No abstract

B cell differentiation requires adhesion of B cell progenitors to bone marrow (BM) or fetal liver stroma. We show that B lymphoid cells can adhere to the BM stroma cell line CS 1.3, in vitro. Two monoclonal antibodies, SAB-1 and SAB-2, inhibited the adhesion of a B220+ progenitor B cell line but did not interfere with the binding of cytoplasmic mu chain-positive pre-B cells or mature B cells to the BM stromal cell line. Injection of both SAB-1 and SAB-2 antibodies into pregnant mice reduced by 90% the number of B220+n B lineage cells in the livers of their embryos. Livers from such embryos also were virtually devoid of cells able to give rise to B cell colonies in soft agar cultures (CFU-preB). Either antibody separately had no effect. Flow cytometry analysis show that SAB-1 is present on CS 1.3 stroma cells and on a pre-B cell line while SAB-2 is present on pro-B and pre-B cell lines, but not on CS 1.3 stromal cells. SAB-1 and SAB-2 react with different molecules and neither antibody seems to recognize CD44, and adhesion molecule that may also participate in B cell differentiation. Proteinase K and trypsin can digest both SAB-1 and SAB-2 antigens from viable cells suggesting that both are cell surface proteins. We propose that antibodies SAB-1 and SAB-2 probably recognize novel cell-cell adhesion molecules, and that these molecules are involved in the interactions between B cell progenitors and stroma cells.

Two isoenzymes of cAMP-dependent protein kinases were found in MCF-7 cytosol. The regulatory (cAMP-binding) subunit of protein kinase I (predominant form) has an apparent molecular weight (MW) of 49,000 and the two forms of regulatory subunits of protein kinase II have MWs of 52,000 and 54,000. Substantial amounts of the 49,000 protein cochromatographed on DEAE cellulose with protein kinase II. The quantities of protein kinase holoenzyme activity are strongly influenced by extraction procedures: the use of EDTA and of the protease inhibitor benzamidine can lead to extensive dissociation. On the other hand, high yields of cAMP-dependent protein kinase holoenzyme activity were consistently obtained with 150 mM KCl.