A susceptibility gene for alveolar lung tumors in the mouse maps between Hsp70.3 and G7 within the H2 complex

Downregulation of HSPA2 inhibits proliferation via ERK1/2 pathway and endoplasmic reticular stress in lung adenocarcinoma

Background

To explore the mechanisms of HSPA2 downregulation in inhibiting the proliferation of lung adenocarcinoma.

Methods

We obtained 85 specimens of human lung adenocarcinoma and specimens of adjacent nontumor tissues from the First Affiliated Hospital, School of Medicine, Zhejiang University. We then analyzed the expression of HSPA2 in these tissues and in lung adenocarcinoma and normal lung cell lines. Human lung adenocarcinoma cell lines were transfected with siRNA silencing HSPA2 and subjected to colony forming, Thiazolyl blue tetrazolium bromide (MTT), propidium iodide flow cytometry, immunofluorescence assay and western blotting to explore the causes of the reduction in the proliferation of lung adenocarcinoma cells and the endoplasmic reticulum stress induced by HSPA2 downregulation. Finally, we confirmed these mechanisms via rescue assay.

Results

Greater HSPA2 expression was found in the lung adenocarcinoma specimens than in the specimens of adjacent nontumor tissues, and greater expression was found in lung adenocarcinoma cell lines than in normal cell lines. HSPA2 knockdown via siRNA reduced proliferation and led to G1/S phase cell cycle arrest in the lung adenocarcinoma cell lines. G1/S phase cell cycle arrest triggered by HSPA2 downregulation could be attributed, at least in part, to phosphorylation and activation of the Erk1/2 pathway and probably to activation of IRE1α/PERK-mediated endoplasmic reticulum stress.

Conclusions

HSPA2 plays an important role in the origin and development of lung adenocarcinoma. It is thus deserving of further study as a promising clinical therapeutic target.

Epithelial NF-kappaB activation promotes urethane-induced lung carcinogenesis

Chronic inflammation is linked to carcinogenesis in several organ systems. In the lungs, NF-kappaB, a central effector of inflammatory responses, is frequently activated in non-small-cell lung cancer, but its role in tumor promotion has not been studied. Several lines of evidence indicate that ethyl carbamate (urethane)-induced lung tumor formation, a prototypical mouse model of multistage lung carcinogenesis, is potentiated by inflammation. We found that mouse strains susceptible to lung tumor formation (FVB, BALB/c) exhibited early NF-kappaB activation and inflammation in the lungs after urethane treatment. However, a resistant strain (C57B6) failed to activate NF-kappaB or induce lung inflammation. In FVB mice, we identified urethane-induced NF-kappaB activation in airway epithelium, as well as type II alveolar epithelial cells and macrophages. Using an inducible transgenic mouse model (FVB strain) to express a dominant inhibitor of NF-kappaB specifically in airway epithelial cells, we found that urethane-induced lung inflammation was blocked and tumor formation was reduced by >50%. Selective NF-kappaB inhibition resulted in increased apoptosis of airway epithelial cells at 2 weeks after urethane treatment in association with a marked reduction of Bcl-2 expression. These studies indicate that NF-kappaB signaling in airway epithelium is integral to tumorigenesis in the urethane model and identify the NF-kappaB pathway as a potential target for chemoprevention of lung cancer.

Susceptibility to neoplastic and non-neoplastic pulmonary diseases in mice: genetic similarities

