title: Ultrastructural localization of tyrosine hydroxylase in human peripheral blood mononuclear cells: effect of stimulation with phytohaemagglutinin.
abstract: Using immunocytochemistry coupled to fluorescence and electron microscopy, we investigated the expression and ultrastructural localization of tyrosine hydroxylase (TH, EC 1.14.16.2), the rate-limiting enzyme in the biosynthesis of catecholamines, in human peripheral blood mononuclear cells (PBMCs), with PC12 cells as positive controls. In unstimulated PBMCs, TH-specific immunoreactivity was localized to the plasma membrane. However, after stimulation with the polyclonal mitogen phytohaemagglutinin (PHA), TH immunoreactivity was almost completely localized to electron-dense cytoplasmic granules, which resembled those found in PC12. TH-positive granules, however, were larger (300-500 nm) than in PC12 cells (100-200 nm). Flow cytometry analysis of TH expression showed about 46-50% positive cells in unstimulated PBMCs and in PHA-stimulated PBMCs in the G0/G1 phase of the cell cycle, but more than 80% positive cells in PHA-stimulated PBMCs in the S+G2/M phase. In agreement with previous observations, PHA stimulation also induced de novo expression of TH mRNA as well as increased intracellular catecholamine content, suggesting the occurrence of TH upregulation at the level of both gene expression and enzyme activity. The ultrastructural localization of TH in human PBMCs seems therefore regulated by cell stimulation and related to the functional activity of the enzyme.
authors.affiliation: Department of Clinical and Biological Sciences, Laboratory of Human Morphology Luigi Cattaneo, University of Insubria, Varese, Italy.
authors.forename: Marcella
authors.initials: M
authors.lastname: Reguzzoni
authors.forename: Marco
authors.initials: M
authors.lastname: Cosentino
authors.forename: Emanuela
authors.initials: E
authors.lastname: Rasini
authors.forename: Franca
authors.initials: F
authors.lastname: Marino
authors.forename: Marco
authors.initials: M
authors.lastname: Ferrari
authors.forename: Raffaella
authors.initials: R
authors.lastname: Bombelli
authors.forename: Terenzio
authors.initials: T
authors.lastname: Congiu
authors.forename: Marina
authors.initials: M
authors.lastname: Protasoni
authors.forename: Daniela
authors.initials: D
authors.lastname: Quacci
authors.forename: Sergio
authors.initials: S
authors.lastname: Lecchini
authors.forename: Mario
authors.initials: M
authors.lastname: Raspanti
authors.forename: Gianmario
authors.initials: G
authors.lastname: Frigo
mesh_terms: D006801:Humans; D007150:Immunohistochemistry; D007700:Kinetics; D007963:Leukocytes, Mononuclear / Q000187:drug effects / Q000201:enzymology* / Q000648:ultrastructure; D016253:Microscopy, Immunoelectron; D010835:Phytohemagglutinins / Q000494:pharmacology*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014158:Transcription, Genetic; D014446:Tyrosine 3-Monooxygenase / Q000097:blood* / Q000235:genetics / Q000648:ultrastructure
chemical_list: D010835:Phytohemagglutinins; D012333:RNA, Messenger; D014446:Tyrosine 3-Monooxygenase