Exosome-driven antigen transfer for MHC class II presentation facilitated by the receptor binding activity of influenza hemagglutinin.

The mechanisms underlying MHC class I-restricted cross-presentation, the transfer of Ag from an infected cell to a professional APC, have been studied in great detail. Much less is known about the equivalent process for MHC class II-restricted presentation. After infection or transfection of class II-negative donor cells, we observed minimal transfer of a proteasome-dependent "class I-like" epitope within the influenza neuraminidase glycoprotein but potent transfer of a classical, H-2M-dependent epitope within the hemagglutinin (HA) glycoprotein.

The alpha4 and alpha7 subunits and assembly of the 20S proteasome.

The detailed mechanism of eukaryotic 20S proteasome assembly is currently unknown. In the present study, we demonstrate that the 20S proteasome subunits alpha4 and alpha7 interact with each other as well as all the alpha-subunits in vivo and in vitro. The N-terminal parts of alpha4 and alpha7 are essential for these newly discovered interactions in vitro.

Human immunodeficiency virus-1 Tat protein interacts with distinct proteasomal alpha and beta subunits.

The human immunodeficiency virus-1 (HIV-1) Tat protein was previously reported to compete the association of PA28 regulator with the alpha rings of the 20S proteasome and to inhibit its peptidase activity. However, the distinct interaction sites within the proteasome complex remained to be determined. Here we show that HIV-1 Tat binds to alpha4 and alpha7, six beta subunits of the constitutive 20S proteasome and the interferon-gamma-inducible subunits beta2i and beta5i.