Human Prion Protein Mutants with Deleted and Inserted Octarepeats Undergo Different Pathways to Trigger Cell Apoptosis

Octarepeats region sequence is one of the most important characteristics of PrP topology. To explore the mechanism of deleted and inserted octarepeats mutants PrP-caused apoptosis, wild-type PrP (PrP-PG5), and PrP with deleted octarepeats (PrP-PG0) and with four (PrP-PG9) and seven (PrP-PG12) extra octarepeats were transiently induced into SH-SY5Y cell. The results indicated PrP-PG9 and PrP-PG12 mainly retained in fraction of cytoplasm, while PrP-PG5 and PrP-PG0 presented both in cell membrane and cytoplasm. Cells expressing PrP-PG9 and PrP-PG12 were sensitive to endoplasmic reticulum (ER) stimuli, tunicamycin, and brefeldin A. ER-stress-related proteins, Grp94, XBP1, TRAF2, and CHOP, were significantly increased in cells expressing PrP-PG9 and PrP-PG12, while Grp78 increased markedly 12 h and pro-caspase-12 decreased sharply 20 h post-transfection. It indicates that expressions of PrP mutants with inserted octarepeats cause ER stress and lead to cell apoptosis lately. Meanwhile, cellular Cytochrome C increased and Bcl-2 decreased obviously in cells expressing PrP-PG0, indicating triggering a mitochondrial-related apoptosis. These data highlight that PrP mutants in region of octarepeats may undergo different pathways to trigger cell apoptosis, in which PrPs with inserted octarepeats via ER stress and PrP mutant without octarepeats via mitochondrial-related pathway.