BACKGROUND/AIM: 9-[2-(phosphonomethoxy)ethyl] guanine (PMEG) is a guanine acyclic nucleotide analog whose targeted prodrugs are being investigated for chemotherapy of lymphomas. Its antiproliferative effects have been attributed to cell cycle arrest and induction of apoptosis, however, the underlying mechanisms remain poorly understood. The objective of this study was to determine the requirements for caspase and CD95/Fas activation in PMEG-induced apoptosis. Additionally, the influence of PMEG on cell cycle regulatory proteins was explored. MATERIALS AND METHODS: CCRF-CEM cells were exposed to PMEG with/without caspase inhibitor or anti-Fas blocking antibody and assayed for phosphatidyl serine externalization, mitochondrial depolarization and the cleavage of procaspase 3 and the nuclear protein poly (ADP-ribose) polymerase (PARP). RESULTS: Despite an observed increase of caspase 3, 8 and 9 proteolytic activity, neither pretreatment of the cells with cell-permeable caspase inhibitors nor blocking the death receptor with anti-Fas antibody did prevent apoptosis induced by PMEG. CONCLUSION: PMEG-induced apoptosis is caspase- and CD95/Fas-independent.
- MeSH
- aktivace enzymů MeSH
- antigeny CD95 metabolismus MeSH
- apoptóza účinky léků fyziologie MeSH
- buněčný cyklus účinky léků fyziologie MeSH
- cyklin E biosyntéza genetika MeSH
- cyklin-dependentní kinasy biosyntéza metabolismus MeSH
- guanin analogy a deriváty farmakologie MeSH
- inhibiční proteiny cyklin-dependentních kinas biosyntéza metabolismus MeSH
- kaspasy metabolismus MeSH
- lidé MeSH
- membránový potenciál mitochondrií účinky léků MeSH
- mitochondrie účinky léků fyziologie MeSH
- nádorové buněčné linie MeSH
- onkogenní proteiny biosyntéza genetika MeSH
- organofosforové sloučeniny farmakologie MeSH
- S fáze účinky léků MeSH
- signální transdukce MeSH
- T-lymfocyty cytologie účinky léků enzymologie metabolismus MeSH
- vztah mezi dávkou a účinkem léčiva MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Cross-linking the B cell Ag receptor (BCR) to surface Fc receptors for IgG (Fc gamma R) inhibits G1-to-S progression; the mechanism by which this occurs is not completely known. We investigated the regulation of three key cell cycle regulatory components by BCR-Fc gamma R co-cross-linking: G1-cyclins, cyclin-dependent kinases (Cdks), and the retinoblastoma gene product (Rb). Rb functions to suppress G1-to-S progression in mammalian cells. Rb undergoes cell-cycle-dependent phosphorylation, leading to its inactivation and thereby promoting S phase entry. We demonstrate in this paper for the first time that BCR-induced Rb phosphorylation is abrogated by co-cross-linking with Fc gamma R. The activation of Cdk4/6- and Cdk2-dependent Rb protein kinases is concomitantly blocked. Fc gamma R-mediated inhibition of Cdk2 activity results in part from an apparent failure to express Cdk2 protein. By contrast, inhibition of Cdk4/6 activities is not due to suppression of Cdk4/6 or cyclins D2/D3 expression or inhibition of Cdk-activating kinase activity. Cdk4- and Cdk6-immune complexes recovered from B cells following BCR-Fc gamma R co-cross-linking are devoid of coprecipitated D-type cyclins, indicating that inhibition of their Rb protein kinase activities is due in part to the absence of bound D-type cyclin. Thus, BCR-derived activation signals that up-regulate D-type cyclin and Cdk4/6 protein expression remain intact; however, Fc gamma R-mediated signals block cyclin D-Cdk4/6 assembly or stabilization. These results suggest that assembly or stabilization of D-type cyclin holoenzyme complexes 1) is an important step in the activation of Cdk4/6 by BCR signals, and 2) suffice in providing a mechanism to account for inhibition of BCR-stimulated Rb protein phosphorylation by Fc gamma R.
- MeSH
- aktivace enzymů imunologie MeSH
- B-lymfocyty enzymologie imunologie metabolismus MeSH
- buněčná diferenciace imunologie MeSH
- cyklin D MeSH
- cyklin E antagonisté a inhibitory biosyntéza MeSH
- cyklin-dependentní kinasa 2 MeSH
- cyklin-dependentní kinasa 4 MeSH
- cyklin-dependentní kinasa 6 MeSH
- cyklin-dependentní kinasa 9 MeSH
- cyklin-dependentní kinasy antagonisté a inhibitory biosyntéza metabolismus MeSH
- cykliny antagonisté a inhibitory biosyntéza MeSH
- DNA antagonisté a inhibitory biosyntéza MeSH
- fosforylace MeSH
- G1 fáze imunologie MeSH
- holoenzymy biosyntéza MeSH
- imunoglobuliny - Fab fragmenty farmakologie MeSH
- inhibitor p27 cyklin-dependentní kinasy MeSH
- kinasy CDC2-CDC28 * MeSH
- myši inbrední BALB C MeSH
- myši MeSH
- nádorové supresorové proteiny * MeSH
- protein-serin-threoninkinasy antagonisté a inhibitory biosyntéza metabolismus MeSH
- proteiny asociované s mikrotubuly biosyntéza MeSH
- proteiny buněčného cyklu * MeSH
- protilátky anti-idiotypické farmakologie MeSH
- protoonkogenní proteiny * MeSH
- receptory antigenů B-buněk antagonisté a inhibitory imunologie metabolismus fyziologie MeSH
- receptory IgG metabolismus MeSH
- retinoblastomový protein antagonisté a inhibitory metabolismus MeSH
- RNA antagonisté a inhibitory biosyntéza MeSH
- upregulace imunologie MeSH
- zvířata MeSH
- Check Tag
- myši MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
- Research Support, U.S. Gov't, Non-P.H.S. MeSH
- Research Support, U.S. Gov't, P.H.S. MeSH
