Activation effects of a prion protein fragment [PrP-(106-126)] on human leucocytes.

Prion-related encephalopathies are characterized by the intra- cerebral accumulation of an abnormal isoform of the cellular prion protein (PrPC) named scrapie prion protein (PrPSc). The pathological forms of this protein and its cellular precursor are not only expressed in the brain but also, at lower concentrations, in peripheral tissues. We recently showed that a synthetic peptide corresponding to residues 106–126 [PrP-(106–126)] of the human PrP is toxic to neurons and trophic to astrocytes in itro. Our experiments were aimed at verifying whether PrP-(106–126) and other peptides corresponding to fragments of the amyloid protein purified from brains of patients with Gerstmann–Stra6ussler– Scheinker disease – namely PrP-(89–106), PrP-(106–114), PrP- (127–147) – were capable of stimulating circulating leucocytes. Native PrP expression in human lymphocytes, monocytes and neutrophils was first confirmed using PCR amplification of total RNA, after reverse transcription, and immunoblot analysis of cell extracts with anti-PrP antibodies. PrP-(106–126), but not the other peptides, increased membrane microviscosity, intracellular Ca5+ concentration and cell migration in circulating leucocytes, and O5−d production in monocytes and neutrophils. Membrane microviscosity was determined by the fluorescence polarization technique, using diphenylhexatriene as a probe, 300 s after the addition of PrP-(106–126) to the cell suspension in the con- centration range 5–50 μM. The increase in intracellular Ca5+ elicited by PrP-(106–126) was dose-dependent in the range 5–500 μM. PrP-(106–126) stimulated O5−d production in monocytes and neutrophils in a dose- (10–300 μM) and time- (5–30 min) dependent manner in the presence of 10 μM dihydrocytochalasin B. Both the increase in Ca5+ concentration and the O5−d production were partially sensitive to pertussis toxin. PrP-(106–126) stimulated leucocyte migration in a dose- dependent (30–300 μM) manner and, at the highest concentration used, this migration was comparable with that elicited by 2n5 nM interleukin 8 or 10 nM fMet-Leu-Phe peptide