Marilene H. Lopes

Stress-inducible protein 1 is a cell surface ligand for cellular prion that triggers neuroprotection

Prions are composed of an isoform of a normal sialoglycoprotein called PrPc, whose physiological role has been under investigation, with focus on the screening for ligands. Our group described a membrane 66 kDa PrPc‐binding protein with the aid of antibodies against a peptide deduced by complementary hydropathy. Using these antibodies in western blots from two‐dimensional protein gels followed by sequencing the specific spot, we have now identified 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 specific and high affinity manner with a Kd of 10−7 M. The interaction sites were mapped to amino acids 113–128 from PrPc and 230–245 from STI1. Cell surface binding and pull‐down experiments showed that recombinant PrPc binds to cellular STI1, and co‐immunoprecipitation assays strongly suggest that both proteins are associated in vivo. Moreover, PrPc interaction with either STI1 or with the peptide we found that represents the binding domain in STI1 induce neuropro tective signals that rescue cells from apoptosis.

Interaction of Cellular Prion and Stress-Inducible Protein 1 Promotes Neuritogenesis and Neuroprotection by Distinct Signaling Pathways

Understanding the physiological function of the cellular prion (PrPc) depends on the investigation of PrPc-interacting proteins. Stress-inducible protein 1 (STI1) is a specific PrPc ligand that promotes neuroprotection of retinal neurons through cAMP-dependent protein kinase A (PKA). Here, we examined the signaling pathways and functional consequences of the PrPc interaction with STI1 in hippocampal neurons. Both PrPc and STI1 are abundantly expressed and highly colocalized in the hippocampus in situ, indicating that they can interact in vivo. Recombinant STI1 (His6-STI1) added to hippocampal cultures interacts with PrPc at the neuronal surface and elicits neuritogenesis in wild-type neurons but not in PrPc-null cells. This effect was abolished by antibodies against either PrPc or STI1 and was dependent on the STI1 domain that binds PrPc. Binding of these proteins induced the phosphorylation/activation of the mitogen-activated protein kinase, which was essential for STI1-promoted neuritogenesis. His6-STI1, but not its counterpart lacking the PrPc binding site, prevented cell death via PKA activation. These results demonstrate that two parallel effects of the PrPc–STI1 interaction, neuritogenesis and neuroprotection, are mediated by distinct signaling pathways.

Endocytosis of Prion Protein Is Required for ERK1/2 Signaling Induced by Stress-Inducible Protein 1

The secreted cochaperone STI1 triggers activation of protein kinase A (PKA) and ERK1/2 signaling by interacting with the cellular prion (PrPC) at the cell surface, resulting in neuroprotection and increased neuritogenesis. Here, we investigated whether STI1 triggers PrPC trafficking and tested whether this process controls PrPC-dependent signaling. We found that STI1, but not a STI1 mutant unable to bind PrPC, induced PrPC endocytosis. STI1-induced signaling did not occur in cells devoid of endogenous PrPC; however, heterologous expression of PrPC reconstituted both PKA and ERK1/2 activation. In contrast, a PrPC 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 PrPC endocytosis is a necessary step to modulate STI1-dependent ERK1/2 signaling involved in neuritogenesis.

Metabotropic glutamate receptors transduce signals for neurite outgrowth after binding of the prion protein to laminin γ1 chain

The prion protein (PrPC) is highly expressed in the nervous system, and its abnormal con‐former is associated with prion diseases. PrPC is anchored to cell membranes by glycosylphosphatidylinositol, and transmembrane proteins are likely required for PrPC‐mediated intracellular signaling. Binding of laminin (Ln) to PrPC modulates neuronal plasticity and memory. We addressed signaling pathways triggered by PrPC‐Ln interaction in order to identify transmembrane proteins involved in the transduction of PrPC‐Ln signals. The Ln γl‐chain peptide, which contains the Ln binding site for PrPC, induced neuritogenesis through activation of phos‐pholipase C (PLC), Ca2+ mobilization from intracellular stores, and protein kinase C and extracellular signalregulated kinase (ERK1/2) activation in primary cultures of neurons from wild‐type, but not PrPC‐null mice. Phage display, coimmunoprecipitation, and colocalization experiments showed that group I metabotropic glutamate receptors (mGluRl/5) associate with PrPC. Expression of either mGluRl or mGluR5 in HEK293 cells reconstituted the signaling pathways mediated by PrPC‐Ln γl peptide interaction. Specific inhibitors of these receptors impaired PrPC‐Ln γl peptide‐induced signaling and neuri‐togenesis. These data show that group I mGluRs are involved in the transduction of cellular signals triggered by PrPC‐Ln, and they support the notion that PrPC participates in the assembly of multiprotein complexes with physiological functions on neurons.—Beraldo, F. H., Arantes, C. P., Santos, T. G., Machado, C. F., Roffe, M., Hajj, G. N., Lee, K. S., Magalhães, A. C., Caetano, F. A., Mancini, G. L., Lopes, M. H., Amãrico, T. A., Magdesian, M. H., Ferguson, S. S. G., Linden, R., Prado, M. A. M., Martins, V. R. Metabotropic glutamate receptors transduce signals for neurite outgrowth after binding of the prion protein to laminin γl chain. FASEB J. 25, 265–279 (20ll). www.fasebj.org

Cellular prion protein interaction with vitronectin supports axonal growth and is compensated by integrins

The physiological functions of the cellular prion protein, PrPC, as a cell surface pleiotropic receptor are under debate. We report that PrPC interacts with vitronectin but not with fibronectin or collagen. The binding sites mediating this PrPC-vitronectin interaction were mapped to residues 105-119 of PrPC and the residues 307-320 of vitronectin. The two proteins were co-localized in embryonic dorsal root ganglia from wild-type mice. Vitronectin addition to cultured dorsal root ganglia induced axonal growth, which could be mimicked by vitronectin peptide 307-320 and abrogated by anti-PrPC antibodies. Full-length vitronectin, but not the vitronectin peptide 307-320, induced axonal growth of dorsal root neurons from two strains of PrPC-null mice. Functional assays demonstrated that relative to wild-type cells, PrPC-null dorsal root neurons were more responsive to the Arg-Gly-Asp peptide (an integrin-binding site), and exhibited greater αvβ3 activity. Our findings indicate that PrPC plays an important role in axonal growth, and this function may be rescued in PrPC-knockout animals by integrin compensatory mechanisms.