Chronic inflammation predisposes toward many types of cancer. Chronic bronchitis and asthma, for example, heighten the risk of lung cancer. Exactly which inflammatory mediators (e.g., oxidant species and growth factors) and lung wound repair processes (e.g., proangiogenic factors) enhance pulmonary neoplastic development is not clear. One approach to uncover the most relevant biochemical and physiological pathways is to identify genes underlying susceptibilities to inflammation and to cancer development at the same anatomic site. Mice develop lung adenocarcinomas similar in histology, molecular characteristics, and histogenesis to this most common human lung cancer subtype. Over two dozen loci, called Pas or pulmonary adenoma susceptibility, Par or pulmonary adenoma resistance, and Sluc or susceptibility to lung cancer genes, regulate differential lung tumor susceptibility among inbred mouse strains as assigned by QTL (quantitative trait locus) mapping. Chromosomal sites that determine responsiveness to proinflammatory pneumotoxicants such as ozone (O3), particulates, and hyperoxia have also been mapped in mice. For example, susceptibility QTLs have been identified on chromosomes 17 and 11 for O3-induced inflammation (Inf1, Inf2), O3-induced acute lung injury (Aliq3, Aliq1), and sulfate-associated particulates. Sites within the human and mouse genomes for asthma and COPD phenotypes have also been delineated. It is of great interest that several susceptibility loci for mouse lung neoplasia also contain susceptibility genes for toxicant-induced lung injury and inflammation and are homologous to several human asthma loci. These QTLs are described herein, candidate genes are suggested within these sites, and experimental evidence that inflammation enhances lung tumor development is provided.

Tnfa and Il-10 deficiencies have contrasting effects on lung tumor susceptibility: gender-dependent modulation of IL-10 haploinsufficiency

Epidemiologic evidence suggests that pulmonary diseases with a prominent chronic inflammatory component elevate lung cancer risk. Genetic manipulations of mouse models of lung inflammation and tumorigenesis can be used to investigate this association. The genes encoding pro-inflammatory tumor necrosis factor-alpha (TNFalpha) and antiinflammatory IL-10 cytokines map within quantitative trait loci that regulate susceptibility to lung tumor development in mice; sensitive A/J and resistant C57BL/6J (B6) mice have different Tnfa and Il-10 alleles. Genetic ablation studies were performed to examine whether these genes would qualify as candidate tumor modifiers. Tnfa null (-/-) mice on a B6 background and B6.129 Il-10(-/-) mice were intercrossed with A/J mice and subjected to urethane carcinogenesis; lung tumor multiplicity was determined 20 weeks later. In the absence of one copy of Tnfa, tumor number. Male Il-10(+/+) mice developed more tumors than did female mice (P < 0.001), absence of one copy of Il-10 raised tumor number in female mice to that observed in +/+ males, but no change in multiplicity occurred in Il-10 hemizygous males. Thus, a deficit of pro-inflammatory TNFalpha decreased the number of tumors, whereas diminished gene copy number of anti-inflammatory IL-10 increased tumorigenesis; manifestation of an effect of Il-10 haploinsufficiency is gender dependent. These studies support a role for inflammation in lung cancer susceptibility.

Confirmation of the mapping of a 12-O-tetradecanoylphorbol-13-acetate promotion susceptibility locus, Psl1, to distal mouse chromosome 9

Susceptibility to two-stage skin carcinogenesis in the mouse is affected by several genes. In addition, studies suggest that genes that modify the response of mice to skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate (TPA) also may influence histologic changes in the skin as the result of TPA treatment. One TPA susceptibility locus, Psl1, previously was mapped to distal chromosome 9. The mapping of this locus was confirmed by marker-based genotypic selection. Furthermore, Psl1 or a gene closely linked to Psl1 influenced epidermal hyperplasia and epidermal labeling index of mice treated with TPA.

Mouse model for lung tumorigenesis through Cre/lox controlled sporadic activation of the K-Ras oncogene

The onset of human lung cancer occurs through sequential mutations in oncogenes and tumor suppressor genes. Mutations in K-Ras play a prominent role in human non-small cell lung cancer. We have developed a mouse lung tumor model in which K-Ras can be sporadically activated through Cre-lox mediated somatic recombination. Adenoviral mediated delivery of Cre recombinase in lung epithelial cells gave rise to rapid onset of tumorigenesis, yielding pulmonary adenocarcinomas with 100% incidence after a short latency. The lung tumor lesions shared many features with human non-small cell lung cancer. Our data show that sporadic expression of the K-Ras oncogene is sufficient to elicit lung tumorigenesis. Therefore this model has many advantages over conventional transgenic models used thus far.

