Comparison of the prevalence of KRAS-LCS6 polymorphism (rs61764370) within different tumour types (colorectal, breast, non-small cell lung cancer and brain tumours). A study of the Czech population

Regulation of KRAS protein expression by miR-544a and KRAS-LCS6 polymorphism in wild-type KRAS sporadic colon adenocarcinoma

Colorectal carcinoma (CRC) results from the accumulation of genetic mutations and alterations in signaling pathways. KRAS is mutated in 40% of CRC cases and is involved in increased tumor cells proliferation and survival. Although KRAS mutations are a dominant event in CRC tumorigenesis, increased wild-type KRAS expression has a similar effect on accelerated tumor growth. In this study, we investigated the KRAS status in correlation with clinicopathological features in sporadic CRC and more importantly the role of let-7a-5p and miR-544a-3p in the regulation of wild-type KRAS protein expression in the tumor center (T1) and invasive tumor front (T2). Analysis showed that 39.1% of tumor samples had KRAS mutations. In wild-type KRAS tumors, 62.0% were positive for KRAS protein expression and there was a higher percentage of KRAS-positive tumor cells and a higher intensity of immunohistochemical reaction in T2 than in T1 samples. This could not be attributed to differences in KRAS mRNA levels, suggesting regulation via miR-544a-3p expression which was significantly decreased in T2 samples. Furthermore, we demonstrated that tumor samples carrying the KRAS-LCS6 variant allele had significantly higher protein expression of the wild-type KRAS. Our results suggest the role of the KRAS-LCS6 polymorphism and miR-544a-3p expression in the regulation of wild-type KRAS protein expression in sporadic CRC.

Prevalence of BRAF gene mutation in samples of primary and metastatic colorectal cancer: A meta-analysis

INTRODUCTION

Understanding the prevalence and biology of BRAF gene can improve the treatment methods of cancerous patients. This study aims to estimate the prevalence of BRAF gene mutation in samples of primary and metastatic colorectal cancer using meta-analysis method.

METHODS

We searched PubMed, Scopus, ScienceDirect, Ovid and Google Scholar motor engine using MeSH terms of relevant keywords. During the screening phase, titles, abstracts and full texts were reviewed and risk of bias was assessed for all selected papers based on Newcastle-Ottawa Scale (NOS) checklist. The results of the primary studies were combined using meta-analysis.

RESULTS

Of 95 eligible studies entered into the meta-analysis, prevalence of BRAF gene mutation had been assessed among 19,484 primary tumour samples as well as 12,256 metastatic samples. The total prevalence of BRAF gene mutation among primary tumour samples was estimated as of 10.16% (8.09-12.22) in the world, 0.41% (0-1.89) in EMRO region, 10.06% (7.54-12.59) in EURO region, 10.33% (7.24-13.43) in SEARO region and 11.33% (7.29-15.37) in WPRO region. The pooled estimates for BRAF gene mutation in metastatic samples were 6.53% (5.09-7.96), 8.07% (5.57-10.56), 5.38% (3.75-7.02) and 5.55% (1.72-9.38) for all regions, EURO, WPRO and PAHO regions respectively.

CONCLUSION

Our results showed evidences of BRAF gene mutation in one-tenth of primary colorectal tumour samples in EURO, PAHO, SEARO and WPRO regions which was considerably higher than that of the EMRO region.

A genetic variant rs13293512 in the promoter of let-7 is associated with an increased risk of breast cancer in Chinese women

Growing evidence has demonstrated that single-nucleotide polymorphisms (SNPs) in the promoter of miRNA may influence individuals’ susceptibility to human diseases. We examined two SNPs rs10877887 and rs13293512 in the promoters of let-7 family to determine if the two SNPs were related to the occurrence of breast cancer (BC). Genotyping of the two SNPs was performed by PCR and restriction fragment length polymorphism analysis or TaqMan assay in 301 BC patients and 310 age matched controls. We found a higher frequency of rs13293512 CC genotype and rs13293512 C allele amongst BC patients (CC vs TT: adjusted odds ratio (OR) = 1.78; 95% CI: 1.14–2.80; P=0.012; C vs T: adjusted OR = 1.33; 95% CI: 1.06–1.67; P=0.013). Stratification analysis showed that rs13293512 CC genotype was associated with an increased risk of BC in patients with negative estrogen receptor (adjusted OR = 2.39; 95% CI: 1.32–4.30; P=0.004), patients with negative progesterone receptor (adjusted OR = 1.92; 95% CI: 1.11–3.33; P=0.02), patients with T1-2 stage cancer (adjusted OR = 1.77; 95% CI: 1.07–2.93; P=0.03), and patients with N1-3 stage cancer (adjusted OR = 1.89; 95% CI: 1.13–3.17; P=0.015). These findings suggest that rs13293512 in the promoter of let-7a-1/let-7f-1/let-7d cluster may be a possible biomarker for the development of BC in Chinese women.

