Establishment of human osteosarcoma cell lines with high metastatic potential to lungs and their utilities for therapeutic studies on metastatic osteosarcoma

Relevant animal models for metastasis of osteosarcoma is needed to understand the biology and to develop the treatment modality of metastasis of human osteosarcoma. Therefore, we screened six human osteosarcoma cell lines for metastatic ability in nude mice. The HuO9 cell line was identified as being metastatic to the lung after intravenous injection. We established two sublines, HuO9-M112 and HuO9-M132, with high metastatic potential to the lung from the parental HuO9 cells by in vivo selection. There were no differences between these two sublines and the parental cells in the growth rate in vitro and the tumorigenicity after subcutaneous injection in nude mice, however, mice injected with the metastatic sublines became moribund earlier than mice injected with the parental HuO9 cells did. Thus, adriamycin (ADR) and recombinant interleukin-12 (IL-12) were administered to mice injected with the HuO9-M112 subline to suppress experimental lung metastases. Production of lung colonies was significantly suppressed and the prognoses of mice were significantly improved by both ADR and IL-12 treatments. These results indicate that both ADR and IL-12 are effective agents against pulmonary metastatic osteosarcoma, and that these sublines are useful for studies on the biological behavior and treatment of pulmonary metastatic osteosarcoma.

E-cadherin gene variants in gastric cancer families whose probands are diagnosed with diffuse gastric cancer

To identify germline E-cadherin mutations responsible for the predisposition to diffuse gastric cancer (DGC) among the Japanese, we screened 17 patients with familial aggregation of gastric cancer by sequencing analysis. All the patients were diagnosed with DGC and had at least 1 sibling with gastric cancer. Two novel E-cadherin gene variants were detected. One was detected in 1 patient only and associated with an amino acid substitution (Val/Met) at codon 832 in the region essential for binding to beta-catenin. The M832 variant was detected not only in the proband but also in 2 other gastric cancer patients in the family. Immunohistochemical analysis of gastric cancer tissue from the proband revealed that E-cadherin expression was markedly reduced and beta-catenin expression was also reduced in cancer cells. However, no significant difference in the activity of beta-catenin binding was detected between the M832 variant and V832 wild-type E-cadherin in immunofluorescence and immunoprecipitation/Western blot analyses. The other was detected in 5 patients and was located in the splice donor site (IVS1+6T/C); however, RT-PCR analysis indicated that the IVS+6C variant did not cause an aberrant splicing. Thus, the M832 variant could be a germline mutation causative of familial aggregation of DGC, although further functional studies are needed to understand the pathogenic significance of this variant.

MYO18B, a candidate tumor suppressor gene at chromosome 22q12.1, deleted, mutated, and methylated in human lung cancer

Loss of heterozygosity on chromosome 22q has been detected in approximately 60% of advanced nonsmall cell lung carcinoma (NSCLC) as well as small cell lung carcinoma (SCLC), suggesting the presence of a tumor suppressor gene on 22q that is involved in lung cancer progression. Here, we isolated a myosin family gene, MYO18B, located at chromosome 22q12.1 and found that it is frequently deleted, mutated, and hypermethylated in lung cancers. Somatic MYO18B mutations were detected in 19% (14/75) of lung cancer cell lines and 13% (6/46) of primary lung cancers of both SCLC and NSCLC types. MYO18B expression was reduced in 88% (30/34) of NSCLC and 47% (8/17) of SCLC cell lines. Its expression was restored by treatment with 5-aza-2'-deoxycytidine in 11 of 14 cell lines with reduced MYO18B expression, and the promoter CpG island of the MYO18B gene was methylated in 17% (8/47) of lung cancer cell lines and 35% (14/40) of primary lung cancers. Furthermore, restoration of MYO18B expression in lung carcinoma cells suppressed anchorage-independent growth. These results indicate that the MYO18B gene is a strong candidate for a novel tumor suppressor gene whose inactivation is involved in lung cancer progression.

