The AML1-MTG8 Leukemic Fusion Protein Forms a Complex with a Novel Member of the MTG8(ETO/CDR) Family, MTGR1

ABSTRACT

The AML1-CBFβ transcription factor complex is essential for the definitive hematopoiesis of all lineages and is the most frequent target of chromosomal rearrangements in human leukemia. In the t(8;21) translocation associated with acute myeloid leukemia (AML), the AML1(CBFA2/PEBP2αB) gene is juxtaposed to the MTG8(ETO/CDR) gene. We show here that the resultant AML1-MTG8 gene product specifically and strongly interacts 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 evolutionarily conserved regions (NHR1 to NHR4). Ectopic expression of AML1-MTG8 in L-G murine myeloid progenitor cells inhibits differentiation to mature neutrophils and induces cell proliferation in response to granulocyte colony-stimulating factor (G-CSF). Analysis with C-terminal deletion mutants of AML1-MTG8 indicated that the region of 51 residues (488 to 538), which contains NHR2, is essential for the induction of G-CSF-dependent cell proliferation. Immunoprecipitation analysis indicates 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.

ACKNOWLEDGMENTS

I.K., K.I., and F.M. contributed equally to this work.

We thank T. Honjyo for L-G cells, A. D. Miller for retrovirus vectors, David Baltimore for BOSC23 cells, Y. Ito for TCRβ-CAT plasmid, and T. Kitamura for suggestions about retrovirus infection. We also thank H. Ichikawa for helpful discussions, N. Munakata for suggestions about protein structure, and M. Mori and C. Hatanaka for technical assistance. We thank Kazusa DNA Research Institute for help in screening the KG1 cDNA library.

This work was supported in part by a Grant-in-Aid for Scientific Research on Priority Areas from the Ministry of Education, Science and Culture; by a grant from the Special Coordination Funds for the Promotion of Science and Technology from the Science and Technology Agency; by a Grant-in-Aid for the Comprehensive 10-Year Strategy for Cancer Control and the Grant for Research on Aging and Health from the Ministry of Health and Welfare; and by the Program for Promotion of Fundamental Studies in Health Sciences of the Organization for Drug ADR Relief, R&D Promotion and Product Review of Japan.