A study of BP1 function in lymphocyte development through a generation of BP1-gene knock-out mice.

1995 Fiscal Year Final Research Report Summary

• Project/Area Number: 06670358
• Research Category: Grant-in-Aid for General Scientific Research (C)
• Allocation Type: Single-year Grants
• Research Field: Immunology
• Research Institution: SCIENCE UNIVERSITY OF TOKYO (1995); Kyushu University (1994)
• Principal Investigator: KITAMURA Daisuke SCIENCE UNIVERSITY OF TOKYO, RESEARCH INSTITUTE FOR BIOLOGICAL SCIENCES, PROFESSOR, 生命科学研究所, 教授 (70204914)
• Project Period (FY): 1994 – 1995
• Keywords: BP1 / aminopeptidase A / gene targeting / B cell development / pre-B cell / knock-out mouse

Research Abstract

BP1 is a 140 kD type-II transmembrane glyoprotein expressed as a homodimer on a surface of precursor (pre-) B cells selectively in a lymphoid-cell lineage. Cloning and analysis of a cDNA cording for BP1 revealed its identity as aminopeptidase A (APA), a Zn^<2+>/Ca^<2+>-dependent peptidase present in a broad range of organs like kidney or small intestine. A well known function of APA is to convert angiotensin II into less active angiotensin III, thus involved in regulation of blood pressure. Also, APA is probably involved in digestion of peptides in small intestine. In the present study, a possible role of BP1 in B cell development was assessed by generating and analyzing BP1-gene knock-out mice. Lymphocyte cellularity of bone marrow, thymus, spleen and lymph-nodes in the mutant mice was grossly normal when analyzed by flow cytometry after staining the cells with a panel of monoclonal antibodies against various cell-surface antigens. Proliferative responses to cytokines such as interleu kin (IL) -7, IL-3 and GM-CSF of the BP1-deficient bone marrow cells were comparable to normal ones, indicating that development of lymphoid and myeloid progenitors is independent of BP1 protein. Mature B cells from spleens of the mutants also normally responded to anti-IgM antibody, CD40-ligand and LPS, suggesting that functional competernce of such cells are unaffected. Finally, B-cell progenitors of the mutants immigrated into the bone marrow of the recipient mice to the same extent as those of wild-type mice and also observed was equal contribution of the donor cells in the mutant and wild-type recipients in a bone-marrow chimera experiment. Thus, although BP1 is expressed in pre-B cells and bone-marrow stroma cells supporting the growth of the pre-B cells, BP1 is dispensable for the development, homing and maturation of pre-B cells. The BP1-deficient mice were healthy, fertile, grew up normally and no gross deformity of organs were noticed. Therefore roles of BP1 in other organs were not obvious. Genetic redundancy of metalopeptidase may possibly have concealed the overt phenotype of the BP1-deficiency. Alternative reverse genetic approaches such as dominant-negative transgenic or inducible gene knock-out mice as well as an identification of physiological substrates of BP1 would be necessary to disclose a real function of BP1.