Genetic polymorphism of CYP2A6 gene and tobacco-induced lung cancer risk in male smokers

Cytochrome P450 2A6 (CYP2A6) is the principal enzyme involved in the metabolic activation of tobacco-specific nitrosamines to their ultimate carcinogenic forms and metabolism of nicotine. We investigated the effects of the CYP2A6*4, an entire CYP2A6 gene deletion-type polymorphism, on lung cancer risk and daily cigarette consumption in Japanese male smokers via a hospital-based case control study. The frequency of the CYP2A6*4 variant was compared in 370 lung cancer patients and 380 control smokers. A markedly reduced adjusted odds ratio for lung cancer risk, 0.23 [95% confidence interval, 0.08-0.67], was seen in the group with homozygous deletion (*4/*4) when the odds ratio for a group with homozygous wild (*1A/*1A) was defined to be 1.00 by logistic regression. The subjects with lung cancer were additionally divided into three groups according to the histological classification of the cancer and examined for an association with the CYP2A6 polymorphism. The *4/*4 genotype was not found in patients with squamous cell carcinoma (0 of 105) or small cell carcinoma (0 of 44), indicating that subjects with the *4/*4 genotype have low risk for lung cancers, particularly those caused by tobacco smoke. Furthermore, a significant reduction of daily cigarette consumption was observed in smokers with the *4/*4 genotype, suggesting a possibility that complete lack of CYP2A6 appeared to affect the smoking behavior. These data suggest that male smokers possessing the *1A/*1A genotype have higher risk for tobacco-induced lung cancers.

Mutation and expression of the beta-catenin-interacting protein ICAT in human colorectal tumors

BACKGROUND

Aberrant activation of Wnt signaling caused by mutations in the tumor suppressor adenomatous polyposis coli or beta-catenin is a critical event in the development of human colorectal tumors. We have recently identified the ICAT gene, which encodes a small protein that interacts with beta-catenin and represses Wnt signaling.

METHODS

We examined the prevalence of mutations in the entire ICAT coding sequence and intronic splice donor and acceptor regions of ICAT by PCR-SSCP and also the expression of the ICAT gene by RT-PCR.

RESULTS

The ICAT gene was mapped to chromosome 1p36.1-p36.2, which is implicated in the pathogenesis of various types of cancers. However, no mutations in ICAT were detected among 128 colorectal tumors. Instead, ICAT was found to be overexpressed in almost half of colorectal carcinomas. Cases exhibiting ICAT overexpression showed a significantly higher incidence of well-differentiated adenocarcinoma and positive lymphatic permeation.

CONCLUSION

Our results suggest that ICAT is not the putative tumor suppressor on 1p36.1-p36.2, although aberrant overexpression of ICAT may play a role in the pathogenesis of colorectal carcinomas.

Contribution of the NQO1 and GSTT1 polymorphisms to lung adenocarcinoma susceptibility

Lung adenocarcinoma has replaced squamous cell lung carcinoma as the most frequent histological subtype in lung cancers. However, genetic factors that affect cancer susceptibility are much less understood in adenocarcinoma than in squamous cell carcinoma. In this study, polymorphisms in five genes involved in the metabolism of carcinogens or in the repair of damaged DNA in lung cells, NQO1-Pro187Ser, GSTT1-positive/null, GSTM1-positive/null, CYP1A1-Ile462Val, and OGG1-Ser326Cys, were examined for association with lung adenocarcinoma risk in a case-control study of 198 patients and 152 control subjects. The NQO1 and GSTT1 polymorphisms were associated with lung adenocarcinoma risk with adjusted odds ratio of 2.15 for the NQO1-Pro/Pro genotype versus the Ser/Ser genotype and adjusted odds ratio of 1.61 for the GSTT1-null genotype versus the positive genotype, respectively. Furthermore, individuals with the combined genotype of NQO1-Pro/Pro and GSTT1-null showed greater risk compared with those of NQO1-Ser/Ser and GSTT1-positive. In contrast, significant association was not observed for the GSTM1, CYP1A1, and OGG1 polymorphisms with lung adenocarcinoma risk, although several studies have shown their implication in the risk for squamous cell lung carcinoma. The result indicates that the NQO1-Pro/Pro and GSTT1-null genotypes are risk factors for lung adenocarcinoma development, and that the genetic factors for susceptibility to adenocarcinoma are different from those to squamous cell carcinoma. The enhanced risk of the NQO1-Pro/Pro genotype combined with the GSTT1-null genotype was more evident in smokers than in nonsmokers. Therefore, carcinogens in tobacco smoke, which are activated by NQO1 and detoxified by GSTT1, could have a role in lung adenocarcinoma development.