Tumor necrosis factor-alpha gene mutations and genotype changes in renal cell carcinoma

PURPOSE

We tested the hypothesis that genotype changes in the promoter region of tumor necrosis factor-alpha and exon 1 are associated with renal cell carcinoma.

MATERIALS AND METHODS

We analyzed genotypic changes at the 3 polymorphic loci of tumor necrosis factor-alpha -238, -308 and 488 using tumor and normal tissues from 81 Japanese patients with renal cell carcinoma.

RESULTS

Of the 81 patients 14 (17%) had point mutations from G to A, including 8 (57%) with point mutations at multiple loci. Six of the 8 patients (75%) with point mutations at multiple loci were classified with stage 4 renal cell carcinoma. Of the 81 patients 14 were classified with stage 4 carcinoma, including 9 (64%) with point mutation from G to A. Normal tissue from cancer patients showed an increased frequency of the GA genotype at loci -238 and 488 compared to healthy controls (37% versus 9% and 30% versus 12%, respectively). The relative risk of renal cell carcinoma was 6.5-fold higher in patients with the GA genotype at locus -238 (p <0.001) and 2.9-fold higher in those with the GA genotype at locus 488 (0.01 < p <0.025) when comparing normal tissue from renal cell carcinoma patients with that of healthy controls.

CONCLUSIONS

Point mutation from G to A, and the GA genotype at loci -238 and 488 of the TNF-alpha gene were common in patients with advanced renal cell carcinoma. The genotype change at loci -238 and 488 of the TNF-alpha gene are associated with renal cancer pathogenesis.

Lymphocytes from H2 mice produce lower levels of several cytokines than congenic H2 or H2 mice

Inbred mice of congenic strains that differ only in their H2 haplotype were used to examine the effects of MHC genes on production of cytokines. Spleen and lymph node cells were stimulated with mitogens in vitro, and cytokine protein was assessed by ELISA and/or bioassays. Cells from H2b mice synthesized less IL-3, IL-4, IL-5, TNF and IL-10 (less clearly) than the equivalent cells from H2k or H2d mice. Production of IL-6 by H2b spleen and lymph node cells was lower than that by cells from H2d mice. In addition, lower lymphoproliferative responses were observed in lymph node cultures from H2b mice. These effects were evident in congenic B10 and BALB strains. B10 H2b mice stimulated in vivo with anti-CD3 had lower levels of IFN-gamma and IL-5 protein in their serum compared with equivalent H2k and H2d mice. Because class I- or II-mediated antigen presentation was not required in our model, an immunoregulatory gene in the central MHC is implicated. Preliminary studies of MHC recombinant mice suggested that the gene or genes responsible lie telomeric of IEbeta. Evidence that the H2b haplotype carries an immunoregulatory allele with a small but consistent effect on cytokine production warrants further investigation.

A novel locus affecting serum levels of IgG2a maps to the murine H2 region

The effects of genes in the murine H2 region on basal immunoglobulin levels were investigated and ratios of IgG1/IgG2a were calculated, as low ratios indicate a Th1 cytokine mileu. H2b mice with B10 or BALB genetic backgrounds had higher levels of IgG2a than H2k and H2d congenic strains, and hence had low IgG1/IgG2a ratios. B10 (H2b) mice generally had high levels of IgG2b, IgG3, IgA and IgM, but this outcome was more variable. The high IgG2a phenotype was denoted Igis1 (Immunoglobulin isotype-1) and mapped telomeric of IEbeta using B10.A(4R) mice (high IgG2a) and B10.A(3R) and B10.A(5R) mice (low IgG2a). Further mapping in B10.A(2R), B10.A(1R) and B10.A(18R) mice placed Igis1 in the 27kb region between G7c and G7e.

