title: Induction of apoptosis by Se-MSC in U937 human leukemia cells through release of cytochrome c and activation of caspases and PKC-delta: mutual regulation between caspases and PKC-delta via a positive feedback mechanism.
abstract: Se-methylselenocysteine (Se-MSC) has been shown to possess potent chemopreventive and anti-tumor properties. However, its exact mechanism of action is still not well understood. The present study investigated the mechanism of Se-MSC on the induction of apoptosis using U937 human leukemia cells. Se-MSC induced dose- and time-dependent apoptosis of U937 cells as assessed by flow cytometry analysis, DNA fragmentation, and proteolytic cleavage of poly-(ADP-ribose) polymerase (PARP). Se-MSC increased time- and dose-dependent cytochrome c accumulation in the cytosol, which was greatly inhibited by overexpression of Bcl-2, suggesting that the apoptotic effect by Se-MSC in U937 cells is mitochondrial-dependent. Se-MSC also induced activation of caspases, followed by proteolytic cleavage of PKC-delta. The Se-MSC-induced apoptosis required activities of caspases since pretreatment of a pan-caspase inhibitor z-VAD-fmk greatly suppressed the Se-MSC-induced apoptosis as well as proteolytic cleavage of PKC-delta, suggesting activation of caspases is critical for the Se-MSC-induced apoptosis, and caspases lie upstream of PKC-delta. The Se-MSC-induced apoptosis of U937 cells also required activity of PKC-delta because pretreatment of rottlerin, a specific PKC-delta inhibitor greatly blocked the Se-MSC-induced apoptosis as well as processing and activities of caspases, suggesting activation of PKC-delta is also important for the Se-MSC-induced apoptosis of U937 cells, and PKC-delta lies upstream of caspases. Together, our data suggest the apoptotic mechanism by Se-MSC in U937 cells may be related to cytochrome c release from the mitochondria, and mutual activation between caspases and PKC-delta via a positive feedback mechanism, which may potentiate the apoptotic action by Se-MSC in U937 cells.
authors.affiliation: Chronic Disease Research Center and Institute for Medical Science, School of Medicine Keimyung University, Daegu 700-712, South Korea.
authors.forename: Byeong-Churl
authors.initials: BC
authors.lastname: Jang
authors.forename: Eun-Seok
authors.initials: ES
authors.lastname: Choi
authors.forename: Ki-Jo
authors.initials: KJ
authors.lastname: Im
authors.forename: Won-Ki
authors.initials: WK
authors.lastname: Baek
authors.forename: Taek Kyu
authors.initials: TK
authors.lastname: Kwon
authors.forename: Min-Ho
authors.initials: MH
authors.lastname: Suh
authors.forename: Sang-Pyo
authors.initials: SP
authors.lastname: Kim
authors.forename: Jong-Wook
authors.initials: JW
authors.lastname: Park
authors.forename: Seong-Il
authors.initials: SI
authors.lastname: Suh
mesh_terms: D000098:Acetophenones / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects*; D001578:Benzopyrans / Q000494:pharmacology; D020169:Caspases / Q000378:metabolism*; D003545:Cysteine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D045304:Cytochromes c / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D025461:Feedback, Physiological; D006801:Humans; D016566:Organoselenium Compounds / Q000494:pharmacology*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism*; D051745:Protein Kinase C-delta; D021381:Protein Transport / Q000187:drug effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000235:genetics / Q000378:metabolism; D017279:Selenocysteine / Q000031:analogs & derivatives; D020298:U937 Cells
chemical_list: D000098:Acetophenones; D001578:Benzopyrans; D016566:Organoselenium Compounds; D019253:Proto-Oncogene Proteins c-bcl-2; D017279:Selenocysteine; D045304:Cytochromes c; C085746:rottlerin; D011065:Poly(ADP-ribose) Polymerases; C497258:PRKCD protein, human; D011493:Protein Kinase C; D051745:Protein Kinase C-delta; D020169:Caspases; D003545:Cysteine; C002979:selenomethylselenocysteine