Localization of a human lung adenocarcinoma susceptibility locus, possibly syntenic to the mouse Pas1 locus, in the vicinity of the D12S1034 locus on chromosome 12p11.2-p12.1

RASSF7 and RASSF8 proteins are predictive factors for development and metastasis in malignant thyroid neoplasms

OBJECTIVES

To study the expression status of Ras-association domain family 7 (RASSF7) and Ras-association domain family 8 (RASSF8) in nodular thyroid goiter (NTG), medullary thyroid carcinoma (MTC), and papillary thyroid carcinoma (PTC) and establish whether a correlation exists between the presence of RASSF7 and RASSF8 proteins and clinicopathological parameters of the disease.

MATERIALS AND METHODS

RASSF7 and RASSF8 protein expression was examined immunohistochemically on paraffin-embedded thyroid tissues from 112 cases with PTC, 20 cases with MTC, and 38 cases with NTG.

RESULTS

The immunohistochemical expression of RASSF7 and RASSF8 was higher in PTC and MTC than in NTG (P < 0.001). In thyroid carcinomas, RASSF7 and RASSF8 expression was significantly correlated with a more advanced TNM stage (P = 0.035, P = 0.037), age, sex, lymph node metastasis (P = 0.006, P = 0.002), and tumor size (P = 0.012, P = 0.015).

CONCLUSIONS

RASSF7 and RASSF8 expression was increased in PTC and MTC compared to NTG, and this may be linked to the development and progression of thyroid carcinoma. In addition, these proteins were correlated with more advanced tumor stages, tumor size, and metastasis.

[COPD and lung cancer: epidemiological and biological links]

Lung cancer and chronic obstructive lung disease (COPD) are two common fatal diseases. Apart from their common link to tobacco, these two diseases are usually considered to be the result of separate distinct mechanisms. In the past 15 years, numerous studies have produced arguments in favour of a relationship between these two pathologies that goes beyond a simple addition of risk factors. At the epidemiological level, there are data that demonstrate an increased incidence of bronchial carcinoma in patients with COPD. The links between these two pathologies are still unexplained but there are numerous arguments supporting a common physiopathology. Common genetic and epigenetic abnormalities, mechanical factors and signalisation pathways have been quoted. COPD and lung cancer appear to be two diseases possessing a genetic basis that creates a predisposition to environmental or toxic assaults, resulting in a different clinical manifestation in each disease. Consequently, improvements in the management of these two diseases will involve a more intensive investigation of their physiopathology, and require a closer collaboration between research centres and clinical units.

N-terminal RASSF family: RASSF7-RASSF10

Epigenetic inactivation of tumor suppressor genes is a hallmark of cancer development. RASSF1A (Ras Association Domain Family 1 isoform A) tumor suppressor gene is one of the most frequently epigenetically inactivated genes in a wide range of adult and children's cancers and could be a useful molecular marker for cancer diagnosis and prognosis. RASSF1A has been shown to play a role in several biological pathways, including cell cycle control, apoptosis and microtubule dynamics. RASSF2, RASSF4, RASSF5 and RASSF6 are also epigenetically inactivated in cancer but have not been analysed in as wide a range of malignancies as RASSF1A. Recently four new members of the RASSF family were identified these are termed N-Terminal RASSF genes (RASSF7-RASSF10). Molecular and biological analysis of these newer members has just begun. This review highlights what we currently know in respects to structural, functional and molecular properties of the N-Terminal RASSFs.