Short-term memory formation and long-term memory consolidation are enhanced by cellular prion association to stress-inducible protein 1

Cellular prion protein (PrP(C)) is a cell surface glycoprotein that interacts with several ligands such as laminin, NCAM (Neural-Cell Adhesion Molecule) and the stress-inducible protein 1 (STI1). PrP(C) association with these proteins in neurons mediates adhesion, differentiation and protection against programmed cell death. Herein, we used an aversively motivated learning paradigm in rats to investigate whether STI1 interaction with PrP(C) affects short-term memory (STM) formation and long-term memory (LTM) consolidation. Blockage of PrP(C)-STI1 interaction with intra-hippocampal infusion of antibodies against PrP(C) or STI1 immediately after training impaired both STM and LTM. Furthermore, infusion of PrP(C) peptide 106-126, which competes for PrP(C)-STI1 interaction, also inhibited both forms of memory. Remarkably, STI1 peptide 230-245, which includes the PrP(C) binding site, had a potent enhancing effect on memory performance, which could be blocked by co-treatment with the competitive PrP(C) peptide 106-126. Taken together, these results demonstrate that PrP(C)-STI1 interaction modulates both STM and LTM and suggests a potential use of ST11 peptide 230-245 as a pharmacological agent.

The interaction between prion protein and laminin modulates memory consolidation

Cellular prion protein (PrPc) has a pivotal role in prion diseases. PrPc is a specific receptor for laminin (LN) γ1 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 ( and ) 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 peptide was reversed by co‐infusion of a LN γ1 chain‐derived peptide containing the PrPc‐binding site, suggesting that PrPc–LN interaction is indeed crucial for memory consolidation. In addition, 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.

Prion protein and its ligand stress inducible protein 1 regulate astrocyte development

Prion protein (PrPC) interaction with stress inducible protein 1 (STI1) mediates neuronal survival and differentiation. However, the function of PrPC 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 PrPC‐null astrocytes were not affected by STI1 treatment. At embryonic day 17, cultured astrocytes and brain extracts derived from PrPC‐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 PrPC‐null animals. Furthermore, PrPC‐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 PrPC‐null astrocytes in a protein kinase C‐dependent manner. Taken together, our data show that PrPC and STI1 are essential to astrocyte development and act through distinct signaling pathways.

Enhanced neural progenitor/stem cells self-renewal via the interaction of stress-inducible protein 1 with the prion protein.

Prion protein (PrPC), 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 PrPC‐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+/+) and PrPC‐null (Prnp0/0) 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 PrPC suggest that they may associate and function as a complex in neurosphere‐derived stem cells. The formation of neurospheres from Prnp0/0 mice was reduced significantly when compared with their wild‐type counterparts. In addition, blockade of secreted STI1, and its cell surface ligand, PrPC, with specific antibodies, impaired Prnp+/+ neurosphere formation without further impairing the formation of Prnp0/0 neurospheres. Alternatively, neurosphere formation was enhanced by recombinant STI1 application in cells expressing PrPC but not in cells from Prnp0/0 mice. The STI1‐PrPC 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‐PrPC 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. STEM CELLS 2011;29:1126–1136

Surgical outcome in mesial temporal sclerosis correlates with prion protein gene variant.

Background: Mesial temporal lobe epilepsy related to hippocampal sclerosis (MTLE-HS) is the most common surgically remediable epileptic syndrome. Ablation of the cellular prion protein (PrPc) gene (PRNP) enhances neuronal excitability of the hippocampus in vitro and sensitivity to seizure in vivo, indicating that PrPc might be related to epilepsy. Objective: To evaluate the genetic contribution of PRNP to MTLE-HS. Methods: The PRNP coding sequence of DNA from peripheral blood cells of 100 consecutive patients with surgically treated MTLE-HS was compared to that from a group of healthy controls adjusted for sex, age, and ethnicity (n = 180). The presence of PRNP variant alleles was correlated with clinical and presurgical parameters as well as surgical outcome. Results: A variant allele at position 171 (Asn→Ser), absent in controls, was found in heterozygosis (Asn171Ser) in 23% of patients (p < 0.0001). The PRNP genotypes were not correlated with any clinical or presurgical data investigated. However, patients carrying the Asn171Ser variant had a five times higher chance of continuing to have seizures after temporal lobectomy (95% CI 1.65 to 17.33, p = 0.005) than those carrying the normal allele. At 18 months after surgery, 91.8% of patients with the normal allele at codon 171 were seizure free, in comparison to 68.2% of those carrying Asn171Ser (p = 0.005). Conclusions: The PRNP variant allele Asn171Ser is highly prevalent in patients with medically untreatable MTLE-HS and influences their surgical outcome. The results suggest that the PRNP variant allele at codon 171 (Asn171Ser) is associated with epileptogenesis in MTLE-HS.