title: Hydrogen peroxide produced during gamma-glutamyl transpeptidase activity is involved in prevention of apoptosis and maintainance of proliferation in U937 cells.
abstract: It has been reported in several cell lines that exposure to low levels of reactive oxygen species can exert a stimulatory effect on their proliferation. We have previously shown that mild oxidative conditions can also counteract apoptotic stimuli. A constitutive cellular production of low levels of superoxide and hydrogen peroxide originates from various sources; among these, gamma-glutamyl transpeptidase (GGT), the plasma membrane-bound activity in charge of metabolizing extracellular reduced glutathione, has recently been included. Since the inhibition of GGT is a sufficient stimulus for the induction of apoptosis in selected cell lines, we investigated whether this effect might result from the suppression of the mentioned GGT-dependent prooxidant reactions, on the theory that the latter may represent a basal antiapoptotic and proliferative signal for the cell. Experiments showed that: 1) GGT activity in U937 monoblastoid cells is associated with the production of low levels of hydrogen peroxide, and two independent GGT inhibitors cause a dose-dependent decrease of such GGT-dependent production of H2O2; 2) GGT inhibition with acivicin results in cell growth arrest, and induces cell death and DNA fragmentation with the ladder appearance of apoptosis; 3) treatment of cells with catalase--and even more with Trolox C--is able to decrease their proliferative rate; 4) GGT inhibition (with suppression of H2O2 production) results in a down-regulation of poly(ADP-ribose) polimerase (PARP) activity, which precedes the proteolytic cleavage of PARP molecule, such as that typically induced by caspases. The reported data suggest that the low H2O2 levels originating as a by-product during GGT activity are able to act as sort of a 'life signal' in U937 cells, insofar as they can maintain cell proliferation and protect against apoptosis, possibly through an up-regulation of PARP activity.
authors.affiliation: Institute of General Pathology, University of Siena Medical School, I-53100 Siena, Italy.
authors.forename: B
authors.initials: B
authors.lastname: del Bello
authors.forename: A
authors.initials: A
authors.lastname: Paolicchi
authors.forename: M
authors.initials: M
authors.lastname: Comporti
authors.forename: A
authors.initials: A
authors.lastname: Pompella
authors.forename: E
authors.initials: E
authors.lastname: Maellaro
mesh_terms: D000975:Antioxidants / Q000378:metabolism / Q000494:pharmacology; D017209:Apoptosis; D002374:Catalase / Q000378:metabolism / Q000494:pharmacology; D002455:Cell Division / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism; D006801:Humans; D006861:Hydrogen Peroxide / Q000378:metabolism*; D007555:Isoxazoles / Q000494:pharmacology; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D013482:Superoxide Dismutase / Q000378:metabolism / Q000494:pharmacology; D020298:U937 Cells; D005723:gamma-Glutamyltransferase / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D000975:Antioxidants; D004791:Enzyme Inhibitors; D007555:Isoxazoles; D006861:Hydrogen Peroxide; D002374:Catalase; D013482:Superoxide Dismutase; D005723:gamma-Glutamyltransferase; D011065:Poly(ADP-ribose) Polymerases; D005978:Glutathione; C006303:acivicin