Tobacco, Genetic Susceptibility and Lung cancer

Exposure to tobacco smoke is an established risk factor for lung cancer, although a possible role for genetic susceptibility in the development of lung cancer has been inferred from familial clustering of the disease and segregation analysis. Findings of familial aggregation and statistical evidence for a major susceptibility gene have led to the search for high penetrant, rare, single genes and low penetrant, high frequency susceptibility genes for lung cancer. The relatively small number of linkage studies conducted to date, have identified potential lung cancer susceptibility loci on chromosomes 6q, 12p, and 19q. A variety of studies have examined single nucleotide polymorphisms of several low penetrant, high frequency genes encoding for enzymes involved in the metabolism of carcinogens and DNA damage repair, as likely candidate susceptibility genes. These studies have produced somewhat conflicting findings and, when significant, only modest associations have been reported. Relatively few studies have looked for potential gene-environment interactions, explored associations between two or more genetic polymorphisms or evaluated interactions between genetic polymorphisms and endogenous risk factors. Few large scale genome wide association studies conducted recently have provided evidence that common variation on chromosome 15q25.1, 5p15.33 and 6p21.33 influences lung cancer risk and cancer types with strong environmental risk factors. It is hoped that newer research strategies, selecting candidate genes within pathways and genotype at multiple markers within a gene, employing new technologies, may allow complete coverage of the variation within candidate genes in multiple pathways and to unravel the genetic susceptibility to lung cancer. This knowledge could, in turn, be used to identify persons at risk, to individualize treatments such as chemoprevention, to personalize harms of smoking and to motivate cessation.

The N-terminal RASSF family: a new group of Ras-association-domain-containing proteins, with emerging links to cancer formation

The RASSF (Ras-association domain family) has recently gained several new members and now contains ten proteins (RASSF1-10), several of which are potential tumour suppressors. The family can be split into two groups, the classical RASSF proteins (RASSF1-6) and the four recently added N-terminal RASSF proteins (RASSF7-10). The N-terminal RASSF proteins have a number of differences from the classical RASSF members and represent a newly defined set of potential Ras effectors. They have been linked to key biological processes, including cell death, proliferation, microtubule stability, promoter methylation, vesicle trafficking and response to hypoxia. Two members of the N-terminal RASSF family have also been highlighted as potential tumour suppressors. The present review will summarize what is known about the N-terminal RASSF proteins, addressing their function and possible links to cancer formation. It will also compare the N-terminal RASSF proteins with the classical RASSF proteins and ask whether the N-terminal RASSF proteins should be considered as genuine members or imposters in the RASSF family.

Common polymorphisms in D12S1034 flanking genes RASSF8 and BHLHB3 are not associated with lung adenocarcinoma risk

The reported association between D12S1034 and lung adenocarcinoma (ADCA) risk [Yanagitani N, Kohno T, Sunaga N, et al. Localization of a human lung adenocarcinoma susceptibility locus, possibly syntenic to the mouse Pas1 locus, in the vicinity of the D12S1034 locus on chromosome 12p11.2-p12.1. Carcinogenesis. 2002;23:1177-83] prompted us to carry out a case-control study in lung ADCA and healthy control subjects to test possible involvement of single-nucleotide polymorphisms (SNPs) in D12S1034 flanking genes RASSF8 and BHLHB3, whose minimal distances from D12S1034 are approximately 16-24 kb. RASSF8 contains a RAS-associated domain and is a candidate tumor suppressor, whereas BHLHB3 is a basic helix-loop-helix domain-containing protein that functions as a transcriptional repressor. We observed no significant association between common SNPs in RASSF8 (rs1546550 in the 3'-UTR and 3 intronic SNPs) and BHLHB3 (Ala298Val and rs1048155 in the 3'-UTR) with lung ADCA risk. However, patient groups carrying one or two copies of the BHLHB3 Val298 variation (i.e., Ala/Val or Val/Val genotypes) had a higher proportion of short-term survivors (hazard ratio, 1.8; 95% confidence interval, 1.2-2.7) compared with those carrying the Ala/Ala genotype. A replication study in an independent Norwegian lung cancer population of multiple cancer histotypes failed to replicate the significant association of BHLHB3 Ala298Val with survival; such association, however, was confirmed by analysis of ADCA only from both populations. Our results suggest that BHLHB3 variants may affect lung ADCA prognosis.

