Mouse pulmonary adenoma susceptibility 1 locus is an expression QTL modulating Kras-4A

Arsenic up-regulates PD-L1 and enhances lung tumorigenesis through activation of STAT3 in alveolar epithelial type 2 cells

Arsenic is a carcinogen and chronic exposure to arsenic increases the risk of many cancers, including lung cancer. However, the underlying mechanism is not clear. Using A/J mice as a model, our previous animal study has shown that chronic arsenic exposure up-regulates PD-L1 on lung tumor cells which interacts with PD-1 on T cells and inhibits T cell anti-tumor function resulting in increased lung tumorigenesis. In a subsequent in vitro study, we further found that arsenic up-regulated PD-L1 by activating STAT3 at tyrosine 705 in lung epithelial cells, and inhibition of STAT3 mitigated arsenic-induced PD-L1 up-regulation. The present study aims to determine whether STAT3 regulates PD-L1 in the lung of A/J mice and the type of cells from which lung tumor develops upon arsenic exposure. For that purpose, a mouse line with STAT3 conditional knockout in alveolar type 2 (AT2) cells was developed. Our results indicate that arsenic exposure up-regulates PD-L1 in AT2 cells through activating STAT3 in A/J mice. Conditional knockout of STAT3 in AT2 cells inhibited arsenic-induced PD-L1 up-regulation and lung tumor formation. Thus, our findings reveal that STAT3 is the upstream regulator of arsenic-induced PD-L1 up-regulation in AT2 cells and the inhibition of T cell anti-tumor function in the lung, and that AT2 cells are sensitive to arsenic exposure and from which arsenic-enhanced lung tumor formation in A/J mice.

CASC1 Expression in Bladder Cancer Is Regulated by Exosomal miRNA-150: A Comprehensive Pan-Cancer and Bioinformatics Study

This study explored the role of cancer susceptibility 1 (CASC1) in tumorigenesis and development as well as the key pathways affecting bladder cancer progression. CASC1 was examined in various normal tissues in humans using the HPA database to quantify its expression level and subcellular localization. CASC1 is abundantly expressed in tumor tissues, primarily in cytoplasmic vesicles and stroma. TIMER2 was used to analyze the correlation between CASC1 expression levels and the types of infiltrates associated with immune cells and immunosuppressive cells. MDSC, Treg, M2, and CAF were significantly correlated with CASC1 expression in various tumors. Comparing patients with and without CASC1 mutation, those with CASC1 mutation had worse overall survival, progression-free survival, and disease-free survival. The correlation between has-miR-150 and CASC1 (for the case of bladder cancer) was then analyzed, and the related ceRNA network was mapped. A negative relationship between CASC1 expression and has-miR-150 expression was found in cases of bladder cancer. And the presence of miR-150-targeted CASC1 may be associated with bladder cancer progression. CASC1 is expressed at elevated levels in various tumor tissues, and it is associated with tumorigenesis and development. Exosomes containing miR-150-targeted CASC1 may affect the progression of bladder cancer.

Oncogenes in high grade serous adenocarcinoma of the ovary

High grade serous ovarian cancer is characterized by relatively few mutations occurring at low frequency, except in TP53. However other genetic aberrations such as copy number variation alter numerous oncogenes and tumor suppressor genes. Oncogenes are positive regulators of tumorigenesis and play a critical role in cancer cell growth, proliferation, and survival. Accumulating evidence suggests that they are crucial for the development and the progression of high grade serous ovarian carcinoma (HGSOC). Though many oncogenes have been identified, no successful inhibitors targeting these molecules and their associated pathways are available. This review discusses oncogenes that have been identified recently in HGSOC using different screening strategies. All the genes discussed in this review have been functionally characterized both in vitro and in vivo and some of them are able to transform immortalized ovarian surface epithelial and fallopian tube cells upon overexpression. However, it is necessary to delineate the molecular pathways affected by these oncogenes for the development of therapeutic strategies.

