p16/CDKN2 gene and p53 gene alterations in Japanese non-smoking female lung adenocarcinoma

Gene mutation discovery research of non-smoking lung cancer patients due to indoor radon exposure

Although the incidence and mortality for most cancers such as lung and colon are decreasing in several countries, they are increasing in several developed countries because of an unhealthy western lifestyles including smoking, physical inactivity and consumption of calorie-dense food. The incidences for lung and colon cancers in a few of these countries have already exceeded those in the United States and other western countries. Among them, lung cancer is the main cause of cancer death in worldwide. The cumulative survival rate at five years differs between 13 and 21 % in several countries. Although the most important risk factors are smoking for lung cancer, however, the increased incidence of lung cancer in never smokers(LCINS) is necessary to improve knowledge concerning other risk factors. Environmental factors and genetic susceptibility are also thought to contribute to lung cancer risk. Patients with lung adenocarcinoma who have never smoking frequently contain mutation within tyrosine kinase domain of the epidermal growth factor receptor(EGFR) gene. Also, K-ras mutations are more common in individuals with a history of smoking use and are related with resistance to EFGR-tyrosine kinase inhibitors. Recently, radon(Rn), natural and noble gas, has been recognized as second common reason of lung cancer. In this review, we aim to know whether residential radon is associated with an increased risk for developing lung cancer and regulated by several genetic polymorphisms.

Frequent aberrant methylation of the promoter region of sterile alpha motif domain 14 in pulmonary adenocarcinoma

Aberrant methylation of promoter CpG islands is known to be a major inactivation mechanism of tumor-suppressor and tumor-related genes. In order to identify novel hypermethylated genes in early stage lung adenocarcinoma, we carried out methylated CpG island amplification, modified suppression subtractive hybridization, and methylation-specific polymerase chain reaction to identify aberrant methylation of CpG islands in the A/J mouse lung adenoma model, which histologically mimics the early stage of human pulmonary adenocarcinoma. Through methylated CpG island amplification, suppression subtractive hybridization, and differential screening, we detected five genes, three of which have human homologs. Two of them showed downregulation of their expression in human lung adenocarcinoma. Of these two genes, we selected sterile alpha motif domain 14 (SAMD14) and further analyzed its methylation status and expression level by methylation-specific polymerase chain reaction and quantitative real-time polymerase chain reaction. Most of the lung adenocarcinoma cell lines showed suppressed expression of SAMD14 together with hypermethylation at the promoter region, although an immortalized bronchial epithelium cell line (PL16B) did not show hypermethylation and did express SAMD14. The expression of SAMD14 in A549 was rescued by treatment with the demethylation agent 5-aza-2'-deoxycytidine. These data indicate that hypermethylation of the SAMD14 gene promoter region is associated with silencing of its expression. Hypermethylation at the CpG site of the SAMD14 promoter region was detected frequently in early invasive adenocarcinoma (8/24, 33.3%) but not in in situ adenocarcinoma (0/7, 0%) or normal lung tissue (0/31, 0%). Hypermethylation of the SAMD14 gene is a specific event in pulmonary adenocarcinogenesis and malignant progression.

Inactivation of the p16 gene by hypermethylation and loss of heterozygosity in adenocarcinoma of the lung

We investigated the aberrant promoter hypermethylation of p16, p15 and p14 genes and loss of heterozygosity (LOH) at 9p21-22 in 48 cases of adenocarcinoma of the lung. The frequencies of hypermethylation of genes were as follows: p16, 25.0%; p15, 22.9%; and p14, 18.8%. The frequency of LOH at chromosome 9p21-22 was 60.9%. The frequency of two-hit inactivation of the p16 gene by hypermethylation and LOH was 21.7%. Two-hit inactivation of the p16 gene showed loss of protein expression and was significantly correlated with tumor size, tumor grade and the Ki-67 labeling index. Hypermethylation of the p16 gene was not significantly correlated with hypermethylation of the p15 and p14 genes, both of which are close to the p16 gene locus, suggesting that hypermethylation of these genes occurs selectivity. In conclusion, biallelic inactivation of the p16 gene by hypermethylation and LOH might cause loss of p16 expression and play an important role in the development of adenocarcinoma of the lung. Therefore, controlling and monitoring for hypermethylation of the p16 gene may be partially useful for treatment and early diagnosis of adenocarcinoma of the lung.

Reduced HGF expression in subcutaneous CT26 tumor genetically modified to secrete NK4 and its possible relation with antitumor effects

Tumor-stromal interactions, which are regulated by stromal-derived HGF and tumor-derived HGF inducers, are essential for tumor cell acquisition of such malignant properties as invasion and metastasis. NK4, a proteolytic cleavage product of HGF, has antitumor activities as both an HGF antagonist and an angiogenesis inhibitor. In this study, we examined the in vitro and in vivo behaviors of mouse colon adenocarcinoma C T26 cells modified by gene transfer to secrete NK4, and investigated the influence of NK4 on expression of HGF and HGF inducers associated with tumor-stromal interactions. In vitro cell proliferation rates of NK4 transfectant (C T26-NK4) and mock transfectant (C T26-NEO) were essentially the same, and scattering and invasion were stimulated by HGF in C T26-NEO, but not in C T26-NK4. In syngeneic BALB/c female mice, subcutaneous tumor growth of C T26-NK4 was potently suppressed, and the survival was prolonged significantly. Immunohistochemistry showed significantly decreased microvessels and increased apoptotic cells in C T26-NK4 tumor compared with control. Interestingly, HGF, strongly expressed in C T26-NEO tumor stroma, was reduced in C T26-NK4. In vitro, conditioned medium of C T26-NK4 inhibited fibroblast-derived HGF production, which was increased by that of C T26-NEO. Moreover, although similar constitutive expression levels of PDGF and TGF-alpha (both HGF inducers) were detected in C T26-NK4 and C T26-NEO in semiquantitative RT-PCR analyses, the expression was up-regulated by HGF in C T26-NEO, but not C T26-NK4. These results suggest that NK4 may exert antitumor activities not only by antagonizing HGF, but also by inhibiting HGF amplification via tumor-stromal interactions. Continuous, abundant NK4 production induced at a tumor site by gene transfer should show multiple antitumor activities with potential therapeutic benefit.

Progress in understanding the molecular pathogenesis of human lung cancer

We review the molecular pathogenesis of lung cancer including alterations in dominant oncogenes, recessive oncogenes/tumor suppressor genes, alterations in growth regulatory signaling pathways, abnormalities in other pathways, such as apoptosis, autocrine and paracrine growth stimulatory loops, angiogenesis, and host immune responses, other mechanisms of genetic changes, such as microsatellite and methylation alterations, and the potential for inherited predisposition to lung cancer. These changes are related to multistage carcinogenesis involving preneoplastic lesions, and lung development and differentiation. The translational applications of these findings for developing new ways of early detection, prevention, treatment, and prognosis of lung cancer are discussed.