A functional switch from lung cancer resistance to susceptibility at the Pas1 locus in Kras2LA2 mice

Pulmonary adenoma susceptibility 1 (Pas1) is the major mouse lung cancer susceptibility locus on chromosome 6 (ref. 1). Kras2 is a common target of somatic mutation in chemically induced mouse lung tumors and is a candidate Pas1 gene. M. spretus mice (SPRET/Ei) carry a Pas1 resistance haplotype for chemically induced lung tumors. We demonstrate that the SPRET/Ei Pas1 allele is switched from resistance to susceptibility by fixation of the parental origin of the mutant Kras2 allele. This switch correlates with low expression of endogenous Kras2 in SPRET/Ei. We propose that the Pas1 modifier effect is due to Kras2, and that a sensitive balance between the expression levels of wild-type and mutant alleles determines lung tumor susceptibility. These data demonstrate that cancer predisposition should also be considered in the context of somatic events and could have major implications for the design of human association studies to identify cancer susceptibility genes.

A V141L polymorphism of the human LRMP gene is associated with survival of lung cancer patients

Mouse Lrmp and Casc1 genes are candidates for the pulmonary adenoma susceptibility 1 (Pas1) locus, the major determinant of strain variation in lung tumor susceptibility. These genes contain coding and non-coding single nucleotide polymorphisms (SNPs) strongly associated with lung tumor risk in mice. Analysis of LRMP and CASC1 gene SNPs in 361 lung adenocarcinoma (ADCA) patients and 327 healthy controls revealed common SNPs in LRMP (V141L and S197C) and CASC1 (R33S and three intronic variations), and none showed a significant association with lung ADCA risk. However, in the time-dependent Cox regression model, after adjustment for age, gender, smoking history and clinical stage, the carrier status of the Leu variation (V141L) of the LRMP gene was associated with higher mortality in patients with age at tumor onset < or = 65 years [hazard ratio (HR) 2.3; 95% CI 1.4-3.7; P = 0.001]. These findings suggest that the LRMP V141L polymorphism can predict survival in lung ADCA and that the role of LRMP and CASC1 in human lung cancer risk may differ from that in mice.

Familial lung cancer: genetic susceptibility and relationship to chronic obstructive pulmonary disease

Lung cancer continues to be the leading cause of cancer death, and although most lung cancer is attributable to cigarette smoking, underlying genetic susceptibility is suggested by studies demonstrating familial aggregation. The first family linkage study of lung cancer has identified linkage of lung, laryngeal, and pharyngeal cancer in families to a region on chromosome 6q23-25. Because lung cancer and chronic obstructive pulmonary disease (COPD) are known to aggregate in families beyond shared risk associated with smoking, the linkage results are compared and contrasted with results from genomewide linkage and association studies and candidate gene studies searching for genes for lung cancer, lung function, and COPD. Linkage on chromosome 6q to both lung cancer and lung function, and on 12 to lung cancer, COPD, and lung function, together with overlap in candidate genes for these outcomes, suggests that future research into underlying genetic mechanisms of lung disease would benefit from broadening the collection of family history data and better defining the "high risk" population. As familial risk of lung disease is better defined, referral into screening programs and prevention trials can be better targeted to reach families with both a history of lung cancer and COPD.

Allelic association of the human homologue of the mouse modifier Ptprj with breast cancer

Human homologues of mouse cancer modifier genes may play a role in cancer risk and prognosis. A proportion of the familial risk of common cancers may be attributable to variants in such genes, each contributing to a small effect. The protein tyrosine phosphatase receptor type J (PTPRJ) has been recently identified as being the protein encoded by the Scc1 mouse gene (susceptibility to colon cancer-1). In addition, the PTPRJ gene has been shown to be somatically altered in several human cancer types such as colon, lung and breast cancers and to have the characteristics of a tumour-suppressor gene. The purpose of this study was to determine whether common variants in the PTPRJ gene represent low penetrance breast cancer susceptibility alleles. To test this hypothesis, we assessed single nucleotide polymorphisms (SNPs) tagging the common SNPs and haplotypes of the gene in 4512 cases and 4554 controls from the East Anglian population. We observed a difference in the haplotype frequency distributions between cases and controls (P = 0.0023, OR = 0.81 [0.72-0.92]). Thus, carrying a specific PTPRJ haplotype confers a protective effect on the risk of breast cancer. This result establishes the principle that mouse cancer modifier genes are candidates for low penetrance human breast cancer susceptibility genes.

