PRION PROTEIN-FRAGMENT-106-126 INDUCES APOPTOTIC CELL-DEATH AND IMPAIRMENT OF L-TYPE VOLTAGE-SENSITIVE CALCIUM-CHANNEL ACTIVITY IN THE GH3 CELL-LINE

The prion diseases are transmissible neurodegenerative pathologies cha racterized by the accumulation of altered forms of the prion protein ( PrP), termed PrPSc, in the brain, Previous studies have shown that a s ynthetic peptide homologous to residues 106-126 of PrP (PrP 106-126) m aintains many characteristics of PrPSc, i.e., the ability to form amyl oid fibrils and to induce apoptosis in neurons. We have investigated t he intracellular mechanisms involved in the cellular degeneration indu ced by PrP 106-126, using the GH3 cells as a model of excitable cells, When assayed in serum-deprived conditions (48 hr), PrP 106-126 (50 mu M) induced cell death time-dependently, and this process showed the c haracteristics of the apoptosis, This effect was specific because a pe ptide with a scrambled sequence of PrP 106-126 was not effective, Then we performed microfluorimetric analysis of single cells to monitor in tracellular calcium concentrations and showed that PrP 106-126 caused a complete blockade of the increase in the cytosolic calcium levels in duced by K+ (40 mM) depolarization, Conversely, the scrambled peptide was ineffective, The L-type voltage-sensitive calcium channel blocker nicardipine (1 mu M) also induced apoptosis in GH3 cells, suggesting t hat the blockade of Ca2+ entry through this class of calcium channels may cause GH3 apoptotic cell death, We thus analyzed, by means of elec trophysiological studies, whether Prp 106-126 modulate L-type calcium channels activity and demonstrated that the apoptotic effect of PrP 10 6-126 was due to a dose-dependent inactivation of the L-type calcium c hannels. These data demonstrate that the prion protein fragment 106-12 6 induces a GH3 apoptotic cell death inducing a selective inhibition o f the activity of the L-type voltage-sensitive calcium channels, (C) 1 998 Wiley-Liss, Inc.