Signaling through HLA-DR induces PKC beta-dependent B cell death outside rafts.

Signals through HLA-DR molecules contribute to optimal activation of antigen-presenting cells (APC) during T cell/APC interactions participating in the generation of productive interactions, and to the induction of APC death, which has been postulated to play a role in the termination of the immune response. To understand how these molecules accommodate both cellular responses, we studied the not yet well-defined signaling events and the biochemical requirements for HLA-DR-mediated death. We demonstrate that in B cells the HLA-DR-activated protein kinase C (PKC) beta is required for HLA-DR-mediated death whereas the HLA-DR-activated Src family of PTK is redundant. In contrast to HLA-DR-mediated activation of Src kinase Lyn, the aggregation of HLA-DR molecules in lipid rafts is not required for HLA-DR-mediated PKC beta activation nor for the induction of cell death. Indeed, the bulk of HLA-DR-activated PKC beta reside outside rafts. This is the first report showing that HLA-DR-induced PKC beta activation is essential for the induction of B cell death via HLA-DR, and that these HLA-DR-mediated events do not require the integrity of rafts.