title: Investigation into the role of phosphatidylserine in modifying the susceptibility of human lymphocytes to secretory phospholipase A(2) using cells deficient in the expression of scramblase.
abstract: Normal human lymphocytes resisted the hydrolytic action of secretory phospholipase A(2) but became susceptible to the enzyme following treatment with a calcium ionophore, ionomycin. To test the hypothesis that this susceptibility requires exposure of the anionic lipid phosphatidylserine on the external face of the cell membrane, experiments were repeated with a human Burkitt's lymphoma cell line (Raji cells). In contrast to normal lymphocytes or S49 mouse lymphoma cells, most of the Raji cells (83%) did not translocate phosphatidylserine to the cell surface upon treatment with ionomycin. Those few that did display exposed phosphatidylserine were hydrolyzed immediately upon addition of phospholipase A(2). Interestingly, the remaining cells were also completely susceptible to the enzyme but were hydrolyzed at a slower rate and after a latency of about 100s. In contradistinction to the defect in phosphatidylserine translocation, Raji cells did display other physical membrane changes upon ionomycin treatment that may be relevant to hydrolysis by phospholipase A(2). These changes were detected by merocyanine 540 and trimethylammonium diphenylhexatriene fluorescence and were common among normal lymphocytes, S49 cells, and Raji cells. The levels of these latter effects corresponded well with the relative rates of hydrolysis among the three cell lines. These results suggested that while phosphatidylserine enhances the rate of cell membrane hydrolysis by secretory phospholipase A(2), it is not an absolute requirement. Other physical properties such as membrane order contribute to the level of membrane susceptibility to the enzyme independent of phosphatidylserine.
authors.affiliation: Department of Physiology and Developmental Biology, Brigham Young University, Provo, Utah 84602, USA.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Nelson
authors.forename: Lyndee L
authors.initials: LL
authors.lastname: Francom
authors.forename: Lynn
authors.initials: L
authors.lastname: Anderson
authors.forename: Kelly
authors.initials: K
authors.lastname: Damm
authors.forename: Ryan
authors.initials: R
authors.lastname: Baker
authors.forename: Joseph
authors.initials: J
authors.lastname: Chen
authors.forename: Sarah
authors.initials: S
authors.lastname: Franklin
authors.forename: Amy
authors.initials: A
authors.lastname: Hamaker
authors.forename: Izadora
authors.initials: I
authors.lastname: Izidoro
authors.forename: Eric
authors.initials: E
authors.lastname: Moss
authors.forename: Mikayla
authors.initials: M
authors.lastname: Orton
authors.forename: Evan
authors.initials: E
authors.lastname: Stevens
authors.forename: Celestine
authors.initials: C
authors.lastname: Yeung
authors.forename: Allan M
authors.initials: AM
authors.lastname: Judd
authors.forename: John D
authors.initials: JD
authors.lastname: Bell
mesh_terms: D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000235:genetics / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology; D006801:Humans; D006868:Hydrolysis; D008214:Lymphocytes / Q000166:cytology / Q000201:enzymology*; D051379:Mice; D010718:Phosphatidylserines / Q000235:genetics / Q000378:metabolism*; D054497:Phospholipases A2, Secretory / Q000235:genetics / Q000378:metabolism*; D049294:Phospholipid Transfer Proteins / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D010718:Phosphatidylserines; D049294:Phospholipid Transfer Proteins; D054497:Phospholipases A2, Secretory