Human c-fgr induces a monocyte-specific enzyme in NIH 3T3 cells

Cell sorting enriches osteogenic populations in rat bone marrow stromal cell cultures

The presence of multiple cell types in bone marrow stromal populations complicates interpretation of cytokine and hormone effects on the osteoprogenitors present, indicating a need for a method for purification of the osteoprogenitor population. Flow cytometric sorting of 7 day primary rat bone marrow stromal cell cultures was performed on the basis of alkaline phosphatase (AP) expression with an antibody against AP (RBM 211.13). The resultant AP(high), AP(low), or control cells were plated to determine osteoprogenitor, macrophage, and adipocyte distribution and frequency. Approximately 50% of osteoprogenitor/bone nodule-forming cells were lost during processing/sorting when compared with unsorted controls. Nevertheless, within the AP(high) fraction, the numbers of AP-positive colonies and osteoprogenitors (bone nodules) were significantly enriched compared with the unfractionated control; the increase in osteoprogenitor frequency ranged from approximately 2 to 100-fold. There were few assayable osteoprogenitors in either the AP(high) or AP(low) fractions in the absence of dexamethasone (dex), suggesting that RBM stroma contains largely dex-dependent osteoprogenitor populations, and that dex may regulate osteoprogenitors subsequent to the upregulation of AP. Osteoprogenitor/bone nodule numbers in either the AP(high) or AP(low) fraction did not follow a linear relationship with decreasing plating density. The AP(high) fraction of cells was depleted for adipocyte and macrophage colonies. In contrast, within the AP(low) fraction of cells, adipocyte and macrophage colonies were consistently enriched. We conclude that flow-cytometric sorting of RBM stromal populations according to high or low AP expression is an effective technique for enrichment of AP-positive colonies and osteoprogenitors/bone nodule-forming cells.

Lineage- and differentiation stage-specific expression of LSM-1 (LPAP), a possible substrate for CD45, in human hematopoietic cells

CD45, a transmembrane tyrosine phosphatase, is found on almost all nucleated hematopoietic cells and plays a crucial role in lymphocyte activation and differentiation. We recently achieved isolation of the human LSM-1 (hLSM-1) gene, whose product is a possible substrate for CD45, and we raised antibodies against the hLSM-1 protein. hLSM-1 expression in hematopoietic cells was examined with Northern and Western blot, fluorescence-activated cell sorter, and immunocytochemical analyses. It was found that in the lymphoid lineage, T and B lymphocytes as well as NK cells expressed LSM-1, whereas terminally differentiated plasma cells did not. As for the myeloid lineage, immature myeloid cells expressed LSM-1, whereas terminally differentiated granulocytes and monocytes did not. In the erythroid lineage, normal erythroblasts expressed very low levels of LSM-1, while erythroid cell lines (K562 and HEL) did not. Megakaryocytes did not express LSM-1. Both CD34+/CD33- and CD34+/CD33+ hematopoietic progenitor cells weakly expressed LSM-1. These results showed that LSM-1 is expressed in a lineage- and differentiation stage-specific fashion.

Activity of Fgr protein-tyrosine kinase is reduced in neutrophils of patients with myelodysplastic syndromes and chronic myelogenous leukemia

The Fgr protein-tyrosine kinase, p55(c-fgr), is specifically expressed and functions in cells of myelomonocytic lineages. We examined levels of expression and enzymatic activity of p55(c-fgr) peripheral blood neutrophils of patients with myelodysplastic syndromes (MDS) and chronic myelogenous leukemia (CML) by comparison with those of normal individuals. While neutrophils of eight normal subjects gave uniform results, the specific enzymatic activity of p55(c-fgr), a ratio of the total kinase activity versus the protein level was reduced in seven out of eight patients with MDS and all of five patients with CML. The specific kinase activity of p55(c-fgr) correlated significantly with the activity of neutrophil alkaline phosphatase (NAP) which has been considered to be a marker of neutrophil maturity (r=0.568, P<0.01). The reduced activity of this tyrosine kinase was considered to be a biological parameter for immaturity and to reflect dysfunction of neutrophils of patients with MDS and with CML.

Dexamethasone alters the subpopulation make-up of rat bone marrow stromal cell cultures

Bone marrow stromal cells comprise a heterogeneous population including fibroblastic, adipocytic, hemopoietic, and osteogenic cells. Although the conditions under which different lineages are regulated have not been fully elucidated, dexamethasone clearly stimulates osteogenic expression in stromal cultures. The purpose of this study was to begin to elucidate and quantify some of the subpopulations present when rat bone marrow stromal cells are grown with or without dexamethasone under conditions favoring bone formation. Bone marrow stromal cells from young adult rats were cultured with ascorbic acid, beta-glycerophosphate, and with or without dexamethasone for various periods of time. Culture dishes were then analyzed for cell counts, or stained with either histochemical or immunohistochemical stains, and colony types were quantitated, or cells were processed for flow cytometry. Dexamethasone significantly increased the number of alkaline phosphatase (AP) positive colonies, von Kossa positive bone nodules, alpha-naphthylbutyrate esterase positive colonies, and ED2 positive (macrophage) colonies. The number of adipocytic foci was largely unaffected in these experiments. Flow cytometry confirmed colony counts and showed stimulation by dexamethasone of AP positive cells and macrophages, and in addition, the reduction of hemopoietic cells expressing leukocyte common antigen. These data show conclusively that when rat bone marrow stromal populations are grown under conditions stimulating osteoprogenitor differentiation and bone formation, the stromal subpopulation make-up, including expression of hemopoietic lineages, is markedly altered.