At least four loci and gender are associated with susceptibility to the chemical induction of lung adenomas in A/J x BALB/c mice

Four putative quantitative trait loci (QTLs) that influence susceptibility to the induction of lung adenomas by urethane in an F2 cross between A/J and BALB/cOlaHsd have been mapped. Following microsatellite typing of mice with resistant and susceptible phenotypes at 97 microsatellite marker loci, a major locus was identified on chromosome 18 with a lod score of 15. This was responsible for an 8- to 10-fold increase in tumor multiplicity in males and females, respectively, having the AA and CC genotypes at the D18Mit188 marker locus. It mapped close to Dcc (deleted in colorectal cancer). A locus on chromosome 4 (lod score 6.5) had the resistant allele in strain A/J and the susceptible allele in BALB/c, with a 14-fold difference in tumor multiplicity between mice of the AA and CC genotypes. This mapped close to the Cdkn2a (cyclin-dependent kinase inhibitor 2A) locus, which is commonly deleted in mouse lung tumors. Two loci with smaller effects (lod scores 3.03 and 3.25) were identified on chromosomes 1 and 11. There was also significant sexual dimorphism in tumor multiplicity both among 151 F2 hybrids and among 52 mice resulting from a backcross to strain A/J, with males having higher tumor counts than females.

Additional evidence that the K-ras protooncogene is a candidate for the major mouse pulmonary adenoma susceptibility (Pas-1) gene

A locus for mouse pulmonary adenoma susceptibility, Pas-1, has been mapped on distal chromosome 6, where the K-ras gene is located. Allele-specific activation and expression of the K-ras allele from the susceptible parent has been observed in lung tumors from F1 hybrid mice. We report here genetic mapping of lung tumor susceptibility genes in urethane-treated A x B and B x A recombinant inbred (RI) mice using microsatellite markers to seek further evidence for the K-ras gene as candidate for Pas-1. The K-ras genotype differs between the A/J and C57BL/6J progenitors of the RI strains, and distal chromosome 6 contained a major lung tumor susceptibility determinant in the RI mice. Additional evidence that Pas-1 is K-ras involved linkage analysis of (A/JOLaHsd x BALB/ cOLaHsd) F2 intercross mice whose parents shared the same K-ras genotype. In contrast to the results with the A x B and B x A RI strains, no distal chromosome 6 site was significantly associated with tumor development in these F2 mice. In addition to this major locus, linkage analysis of the RI mice revealed additional quantitative trait loci for susceptibility on chromosomes 10, 17, and 19. These loci may serve as modifiers of Pas-1. The relationship between the K-ras genotype and the frequency of K-ras mutations in urethane-induced lung tumors from the RI mice was also explored. All 18 tumor DNAs from RI mice with high susceptibility contained an AT-->TA transversion at the second base of K-ras codon 61. This was also true for DNAs from 27 of 27 (100%) tumors in mice with high intermediate susceptibility. In RI strains with a low intermediate susceptibility, the DNA from 39 of 47 (83%) tumors contained an AT-->TA transversion at codon 61, and only 13 of 21 (62%) tumors had this mutation in the most resistant group. This reflects a positive correlation between the frequency of K-ras mutations in lung tumors of A x B or B x A RI strains and their susceptibility to lung carcinogenesis. Since K-ras appears to be Pas-1, these results suggest that some RI mice that have the resistant K-ras or Pas-1 allele undergo tumor development by a K-ras-independent route.

