Effect of cigarette smoke exposure and mutant Kras overexpression on pancreatic cell proliferation

Let-7a Downregulation Accompanied by KRAS Mutation Is Predictive of Lung Cancer Onset in Cigarette Smoke-Exposed Mice

BACKGROUND

Let-7 is a tumor suppressor microRNA targeting the KRAS lung oncogene. Let-7a downregulation is reversible during the early stages of lung carcinogenesis but is irreversible in cancer cells. The aim of this study is to shed light on the relationship between oncogene (KRAS) mutation and let-7a downregulation in cigarette smoke (CS)-induced lung carcinogenesis.

METHODS

A total of 184 strain H Swiss albino mice were either unexposed (control) or exposed to CS for 2 weeks (short CS) or 8 months (long CS). After 8 months, the lungs were individually collected. The following end points have been evaluated: (a) DNA methylation of the let-7a gene promoter by bisulphite-PCR and pyrosequencing; (b) let-7a expression by qPCR; (c) KRAS mutation by DNA pyrosequencing; (d) cancer incidence by histopathological examination.

RESULTS

let-7a expression decreased by 8.3% in the mice exposed to CS for two weeks (CS short) and by 33.4% (p ≤ 0.01) in the mice exposed to CS for 8 months (CS long). No significant difference was detected in the rate of let-7a-promoter methylation between the Sham-exposed mice (55.1%) and the CS short-(53%) or CS long (51%)-exposed mice. The percentage of G/T transversions in KRAS codons 12 and 13 increased from 2.3% (Sham) to 6.4% in CS short- and to 11.5% in CS long-exposed mice. Cancer incidence increased significantly in the CS long-exposed mice (11%) as compared to both the Sham (4%) and the CS short-exposed (2%) mice. In the CS long-exposed mice, the correlation between let-7a expression and the number of KRAS mutations was positive (R = +0.5506) in the cancer-free mice and negative (R = -0.5568) in the cancer-bearing mice.

CONCLUSIONS

The effects of CS-induced mutations in KRAS are neutralized by the high expression of let-7a in cancer-free mice (positive correlation) but not in cancer-bearing mice where an irreversible let-7a downregulation occurs (negative correlation). This result provides evidence that both genetic (high load of KRAS mutation) and epigenetic alterations (let-7a irreversible downregulation) are required to produce lung cancer in CS-exposed organisms.

A Circulating Exosome RNA Signature Is a Potential Diagnostic Marker for Pancreatic Cancer, a Systematic Study

Simple Summary

Most patients with pancreatic cancer are diagnosed at an advanced stage due to the lack of tools with high sensitivity and specificity for early detection. Aberrant gene expression occurs in pancreatic cancer, which can be packaged into nanoparticles (also known as exosomes or nano-sized extracellular vesicles) and then released into blood. In this study, we aimed to evaluate the diagnostic value of a circulating exosome RNA signature in pancreatic cancer. Our findings indicate that the circulating exosome RNA signature is a potential marker for the early detection or diagnosis of pancreatic cancer.

Abstract

Several exosome proteins, miRNAs and KRAS mutations have been investigated in the hope of carrying out the early detection of pancreatic cancer with high sensitivity and specificity, but they have proven to be insufficient. Exosome RNAs, however, have not been extensively evaluated in the diagnosis of pancreatic cancer. The purpose of this study was to investigate the potential of circulating exosome RNAs in pancreatic cancer detection. By retrieving RNA-seq data from publicly accessed databases, differential expression and random-effects meta-analyses were performed. The results showed that pancreatic cancer had a distinct circulating exosome RNA signature in healthy individuals, and that the top 10 candidate exosome RNAs could distinguish patients from healthy individuals with an area under the curve (AUC) of 1.0. Three (HIST2H2AA3, LUZP6 and HLA-DRA) of the 10 genes in exosomes had similar differential patterns to those in tumor tissues based on RNA-seq data. In the validation dataset, the levels of these three genes in exosomes displayed good performance in distinguishing cancer from both chronic pancreatitis (AUC = 0.815) and healthy controls (AUC = 0.8558), whereas a slight difference existed between chronic pancreatitis and healthy controls (AUC = 0.586). Of the three genes, the level of HIST2H2AA3 was positively associated with KRAS status. However, there was no significant difference in the levels of the three genes across the disease stages (stages I–IV). These findings indicate that circulating exosome RNAs have a potential early detection value in pancreatic cancer, and that a distinct exosome RNA signature exists in distinguishing pancreatic cancer from healthy individuals.

Emerging incidence trends and application of curative treatments of pancreatic cancer in the USA

Annual pancreatic tumor incidence rates have been increasing. We explored pancreatic tumor incidence trends by treatment and clinicopathologic features.Data from the Surveillance, Epidemiology and End Results (SEER) was retrieved to evaluate temporal trends and pancreatic cancer rates from 2000 to 2015. Joinpoint regression analyses were carried out to examine trend differences.Overall, the incidence of pancreatic cancer was on the increase. The initial APC increased at a rate of 2.22% from 2000 to 2012, and increased from 2012 to 2015 at a rate of 9.05%. Joinpoint analyses revealed that trends within different demographics of pancreatic cancer showed different characteristics. The rate of pancreatic cancer also varied with histologic types. In addition, the trends by cancer stage showed significant increase incidences of stage I and II pancreatic cancer from 2000 to 2013 (stage I: APC: 2.71%; stage II: APC: 4.87%). Incidences of patients receiving surgery increased from 2000 to 2008 (APC: 7.55%), 2008 to 2011 (APC: 2.17%) and then there was a significant acceleration from 2011 to 2015 (APC: 10.51%). The incidence of cases in stage II receiving surgery increased significantly from 2004 to 2009 (APC: 9.28%) and 2009 to 2013 (APC: 2.57%). However, for cases in stage I, the incidence of cases with surgery decreased significantly since 2009 (APC: -4.14%). Patients undergoing surgical treatment without chemotherapy and radiotherapy had the higher rates compared with those who received other combined treatments.Pancreatic cancer has been increasing overall, but patterns differ by demographics and clinicopathologic features. Efforts to identify and treat more eligible candidates for curative therapy could be beneficial.

Meta-analysis of mRNA expression profiles to identify differentially expressed genes in lung adenocarcinoma tissue from smokers and non-smokers

Compared to other types of lung cancer, lung adenocarcinoma patients with a history of smoking have a poor prognosis during the treatment of lung cancer. How lung adenocarcinoma-related genes are differentially expressed between smoker and non-smoker patients has yet to be fully elucidated. We performed a meta-analysis of four publicly available microarray datasets related to lung adenocarcinoma tissue in patients with a history of smoking using R statistical software. The top 50 differentially expressed genes (DEGs) in smoking vs. non‑smoking patients are shown using heat maps. Additionally, we conducted KEGG and GO analyses. In addition, we performed a PPI network analysis for 8 genes that were selected during a previous analysis. We identified a total of 2,932 DEGs (1,806 upregulated, 1,126 downregulated) and five genes (CDC45, CDC20, ANAPC7, CDC6, ESPL1) that may link lung adenocarcinoma to smoking history. Our study may provide new insights into the complex mechanisms of lung adenocarcinoma in smoking patients, and our novel gene expression signatures will be useful for future clinical studies.