Association of amino acid substitution polymorphisms in DNA repair genes TP53, POLI, REV1 and LIG4 with lung cancer risk

Single nucleotide polymorphisms (SNPs) were searched for in 36 genes involved in diverse DNA repair pathways, and 50 nonsynonymous (associated with amino acid changes) SNPs identified were assessed for associations with lung cancer risk by a case-control study consisting of 752 adenocarcinoma cases, 250 squamous cell carcinoma cases and 685 controls. An SNP, Arg72Pro, of the TP53 gene encoding a DNA damage response protein showed the strongest association with squamous cell carcinoma risk (OR Pro/Pro vs. Arg/Arg = 2.2), while 2 other SNPs, Phe257Ser of the REV gene encoding a translesion DNA polymerase and Ile658Val of the LIG4 gene encoding a DNA double-strand break repair protein, also showed associations (OR Ser/Ser vs. Phe/Phe = 2.0 and OR Ile/Val vs. Ile/Ile = 0.4, respectively). An SNP, Thr706Ala, in the POLI gene encoding another translesion DNA polymerase was associated with adenocarcinoma and squamous cell carcinoma risk, particularly in individuals of ages < 61 years (OR Ala/Ala + Ala/Thr vs. Thr/Thr = 1.5 and 2.4, respectively). POLI is the human counterpart of PolI, a strong candidate for the Par2 (pulmonary adenoma resistance 2) gene responsible for adenoma/adenocarcinoma susceptibility in mice. The present results suggest that these 4 SNPs function as genetic factors underlying lung cancer susceptibility by modulating activities to maintain the genome integrity of each individual.

Molecular footprints of human lung cancer progression

Lung cancer is the leading cause of cancer-related death in the world. To understand the molecular processes and pathways of, and contributing factors to lung cancer progression, genetic alterations in various progression stages of lung cancer cells have been studied, since these alterations can be regarded as molecular footprints representing the individual processes of multistage lung carcinogenesis. The results indicate that defects in both the p53 and RB/p16 pathways are essential for the malignant transformation of lung epithelial cells. Several other genes, such as K-ras, PTEN and MYO18B, are genetically altered less frequently than p53 and RB/p16 in lung cancer cells, suggesting that alterations in these genes are associated with further malignant progression or unique phenotypes in a subset of lung cancer cells. However, it is still unclear what genes control the metastatic potential of lung cancer cells. Further analyses of molecular footprints in lung cancer cells, in particular in the cells of metastatic sites, will give us valuable information to fully understand the process of lung cancer progression, and to find novel ways of controlling it. Molecular footprints at the sites of p53 mutations and p16 deletions further indicate that DNA repair activities for G:C to T:A transversion and non-homologous end-joining of DNA double-strand breaks play important roles in the accumulation of genetic alterations in lung cancer cells. Thus, identification of environmental as well as genetic factors inducing or suppressing the occurrence of such alterations would be a clue to find novel ways of lung cancer prevention.

Loss of heterozygosity of chromosome 12p does not correlate with KRAS mutation in non-small cell lung cancer