Clinicopathological significance of epigenetic inactivation of RASSF1A at 3p21.3 in stage I lung adenocarcinoma

PURPOSE

Chromosome 3p is deleted frequently in various types of human cancers, including lung cancer. Recently, the RASSF1A gene was isolated from the 3p21.3 region homozygously deleted in lung and breast cancer cell lines, and it was shown to be inactivated by hypermethylation of the promoter region in lung cancers. In this study, we investigated the pathogenetic and clinicopathological significances of RASSF1A methylation in the development and/or progression of lung adenocarcinoma.

EXPERIMENTAL DESIGN

Association of RASSF1A methylation with clinicopathological features, allelic imbalance at 3p21.3, p53 mutations, and K-ras mutations was examined in 110 stage I lung adenocarcinomas.

RESULTS

Thirty-five of 110 (32%) tumors showed RASSF1A methylation. RASSF1A methylation was dominantly detected in tumors with vascular invasion (P = 0.0242) or pleural involvement (P = 0.0305), and was observed more frequently in poorly differentiated tumors than in well (P = 0.0005) or moderately (P = 0.0835) differentiated tumors. Furthermore, RASSF1A methylation correlated with adverse survival by univariate analysis (P = 0.0368; log-rank test) as well as multivariate analysis (P = 0.032,; risk ratio 2.357; 95% confidence interval, 1.075-5.169). The correlation between RASSF1A methylation and allelic imbalance at 3p21.3 was significant (P = 0.0005), whereas the correlation between RASSF1A methylation and p53 mutation was borderline (P = 0.0842). However, there was no correlation or inverse correlation between RASSF1A methylation and K-ras mutation (P = 0.2193).

CONCLUSIONS

These results indicated that epigenetic inactivation of RASSF1A plays an important role in the progression of lung adenocarcinoma, and that RASSF1A hypermethylation appears to be a useful molecular marker for the prognosis of patients with stage I lung adenocarcinoma.

[Genetic factors involved in cancer susceptibility]

Cancers can be classified as hereditary or sporadic based on the difference in the involvement of genetic factors. Hereditary cancers, which account for approximately 2% of all cancers, are caused by germline mutations of defined genes inherited in an autosomal dominant or recessive manner. Dozens of tumor suppressor genes, oncogenes and DNA repair genes have been identified as being responsible for hereditary cancers. Common cancers (sporadic cancers) make up the remaining 98% of all cancers. It is considered that susceptibility to sporadic cancers in each individual is determined by the combination of multiple genetic polymorphisms. Case-control studies, mainly focusing on the genes involved in drug metabolisms and DNA repair, have shown that dozens of genes are associated with cancer risks.

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

Pulmonary adenoma susceptibility 1 (Pas1) is a major locus affecting inherited predisposition to the development of lung adenocarcinoma in mice, and is mapped to chromosome 6q near the Kras2 gene. However, it is still unclear whether the PAS1 locus on human chromosome 12p11.2-p12.1, the region showing synteny to the mouse Pas1 region, is involved in susceptibility to human lung adenocarcinoma development. Thus, we conducted a case-control study of 100 lung adenocarcinoma cases and 100 controls using 20 highly polymorphic microsatellite markers dispersed in a 13 cM region covering a putative PAS1 locus. The differences in the allele and genotype distributions were observed at several loci, and the difference was at a maximum at the D12S1034 locus (P = 0.034 and P = 0.036, respectively). The differences in the allele and genotype distributions at D12S1034 remained significant in the analysis in which 239 lung adenocarcinoma cases and 63 controls were added to the 100 cases and 100 controls used for the initial screening (P = 0.031 and P = 0.027, respectively). The D12S1034 locus was located 800-1350 kb proximal to the KRAS2 locus, and in the region syntenic to the core Pas1 region of approximately 1.5 Mb in size where a single haplotype is shared by several mouse-inbred strains susceptible to lung adenocarcinoma development. These results indicate that the PAS1 locus is located in the vicinity of D12S1034 and a genetic variation(s) at this locus is involved in susceptibility to human lung adenocarcinoma.