Use of quantitative trait loci to map murine lung tumor susceptibility genes

During the last decade new methods for mapping quantitative trait loci (QTLs) have helped geneticists uncover disease-associated genes. Genetic dissection of complex multigenic diseases such as cancer is being accomplished in part by mapping QTLs in experimental crosses of mice [1]. With the recent construction of dense genetic linkage maps for the mouse, mapping of quantitative trait loci has become practical [2]. Over 6000 polymorphic simple sequence length repeat markers (microsatellite markers) have been mapped in the mouse genome [3], and new analytical approaches to linkage analysis have made QTL mapping a powerful technique for identifying cancer genes [4-7]. In this overview we discuss the design of QTL mapping studies and some of the findings from studies on the mapping of murine lung tumor susceptibility loci.

Molecular Analysis of the Major MHC Recombinational Hot Spot Located Within the G7c Gene of the Murine Class III Region That Is Involved in Disease Susceptibility

Recombination within the MHC does not occur at random, but crossovers are clustered in hot spots. We previously described a recombinational hotspot within the 50-kb Hsp70.3–G7 interval in the class III region of the mouse MHC. The parental haplotypes of recombinants with crossovers in this region represent the majority of the laboratory haplotypes (a, b, d, dx, k, m, p, px, q, s, and u). Using microsatellite markers and sequence-based nucleotide polymorphisms, the breakpoint intervals of 30 recombinants were mapped to a 5-kb-long interval within the G7c gene adjacent to G7a. Recombination within the G7c hot spot does not appear to be restricted to certain haplotypes. Sequence motifs that had been suggested to be associated with site-restricted meiotic recombination were absent in the vicinity of the G7c hot spot, and hence, these sequence motifs are no prerequisite for meiotic recombination. The G7c hot spot resides in a region to which a number of disease susceptibility loci have been mapped, including susceptibility to cleft palate, experimental autoimmune allergic orchitis, and chemically induced alveolar lung tumors. The exact localization of crossovers in recombinants that have been used in functional studies is important for mapping susceptibility genes and limits the number of candidate genes.

Association of the TNFa2 microsatellite allele with the presence of colorectal cancer

Independently, our two groups collaborating in this report performed association studies to consider the influence of the TNF region within the human MHC on the presence of colorectal cancer. In the Glasgow Study, 84 colorectal cancer patients were compared with 91 controls at the TNFa microsatellite locus. Analysis of individual alleles by Fisher's exact test revealed a significant overrepresentation of the TNFa2 allele in the colorectal cancer group, after correcting for multiple comparisons. In the Essen Study, 47 colorectal cancer patients were compared with 117 matched controls, and the hypothesis of TNFa2 overrepresentation in colorectal cancer was confirmed. These data provide evidence for the involvement of the TNF locus in the pathogenetic etiology of colorectal cancer.

Complex interactions of new quantitative trait loci, Sluc1, Sluc2, Sluc3, and Sluc4, that influence the susceptibility to lung cancer in the mouse

Many complex traits, including susceptibility to lung cancer, are controlled by multiple genes--quantitative trait loci (QTLs). We facilitated the mapping of QTLs by making use of recombinant congenic strains (RCS), a system of mouse inbred strains in which the genetic complexity is reduced, and by applying MQM-mapping (multiple-QTL models or marker-QTL-marker), a multilocus method with an increased power of detecting of individual QTLs and interacting QTLs (epistasis). The mouse strain O20 develops significantly larger N-ethyl-N-nitrosourea induced lung tumours than mice of the RC strain OcB-9 (ref. 5); the latter share approximately 87.5% of their genes with strain O20 and 12.5% with strain B10.O20 (refs 6,7). QTL analysis of 222 (OcB-9 x O20) F2 mice revealed four new loci that influence susceptibility to lung cancer (Sluc genes). They are involved in two significant, partly counteracting interactions which mask their individual main effects: Sluc1 (on chromosome 19) interacts with Sluc2 (chromosome 2), and Sluc3 (chromosome 6) interacts with Sluc4 (chromosome 11). Together with the data of van Wezel et al. in the accompanying report, our results indicate that interactions between tumour susceptibility genes are a common phenomenon which complicates their mapping.