Radiobiology Division

8. Radiobiology Division

　The Radiobiology Division is currently focusing on the positional cloning of disease genes, especially of leukemia-related genes, and tumor suppressor genes. Functional analysis of several tumor-associated genes including AML1, which were successfully isolated by a genome-analysis based approach, is also underway.
Cloning and Genome Structure of Leukemia-associated Genes

　The t(16;21)(q24;q22) translocation is a rare but recurrent chromosomal abnormality associated with therapy-related myeloid malignancies and is a variant of the t(8;21) translocation in which the AML1 gene on chromosome 21 is rearranged. The structural analysis of cDNAs from the leukemic cells of patients carrying t(16;21) showed that AML1 is fused to a novel gene named MTG16 which shows high homology to MTG8.⁽¹²⁹⁾ As in t(8;21), the t(16;21) breakpoints occurred between exons 5 and 6 of AML1, and between exons 1 and 2 or exons 3 and 4 of MTG16. The two genes are fused in-frame, resulting in the characteristic chimeric transcripts of this translocation. Thus, the AML1-MTG16 gene fusion in t(16;21) leukemia results in the production of a protein that is very similar to the AML1-MTG8 chimeric protein.
　The RBP56/hTAFII68, FUS/TLS and EWS proteins comprise a sub-family of RNA binding proteins. Rearrangement of the FUL/TLS gene and the EWS gene has been found in several types of malignant tumors, and the resultant fusion proteins play an important role in the pathogenesis of these tumors. Analysis of the genomic structure of the RBP56/hTAFII68 gene indicated that the RBP56/hTAFII68 gene spans about 37 kb and consists of 16 exons. Comparison of the structure of the genes indicated that RBP56/hTAFII68,FUS/TLS and EWS most likely originate from the same ancestor gene.⁽¹³⁰⁾
Functional Analysis of Leukemia-associated Gene Products

　The AML1 transcription factor is a target of chromosome translocations associated with acute myeloid leukemia and myelodysplastic symdrome. In the t(8;21) translocation, the AML1 (CBFA2/PEBP2aB) gene becomes fused to the MTG8 (ETO) gene. Immunoprecipitaion analysis showed that p300 and CREB-binding protein (CBP) interact with AML1. The C-terminal region of AML1 is responsible for the induction of cell differentiation and for the interaction with p300. Overexpression of p300 stimulates AML1-dependent transcription and the induction of cell differentiation. These results suggested that p300 plays critical roles in AML1-dependent transcription during the differentiation of myeloid cells. Thus, AML1 and its associated factor p300, both of which are targets of chromosomal rearrangements in human leukemia, function cooperatively in the differentiation of myeloid cells.⁽¹³¹⁾
　The AML1-MTG8 gene product was found to specifically and strongly interact with an 85-kDa phosphoprotein. Molecular cloning of cDNA indicated that the AML1-MTG8-binding protein (MTGR1) is highly related to MTG8 and similar to Drosophila Nervy. Comparison of amino acid sequences among MTGR1, MTG8 and Nervy revealed four evolutionary conserved regions (NHR1 to NHR4). Analysis of C-terminal deletion mutants of AML1-MTG8 indicated that the region containing NHR2 is essential for the induction of G-CSF-dependent cell proliferation. Immunoprecipitation analysis indicated that this region is required for AML1-MTG8 to form a stable complex with MTGR1. Overexpression of MTGR1 stimulates AML1-MTG8 to induce G-CSF-dependent proliferation of L-G cells and to interfere with AML1-dependent transcription. These results suggest that AML1-MTG8 could function as a complex with MTGR1 and that the complex might be important in promoting leukemogenesis.⁽¹³²⁾
Genome Analysis and Genetic Alterations in Human Cancers

　Detailed analyses of several chromosomal regions including 11q23.2, 21q11 and 11q22 which are associated with lung cancer⁽⁶⁵⁾ and pseudoachondroplasia⁽¹³³⁾ were performed using NotI restriction maps of chromosome 21q and 11q. Fluorescence in situ hybridization (FISH) analysis was applied to detect t(12;21) using probes covering the TEL(ETV6) and the AML1 gene to clarify the incidence of abnormality of t(12;21) in Japanese childhood acute lymphoblastic leukemia (ALL). The incidence among Japanese (9.5%) was lower than that among other nations (20-30%).⁽¹³⁴⁾
Monitoring of Solar-UV Exposure with Biodosimetry

　Spore dosimetry has been developed in this laboratory as a prototype biodosimeter for measurement of genotoxic solar-UV radiation. The dosimeter was incorporated into monitoring badges, and the first large-scale monitoring of solar-UV exposure has been performed in schoolchildren at five cities in Japan.⁽¹³⁵⁾




