Biology Division

4. Biology Division

To elucidate the molecular mechanisms of human cancer progression, the following projects are underway in the Biology Division. The main project of the Division is the identification of novel tumor suppressor genes and oncogenes involved in the genesis and progression of human cancer. Functional analyses of several cancer-related genes are also in progress. Recently two other projects have started in the Division. One is the involvement of genomic instability in human carcinogenesis, and the other is the molecular mechanisms of invasion and metastasis.
Genetic Alterations in Human Cancers

Tumor suppressor genes are located at loci showing loss of heterozygosity (LOH) or homozygous deletion in tumors. Allelotype analysis of small cell lung carcinoma revealed that the frequencies of LOH on chromosomes 3p, 5q, 13q, 17p and 22q were significantly higher than those on other chromosome arms.⁽⁵⁶⁾ It was indicated that the p16 gene on chromosome 9p and the DCC gene on chromosome 18q are involved in the progression of neuroblastoma.^(57-60) Allelotype analysis also indicated that chromosomes 7q and 12p were deleted in ovarian cancers.^(61,62) The transforming growth factor b type II receptor gene is infrequently mutated in lung and colon cancers, while the APC gene is also infrequently mutated in non-colonic neoplastic tissues.^(63-65) The EVI-1 gene is activated by translocation involving chromosome 3q26in CML blastic crisis and AML after MDS.^{(66, 67)}
Functional Analysis of Cancer-related Genes

There are several projects in the Division that aim to elucidate the pathogenetic significance of tumor suppressor gene inactivation in human cancer. Phosphorylation mechanisms of the RB and p53 genes were investigated in association with the inactivation of those genes.^(68-71) The result indicated that DNA damage induces phosphorylation of the amino terminus of p53, and that the phosphorylation alleviates inhibition by MDM2.^{(69, 70)} Dysregulation of the cell-cycle and apoptosis control is associated with the induction of DNA damage in cells with germ-line p53 mutations.⁽⁷²⁾ A tetracycline-dependent inducible system for the expression of the RB and p53 gene was developed in an osteogenic sarcoma cell line Saos2.⁽⁷³⁾ In this system, differentiation was induced by RB expression whereas apoptosis was induced by p53 expression. The wild-type p16 gene can induce G1 arrest in a non-small cell lung carcinoma cell line with inactivated p16.⁽⁷⁴⁾ Peptide sequences in the raf-p74 protein bound to the ras-p21 protein were determined.⁽⁷⁵⁾
Isolation of a Gene Involved in the Repair of an Oxidative DNA Damage, 8-hydroxyguanine

To elucidate the molecular mechanisms of DNA repair system for 8-hydroxyguanine, that is a major form of oxygen free radical-induced DNA damage, a human homologue (hOGG1) of the yeast OGG1 (oxoguanine DNA glycosylase) gene was isolated, and the enzymatic activity of the hOGG1 protein was analyzed.^(76-78) The OGG1 protein has both 8-hydroxyguanine DNA glycosylase and AP lyase activities, suggesting that the hOGG1 gene is a functional human homologue of the yeast OGG1 gene and is involved in the repair system for 8-hydroxyguanine in damaged DNA.
Genomic Instability and Carcinogenesis

Since it has been shown that genomic instability is present in a variety of cancer cells and in cancer-prone families, the prevalence of microsatellite instability was investigated in gastric cancer-prone families. Genomic instability represented by the replication-error phenotype was frequently detected in early stage gastric cancer of patients with family histories of gastric cancer aggregation, suggesting that inherited disorders in mismatch repair systems contribute to high susceptibility to gastric cancers in a subset of gastric cancer prone families.⁽⁷⁹⁾
Identification of Genes Involved in Metastasis

Eight genes were previously identified as being differentially expressed in association with the metastatic potential of K-1735 mouse melanoma cells by the mRNA differential display method. Integrin a6 and two unknown genes were expressed in high-metastatic cells, whereas b-tropomyosin, macrophage colony-stimulating factor, inhibin/activin bB subunit, and two unknown genes were expressed in low-metastatic cells. These results indicates that the metastatic potential of tumor cells is regulated by activation and/or inactivation of several specific genes, including cell adhesion molecules, cytoskeletal protein, and growth factor genes. Molecular cloning and sequence analysis revealed that one of the genes expressed in highly metastatic cells is a novel member of the Sox family genes, and thus, was designated Sox21.⁽⁸⁰⁾




