Protein geranylgeranylation is critical for the regulation of survival and proliferation of lymphoma tumor cells.
ABSTRACT Prenylation is essential for membrane localization and participation of proteins in various signaling pathways. The following study was conducted to examine the importance of protein farnesylation and geranylgeranylation for the regulation of lymphoma cell survival and proliferation.
Lymphoma cells were treated with the beta-hydroxy-beta-methylglutaryl-CoA reductase inhibitor lovastatin, which inhibits protein farnesylation and geranylgeranylation by the depletion of intracellular pools of farnesylpyrophosphate and geranylgeranylpyrophosphate. In addition, farnesyl transferase and geranylgeranyl transferase activities were specifically inhibited by FTI-277 and GGTI-298, respectively.
Only inhibition of geranylgeranylation by lovastatin led to reduction of cell viability in lymphoma cell lines and purified tumor cells from lymphoma patients in a time- and dose-dependent way. Reduction in the number of viable cells was mediated by both induction of apoptosis and inhibition of proliferation. In addition, GGTI-298 was more effective in induction of apoptosis and inhibition of proliferation than FTI-277. Apoptosis induced by inhibition of protein geranylgeranylation was associated with a reduction of Mcl-1 protein levels, collapse of the mitochondrial transmembrane potential, and caspase-3 activation. Inhibition of proliferation resulted from the induction of G(1) arrest. Furthermore, lovastatin at low concentrations sensitized lymphoma cells to dexamethasone, including cells resistant to this drug.
These results indicate that protein geranylgeranylation is critical for the regulation of lymphoma tumor cell survival and proliferation and that pharmacological agents such as lovastatin or geranylgeranyl transferase inhibitors, alone or in combination with other drugs, may be useful in the treatment of lymphoma.
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ABSTRACT: Rituximab is used in the treatment of CD20+ B cell lymphomas and other B cell lymphoproliferative disorders. Its clinical efficacy might be further improved by combinations with other drugs such as statins that inhibit cholesterol synthesis and show promising antilymphoma effects. The objective of this study was to evaluate the influence of statins on rituximab-induced killing of B cell lymphomas. Complement-dependent cytotoxicity (CDC) was assessed by MTT and Alamar blue assays as well as trypan blue staining, and antibody-dependent cellular cytotoxicity (ADCC) was assessed by a 51Cr release assay. Statins were found to significantly decrease rituximab-mediated CDC and ADCC of B cell lymphoma cells. Incubation of B cell lymphoma cells with statins decreased CD20 immunostaining in flow cytometry studies but did not affect total cellular levels of CD20 as measured with RT-PCR and Western blotting. Similar effects are exerted by other cholesterol-depleting agents (methyl-beta-cyclodextrin and berberine), but not filipin III, indicating that the presence of plasma membrane cholesterol and not lipid rafts is required for rituximab-mediated CDC. Immunofluorescence microscopy using double staining with monoclonal antibodies (mAbs) directed against a conformational epitope and a linear cytoplasmic epitope revealed that CD20 is present in the plasma membrane in comparable amounts in control and statin-treated cells. Atomic force microscopy and limited proteolysis indicated that statins, through cholesterol depletion, induce conformational changes in CD20 that result in impaired binding of anti-CD20 mAb. An in vivo reduction of cholesterol induced by short-term treatment of five patients with hypercholesterolemia with atorvastatin resulted in reduced anti-CD20 binding to freshly isolated B cells. Statins were shown to interfere with both detection of CD20 and antilymphoma activity of rituximab. These studies have significant clinical implications, as impaired binding of mAbs to conformational epitopes of CD20 elicited by statins could delay diagnosis, postpone effective treatment, or impair anti-lymphoma activity of rituximab.PLoS Medicine 04/2008; 5(3):e64. · 16.27 Impact Factor
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PLoS Medicine 04/2008; 5(3):e77. · 16.27 Impact Factor