Capturing the primordial Kras mutation initiating urethane carcinogenesis

The environmental carcinogen urethane exhibits a profound specificity for pulmonary tumors driven by an oncogenic Q₆₁L/R mutation in the gene Kras. Similarly, the frequency, isoform, position, and substitution of oncogenic RAS mutations are often unique to human cancers. To elucidate the principles underlying this RAS mutation tropism of urethane, we adapted an error-corrected, high-throughput sequencing approach to detect mutations in murine Ras genes at great sensitivity. This analysis not only captured the initiating Kras mutation days after urethane exposure, but revealed that the sequence specificity of urethane mutagenesis, coupled with transcription and isoform locus, to be major influences on the extreme tropism of this carcinogen.

Why the carcinogen urethane causes only lung tumours driven by a specific oncogenic mutation in just one Ras gene in mice is unclear. Here, the authors capture mutations immediately after urethane exposure and show that the sequence specificity of mutagenesis, transcriptional status, and Ras genetic loci may all contribute to this specificity.

Genetic Predisposition to Hepatocarcinogenesis in Inbred and Outbred Mouse Lines Selected for High or Low Inflammatory Response

AIRmax and AIRmin mouse strains phenotypically selected for high and low acute inflammatory responsiveness (AIR) are, respectively, susceptible or resistant to developing hepatocellular carcinoma (HCC) induced by the chemical carcinogens urethane and diethylnitrosamine (DEN). Early production of TNF-α, IL-1β, and IL-6 in the liver after DEN treatment correlated with tumor development in AIRmax mice. Transcriptome analysis of livers from untreated AIRmax and AIRmin mice showed specific gene expression profiles in each line, which might play a role in their differential susceptibility to HCC. Linkage analysis with SNP markers in F2 (AIRmax×AIRmin) intercross mice revealed two quantitative trait loci (QTL) in chromosomes 2 and 9, which are significantly associated with the number and progression of urethane-induced liver tumors. An independent linkage analysis with an intercross population from A/J and C57BL/6J inbred mice mapped regions in chromosomes 1 and 7 associated with the progression of urethane-induced liver tumors, evidencing the heterogeneity of HCC genetic control.

A model for RAS mutation patterns in cancers: finding the sweet spot

The three RAS genes - HRAS, NRAS and KRAS - are collectively mutated in one-third of human cancers, where they act as prototypic oncogenes. Interestingly, there are rather distinct patterns to RAS mutations; the isoform mutated as well as the position and type of substitution vary between different cancers. As RAS genes are among the earliest, if not the first, genes mutated in a variety of cancers, understanding how these mutation patterns arise could inform on not only how cancer begins but also the factors influencing this event, which has implications for cancer prevention. To this end, we suggest that there is a narrow window or 'sweet spot' by which oncogenic RAS signalling can promote tumour initiation in normal cells. As a consequence, RAS mutation patterns in each normal cell are a product of the specific RAS isoform mutated, as well as the position of the mutation and type of substitution to achieve an ideal level of signalling.

Strain-related differences in mouse lung gene expression over a two-year period of inhalation exposure to styrene: Relevance to human risk assessment

Both CD-1 and C57BL/6 wildtype (C57BL/6-WT) mice show equivalent short-term lung toxicity from exposures to styrene, while long-term tumor responses are greater in CD-1 mice. We analyzed lung gene expression from styrene exposures lasting from 1-day to 2-years in male mice from these two strains, including a Cyp2f2(-/-) knockout (C57BL/6-KO) and a Cyp2F1/2A13/2B6 transgenic mouse (C57BL/6-TG). With short term exposures (1-day to 1-week), CD-1 and C57BL/6-WT mice had thousands of differentially expressed genes (DEGs), consistent with changes in pathways for cell proliferation, cellular lipid metabolism, DNA-replication and inflammation. C57BL/6-WT mice responded within a single day; CD-1 mice required several days of exposure. The numbers of exposure related DEGs were greatly reduced at longer times (4-weeks to 2-years) with enrichment only for biological oxidations in C57BL/6-WT and metabolism of lipids and lipoproteins in CD-1. Gene expression results indicate a non-genotoxic, mouse specific mode of action for short-term styrene responses related to activation of nuclear receptor signaling and cell proliferation. Greater tumor susceptibility in CD-1 mice correlated with the presence of the Pas1 loci, differential Cytochrome P450 gene expression, down-regulation of Nr4a, and greater inflammatory pathway activation. Very few exposure-related responses occurred at any time in C57BL/6-KO or -TG mice indicating that neither the short term nor long term responses of styrene in mice are relevant endpoints for assessing human risks.

