K-ras 4A and 4B mRNA levels correlate with superoxide in lung adenocarcinoma cells, while at the protein level, only mutant K-ras 4A protein correlates with superoxide

Arsenite malignantly transforms human prostate epithelial cells in vitro by gene amplification of mutated KRAS

Inorganic arsenic is an environmental human carcinogen of several organs including the urinary tract. RWPE-1 cells are immortalized, non-tumorigenic, human prostate epithelia that become malignantly transformed into the CAsE-PE line after continuous in vitro exposure to 5μM arsenite over a period of months. For insight into in vitro arsenite transformation, we performed RNA-seq for differential gene expression and targeted sequencing of KRAS. We report >7,000 differentially expressed transcripts in CAsE-PE cells compared to RWPE-1 cells at >2-fold change, q<0.05 by RNA-seq. Notably, KRAS expression was highly elevated in CAsE-PE cells, with pathway analysis supporting increased cell proliferation, cell motility, survival and cancer pathways. Targeted DNA sequencing of KRAS revealed a mutant specific allelic imbalance, ‘MASI’, frequently found in primary clinical tumors. We found high expression of a mutated KRAS transcript carrying oncogenic mutations at codons 12 and 59 and many silent mutations, accompanied by lower expression of a wild-type allele. Parallel cultures of RWPE-1 cells retained a wild-type KRAS genotype. Copy number analysis and sequencing showed amplification of the mutant KRAS allele. KRAS is expressed as two splice variants, KRAS4a and KRAS4b, where variant 4b is more prevalent in normal cells compared to greater levels of variant 4a seen in tumor cells. 454 Roche sequencing measured KRAS variants in each cell type. We found KRAS4a as the predominant transcript variant in CAsE-PE cells compared to KRAS4b, the variant expressed primarily in RWPE-1 cells and in normal prostate, early passage, primary epithelial cells. Overall, gene expression data were consistent with KRAS-driven proliferation pathways found in spontaneous tumors and malignantly transformed cell lines. Arsenite is recognized as an important environmental carcinogen, but it is not a direct mutagen. Further investigations into this in vitro transformation model will focus on genomic events that cause arsenite-mediated mutation and overexpression of KRAS in CAsE-PE cells.

Therapeutic potential of NADPH oxidase 1/4 inhibitors

The NADPH oxidase (NOX) family of enzymes produces ROS as their sole function and is becoming recognized as key modulators of signal transduction pathways with a physiological role under acute stress and a pathological role after excessive activation under chronic stress. The seven isoforms differ in their regulation, tissue and subcellular localization and ROS products. The most studied are NOX1, 2 and 4. Genetic deletion of NOX1 and 4, in contrast to NOX2, has revealed no significant spontaneous pathologies and a pathogenic relevance of both NOX1 and 4 across multiple organs in a wide range of diseases and in particular inflammatory and fibrotic diseases. This has stimulated interest in NOX inhibitors for therapeutic application. GKT136901 and GKT137831 are two structurally related compounds demonstrating a preferential inhibition of NOX1 and 4 that have suitable properties for in vivo studies and have consequently been evaluated across a range of disease models and compared with gene deletion. In contrast to gene deletion, these inhibitors do not completely suppress ROS production, maintaining some basal level of ROS. Despite this and consistent with most gene deletion studies, these inhibitors are well tolerated and slow or prevent disease progression in a range of models of chronic inflammatory and fibrotic diseases by modulating common signal transduction pathways. Clinical trials in patients with GKT137831 have demonstrated excellent tolerability and reduction of various markers of chronic inflammation. NOX1/4 inhibition may provide a safe and effective therapeutic strategy for a range of inflammatory and fibrotic diseases.

LINKED ARTICLES

This article is part of a themed section on Redox Biology and Oxidative Stress in Health and Disease. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v174.12/issuetoc.

The complex landscape of pancreatic cancer metabolism

Pancreatic ductal adenocarcinomas (PDA) are extremely aggressive cancers and currently available therapies are only minimally effective in treating this disease. Tackling this devastating cancer has been a major challenge to the scientific and medical communities, in part due to its intense therapeutic resistance. One of the aspects of this tumor that contributes to its aggressive behavior is its altered cellular metabolism. Indeed, PDA cells seem to possess the ability to adapt their metabolism to the particular environment to which they are exposed, including utilizing diverse fuel sources depending on their availability. Moreover, PDA tumors are efficient at recycling various metabolic substrates through activation of different salvage pathways such as autophagy and macropinocytosis. Together, these diverse metabolic adaptations allow PDA cells to survive and thrive in harsh environments that may lack nutrients and oxygen. Not surprisingly, given its central role in the pathogenesis of this tumor, oncogenic Kras plays a critical role in much of the metabolic reprogramming seen in PDA. In this review, we discuss the metabolic landscape of PDA tumors, including the molecular underpinnings of the key regulatory nodes, and describe how such pathways can be exploited for future diagnostic and therapeutic approaches.