Breast Cancer and miR-SNPs: The Importance of miR Germ-Line Genetics

Recent studies in cancer diagnostics have identified microRNAs (miRNAs) as promising cancer biomarkers. Single nucleotide polymorphisms (SNPs) in miRNA binding sites, seed regions, and coding sequences can help predict breast cancer risk, aggressiveness, response to stimuli, and prognosis. This review also documents significant known miR-SNPs in miRNA biogenesis genes and their effects on gene regulation in breast cancer, taking into account the genetic background and ethnicity of the sampled populations. When applicable, miR-SNPs are evaluated in the context of other patient factors, including mutations, hormonal status, and demographics. Given the power of miR-SNPs to predict patient cancer risk, prognosis, and outcomes, further study of miR-SNPs is warranted to improve efforts towards personalized medicine.

Association of KRAS and NRAS gene polymorphisms with Wilms tumor risk: a four-center case-control study

Wilms tumor is a type of pediatric solid tumor that arises partly due to somatic and germline mutations. Single-nucleotide polymorphisms (SNPs) in the RAS gene reportedly modify the risk for several types of human malignancies. We conducted a multicenter study to investigate whether RAS gene variants predispose individuals to Wilms tumor. Four SNPs in RAS were genotyped in 355 Wilms tumor cases and 1070 controls. The SNPs included rs12587 G>T, rs7973450 A>G and rs7312175 G>A in KRAS, and rs2273267 A>T in NRAS. Individuals harboring the rs12587 GT genotype were more likely to develop Wilms tumor than those carrying the GG genotype (adjusted odds ratio [OR]=1.30, 95% confidence interval [CI]=1.004-1.68, P=0.046). However, the other three SNPs seemed not to influence the risk for Wilms tumor. Compared to individuals without a risk genotype, those harboring one to three KRAS risk genotypes had an adjusted OR of 1.28 for developing Wilms tumor (95% CI=1.002-1.64, P=0.048). Stratification analysis revealed that rs12587 GT/TT was associated with Wilms tumor risk in children >18 months old (adjusted OR=1.39, 95% CI=1.02-1.89, P=0.037). Our findings indicate that the rs12587 G>T polymorphism in KRAS is associated with increased Wilms tumor susceptibility.

RAS-mediated oncogenic signaling pathways in human malignancies

Abnormally activated RAS proteins are the main oncogenic driver that governs the functioning of major signaling pathways involved in the initiation and development of human malignancies. Mutations in RAS genes and or its regulators, most frequent in human cancers, are the main force for incessant RAS activation and associated pathological conditions including cancer. In general, RAS is the main upstream regulator of the highly conserved signaling mechanisms associated with a plethora of important cellular activities vital for normal homeostasis. Mutated or the oncogenic RAS aberrantly activates a web of interconnected signaling pathways including RAF-MEK (mitogen-activated protein kinase kinase)-ERK (extracellular signal-regulated kinase), phosphoinositide-3 kinase (PI3K)/AKT (protein kinase B), protein kinase C (PKC) and ral guanine nucleotide dissociation stimulator (RALGDS), etc., leading to uncontrolled transcriptional expression and reprogramming in the functioning of a range of nuclear and cytosolic effectors critically associated with the hallmarks of carcinogenesis. This review highlights the recent literature on how oncogenic RAS negatively use its signaling web in deregulating the expression and functioning of various effector molecules in the pathogenesis of human malignancies.

Mitochondrial determinants of cancer health disparities

Mitochondria, which are multi-functional, have been implicated in cancer initiation, progression, and metastasis due to metabolic alterations in transformed cells. Mitochondria are involved in the generation of energy, cell growth and differentiation, cellular signaling, cell cycle control, and cell death. To date, the mitochondrial basis of cancer disparities is unknown. The goal of this review is to provide an understanding and a framework of mitochondrial determinants that may contribute to cancer disparities in racially different populations. Due to maternal inheritance and ethnic-based diversity, the mitochondrial genome (mtDNA) contributes to inherited racial disparities. In people of African ancestry, several germline, population-specific haplotype variants in mtDNA as well as depletion of mtDNA have been linked to cancer predisposition and cancer disparities. Indeed, depletion of mtDNA and mutations in mtDNA or nuclear genome (nDNA)-encoded mitochondrial proteins lead to mitochondrial dysfunction and promote resistance to apoptosis, the epithelial-to-mesenchymal transition, and metastatic disease, all of which can contribute to cancer disparity and tumor aggressiveness related to racial disparities. Ethnic differences at the level of expression or genetic variations in nDNA encoding the mitochondrial proteome, including mitochondria-localized mtDNA replication and repair proteins, miRNA, transcription factors, kinases and phosphatases, and tumor suppressors and oncogenes may underlie susceptibility to high-risk and aggressive cancers found in African population and other ethnicities. The mitochondrial retrograde signaling that alters the expression profile of nuclear genes in response to dysfunctional mitochondria is a mechanism for tumorigenesis. In ethnic populations, differences in mitochondrial function may alter the cross talk between mitochondria and the nucleus at epigenetic and genetic levels, which can also contribute to cancer health disparities. Targeting mitochondrial determinants and mitochondrial retrograde signaling could provide a promising strategy for the development of selective anticancer therapy for dealing with cancer disparities. Further, agents that restore mitochondrial function to optimal levels should permit sensitivity to anticancer agents for the treatment of aggressive tumors that occur in racially diverse populations and hence help in reducing racial disparities.