Role of epigenetic factors in the selection of the alternative splicing isoforms of human KRAS in colorectal cancer cell lines

Mutation-driven activation of KRAS is crucial to cancer development. The human gene yields four mRNA splicing isoforms, 4A and 4B being translated to protein. Their different properties and oncogenic potential have been studied, but the mechanisms deciding the ratio 4A/4B are not known. To address this issue, the expression of the four KRAS isoforms was determined in 9 human colorectal cancer cell lines. HCT116 and SW48 were further selected because they present the highest difference in the ratio 4A/4B (twice as much in HCT116 than in SW48). Chromatin structure was analysed at the exon 4A, characteristic of isoform 4A, at its intronic borders and at the two flanking exons. The low nucleosome occupancy at exon 4A in both cell lines may result in a fast transcriptional rate, which would explain the general lower abundance of isoform 4A, also found in cells and tissues by other authors, but due to its similarity between both cell lines, chromatin structure does not influence alternative splicing. DNA methylation downstream exon 4A significantly differs in HCT116 and SW48 cells, but the CCCTC-binding factor, which affects the processivity of RNA polymerase and the alternative splicing, does not bind the differentially methylated sequences. Quantitative epigenetic analysis at mononucleosomal level revealed significant differences between both cell lines in H3K4me3, H3K27me3, H3K36me3, H3K9ac, H3K27ac and H4K20me1, and the inhibition of some histone-modifying enzymes alters the ratio 4A/4B. It can be concluded that the epigenetic modification of histones has an influence on the selection of isoforms 4A and 4B.

Germline control of somatic Kras mutations in mouse lung tumors

Somatic KRAS mutations are common in human lung adenocarcinomas and are associated with worse prognosis. In mice, Kras is frequently mutated in both spontaneous and experimentally induced lung tumors, although the pattern of mutation varies among strains, suggesting that such mutations are not random events. We tested if the occurrence of Kras mutations is under genetic control in two mouse intercrosses. Codon 61 mutations were prevalent, but the patterns of nucleotide changes differed between the intercrosses. Whole genome analysis with SNPs in (A/J x C57BL/6)F4 mice revealed a significant linkage between a locus on chromosome 19 and 2 particular codon 61 variants (CTA and CGA). In (AIRmax × AIRmin) F2 mice, there was a significant linkage between SNPs located on distal chromosome 6 (around 135 Mbp) and the frequency of codon 61 mutation. These results reveal the presence of two loci, on chromosomes 6 and 19, that modulate Kras mutation frequency in different mouse intercrosses. These findings indicate that somatic mutation frequency and type are not simple random events, but are under genetic control.

Complex genetic control of lung tumorigenesis in resistant mice strains

The SM/J mouse strain is resistant to chemically‐induced lung tumorigenesis despite having a haplotype, in the pulmonary adenoma susceptibility locus (Pas1) locus, that confers tumor susceptibility in other strains. To clarify this inconsistent genotype‐phenotype correlation, we crossed SM/J mice with another resistant strain and conducted genome‐wide linkage analysis in the (C57BL/6J × SM/J)F2 progeny exposed to urethane to induce lung tumors. Overall, >80% of F2 mice of both sexes developed from 1 to 20 lung tumors. Genotyping of 372 F2 mice for 744 informative non‐redundant SNPs dispersed over all autosomal chromosomes revealed four quantitative trait loci (QTLs) affecting lung tumor multiplicity, on chromosomes 3 (near rs13477379), 15 (rs6285067), 17 (rs33373629) and 18 (rs3706601), all with logarithm of the odds (LOD) scores >5. Four QTLs modulated total lung tumor volume, on chromosome 3 (rs13477379), 10 (rs13480702), 15 (rs6285067) and 17 (rs3682923), all with LOD scores >4. No QTL modulating lung tumor multiplicity or total volume was detected in Pas1 on chromosome 6. The present study demonstrates that the SM/J strain carries, at the Pas1 locus, the resistance allele: a finding that will facilitate identification of the Pas1 causal element. More generally, it demonstrates that lung tumorigenesis is under complex polygenic control even in a pedigree with low susceptibility to this neoplasia, suggesting that the genetics of lung tumorigenesis is much more complex than evidenced by the pulmonary adenoma susceptibility and resistance loci that have, so far, been mapped in a small number of crosses between a few inbred strains.