	8. Radiobiology Division



		The Radiobiology Division is currently focusing on the positional cloning of disease genes, especially of leukemia-related genes, and tumor suppressor genes. Functional analysis of several tumor-associated genes including AML1, which were successfully isolated by a genome-analysis based approach, is also underway. Cloning and Genome Structure of Leukemia-associated Genes 　The t(16;21)(q24;q22) translocation is a rare but recurrent chromosomal abnormality associated with therapy-related myeloid malignancies and is a variant of the t(8;21) translocation in which the AML1 gene on chromosome 21 is rearranged. The structural analysis of cDNAs from the leukemic cells of patients carrying t(16;21) showed that AML1 is fused to a novel gene named MTG16 which shows high homology to MTG8.⁽¹²⁹⁾ As in t(8;21), the t(16;21) breakpoints occurred between exons 5 and 6 of AML1, and between exons 1 and 2 or exons 3 and 4 of MTG16. The two genes are fused in-frame, resulting in the characteristic chimeric transcripts of this translocation. Thus, the AML1-MTG16 gene fusion in t(16;21) leukemia results in the production of a protein that is very similar to the AML1-MTG8 chimeric protein. 　The RBP56/hTAFII68, FUS/TLS and EWS proteins comprise a sub-family of RNA binding proteins. Rearrangement of the FUL/TLS gene and the EWS gene has been found in several types of malignant tumors, and the resultant fusion proteins play an important role in the pathogenesis of these tumors. Analysis of the genomic structure of the RBP56/hTAFII68 gene indicated that the RBP56/hTAFII68 gene spans about 37 kb and consists of 16 exons. Comparison of the structure of the genes indicated that RBP56/hTAFII68,FUS/TLS and EWS most likely originate from the same ancestor gene.⁽¹³⁰⁾ Functional Analysis of Leukemia-associated Gene Products 　The AML1 transcription factor is a target of chromosome translocations associated with acute myeloid leukemia and myelodysplastic symdrome. In the t(8;21) translocation, the AML1 (CBFA2/PEBP2aB) gene becomes fused to the MTG8 (ETO) gene. Immunoprecipitaion analysis showed that p300 and CREB-binding protein (CBP) interact with AML1. The C-terminal region of AML1 is responsible for the induction of cell differentiation and for the interaction with p300. Overexpression of p300 stimulates AML1-dependent transcription and the induction of cell differentiation. These results suggested that p300 plays critical roles in AML1-dependent transcription during the differentiation of myeloid cells. Thus, AML1 and its associated factor p300, both of which are targets of chromosomal rearrangements in human leukemia, function cooperatively in the differentiation of myeloid cells.⁽¹³¹⁾ 　The AML1-MTG8 gene product was found to specifically and strongly interact with an 85-kDa phosphoprotein. Molecular cloning of cDNA indicated that the AML1-MTG8-binding protein (MTGR1) is highly related to MTG8 and similar to Drosophila Nervy. Comparison of amino acid sequences among MTGR1, MTG8 and Nervy revealed four evolutionary conserved regions (NHR1 to NHR4). Analysis of C-terminal deletion mutants of AML1-MTG8 indicated that the region containing NHR2 is essential for the induction of G-CSF-dependent cell proliferation. Immunoprecipitation analysis indicated that this region is required for AML1-MTG8 to form a stable complex with MTGR1. Overexpression of MTGR1 stimulates AML1-MTG8 to induce G-CSF-dependent proliferation of L-G cells and to interfere with AML1-dependent transcription. These results suggest that AML1-MTG8 could function as a complex with MTGR1 and that the complex might be important in promoting leukemogenesis.⁽¹³²⁾ Genome Analysis and Genetic Alterations in Human Cancers 　Detailed analyses of several chromosomal regions including 11q23.2, 21q11 and 11q22 which are associated with lung cancer⁽⁶⁵⁾ and pseudoachondroplasia⁽¹³³⁾ were performed using NotI restriction maps of chromosome 21q and 11q. Fluorescence in situ hybridization (FISH) analysis was applied to detect t(12;21) using probes covering the TEL(ETV6) and the AML1 gene to clarify the incidence of abnormality of t(12;21) in Japanese childhood acute lymphoblastic leukemia (ALL). The incidence among Japanese (9.5%) was lower than that among other nations (20-30%).⁽¹³⁴⁾ Monitoring of Solar-UV Exposure with Biodosimetry 　Spore dosimetry has been developed in this laboratory as a prototype biodosimeter for measurement of genotoxic solar-UV radiation. The dosimeter was incorporated into monitoring badges, and the first large-scale monitoring of solar-UV exposure has been performed in schoolchildren at five cities in Japan.⁽¹³⁵⁾