sq-23377 and Leukemia--Hairy-Cell

Hairy cell leukemia (HCL) is an uncommon B-cell malignancy with unknown pathogenesis. In an earlier study, we demonstrated that HCL cells highly express the transcription factor T-box-expressed-in-T-cells (T-bet). T-bet is the master regulator of the T-helper (Th)1 cell response regulating interferon gamma (IFN-gamma) production and also plays a central role in the T-cell independent Th1-like B-cell response. Here, we demonstrate by fluorescence activated cell sorting (FACS) analysis that neoplastic cells from the peripheral blood of five patients with HCL showed an enhanced expression of IFN-gamma after stimulation. Additionally, a comparison with 55 healthy individuals revealed a significant elevation of IFN-gamma in the sera of patients with HCL. Based on our recent findings that a non-neoplastic B-cell subset, the monocytoid B-cells, are T-bet positive and produce IFN-gamma, we propose that monocytoid and hairy B-cells have a similar function and that the T-bet-IFN-gamma axis is involved in the pathogenesis of HCL.

Topics: Antigens, CD; Antigens, CD19; Antigens, Neoplasm; B-Lymphocyte Subsets; Cell Transformation, Neoplastic; Cells, Cultured; Cytokines; Enterotoxins; Gene Expression Regulation, Leukemic; Humans; Immunophenotyping; Integrin alpha Chains; Interferon-gamma; Ionomycin; Leukemia, Hairy Cell; Neoplasm Proteins; T-Box Domain Proteins; T-Lymphocytes; Tetradecanoylphorbol Acetate

Hairy cell leukemia is an uncommon B cell lymphoproliferative disease of unknown etiology. We previously observed that CD20, a membrane protein involved in B cell activation, is hyperphosphorylated on hairy cells and that these cells have unusually high levels of intracellular free Ca2+. Therefore, we used a hairy cell line, HCLL-7876, to study the potential involvement of Ca(2+)-activated protein kinases in CD20 phosphorylation. Addition of the Ca2+ ionophore, ionomycin, increased CD20 phosphorylation both in activated B cells and in cells from the hairy cell line; addition of EGTA to either cell type decreased basal levels of CD20 phosphorylation. Ionomycin treatment of these cells resulted in increased kinase activity of cytosolic extracts toward syntide-2, a synthetic peptide substrate for calcium/calmodulin-dependent kinase II (CaM-KII), with kinetics similar to those of CD20 phosphorylation in the cell line. CD20 isolated from the cell line was a substrate for purified CaM-KII in vitro. Phosphopeptide maps of CD20 from untreated hairy cells or ionomycin-treated HCLL-7876 cells were similar to maps of CD20 that had been phosphorylated in vitro by CaM-KII. These results suggest that the unusually high levels of intracytoplasmic Ca2+ in hairy cells may enhance the phosphorylation of key surface proteins.

Topics: Amino Acid Sequence; Antigens, CD; Antigens, CD20; Antigens, Differentiation, B-Lymphocyte; Calcium; Calcium-Calmodulin-Dependent Protein Kinases; Cell Line; Humans; In Vitro Techniques; Ionomycin; Leukemia, Hairy Cell; Molecular Sequence Data; Peptide Mapping; Peptides; Phosphoproteins; Phosphorylation; Protein Kinase C; Protein Kinases