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.

To test for a role for the cellular prion protein (PrPc) in cell death, we used a PrPc‐binding peptide. Retinal explants from neonatal rats or mice were kept in vitro for 24 h, and anisomycin (ANI) was used to induce apoptosis. The peptide activated both cAMP/protein kinase A (PKA) and Erk pathways, and partially prevented cell death induced by ANI in explants from wild‐type rodents, but not from PrPc‐null mice. Neuroprotection was abolished by treatment with phosphatidylinositol‐specific phospholipase C, with human peptide 106–126, with certain antibodies to PrPc or with a PKA inhibitor, but not with a MEK/Erk inhibitor. In contrast, antibodies to PrPc that increased cAMP also induced neuroprotection. Thus, engagement of PrPc transduces neuroprotective signals through a cAMP/PKA‐dependent pathway. PrPc may function as a trophic receptor, the activation of which leads to a neuroprotective state.

No abstract

Cellular prion protein (PrPc) has a pivotal role in prion diseases. PrPc is a specific receptor for laminin (LN) gamma1 peptide and several lines of evidence indicate that it is also involved in neural plasticity. Here we investigated whether the interaction between PrPc and LN plays a role in rat memory formation. We found that post-training intrahippocampal infusion of PrPc-derived peptides that contain the LN binding site (PrPc163-182 and PrPc173-192) or of anti-PrPc or anti-LN antibodies that inhibit PrPc-LN interaction impaired inhibitory avoidance memory retention. The amnesic effect of anti-PrPc antibodies and PrPc173-192 peptide was reversed by co-infusion of a LN gamma1 chain-derived peptide containing the PrPc-binding site, suggesting that PrPc-LN interaction is indeed crucial for memory consolidation. In addition, PrPc173-192 peptide and anti-PrPc or anti-LN antibodies also inhibited the activation of hippocampal cAMP-dependent protein kinase A (PKA) and extracellular regulated kinase (ERK1/2), two kinases that mediate the up-regulation of signaling pathways needed for consolidation of inhibitory avoidance memory. Our findings show that, through its interaction with LN, hippocampal PrPc plays a critical role in memory processing and suggest that this role is mediated by activation of both PKA and ERK1/2 signaling pathways.

Individual spinal motor neuron identities are specified in large part by the intrinsic repertoire of transcription factors expressed by undifferentiated progenitors and maturing neurons. It is shown here that the transcription factor AML1/Runx1 (Runx1) is expressed in selected spinal motor neuron subtypes after the onset of differentiation and is both necessary and sufficient to suppress interneuron-specific developmental programs and promote maintenance of motor neuron characteristics. These findings show an important role for Runx1 during the consolidation of selected spinal motor neuron identities. Moreover, they suggest a requirement for a persistent suppression of interneuron genes within maturing motor neurons.lateral motor column ͉ median motor column ͉ runt ͉ spinal cord spinal accessory column S pecific transcription factor codes within exclusive ventral progenitor domains regulate motor neuron and interneuron differentiation in the developing spinal cord (1, 2). Some determinants of both lineages are coexpressed in mitotic progenitors (3), raising the questions of what molecules control the divergence and maintenance of motor neuron and interneuron differentiation programs. Genetic studies suggest that the gene Hb9 is required to suppress interneuron programs actively in maturing motor neurons (3, 4), but other effectors of the mechanisms that promote the divergence of motor and interneuron fates remain to be determined.In both invertebrates and vertebrates, the runt/Runx gene family encodes DNA-binding transcription factors that mediate transactivation or repression depending on specific contexts (5). Members of this transcription factor family regulate neuron subtype specification and axon target connectivity in Drosophila (6-8), chick (9, 10), and mice (11-16). The runt/Runx family member AML1/Runx1 (Runx1) is expressed in selected populations of motor neurons in the murine and avian spinal cord, suggesting that it is involved in motor neuron development (13,17). Here, we show that mouse Runx1 is expressed in restricted groups of ventrally exiting cervical motor neurons during their postmitotic development. Loss of Runx1 function does not affect the survival of those motor neurons but results in a loss of expression of motor neuron-specific genes and a concomitant activation of expression of interneuron-specific genes. Conversely, ectopic expression of Runx1 in the spinal cord of developing chick embryos suppresses interneuron gene expression and promotes motor neuron differentiation programs. These results identify a role for Runx1 in the establishment of selected motor neuron identities and suggest that maturing motor neurons must continually suppress interneuron-specific developmental programs.