CANCER GENOMICS DIVISION

8.CANCER GENOMICS DIVISION

    Current research in the Cancer Genomics Division focuses on the positional cloning of disease genes, especially of leukemia-related genes, and tumor suppressor genes. Functional analyses of several tumor-associated gene products including AML1 and the chimeric transcription factor AML1-MTG8 and searches aimed at identifying downstream target genes responsible for leukemo-genesis are also undertaken.
Genome Analysis and Genetic Alterations in Human Cancers

    Human chromosome 11q23 has been suspected to contain a tumor suppressor gene for neuroblastoma (NBL). To isolate a candidate tumor suppressor gene from this region, a detailed LOH analysis was carried out. This allowed narrowing of the region to 1.2Mb. Based on this, sequence analysis of the region was conducted using a BAC contig previously constructed by our division in collaboration with the RIKEN, Genome Sciences Center. A computer analysis predicted 22 genes within the region including seven novel genes. The search for the gene carrying the mutation is ongoing. Other genetic aberrations frequently found in NBL are loss of the distal part of the short arm of chromosome 1, amplification of the MYCN oncogene and 17q gain, all of which are associated with an unfavorable prognosis. Ohira et al. (Chiba Cancer Center Research Institute) identified for the first time a homozygously deleted region within the smallest region at 1p36.2-36.3 in NBL cell lines. The estimated length of the deleted region was 500kb.⁽¹¹²⁾ Our effort to construct a physical map of the 1p35-p36 region contributed to this work. The DNA sequence and gene catalogue of the long arm of human chromosome 21 were reported by the chromosome 21 mapping and sequencing consortium.⁽¹¹³⁾ Many of our DNA markers and sequencing-ready P1, BAC contigs were used to perform this work.
    The t(8;22)(p11.2;q 13.1) is found in rare cases of AML. The breakpoints of the translocation on chromosomes 8 and 22 correspond to the MOZ and p300 loci, respectively. In addition, features of this subgroup of AML, including monocytic arrest and erythrophagocytosis resemble those of classical AML with t(8;16) (p11.2; p3.3), in which MOZ is fused to CBP. Molecular analysis of the translocation breakpoint revealed a novel fusion of MOZ to p300 in AML with t(8;22)(p11.2; q13.1) as predicted.⁽¹¹⁴⁾
    Our previous study showed the AML1-MTG8 fusion protein to be associated with an MTG8-like protein (MTGR1) and this association appears to be required for AML1-MTG8 to stimulate proliferation of myeloid precursor cells. The previously reported cDNA for MTGR1 was shorter than the main RNA. A full length cDNA was then isolated and the genomic structure was determined. This indicated that the genomic structure of MTGR1 is very similar to those of other MTG8-family genes, i.e. MTG8 and MTG16.⁽¹¹⁵⁾
Downstream target genes of AML1

    Transcription factor genes are frequently involved in chromosomal translocations associated with human leukemia. The resulting deregulation of downstream target genes probably contributes to differentiation arrest and aberrant proliferation of hematopoietic progenitor cells. Accordingly, studies to identify the downstream gene products that confer neoplastic properties are a prerequisite for fully understanding the mechanism of leukemogenesis. However, the genes directly responsible for the leukemogenetic process have not been identified for AML1-MTG8 or for other chimeric transcription factors resulting from various chromosome translocations. Ectopic expression of the AML1-MTG8 fusion gene in L-G and 32Dc13 murine myeloid precursor cells stimulates cell proliferation without inducing morphologic terminal differentiation into mature granulocytes in response to granulocyte-colony stimulating factor (G-CSF). It was shown that the expression of AML1-MTG8 elevates expression of the G-CSF receptor (G-CSFR) and that this ectopic expression in L-G cells induces cell proliferation in response to G- CSF, while there is no inhibition of cell differentiation into mature neutrophils.⁽¹¹⁶⁾ Using a differential display technique, 24 genes under the downstream control of AML1-MTG8 were isolated. Among these up-regulated genes, TIS11b (ERF-1, cMG1) was highly expressed in t(8;21) leukemic cells, and the overexpression of TIS11b induced myeloid cell proliferation in response to G-CSF.⁽¹¹⁷⁾ These results suggest that high-level expression of G-CSFR and TIS11b contributes to AML1-MTG8-mediated leukemogenesis.




