Again, these data do not support a key role for TEM-associated CD81 molecules

in HCV infection. Finally, we ensured that MβCD-induced inhibition of HCV entry did not lead to a reduced expression level of another HCV entry factor. We analyzed the expression levels of SR-BI, CLDN-1 and LDL receptor (LDL-R), three other major actors of HCV entry [9]. The tetraspanin CD151 was used PARP inhibitor again as a control. Since no antibody against extracellular loops of CLDN-1 is available for flow cytometry, we performed our analyses by immunoprecipitation of surface biotinylated cell lysates. As shown above, treatment of Huh-7w7/mCD81 cells with MβCD was accompanied by a reduced expression level of CD81, as detected by MT81 (Figure 7). We also found a reduced immunoprecipitation of CD81 by MT81w after MβCD treatment. Cholesterol depletion prior to lysis in Brij 97 likely led to a harsher effect of the detergent leading to a partial dissociation of tetraspanin complexes recognized by MT81w. Interestingly, treatment of Huh-7w7/mCD81 cells with MβCD did not lead to a reduction of cell surface expression of SR-BI, CLDN-1 or LDL-R. It has see more to be noted that SR-BI and CLDN-1 seemed even more expressed after MβCD treatment (Figure 7). This increased expression of SR-BI after MβCD treatment was confirmed by flow cytometry (data not shown) and has been previously described by

others [24, 41–43]. It has also been suggested that CLDN-1 might be in membrane domains GSI-IX research buy resistant to

MβCD treatment [44, 45]. Altogether, our results show that MβCD-induced inhibition of HCV entry was solely due to reduced levels of cholesterol and CD81. Figure 7 Cholesterol depletion and ceramide enrichment do not reduce cell surface expression of other HCV entry factors. Huh-7w7/mCD81 cells were treated with 7.5 mM MβCD, with 0.5 unit Smase/ml or left untreated (NT) 30 min at 37°C. Cells were then surface biotinylated and lysed in buffer containing 1% Brij97 and divalent ions. Immunoprecipitations were performed with indicated mAbs. Immunoprecipitates were revealed by western blotting Urease using peroxidase-conjugated streptavidin. Role of ceramide in TEM-associated CD81 and in HCV infection Beyond cholesterol, sphingolipids are also known to be important for the organization of the plasma membrane. Among them, sphingomyelin can be converted into ceramide by sphingomyelinase (Smase), and increasing ceramide concentration can lead to lipid microdomain reorganization [46]. We have previously reported that ceramide enrichment of the plasma membrane of Huh-7 cells following sphingomyelin hydrolysis by sphingomyelinase strongly inhibits HCV entry and reduces CD81 cell surface expression level by 50% [47]. Since sphingomyelin influences CD81 cell surface expression as well as HCV infection, we sought to determine the effect of the Smase treatment on TEM-associated CD81 population.