Infrequent mutations of the activating transcription factor-2 gene in human lung cancer, neuroblastoma and breast cancer

The activating transcription factor 2 (ATF-2) gene, which encodes a transcription factor involved in multiple intracellular signal transduction pathways, is located on human chromosome 2q32, which is a common region of LOH in human lung cancer. In neuroblastoma and breast cancer, a high incidence of LOH was detected on chromosome 2q. Recently we found that breast cancer is frequently developed in heterozygous mutant mice for the ATF-2 gene. Therefore, the ATF-2 gene was considered as a candidate tumor suppressor gene on 2q. To assess the role of the ATF-2 gene as a tumor suppressor in human carcinogenesis, we examined genetic alterations of the ATF-2 gene in 9 breast cancer cell lines, 10 neuroblastoma cell lines and 46 lung cancer cell lines. For this purpose, we first determined the exon-intron structure of the ATF-2 gene in the human genome. The ATF-2 gene was composed of 14 exons and 13 introns, and the ATG start codon and the TGA stop codon were present in exons 3 and 14, respectively. Genetic variants of the ATF-2 gene were detected in 5 of the 46 (10.6%) lung cancers, but not in neuroblastomas and breast cancers. Three of the five variants detected in lung cancers were genetic polymorphisms, while the remaining two, consisting of non-synonymous and synonymous substitutions, were possibly somatic mutations. The present result indicates that the ATF-2 gene is not a major tumor suppressor gene on chromosome 2q, however, it is possible that ATF-2 alterations may be involved in the development of a small subset of lung cancers.

A single nucleotide polymorphism at the splice donor site of the human MYH base excision repair genes results in reduced translation efficiency of its transcripts

BACKGROUND

Adenine paired with 8-hydroxyguanine, a major oxidatively damaged DNA lesion, is excised by mutY homologue (MYH) base excision repair protein in human cells. Since genetic polymorphisms of DNA repair genes associated with the activities and the expression levels of their products may modulate cancer susceptibility of individuals, we investigated the effect of a single nucleotide polymorphism (SNP) in the MYH gene on the difference in the expression levels of its products.

RESULTS

An aberrant size of the beta type nuclear form transcript was detected in a lung cancer cell line, VMRC-LCD, by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. The transcript contained the intron 1 sequence, and it was due to alternative splicing resulting from IVS1+5G/C SNP. The presence of the upstream open reading frame (ORF) on the 5'-side of the native ORF in the beta type transcript from the IVS1+5C allele could reduce the translation efficiency of the transcript into the nuclear form protein. Thus, expression vectors bearing the 5'-untranslated region sequence of either the IVS1+5G or 5C allele were constructed. In vitro translation analysis, as well as Western blot and quantitative RT-PCR analyses of the H1299 lung cancer cell line transfected with these vectors, revealed that the translation efficiency of the IVS1+5C transcript into MYH protein was much lower (approximately 30) than that of the IVS1+5G transcript.

CONCLUSIONS

The SNP at the splice donor site of the MYH gene resulted in reduced translation efficiency of its transcripts. This is the fourth case of single nucleotide variations that cause alterations in translation initiation sites and translation efficiencies in human cells.