	4. Biology Division



		To elucidate the molecular mechanisms of human cancer progression, the following projects are underway in the Biology Division. The main project of the Division is the identification of novel tumor suppressor genes and oncogenes involved in the genesis and progression of human cancer. Functional analyses of several cancer-related genes are also in progress. Recently two other projects have started in the Division. One is the involvement of genomic instability in human carcinogenesis, and the other is the molecular mechanisms of invasion and metastasis. Genetic Alterations in Human Cancers Tumor suppressor genes are located at loci showing loss of heterozygosity (LOH) or homozygous deletion in tumors. Allelotype analysis of small cell lung carcinoma revealed that the frequencies of LOH on chromosomes 3p, 5q, 13q, 17p and 22q were significantly higher than those on other chromosome arms.⁽⁵⁶⁾ It was indicated that the p16 gene on chromosome 9p and the DCC gene on chromosome 18q are involved in the progression of neuroblastoma.^(57-60) Allelotype analysis also indicated that chromosomes 7q and 12p were deleted in ovarian cancers.^(61,62) The transforming growth factor b type II receptor gene is infrequently mutated in lung and colon cancers, while the APC gene is also infrequently mutated in non-colonic neoplastic tissues.^(63-65) The EVI-1 gene is activated by translocation involving chromosome 3q26in CML blastic crisis and AML after MDS.^{(66, 67)} Functional Analysis of Cancer-related Genes There are several projects in the Division that aim to elucidate the pathogenetic significance of tumor suppressor gene inactivation in human cancer. Phosphorylation mechanisms of the RB and p53 genes were investigated in association with the inactivation of those genes.^(68-71) The result indicated that DNA damage induces phosphorylation of the amino terminus of p53, and that the phosphorylation alleviates inhibition by MDM2.^{(69, 70)} Dysregulation of the cell-cycle and apoptosis control is associated with the induction of DNA damage in cells with germ-line p53 mutations.⁽⁷²⁾ A tetracycline-dependent inducible system for the expression of the RB and p53 gene was developed in an osteogenic sarcoma cell line Saos2.⁽⁷³⁾ In this system, differentiation was induced by RB expression whereas apoptosis was induced by p53 expression. The wild-type p16 gene can induce G1 arrest in a non-small cell lung carcinoma cell line with inactivated p16.⁽⁷⁴⁾ Peptide sequences in the raf-p74 protein bound to the ras-p21 protein were determined.⁽⁷⁵⁾ Isolation of a Gene Involved in the Repair of an Oxidative DNA Damage, 8-hydroxyguanine To elucidate the molecular mechanisms of DNA repair system for 8-hydroxyguanine, that is a major form of oxygen free radical-induced DNA damage, a human homologue (hOGG1) of the yeast OGG1 (oxoguanine DNA glycosylase) gene was isolated, and the enzymatic activity of the hOGG1 protein was analyzed.^(76-78) The OGG1 protein has both 8-hydroxyguanine DNA glycosylase and AP lyase activities, suggesting that the hOGG1 gene is a functional human homologue of the yeast OGG1 gene and is involved in the repair system for 8-hydroxyguanine in damaged DNA. Genomic Instability and Carcinogenesis Since it has been shown that genomic instability is present in a variety of cancer cells and in cancer-prone families, the prevalence of microsatellite instability was investigated in gastric cancer-prone families. Genomic instability represented by the replication-error phenotype was frequently detected in early stage gastric cancer of patients with family histories of gastric cancer aggregation, suggesting that inherited disorders in mismatch repair systems contribute to high susceptibility to gastric cancers in a subset of gastric cancer prone families.⁽⁷⁹⁾ Identification of Genes Involved in Metastasis Eight genes were previously identified as being differentially expressed in association with the metastatic potential of K-1735 mouse melanoma cells by the mRNA differential display method. Integrin a6 and two unknown genes were expressed in high-metastatic cells, whereas b-tropomyosin, macrophage colony-stimulating factor, inhibin/activin bB subunit, and two unknown genes were expressed in low-metastatic cells. These results indicates that the metastatic potential of tumor cells is regulated by activation and/or inactivation of several specific genes, including cell adhesion molecules, cytoskeletal protein, and growth factor genes. Molecular cloning and sequence analysis revealed that one of the genes expressed in highly metastatic cells is a novel member of the Sox family genes, and thus, was designated Sox21.⁽⁸⁰⁾