Expression quantitative trait analysis reveals fine germline transcript regulation in mouse lung tumors

Gene expression modulates cellular functions in both physiologic and pathologic conditions. Herein, we carried out a genetic linkage study on the transcriptome of lung tumors induced by urethane in an (A/J x C57BL/6)F4 intercross population, whose individual lung tumor multiplicity (Nlung) is linked to the genotype at the Pulmonary adenoma susceptibility 1 (Pas1) locus. We found that expression levels of 1179 and 1579 genes are modulated by an expression quantitative trait locus (eQTL) in cis and in trans, respectively (LOD score > 5). Of note, the genomic area surrounding and including the Pas1 locus regulated 14 genes in cis and 857 genes in trans. In lung tumors of the same (A/J x C57BL/6)F4 mice, we found 1124 genes whose transcript levels associated with Nlung (FDR < 0.001). The expression levels of about a third of these genes (n = 401) were regulated by the genotype at the Pas1 locus. Pathway analysis of the sets of genes associated with Nlung and regulated by Pas1 revealed a set of 14 recurrently represented genes that are components or targets of the Ras-Erk and Pi3k-Akt signaling pathways. Altogether our results illustrate the architecture of germline control of gene expression in mouse lung cancer: they highlight the importance of Pas1 as a tumor-modifier locus, attribute to it a novel role as a major regulator of transcription in lung tumor nodules and strengthen the candidacy of the Kras gene as the effector of this locus.

The Pathology of Aging 129S6/SvEvTac Mice

The 129 mouse strain is commonly used for the generation of genetically engineered mice. Genetic drift or accidental contamination during outcrossing has resulted in several 129 substrains. Comprehensive data on spontaneous age-related pathology exist for the 129S4/SvJae substrain, whereas only limited information is available for other 129 substrains. This longitudinal aging study describes the life span and spontaneous lesions of 44 male and 18 female mice of the 129S6/SvEvTac substrain. Median survival time was 778 and 770 days for males and females, respectively. Tumors of lung and Harderian gland were the most common neoplasms in both sexes. Hepatocellular tumors occurred mainly in males. Hematopoietic tumors were observed at low frequency. Suppurative and ulcerative blepharoconjunctivitis was the most common nonneoplastic condition in both sexes. Corynebacteria (primarily Corynebacterium urealyticum and C. pseudodiphtheriticum) were isolated from animals with blepharoconjunctivitis and in some cases from unaffected mice, although a clear causal association between corynebacterial infections and blepharoconjunctivitis could not be inferred. Polyarteritis occurred only in males and was identified as the most common nonneoplastic contributory cause of death. Eosinophilic crystalline pneumonia occurred in both sexes and was a relevant cause of death or comorbidity. Epithelial hyalinosis at extrapulmonary sites was noted at higher frequency in females. This study contributes important data on the spontaneous age-related pathology of the 129S6/SvEvTac mouse substrain and is a valuable reference for evaluation of the phenotype in genetically engineered mice obtained with this 129 substrain.

Rare codons capacitate Kras-driven de novo tumorigenesis

The KRAS gene is commonly mutated in human cancers, rendering the encoded small GTPase constitutively active and oncogenic. This gene has the unusual feature of being enriched for rare codons, which limit protein expression. Here, to determine the effect of the rare codon bias of the KRAS gene on de novo tumorigenesis, we introduced synonymous mutations that converted rare codons into common codons in exon 3 of the Kras gene in mice. Compared with control animals, mice with at least 1 copy of this Kras(ex3op) allele had fewer tumors following carcinogen exposure, and this allele was mutated less often, with weaker oncogenic mutations in these tumors. This reduction in tumorigenesis was attributable to higher expression of the Kras(ex3op) allele, which induced growth arrest when oncogenic and exhibited tumor-suppressive activity when not mutated. Together, our data indicate that the inherent rare codon bias of KRAS plays an integral role in tumorigenesis.