EVI1 is expressed in megakaryocyte cell lineage and enforced expression of EVI1 in UT-7/GM cells induces megakaryocyte differentiation

3q21q26 syndrome, an acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) with chromosomal translocations or inversions between the bands 3q21 and 3q26, is frequently associated with dysmegakaryocytopoiesis and increased platelet counts at the initial diagnosis. Since the EVI1 gene at 3q26 is transcriptionally activated in 3q21q26 syndrome, we assessed the role of EVI1 gene expression in the abnormal megakaryocytic differentiation in 3q21q26 syndrome. RT-PCR analysis of various types of hematopoietic cells revealed that the EVI1 gene is expressed specifically in CD34(+) cells, megakaryocytes, and platelets. UT-7 is a human immature megakaryoblastic leukemia cell line with dependence for the growth on granulocyte-macrophage colony-stimulating factor (GM-CSF) (designated at UT-7/GM) and with a differentiation capacity to erythroid (UT-7/EPO) and megakaryocytic lineages (UT-7/TPO) by erythropoietin (EPO) and thrombopoietin (TPO), respectively. Among three UT-7 sublines, UT-7/GM, UT-7/EPO, and UT-7/TPO, expression of the EVI1 gene was detected at low levels in UT-7/GM and UT-7/EPO cells, but was detected at a higher level in UT-7/TPO cells. When UT-7/GM cells were cultured with TPO, the level of EVI1 expression was increased, along with increased numbers of polynuclear megakaryocytes and expression of the platelet factor 4 (PF-4) gene. Furthermore, forced expression of the EVI1 gene in UT-7/GM cells changed their morphology to polynuclear megakaryocytes, stopped their growth, and induced cell death within a month. These data indicate that expression of the EVI1 gene is involved in progression of megakaryocytic differentiation and, thus, the dysmegakaryocytopoiesis in 3q21q26 syndrome could be partly due to an enhanced differentiation capacity of leukemia cells and/or megakaryocytes by constitutive expression of the EVI1 gene.

Frequent co-localization of Cox-2 and laminin-5 gamma2 chain at the invasive front of early-stage lung adenocarcinomas

Laminin-5 is an extracellular matrix protein that plays a key role in cell migration and tumor invasion. Cox-2 is an induced isoform of cyclooxygenases that plays an important role in carcinogenesis, suppression of apoptosis, angiogenesis, and metastasis of colon cancer. We report frequent co-expression of cox-2 and laminin-5 at the invasive front of early-stage lung adenocarcinomas. We investigated the expression of cox-2 and laminin-5 immunohistochemically in 102 cases of small-sized lung adenocarcinoma (maximum dimension, 2 cm or less). Cox-2 and laminin-5 were expressed in 97 (95.1%) and 82 (80.4%) cases, respectively. Both were preferentially localized in cancer cells at the cancer-stroma interface, although cox-2 tended to show a diffuse staining pattern in some cases. A comparison of their staining patterns revealed a striking similarity in their distribution in 24 cases, and a partial overlap between their localization in another 20 cases. Moreover, an overall correlation was found between the expression levels of cox-2 and laminin-5 (P = 0.018). To gain insight into the mechanisms that regulate the expression of these proteins, we additionally studied their expression in 58 cases of stage I lung adenocarcinoma, in which p53 status was determined by immunohistochemistry, polymerase chain reaction-single strand conformation polymorphism analysis, and direct sequencing. The results showed that tumors with mutant p53 tended to express more cox-2 than those with wild-type p53 (P = 0.080). Also, tumors that overexpressed p53 had higher levels of cox-2 and laminin-5 than those without p53 overexpression (P = 0.032 and 0.047, respectively). Further immunohistochemical analysis showed that tumors that overexpressed both epidermal growth factor receptor (EGFR) and erbB-2 had higher levels of cox-2 and laminin-5 than those without concomitant overexpression of these proteins (P = 0.014 and P = 0.018, respectively). To see whether EGFR signaling is involved in cox-2 and laminin-5 expression, we further conducted in vitro analyses using six lung adenocarcinoma cell lines (A549, HLC-1, ABC-1, LC-2/ad, VMRC-LCD, and L27). Western blot analyses showed that cox-2 mRNA levels, and to a lesser extent laminin-5 gamma2 mRNA levels, correlated with the expression levels of erbB-2 and the phosphorylated form of MAPK/ERK-1/2 protein. The addition of transforming growth factor-alpha increased both cox-2 and laminin-5 gamma2 mRNA levels in A549, ABC-1, and L27 with different kinetics; the induction of cox-2 occurred earlier than that of laminin-5 gamma2. Finally, the migration of ABC-1 cells was inhibited by MAP kinase kinase inhibitor PD98059 and a selective cox-2 inhibitor NS-398. In contrast, the migration of A549 cells was inhibited by PD98059, but much less effectively by NS-398. These results suggest that co-stimulatory mechanisms may exist that increase the expression of cox-2 and laminin-5 at the invasive front of lung adenocarcinomas and that EGFR signaling could be one of the mechanisms. Further investigations are warranted concerning the role of cox-2 and laminin-5 in cancer cell invasion and the significance of p53 and EGFR signaling in the regulation of cox-2 and laminin-5 expression.

