Abstract
In order to identify the cDNAs responsible for hemopoietic supportive activity, expression of mRNAs in hemopoietic supportive bone marrow stromal cells (MS-5) and non-supportive stromal cells (MS-K) were compared by the cDNA subtraction method. A subtracted MS-5-cDNA library, which contains cDNA clones corresponding to mRNAs present in MS-5 cells but not in MS-K cells, was constructed. Screening of subtracted MS-5-cDNA library resulted in the isolation of some clones. Two of them, lipid binding protein (LBP) and haptoglobin (Hp), were expressed specifically in MS-5 cells but not in MS-K cells. The genes of LBP and Hp were subcloned into mammalian expression vector and transfected into hemopoietic non-supportive stromal cells line, MS-K. Then LBP-expressing stable transformants (MS-K-LBP) and Hp-expressing transformants (MS-K-Hp) were cloned. A rosette formation assay was carried out to investigate whether or not the LBP and Hp cause MS-K cells to adhere to hemopoietic cells. MS-K-LBP formed rosettes with hemopoietic cells as MS-5 cells, although the MS-K-Hp and normal MS-K cells did not form rosettes. These data indicate that LBP expressed in hemopoietic supportive stromal cells is partly responsible for the adhesion of hemopoietic stem cells to stromal cells.
