title: Subcellular localization of inositide enzymes in established T-cell lines and activated lymphocytes.
abstract: The specific activity of phosphatidylinositol 4,5-bisphosphate phospholipase C (PIP2-PLC) and inositol 1,4,5-trisphosphate monophosphatase (IP3-MP) involved in phosphoinositide catabolism was found to be significantly lower in the total homogenate of four human lymphoblastoid cell lines, HSB-2, MOLT-4, CEM and JURKAT, than in resting and activated peripheral blood mononuclear cells, ranging from 0.8 to 3.2 and from 1.3 to 3.7 nmol/min/mg for PIP2-PLC and IP3-MP, respectively. In PHA-stimulated cells, the specific activities were enhanced 25 and 35% respectively over the values (8.02 and 7.83 nmol/min/mg, respectively) measured in resting peripheral blood mononuclear cells. After centrifugation on discontinuous sucrose gradient of cell homogenate, PIP2-PLC and IP3-MP activities were found to be predominantly associated with the cytosol fraction (> 69%) in HSB-2 and MOLT-4 cells, with a distribution similar to that found in PHA-stimulated and in resting lymphocytes. In CEM cells, about half of the total activity remained in this fraction, while in JURKAT lymphoblastic cells more than 45% of the total activity was recovered in the high-density membrane fraction (d = 1.20-1.25), the soluble PIP2-PLC and IP3-MP activity accounting for only 13 and 25%, respectively. Conversely, in less differentiated leukemic cells HSB-2 and MOLT-4, conspicuous activity of the ectoenzymes 5'-nucleotidase (5'-NT) and gamma-glutamyltransferase (gamma-GT) was recovered in the soluble fraction. Growing leukemic cells at a distinct level of differentiation have a general reduction in activity but a characteristic distribution of enzymes involved in the transmission of signals usually targeting the cell surface.
authors.affiliation: Laboratorio di Patologia Cellulare, Istituto Cantonale di Patología, Locarno, Switzerland.
authors.forename: R
authors.initials: R
authors.lastname: Graber
authors.forename: G A
authors.initials: GA
authors.lastname: Losa
mesh_terms: D015720:5'-Nucleotidase / Q000097:blood; D002453:Cell Cycle / Q000235:genetics; D002454:Cell Differentiation / Q000502:physiology; D004247:DNA / Q000032:analysis; D006801:Humans; D016130:Immunophenotyping; D000072181:Inositol Polyphosphate 5-Phosphatases; D015458:Leukemia, T-Cell / Q000201:enzymology*; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000201:enzymology; D008213:Lymphocyte Activation; D054801:Phosphoinositide Phospholipase C; D010727:Phosphoric Diester Hydrolases / Q000097:blood*; D010744:Phosphoric Monoester Hydrolases / Q000097:blood*; D010835:Phytohemagglutinins / Q000494:pharmacology; D015290:Second Messenger Systems / Q000502:physiology*; D013347:Subcellular Fractions / Q000201:enzymology*; D014407:Tumor Cells, Cultured; D005723:gamma-Glutamyltransferase / Q000097:blood
chemical_list: D010835:Phytohemagglutinins; D004247:DNA; D005723:gamma-Glutamyltransferase; D010744:Phosphoric Monoester Hydrolases; D015720:5'-Nucleotidase; D000072181:Inositol Polyphosphate 5-Phosphatases; D010727:Phosphoric Diester Hydrolases; D054801:Phosphoinositide Phospholipase C