Cholesterol level determines viability and mitogenicity, but it does not affect sodium butyrate-dependent sensitization of Colo 205 cells to TNF-α-induced apoptosis

Abstract

Transient treatment of human adenocarcinoma COLO 205 cells with lipit raft (LR) modulators (MβCD, NY, IMP) was followed by the challenge with metabolic inhibitors and selected anti-cancer drugs. To overturn cholesterol chelation, the MβCD, NY treatment was followed by cholesterol conjugates (CHOL-MβCD or CHOL-PEG). The TNF-α- and P(Ser473)-PKB/Akt1/2-mediated effects initiated at LR were evaluated with regard to cell viability and mitogenicity. Cholesterol chelators reversibly reduced cell survival, whereas some of the tested compounds had weak effects (CIS, CLA), stimulated (EGCG) or reduced (NaB) cell survival. Cellular localizations of LR-associated molecules (ceramides, Gαi-2 heterotrimeric protein, and TNF-R1) in different cellular compartments including the plasma membrane were observed in the respective photographs from TEM and SEM. Evidence from SEM also showed that TNF-R1 is clustered on the surface of COLO 205 cells without presence of cognate ligand but clustering is promoted by TNF-α, while it vanished after IMP treatment. COLO 205 cells remained immune to TNF-α-induced apoptosis unless NaB was added, in which case NaB-induced cell death was further potentiated by TNF-α. Combined NaB and TNF-α treatment was associated with marked changes in the expression of pro- and antiapoptotic proteins. In this study, we demonstrated that initial excess of prosurvival signals could be diminished by cholesterol chelators, whereas LR-independent cell survival could be targeted by NaB. Apparently, lipid rafts do not participate in NaB-dependent cell death.