8.CANCER GENOMICS DIVISION



	Current research in the Cancer Genomics Division focuses on the positional cloning of disease genes, especially of leukemia-related genes, and tumor suppressor genes. Functional analyses of several tumor-associated gene products including AML1 and the chimeric transcription factor AML1-MTG8 and searches aimed at identifying downstream target genes responsible for leukemo-genesis are also undertaken. Genome Analysis and Genetic Alterations in Human Cancers Human chromosome 11q23 has been suspected to contain a tumor suppressor gene for neuroblastoma (NBL). To isolate a candidate tumor suppressor gene from this region, a detailed LOH analysis was carried out. This allowed narrowing of the region to 1.2Mb. Based on this, sequence analysis of the region was conducted using a BAC contig previously constructed by our division in collaboration with the RIKEN, Genome Sciences Center. A computer analysis predicted 22 genes within the region including seven novel genes. The search for the gene carrying the mutation is ongoing. Other genetic aberrations frequently found in NBL are loss of the distal part of the short arm of chromosome 1, amplification of the MYCN oncogene and 17q gain, all of which are associated with an unfavorable prognosis. Ohira et al. (Chiba Cancer Center Research Institute) identified for the first time a homozygously deleted region within the smallest region at 1p36.2-36.3 in NBL cell lines. The estimated length of the deleted region was 500kb.⁽¹¹²⁾ Our effort to construct a physical map of the 1p35-p36 region contributed to this work. The DNA sequence and gene catalogue of the long arm of human chromosome 21 were reported by the chromosome 21 mapping and sequencing consortium.⁽¹¹³⁾ Many of our DNA markers and sequencing-ready P1, BAC contigs were used to perform this work. The t(8;22)(p11.2;q 13.1) is found in rare cases of AML. The breakpoints of the translocation on chromosomes 8 and 22 correspond to the MOZ and p300 loci, respectively. In addition, features of this subgroup of AML, including monocytic arrest and erythrophagocytosis resemble those of classical AML with t(8;16) (p11.2; p3.3), in which MOZ is fused to CBP. Molecular analysis of the translocation breakpoint revealed a novel fusion of MOZ to p300 in AML with t(8;22)(p11.2; q13.1) as predicted.⁽¹¹⁴⁾ Our previous study showed the AML1-MTG8 fusion protein to be associated with an MTG8-like protein (MTGR1) and this association appears to be required for AML1-MTG8 to stimulate proliferation of myeloid precursor cells. The previously reported cDNA for MTGR1 was shorter than the main RNA. A full length cDNA was then isolated and the genomic structure was determined. This indicated that the genomic structure of MTGR1 is very similar to those of other MTG8-family genes, i.e. MTG8 and MTG16.⁽¹¹⁵⁾ Downstream target genes of AML1 Transcription factor genes are frequently involved in chromosomal translocations associated with human leukemia. The resulting deregulation of downstream target genes probably contributes to differentiation arrest and aberrant proliferation of hematopoietic progenitor cells. Accordingly, studies to identify the downstream gene products that confer neoplastic properties are a prerequisite for fully understanding the mechanism of leukemogenesis. However, the genes directly responsible for the leukemogenetic process have not been identified for AML1-MTG8 or for other chimeric transcription factors resulting from various chromosome translocations. Ectopic expression of the AML1-MTG8 fusion gene in L-G and 32Dc13 murine myeloid precursor cells stimulates cell proliferation without inducing morphologic terminal differentiation into mature granulocytes in response to granulocyte-colony stimulating factor (G-CSF). It was shown that the expression of AML1-MTG8 elevates expression of the G-CSF receptor (G-CSFR) and that this ectopic expression in L-G cells induces cell proliferation in response to G- CSF, while there is no inhibition of cell differentiation into mature neutrophils.⁽¹¹⁶⁾ Using a differential display technique, 24 genes under the downstream control of AML1-MTG8 were isolated. Among these up-regulated genes, TIS11b (ERF-1, cMG1) was highly expressed in t(8;21) leukemic cells, and the overexpression of TIS11b induced myeloid cell proliferation in response to G-CSF.⁽¹¹⁷⁾ These results suggest that high-level expression of G-CSFR and TIS11b contributes to AML1-MTG8-mediated leukemogenesis.