Activating mutations of RAS gene families have been found in a variety of human malignancies, including lung cancer, suggesting their dominant role in tumorigenesis. However, several studies have shown a frequent loss of the wild-type KRAS allele in the tumors of murine models and an inhibition of oncogenic phenotype in tumor cell lines by transfection of wild-type RAS, indicating that wild-type RAS may have oncosuppressive properties. To determine whether loss of wild-type KRAS is involved in the development of human lung cancer, we investigated the mutations of KRAS, NRAS and BRAF in 154 primary non-small cell lung cancers (NSCLCs) as well as 10 NSCLC cell lines that have been shown to have KRAS mutations. We also determined the loss of heterozygosity status of KRAS alleles in these tumors. We detected point mutations of KRAS in 11 (7%) of 154 NSCLCs, with 10 cases at codon 12 and 1 at codon 61, but no mutations of NRAS or BRAF were found. Using the laser capture microdissection technique, we confirmed that 9 of the 11 tumors and 7 of the 10 NSCLC cell lines retained the wild-type KRAS allele. Among the cell lines with heterozygosity of mutant and wild-type KRAS, all of the cell lines tested for expression were shown to express more mutated KRAS than wild-type mRNA, with higher amounts of KRAS protein also being expressed compared to the cell lines with a loss of wild-type KRAS allele. In addition, among 148 specimens available for immunohistochemical analysis, 113 (76%) showed positive staining of KRAS, indicating that the vast majority of NSCLCs continue to express wild-type KRAS. Our findings indicate that the wild-type KRAS allele is occasionally lost in human lung cancer, and that the oncogenic activation of mutant KRAS is more frequently associated with an overexpression of the mutant allele than with a loss of the wild-type allele in human NSCLC development.

Positional cloning of the major quantitative trait locus underlying lung tumor susceptibility in mice

Pulmonary adenoma susceptibility 1 (Pas1), located on chromosome 6, is the major locus affecting inherited predisposition to lung tumor development in mice. We have fine mapped the Pas1 locus to a region of approximately 0.5 megabases by using congenic strains of mice, constructed by placing the Pas1 region of chromosome 6 from A/J mice onto the genetic background of C57BL/6J mice. Systematic characterization of Pas1 candidates establishes the Las1 (lung adenoma susceptibility 1) and Kras2 (Kirsten rat sarcoma oncogene 2) genes as primary candidates for the Pas1 locus. Clearly, Kras2 affects lung tumor progression only, and Las1 is likely to affect lung tumor multiplicity.

Evaluation of a whole-genome amplification method based on adaptor-ligation PCR of randomly sheared genomic DNA

High-throughput genetic studies often require large quantities of DNA for a variety of analyses. Developing and assessing a whole-genome amplification method is thus important, especially with the current desire for large-scale genotyping in previously collected samples for which limited DNA is available. The method we have developed, called PRSG, is based on an adaptor-ligation-mediated PCR of randomly sheared genomic DNA. An unbiased representation was evaluated by performing PCR on 2,607 exons of 367 genes, which are randomly distributed throughout the genome, on PRSG products of hundreds of individuals. An infrequent loss (<1%) of the exon sequence on the PRSG products was found. Out of 307 microsatellites on various chromosomes, 258 (84%) were amplified in both the PRSG product and an original DNA, whereas 49 (16%) microsatellites were lost only in the PRSG product. Array CGH analysis of 287 loci for measuring the relative gene copy number demonstrated that a low bias was detected. Moreover, this method was validated on 100-1,000 laser-captured cells from paraffin-embedded tissues. These data show that PRSG can provide a sufficient amount of genomic sequence for a variety of genetic analyses as well as for long-term storage for future work.

LOH of chromosome 12p correlates with Kras2 mutation in non-small cell lung cancer

Previous observation has shown that the wild-type Kras2 allele is a suppressor of lung cancer in mice. Here we report that loss of heterozygosity (LOH) of chromosome 12p was detected in approximately 50% of human lung adenocarcinomas and large cell carcinomas, and Kras2 mutations were detected at codon 12 in approximately 40% of adenocarcinomas and large cell carcinomas. Interestingly, all of the lung adenocarcinomas and large cell carcinomas containing a Kras2 mutation exhibited allelic loss of the wild-type Kras2 allele when a correlation between LOH of the region on chromosome 12p and Kras2 mutation was made. These results from human lung cancer tissues provide a strong evidence in support of our previous observation in mouse models that the wild-type Kras2 is a tumor suppressor of lung cancer.