KRAS Gene Polymorphisms and their Impact on Breast Cancer Risk in an Iranian Population

Single nucleotide polymorphisms (SNPs) in the let-7 miRNA binding site within the 3’ untranslated region (3’UTR) of KRAS appear related to the risk of cancer. The present case-control study was conducted with 244 BC patients and 204 healthy women to examine whether KRAS polymorphisms (rs61764370 T/G and rs712 G/T) are associated with breast cancer (BC) risk in an Iranian population. The polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP) method was used for genotyping of KRAS SNPs. Our results showed that the rs61764370 TG genotype (OR= 3.73; 95% CI =1.38-10.08; P=0.007) as well as the G allele OR= 3.56; 95% CI =1.33-9.53; P=0.008, respectively) increased the risk of BC. However, the KRAS rs712 TT vs GG+GT genotype in a recessive model was associated with a reduced risk of BC (OR= 0.56; 95% CI =0.38-0.84; P=0.006). In addition, the rs712 T allele decreased the risk of BC compared with the G allele (OR=0.75, 95%CI=0.58-0.97, P=0.031). However, we found no relationship among KRAS SNPs and clinicopathological characteristics of BC patients (P>0.05). Taken together, the present study provided evidence of relationships between KRAS polymorphisms and BC risk in a southeast Iranian population. Additional studies using larger sample sizes and diverse ethnicities are now warranted.

Genetic variation rs7930 in the miR-4273-5p target site is associated with a risk of colorectal cancer

PURPOSE

MicroRNAs (miRNAs) are noncoding RNAs that play roles as tumor suppressors or oncogenes by regulating the expression of target genes via binding to seed-match sequences. Polymorphisms in the miRNA-binding site of a target gene can alter miRNA binding and potentially affect the risk of cancer. The objective of this study was to identify single-nucleotide polymorphisms (SNPs) in miRNA-binding sites and assess their involvement in the risk of colorectal cancer (CRC).

MATERIALS AND METHODS

SNPs in the 3' untranslated regions of genes were selected and assessed for their effects on CRC risk in Korean population using participants in Korean Cancer Prevention Study-II. A detailed study was carried out with the SNP rs7930 in the 3' untranslated region of the translocase of outer mitochondrial membrane 20 (TOMM20) gene. A case-control study (1,545 controls and 620 CRC cases) was conducted to analyze the relationship between polymorphism at rs7930 and the risk of CRC. An interacting miRNA was predicted using web-based software programs, and its interaction with rs7930 in CRC cell lines was investigated by using a luciferase assay.

RESULTS

Individuals carrying the rs7930 AG genotype (G allele) had a 1.721-fold increased risk for CRC in comparison with those with the AA genotype (A allele). The miRNA miR-4273-5p was found to specifically interact with the A allele of rs7930 and to suppress the expression of the target gene (TOMM20) in CRC cell lines.

CONCLUSION

rs7930 is an independent genetic risk factor for CRC susceptibility. Our study suggests a mechanism of how this SNP contributes to CRC carcinogenesis.

Impact of 3'UTR variation patterns of the KRAS gene on the aggressiveness of pancreatobiliary tumors with the KRAS G13D mutation in a Turkish population

OBJECTIVE

Several studies have demonstrated the importance of mutations in codons 12, 13 and 61 and variations in the 3' untranslated region (3'UTR) of the KRAS gene, frequently observed genetic events in the progression of pancreatobiliary tumors (PBT). However, limited data exist on the clinical effect of these alterations. The aim of the current study was to clarify the frequency of relevant alterations of the 3'UTR regions of the KRAS gene and the effect of KRAS 3'UTR polymorphisms on the prognosis of patients with codon 12, 13 and 61 mutations in a Turkish population with PBT.

METHODS

Codons 12, 13, and 61 and 3'UTRs of the KRAS gene were screened by single-strand conformation polymorphism (SSCP) analysis and DNA sequencing in 43 patients and 10 controls. Chi-squared and independent sample T tests were used to evaluate the results of the mutation analysis and clinical features of the patients.

RESULTS

We defined the c.38G > A (rs112445441, p.G13D) (39.54%) mutation and two 3'UTR variations, c.*4066delA (rs560890523) (23.26%) and c.*4065_*4066delAA (rs57698689) (6.98%), in the KRAS gene of Turkish patients. There was a statistically significant relationship between the c.*4066delA (rs560890523) and c.*4065_*4066delAA (rs57698689) variations and invasion and lymph node metastasis status of the patients (p < 0.001). Compared to patients with c.38G > A (rs112445441, p.G13D), patients with c.*4066delA (rs560890523) and c.38G > A (rs112445441, p.G13D) presented more aggressive tumors with highly invasive features. The present study contributes findings regarding the clinical effects of KRAS alterations in PBT. Based on our study, further investigations are required.