Infrequent mutations of the activating transcription factor-2 gene in human lung cancer, neuroblastoma and breast cancer

The activating transcription factor 2 (ATF-2) gene, which encodes a transcription factor involved in multiple intracellular signal transduction pathways, is located on human chromosome 2q32, which is a common region of LOH in human lung cancer. In neuroblastoma and breast cancer, a high incidence of LOH was detected on chromosome 2q. Recently we found that breast cancer is frequently developed in heterozygous mutant mice for the ATF-2 gene. Therefore, the ATF-2 gene was considered as a candidate tumor suppressor gene on 2q. To assess the role of the ATF-2 gene as a tumor suppressor in human carcinogenesis, we examined genetic alterations of the ATF-2 gene in 9 breast cancer cell lines, 10 neuroblastoma cell lines and 46 lung cancer cell lines. For this purpose, we first determined the exon-intron structure of the ATF-2 gene in the human genome. The ATF-2 gene was composed of 14 exons and 13 introns, and the ATG start codon and the TGA stop codon were present in exons 3 and 14, respectively. Genetic variants of the ATF-2 gene were detected in 5 of the 46 (10.6%) lung cancers, but not in neuroblastomas and breast cancers. Three of the five variants detected in lung cancers were genetic polymorphisms, while the remaining two, consisting of non-synonymous and synonymous substitutions, were possibly somatic mutations. The present result indicates that the ATF-2 gene is not a major tumor suppressor gene on chromosome 2q, however, it is possible that ATF-2 alterations may be involved in the development of a small subset of lung cancers.

Alterations in the INK4a/ARF locus and their effects on the growth of human osteosarcoma cell lines

Two different proteins, p16(INK4a) and p14(ARF), encoded by the INK4a/ARF locus play important roles in the RB and p53 pathways, respectively. This study was performed to determine genetic and epigenetic alterations in the INK4a/ARF locus and their effects on the growth of osteosarcoma. Among six cell lines examined, both p16(INK4a) and p14(ARF) exons were homozygously deleted in two cell lines, MG63 and HOS, and both p16(INK4a) and p14(ARF) promoters were methylated in one cell line, U2OS. Wild-type mRNA and proteins for p16(INK4a) and p14(ARF) were expressed in three other cell lines, SaOS2, HuO9, and G292. Transfection studies were performed using two cell lines, U2OS and MG63. Both the RB and p53 genes were wild types in U2OS, whereas p53 but not RB was mutated in MG63. Both p16(INK4a) and p14(ARF) suppressed the growth of U2OS, whereas p16(INK4a) but not p14(ARF) suppressed the growth of MG63. p53 only did not suppress the growth of MG63 either; however, coexpression of p14(ARF) with p53 increased the fraction of the G0/G1 phase in MG63 cells. The data presented here demonstrate the importance of genetic and epigenetic alterations in the INK4a/ARF locus for the growth of osteosarcoma and thus will be useful to further understand the biologic behavior of osteosarcoma in association with the defects in the p53 and RB pathways.

