PA28alphabeta double and PA28beta single transfectant mouse B8 cell lines reveal enhanced presentation of a mouse cytomegalovirus (MCMV) pp89 MHC class I epitope.

摘要

PA28 is an interferon-gamma inducible modulator of proteasome function composed of two subunits, i.e. PA28alpha and PA28beta. Previously we showed that stabile overexpression of the PA28alpha subunit alone supported MHC class I antigen presentation of two viral epitopes. However, no information was obtained on the consequences when PA28alpha and PA28beta function in concert or when PA28beta is overexpressed on its own. Here we demonstrate that overexpression of PA28alpha and beta together is similarly efficient in supporting MHC class I antigen presentation of the MCMV pp89 9mer epitope as PA28alpha alone, excluding a potentially potentiating role of PA28beta. Surprisingly, and despite the fact that PA28beta alone was thought to be inactive and to only stabilize PA28 activity, overexpression of PA28beta also resulted in improved antigen presentation. However, by northernblot and immunoprecipitation experiments we show that while PA28alpha is able to act alone the observed effect in the PA28beta and PA28alphabeta transfectant cell lines is due to increased levels of PA28alphabeta complexes.