contributed equally to this work Prions are composed of an isoform of a normal sialoglycoprotein called PrP c , whose physiological role has been under investigation, with focus on the screening for ligands. Our group described a membrane 66 kDa PrP c -binding protein with the aid of antibodies against a peptide deduced by complementary hydropathy. Using these antibodies in western blots from twodimensional protein gels followed by sequencing the speci®c spot, we have now identi®ed the molecule as stress-inducible protein 1 (STI1). We show that this protein is also found at the cell membrane besides the cytoplasm. Both proteins interact in a speci®c and high af®nity manner with a K d of 10 ±7 M. The interaction sites were mapped to amino acids 113±128 from PrP c and 230±245 from STI1. Cell surface binding and pull-down experiments showed that recombinant PrP c binds to cellular STI1, and co-immunoprecipitation assays strongly suggest that both proteins are associated in vivo. Moreover, PrP c interaction with either STI1 or with the peptide we found that represents the binding domain in STI1 induce neuroprotective signals that rescue cells from apoptosis.

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The prion protein (PrP(C)) is highly expressed in the nervous system, and its abnormal conformer is associated with prion diseases. PrP(C) is anchored to cell membranes by glycosylphosphatidylinositol, and transmembrane proteins are likely required for PrP(C)-mediated intracellular signaling. Binding of laminin (Ln) to PrP(C) modulates neuronal plasticity and memory. We addressed signaling pathways triggered by PrP(C)-Ln interaction in order to identify transmembrane proteins involved in the transduction of PrP(C)-Ln signals. The Ln γ1-chain peptide, which contains the Ln binding site for PrP(C), induced neuritogenesis through activation of phospholipase C (PLC), Ca(2+) mobilization from intracellular stores, and protein kinase C and extracellular signal-regulated kinase (ERK1/2) activation in primary cultures of neurons from wild-type, but not PrP(C)-null mice. Phage display, coimmunoprecipitation, and colocalization experiments showed that group I metabotropic glutamate receptors (mGluR1/5) associate with PrP(C). Expression of either mGluR1 or mGluR5 in HEK293 cells reconstituted the signaling pathways mediated by PrP(C)-Ln γ1 peptide interaction. Specific inhibitors of these receptors impaired PrP(C)-Ln γ1 peptide-induced signaling and neuritogenesis. These data show that group I mGluRs are involved in the transduction of cellular signals triggered by PrP(C)-Ln, and they support the notion that PrP(C) participates in the assembly of multiprotein complexes with physiological functions on neurons.

The secreted cochaperone STI1 triggers activation of protein kinase A (PKA) and ERK1/2 signaling by interacting with the cellular prion (PrP C ) at the cell surface, resulting in neuroprotection and increased neuritogenesis. Here, we investigated whether STI1 triggers PrP C trafficking and tested whether this process controls PrP C -dependent signaling. We found that STI1, but not a STI1 mutant unable to bind PrP C , induced PrP C endocytosis. STI1-induced signaling did not occur in cells devoid of endogenous PrP C ; however, heterologous expression of PrP C reconstituted both PKA and ERK1/2 activation. In contrast, a PrP C mutant lacking endocytic activity was unable to promote ERK1/2 activation induced by STI1, whereas it reconstituted PKA activity in the same condition, suggesting a key role of endocytosis in the former process. The activation of ERK1/2 by STI1 was transient and appeared to depend on the interaction of the two proteins at the cell surface or shortly after internalization. Moreover, inhibition of dynamin activity by expression of a dominant-negative mutant caused the accumulation and colocalization of these proteins at the plasma membrane, suggesting that both proteins use a dynamin-dependent internalization pathway. These results show that PrP C endocytosis is a necessary step to modulate STI1-dependent ERK1/2 signaling involved in neuritogenesis.

