongruent findings, functional data of only two VNTRs (VNTR-243 and VNTR-302) were available thus far, linking the shorter VNTR to higher promoter activity.For the first time, we investigated promoter activity of all six VNTRs of MNS16A in cell lines of colorectal, lung and prostate cancer using Luciferase reporter assay. In all investigated cell lines shorter VNTRs showed higher promoter activity. While this anticipated indirect linear relationship was affirmed for colorectal cancer SW480 (P = 0.006), a piecewise linear regression model provided significantly better model fit in lung cancer A-427 (P = 6.9 × 10−9) and prostate cancer LNCaP (P = 0.039). In silico search for transcription factor binding sites in MNS16A core repeat element suggested a higher degree of complexity involving X-box binding protein 1, general transcription factor II–I, and glucocorticoid receptor alpha in addition to GATA binding protein 1.Further functional studies in additional cancers are requested to extend our knowledge of MNS16A functionality uncovering potential cancer type-specific differences. Risk alleles may vary in different malignancies and their determination in vitro could be relevant for interpretation of genotype data.

<p>Variability within the human <em>TERT</em> gene, telomere length and predisposition to chronic lymphocytic leukemia</p>

“…Hofer et al investigated promoter activity of all six known MNS16A VNTRs in different cell lines and showed the distribution of relative promoter activities of different MNS16A VNTRs determined by luciferase reporter assays. In all investigated cell lines, promoter activity of shorter constructs (also VNTRs-234) was higher than promoter activity of longer constructs, reflecting an indirect correlation between VNTR length and promoter activity 25. In addition, Zhang et al observed that carriers of the SL genotype had lower TERT expression compared to LL carriers when analyzing nasopharyngeal carcinoma tissue by immunohistochemical staining 26…”

“…It has been demonstrated that TERT promoter activity depends on variable numbers of tandem repeats (VNTRs), such as MNS16A, which constitutes a binding site for a transcription factor GATA binding protein 1 (GATA-1) 24. Research on the functional significance of this genetic polymorphism showed that shorter MNS16A is related to higher TERT promoter activity 24,25. This functional polymorphism may play an important role in human longevity, disease progression and response to therapy of patients with non-Hodgkin’s B-cell lymphomas and the development of other cancers 26–29…”

Analysis of MNS16A VNTR polymorphic sequence variations of the TERT gene and associated risk for development of bladder cancer

“…[16] This study showed the SS form of VNTR-243 was associated with an elevated risk of lung cancer. On the contrary, despite the fact that MNS16A polymorphic variation has been studied in numerous contexts related to a number of different cancers, [8,[21][22][23][24][25] results are conflicting, either due to ethnic variations or some other technical reasons. For example, a study conducted in China found no significant differences between MNS16A polymorphisms among pericentenarian and normal controls.…”

“…[8] In addition, two other rare alleles, VNTR-272 and VNTR-333, were also found in cancer cell lines. Classification of VNTR-243 and VNTR-272 as short (S) alleles, and VNTR-302 and VNTR-333 as long (L) alleles, was introduced for the purposes of statistical analysis by Wang et al [21] The MNS16A variable number tandem repeat (VNTR) functional polymorphism has been investigated in various studies including nasopharyngeal carcinoma, [22] colorectal cancer, [8,23] lung cancer, [21,24] prostate cancer, [23,25] bladder cancer, [26] and in the normal human life span. [27] In this study, we aimed to determine whether the MNS16A VNTR polymorphism of the hTERT gene was associated with bladder cancer risk in a Kashmiri population.…”

Variable Number Tandem Repeats (VNTRs) as modifiers of breast cancer risk in carriers of BRCA1 185delAG

“…They are known to modulate biologic processes, including gene expression and protein function [10][11][12][13][14]. These eVNTRs (VNTR expression Quantitative Trait Loci) also mediate risks of developing various cancers [15,16] including breast cancer [17][18][19][20]. A genome-wide investigation of VNTRs as modifiers has been hampered by technical difficulties; however, adVNTR [10,21] became available to genotype VNTRs (i.e., count repeat units) from next generation sequencing (NGS) data.…”