Specifically, Jijoye cells were treated overnight either with proteasome inhibitors (MG132, epoxomicin and PS-341), tripeptidyl peptidase II inhibitors (butabindide and AAF-CMK), a lysosomal acidification inhibitor (chloroquine), an autophagic process inducer (rapamycin) or IFN-γ, which increases proteasome and ERAP activities as well as HLA class I and TAP expression. All drugs were used at the selected concentrations, which correspond to their known biological effect without effects on cell viability.
As shown in Fig. 6, only partial inhibition of proteasomes leads to an increased recognition of Jijoye cells by HPV-specific CTLs, whereas all other treatments failed to affect target cell lysis. Similar results were obtained with BJAB B95.8 cells, whereas BL cells negative for HLA-B53 and HLA-B35, which were used as a negative control in all assays, were unaffected by these PLX4032 ic50 treatments (not shown). These results suggest that proteasomes from BL cells, although less efficient in degrading reference substrates than proteasomes from
LCLs, destroy the HPV epitope, which can, however, be generated and presented after partial inhibition of the proteasomes. To evaluate whether proteasomes from BL cells are able to generate the HPV epitope, we analysed the in vitro FGFR inhibitor degradation of an HPV peptide precursor featuring five amino acids at the C terminus (HPV + 5). Proteasomes were semi-purified from Jijoye cells treated or not with epoxomicin under the same conditions inducing HPV-specific lysis. Subsequently, the in vitro HPV precursor degradation was evaluated at different time-points by HPLC analysis. As shown in Fig. 7, the HPV precursor was degraded in a time-dependent fashion. Glutamate dehydrogenase Proteasomes isolated from Jijoye cells and treated with epoxomicin were still capable of degrading the HPV precursor, albeit to a lesser extent. Interestingly, the appearance of a single peptide was evident during the HPV + 5 degradation. As this peptide eluted from the HPLC column
with the same retention time as the HPV peptide, it was identified as the HPV epitope, a hypothesis confirmed by mass spectroscopy (not shown). The generation of the HPV epitope by proteasomes isolated from untreated Jijoye cells was maximal after 1 hr and subsequently decreased in a time-dependent fashion, suggesting a further degradation to products that were undetectable under our conditions. In contrast, proteasomes isolated from Jijoye cells treated with epoxomicin still generated the HPV epitope, which was not further degraded because its presence could still be detected after 48 hr. These in vitro findings suggest that BL cells treated with proteasome inhibitors do not degrade the HPV epitope, resulting in its presentation by class I molecules.