. (1992). Acetylcholine synthesis and release is enhanced by dibutyryl cyclic AMP in a neuronal cell line derived from mouse septum. J. Neurosci. 12, 793-799. Brentani, R. R. (1988

A conformational transition of the cellular prion protein (PrP(C)) into an aberrantly folded isoform designated scrapie prion protein (PrP(Sc)) is the hallmark of a variety of neurodegenerative disorders collectively called prion diseases. They include Creutzfeldt-Jakob disease and Gerstmann-Stäussler-Scheinker syndrome in humans, scrapie in sheep, bovine spongiform encephalopathy (BSE) in cattle and chronic wasting disease (CWD) in free-ranging deer. In contrast to the deadly properties of misfolded PrP, PrP(C) seems to possess a neuroprotective activity. More-over, animal models indicated that the stress-protective activity of PrP(C) and the neurotoxic effects of PrP(Sc) are somehow interconnected.In this timely book, leading scientists in the field have come together to highlight the apparently incongruous activities of different PrP conformers. The articles outline current research on celluar pathways implicated in the formation and signaling of neurotoxic and physiological PrP isoforms and delineate future research direction. Topics covered include the physiologcial activity of PrP(C) and its possible role as a neurotrophic factor, the finding that aberrant PrP conformers can cause neurodegeneration in the absence of infectious prion propagation, the requirement of the GPI anchor of PrP(C) for the neurotoxic effects of scrapie prions, the pathways implicated in the formation and neurotoxic properties of cytosolically localized PrP, the impact of metal ions on the processing of PrP, and the role of autophagy in the propagation and clearance of PrP(Sc). The book is fully illustrated and chapters include comprehensive reference sections.Essential reading for scientists involved in prion research.

Prion protein (PrP C ), when associated with the secreted form of the stress-inducible protein 1 (STI1), plays an important role in neural survival, neuritogenesis, and memory formation. However, the role of the PrP C -STI1 complex in the physiology of neural progenitor/stem cells is unknown. In this article, we observed that neurospheres cultured from fetal forebrain of wild-type (Prnp 1/1 ) and PrP C -null (Prnp 0/0 ) mice were maintained for several passages without the loss of self-renewal or multipotentiality, as assessed by their continued capacity to generate neurons, astrocytes, and oligodendrocytes. The homogeneous expression and colocalization of STI1 and PrP C suggest that they may associate and function as a complex in neurosphere-derived stem cells. The formation of neurospheres from Prnp 0/0 mice was reduced significantly when compared with their wild-type counterparts. In addition, blockade of secreted STI1, and its cell surface ligand, PrP C , with specific antibodies, impaired Prnp 1/1 neurosphere formation without further impairing the formation of Prnp 0/0 neurospheres. Alternatively, neurosphere formation was enhanced by recombinant STI1 application in cells expressing PrP C but not in cells from Prnp 0/0 mice. The STI1-PrP C interaction was able to stimulate cell proliferation in the neurosphere-forming assay, while no effect on cell survival or the expression of neural markers was observed. These data suggest that the STI1-PrP C complex may play a critical role in neural progenitor/stem cells self-renewal via the modulation of cell proliferation, leading to the control of the stemness capacity of these cells during nervous system development.

Prion protein (PrP(C)) interaction with stress inducible protein 1 (STI1) mediates neuronal survival and differentiation. However, the function of PrP(C) in astrocytes has not been approached. In this study, we show that STI1 prevents cell death in wild-type astrocytes in a protein kinase A-dependent manner, whereas PrP(C)-null astrocytes were not affected by STI1 treatment. At embryonic day 17, cultured astrocytes and brain extracts derived from PrP(C)-null mice showed a reduced expression of glial fibrillary acidic protein (GFAP) and increased vimentin and nestin expression when compared with wild-type, suggesting a slower rate of astrocyte maturation in PrP(C)-null animals. Furthermore, PrP(C)-null astrocytes treated with STI1 did not differentiate from a flat to a process-bearing morphology, as did wild-type astrocytes. Remarkably, STI1 inhibited proliferation of both wild-type and PrP(C)-null astrocytes in a protein kinase C-dependent manner. Taken together, our data show that PrP(C) and STI1 are essential to astrocyte development and act through distinct signaling pathways.