Differential expression of calmodulin-binding proteins in B, T lymphocytes and thymocytes.
Changes in intracellular free Ca2+ are involved in the transmembrane signalling of different cells, including lymphocytes. Since calmodulin (CaM) is a primary receptor for Ca2+ (ref. 4), it may mediate the activation of crucial enzymes after antigen-induced increases in cytosolic Ca2+. Using a biotinylated-CaM (Bio-CaM) detection procedure to identify such proteins, we found that a peptide of relative molecular mass 59,000 (59K) was the predominant soluble CaM-binding protein (CaM-BP) in T cells and B lymphocytes from murine spleen; immunoblotting experiments identified it as a subunit of the CaM-dependent phosphatase, 'calcineurin' (CN). Smaller amounts of larger CaM-BPs, thought to be cytoskeletal-binding proteins, were also detected. CaM-BPs were expressed differentially, with B lymphocytes having four times more of the CN-like protein than T lymphocytes, while in thymocytes, a 65K polypeptide was the major CaM-BP. However, limited proteolysis analysis suggested that this thymus-specific peptide may be a precursor of CN. These data suggest that Ca2+-stimulated protein dephosphorylation may be an important and highly regulated function in lymphoid cells.
D000818:Animals; D001402:B-Lymphocytes / Q000378:metabolism*; D002148:Calmodulin-Binding Proteins / Q000096:biosynthesis* / Q000302:isolation & purification; D002478:Cells, Cultured; D008264:Macrophages / Q000378:metabolism; D051379:Mice; D008970:Molecular Weight; D009928:Organ Specificity; D013154:Spleen / Q000378:metabolism; D013601:T-Lymphocytes / Q000378:metabolism*; D013950:Thymus Gland / Q000378:metabolism*
D002148:Calmodulin-Binding Proteins