Retinoic acid suppresses endothelin-1 gene expression at the transcription level in endothelial cells

Retinoids have been shown to inhibit cell growth, which can result in an anti-atherosclerotic action in the vasculature. Endothelin-1 (ET-1), a potent vasoconstrictor peptide produced in endothelial cells, plays an important role in inducing proliferation of vascular smooth muscle cells. In this study, we investigated the effect of retinoids on the mRNA expression and transcriptional activity of the ET-1 gene in endothelial cells. All-trans retinoic acid (ATRA) suppressed ET-1 mRNA expression in cultured endothelial cells. Synthetic retinoids, Ch55 and Am580 (retinoic acid receptor (RAR) agonists) markedly enhanced this effect, and an RAR antagonist, LE540, blocked this inhibitory effect on ET-1 gene expression. ATRA did not change ET-1 mRNA half-life. Transfection experiments using 5 kb of the ET-1 promoter-reporter gene construct which contains 5 kb of the preproET-1 promoter revealed that ATRA and Ch55 suppressed ET-1 promoter activity, resulting in down-regulation of ET-1 gene transcription. Taken together, retinoids may be another modulator of endothelial cell function through regulation of vasoactive substances at the transcription level.

Inhibition of lung cancer cell growth and induction of apoptosis after reexpression of 3p21.3 candidate tumor suppressor gene SEMA3B

Semaphorins SEMA3B and its homologue SEMA3F are 3p21.3 candidate tumor suppressor genes (TSGs), the expression of which is frequently lost in lung cancers. To test the TSG candidacy of SEMA3B and SEMA3F, we transfected them into lung cancer NCI-H1299 cells, which do not express either gene. Colony formation of H1299 cells was reduced 90% after transfection with wild-type SEMA3B compared with the control vector. By contrast, only 30-40% reduction in colony formation was seen after the transfection of SEMA3F or SEMA3B variants carrying lung cancer-associated single amino acid missense mutations. H1299 cells transfected with wild-type but not mutant SEMA3B underwent apoptosis. We found that lung cancers (n = 34) always express the neuropilin-1 receptor for secreted semaphorins, whereas 82% expressed the neuropilin-2 receptor. Because SEMA3B and SEMA3F are secreted proteins, we tested conditioned medium from COS-7 cells transfected with SEMA3B and SEMA3F and found that medium from wild-type SEMA3B transfectants reduced the growth of several lung cancer lines 30-90%, whereas SEMA3B mutants or SEMA3F had little effect in the same assay. Sequencing of sodium bisulfite-treated DNA showed dense methylation of CpG sites in the SEMA3B 5' region of lung cancers not expressing SEMA3B but no methylation in SEMA3B-expressing tumors. These results are consistent with SEMA3B functioning as a TSG, the expression of which is inactivated frequently in lung cancers by allele loss and promoter region methylation.

Overexpression of candidate tumor suppressor gene FUS1 isolated from the 3p21.3 homozygous deletion region leads to G1 arrest and growth inhibition of lung cancer cells

Recently we identified FUS1 as a candidate tumor suppressor gene (TSG) in the 120 kb 3p21.3 critical region contained in nested lung and breast cancer homozygous deletions. Mutation of FUS1 is infrequent in lung cancers which we have confirmed in 40 other primary lung cancers. In addition, we found no evidence for FUS1 promoter region methylation. Because haploinsufficiency or low expression of Fus1 may play a role in lung tumorigenesis, we tested the effect of exogenously induced overexpression of Fus1 protein and found 60-80% inhibition of colony formation for non-small cell lung cancer lines NCI-H1299 (showing allele loss for FUS1) and NCI-H322 (containing only a mutated FUS1 allele) in vitro. By contrast, a similar level of expression of a tumor-acquired mutant form of FUS1 protein did not significantly suppress colony formation. Also, induced expression of Fus1 under the control of an Ecdysone regulated promoter decreased colony formation 75%, increased the doubling time twofold, and arrested H1299 cells in G1. In conclusion, our data are consistent with the hypothesis that FUS1 may function as a 3p21.3 TSG, warranting further studies of its function in the pathogenesis of human cancers.

hOGG1 exon7 polymorphism and gastric cancer in case-control studies of Japanese Brazilians and non-Japanese Brazilians

