PA28αβ double and PA28β single transfectant mouse B8 cell lines reveal enhanced presentation of a mouse cytomegalovirus (MCMV) pp89 MHC class I epitope

PA28 is an interferon-γ inducible modulator of proteasome function composed of two subunits, i.e. PA28α and PA28β. Previously we showed that stabile overexpression of the PA28α subunit alone supported MHC class I antigen presentation of two viral epitopes. However, no information was obtained on the consequences when PA28α and PA28β function in concert or when PA28β is overexpressed on its own. Here we demonstrate that overexpression of PA28α and β together is similarly efficient in supporting MHC class I antigen presentation of the MCMV pp89 9mer epitope as PA28α alone, excluding a potentially potentiating role of PA28β. Surprisingly, and despite the fact that PA28β alone was thought to be inactive and to only stabilize PA28 activity, overexpression of PA28β also resulted in improved antigen presentation. However, by northernblot and immunoprecipitation we show that while PA28α is able to act alone the observed effect in the PA28β and PA28αβ transfectant cell lines is due to increased levels of PA28αβ complexes. (C) 2000 Elsevier Science Ltd. All rights reserved.