Overexpression of PrPc triggers caspase 3 activation:: potentiation by proteasome inhibitors and blockade by anti-PrP antibodies

We examined the influence of cellular prion protein (PrPc) in the control of cell death in stably transfected HEK293 cell line and in the PrPc-inducible Rov9 cells. PrPc expression in stably transfected HEK293 human cells did not modify basal apoptotic tonus but drastically potentiated staurosporine-stimulated cellular toxicity and DNA fragmentation as well as caspase 3-like activity and immunoreactivity. An identical staurosporine-induced caspase 3 activation was observed after doxycycline in the PrPc-inducible Rov9 cell line. Interestingly, proteasome inhibitors increase PrPc-like immunoreactivity and unmasked a basal caspase 3 activation. Conversely, we show that anti-PrPc antibodies sequestrate PrPc at the cell surface and drastically lower PrPc-dependent caspase activation. We suggest that intracellular PrPc could sensitize human cells to pro-apoptotic phenotype and that blockade of PrPc internalization could be a track to prevent intracellular toxicity associated with PrPc overexpression.