Polymorphism of hOGG1 may be capable of serving as a genetic marker for individual susceptibility to various cancers because of its role in the repair of oxyradical DNA damage. We examined the distribution of the hOGG1 Ser326Cys polymorphism and its presumed correlation with gastric cancer risk in two case-control studies of different ethnic groups in São Paulo, Brazil. Potentially eligible Japanese (JB) and non-Japanese Brazilian (NJB) case subjects were defined as patients with newly diagnosed malignant neoplasms of the stomach in 13 hospitals in São Paulo. Ninety-six JBs and 236 NJBs were adopted as subjects. Two controls were matched for each JB case, and one control for each NJB case. The subjects were interviewed using a questionnaire and their blood samples were collected. A significant difference in the distribution of this polymorphism between the two ethnic groups was observed (chi(2)=58.3, P<0.01). The mutant type (Ser/Cys or Cys/Cys) was predominant (approximately 65%) in the JBs, but was only present in approximately 40% of the NJBs. Logistic regression analysis showed no significant increased risk for either the Ser/Cys or Cys/Cys type in either group. The odds ratios of the Cys allele for gastric cancer were 1.01 (95% confidence interval (CI): 0.52-1.93) in the JBs and 0.85 (95% CI: 0.57-1.26) in the NJBs. In the NJBs, a significant increased risk of smoking was shown only in the Ser/Ser type, and no increased risk was shown in the genotypes with the Cys allele. However, no statistically significant interactions were observed with smoking or other possible confounding factors. No statistically significant difference in the distribution of the polymorphism was observed between the intestinal type and diffuse type of gastric cancer in either the JBs or the NJBs. The ethnic difference in hOGG1 Ser326Cys polymorphism was much greater than the case-control difference, and this polymorphism is unlikely to be associated with gastric cancer.

OGG1 protein suppresses G:C-->T:A mutation in a shuttle vector containing 8-hydroxyguanine in human cells

8-Hydroxyguanine (8-OHG) is an oxidatively damaged mutagenic base which causes G:C-->T:A transversions in DNA. OGG1 was cloned as a human gene encoding a DNA glycosylase that specifically excises 8-OHG from DNA in vitro. However, it was not clear whether OGG1 protein suppresses G:C-->T:A transversions caused by 8-OHG in human cells in vivo. In the present study we have examined the ability of OGG1 protein to suppress G:C-->T:A transversions caused by 8-OHG in human cells by bacterial suppressor tRNA (supF) forward mutation assay using a shuttle vector DNA, pMY189. Introduction of a single 8-OHG residue at position 159 of the supF gene in plasmid pMY189 resulted in a 130-fold increase in mutation frequency compared with untreated plasmid pMY189 after replication in the NCI-H1299 human lung cancer cell line. G:C-->T:A transversions at position 159 were detected in >90% of the supF mutants from the 8-OHG-containing plasmid. The mutation frequency of the 8-OHG-containing plasmid was significantly reduced by overexpression of OGG1 protein in NCI-H1299 cells and, in particular, the occurrence of G:C-->T:A transversion at position 159 in the supF gene was suppressed. Furthermore, frequencies and spectra of mutations of the untreated pMY189 plasmid did not differ significantly with overexpression of OGG1 protein. These results indicate that OGG1 protein has the ability to suppress G:C-->T:A transversions caused by 8-OHG in human cells in vivo.

DNA damage-inducible gene p33ING2 negatively regulates cell proliferation through acetylation of p53

The p33ING1 protein is a regulator of cell cycle, senescence, and apoptosis. Three alternatively spliced transcripts of p33ING1 encode p47ING1a, p33ING1b, and p24ING1c. We cloned an additional ING family member, p33ING2/ING1L. Unlike p33ING1b, p33ING2 is induced by the DNA-damaging agents etoposide and neocarzinostatin. p33ING1b and p33ING2 negatively regulate cell growth and survival in a p53-dependent manner through induction of G(1)-phase cell-cycle arrest and apoptosis. p33ING2 strongly enhances the transcriptional-transactivation activity of p53. Furthermore, p33ING2 expression increases the acetylation of p53 at Lys-382. Taken together, p33ING2 is a DNA damage-inducible gene that negatively regulates cell proliferation through activation of p53 by enhancing its acetylation.