ИСТИНА

Huge proteolytic complex named proteasome catalyzes protein degradation in every eukaryotic cell. It consists of 31 subunits forming four stacked rings and one or two regulatory caps. Two inner rings of the proteolytic part contain three catalytic β-subunits that possess different substrate specificity. Higher vertebrates can express γ-interferon-inducible immuno-β-subunits. Proteasome plays an essential role in continual turnover of intracellular proteins and in antigen processing. Autoimmune diseases such as multiple sclerosis and its murine model EAE are believed to rise from breakdown of tolerance of the immune system. It assumed that immunoproteasome could play an important role in autoimmune diseases. Several classes of chemicals proved to be inhibitors of proteasome and the most active are boronate peptide derivatives. These inhibitors totally inactivate proteasome and result in full stop of intracellular protein turnover and cell death via apoptosis. Another class of inhibitors, epoxy ketones, was shown to be more selective for immunoproteasome and could be used not for full stop of proteasome function, but for fine tuning of altered proteasome functioning. We examined properties of several inhibitors of four different classes, namely peptide boronate bortezomib, peptide aldehyde MG132, lactam lactacystin, and peptide epoxyketones epoxomicin, MG132ek, UK101 and PR-957. For inhibition experiments we used proteasome isolated from eukaryotic cell lines CHO, NSO and HEK, treated and non-treated with γ-interferon, as a model cells contatinig constitutive and immunoproteasome. The upregulation of proteasome immunosubunits was revealed in CHO and NSO cells treated with γ-interferon. The IC50 values for all studied inhibitors were obtained, and Ki in some cases were calculated. The epoxyketones were shown to selectively inhibit in submicromolar concentrations the proteasome sample which contain high amount of immunosubunits.