[Show abstract][Hide abstract] ABSTRACT: Stress-inducible phosphoprotein I (STIP1, STI1, or HOP) is a cochaperone intermediating Hsp70/Hsp90 exchange of client proteins, but it can also be secreted to trigger prion protein-mediated neuronal signaling. Some mothers of children with autism-spectrum disorders (ASD) present antibodies against certain brain proteins, including antibodies against STIP1. Maternal antibodies can cross the fetus blood brain barrier during pregnancy, suggesting the possibility that they can interfere with STIP1 levels and presumably functions. However, it is currently unknown whether abnormal levels of STIP1 have any impact in ASD-related behavior. Here we used mice with reduced (50%) or increased STIP1 levels (5-fold) to test for potential ASD-like phenotypes. We find that increased STIP1 regulates the abundance of Hsp70 and Hsp90, whereas reduced STIP1 does not affect Hsp70, Hsp90 or the prion protein. Interestingly, BAC transgenic mice presenting 5-fold more STIP1 have no major phenotype when examined in a series of behavioral tasks, including locomotor activity, elevated plus maze, Morris water maze and 5-choice serial reaction time task (5-CSRTT). In contrast, mice with reduced STIP1 levels are hyperactive and have attentional deficits on the 5-CSRTT, but have normal performance in the other tasks. We conclude that reduced STIP1 levels can contribute with phenotypes related to ASD. However, future experiments are needed to define whether it is decreased chaperone capacity or impaired prion protein signaling that contributes to these phenotypes.
[Show abstract][Hide abstract] ABSTRACT: In recent years, prion protein (PrP(C)) has been considered as a promising target molecule for cancer therapies, due its direct or indirect participation in tumor growth, metastasis, and resistance to cell death induced by chemotherapy. PrP(C) functions as a scaffold protein, forming multiprotein complexes on the plasma membrane, which elicits distinct signaling pathways involved in diverse biological phenomena and could be modulated depending on the cell type, complex composition, and organization. In addition, PrP(C) and its partners participate in self-renewal of embryonic, tissue-specific stem cells and cancer stem cells, which are suggested to be responsible for the origin, maintenance, relapse, and dissemination of tumors. Interference with protein-protein interaction has been recognized as an important therapeutic strategy in cancer; indeed, the possible interference in PrP(C) engagement with specific partners is a novel strategy. Recently, our group successfully used that approach to interfere with the interaction between PrP(C) and HSP-90/70 organizing protein (HOP, also known as stress-inducible protein 1 - STI1) to control the growth of human glioblastoma in animal models. Thus, PrP(C)-organized multicomplexes have emerged as feasible candidates for anti-tumor therapy, warranting further exploration.
[Show abstract][Hide abstract] ABSTRACT: The 90 kDa ribosomal S6 kinases (RSK) are effectors of the Ras-ERK1/2 signaling pathway. RSK signaling controls proliferation and protein synthesis, and is altered in several types of tumors. BI-D1870 and SL0101 are two widely used inhibitors of RSK. After revision of the literature, discrepancies in the effects of the inhibitors were identified. Herein we report that while SL0101 inhibited mTORC1-p70S6K signaling, BI-D1870 increased p70S6K activation. Both effects were independent of ERK1/2 and RSK, and thus nonspecific. We also demonstrated how these opposite nonspecific effects mislead the identification of the RSK-dependent phosphorylation of rpS6 (S235/236), a known RSK and p70S6K substrate. Phosphorylation of tuberin at S1798 by RSK was proposed to mediate ERK1/2-dependent activation of mTORC1-p70S6K signaling. In glioblastoma-derived cells, phosphorylation of tuberin was abolished after RSK depletion or ERK1/2 inhibition, suggesting that RSK is its main kinase. However, RSK depletion did not reduce PMA-dependent p70S6K phosphorylation, which suggests that tuberin phosphorylation at S1798 is not the main mediator of ERK1/2-dependent activation of mTORC1. Remarkably, tuberin phosphorylation (S1798) followed the activation status of RSK in different cells and experimental conditions, suggesting that phosphorylation of that residue could be used as readout for RSK activation in cells. We confirmed the difference in the effects of SL0101 and BI-D1870 in cellular proliferation assays. Rapamycin potentiated the inhibition of proliferation induced by BI-D1870, but not by SL0101. We thus conclude that SL0101 and BI-D1870 induce distinct off-target effects in mTORC1-p70S6K signaling, and thus, functions previously ascribed to RSK based on these inhibitors should be reassessed.
No preview · Article · Apr 2015 · Cellular Signalling
[Show abstract][Hide abstract] ABSTRACT: Accumulation of protein aggregates is a histopathological hallmark of several neurodegenerative diseases, but in most cases the aggregation occurs without defined mutations or clinical histories, suggesting that certain endogenous metabolites can promote aggregation of specific proteins. One example that supports this hypothesis is dopamine and its metabolites. Dopamine metabolism generates several oxidative metabolites that induce aggregation of α-synuclein, and represents the main etiology of Parkinson's diseases. Because dopamine and its metabolites are unstable and can be highly reactive, we investigated whether these molecules can also affect other proteins that are prone to aggregate, such as cellular prion protein (PrP(C)). In this study, we showed that dopamine treatment of neuronal cells reduced the number of viable cells and increased the production of reactive oxygen species (ROS) as demonstrated in previous studies. Overall PrP(C) expression level was not altered by dopamine treatment, but its unglycosylated form was consistently reduced at 100 μM of dopamine. At the same concentration, the level of phosphorylated mTOR and 4EBP1 was also reduced. Moreover, dopamine treatment decreased the solubility of PrP(C), and increased its accumulation in autophagosomal compartments with concomitant induction of LC3-II and p62/SQSTM1 levels. In vitro oxidation of dopamine promoted formation of high-order oligomers of recombinant prion protein. These results suggest that dopamine metabolites alter the conformation of PrP(C), which in turn is sorted to degradation pathway, causing autophagosome overload and attenuation of protein synthesis. Accumulation of PrP(C) aggregates is an important feature of prion diseases. Thus, this study brings new insight into the dopamine metabolism as a source of endogenous metabolites capable of altering PrP(C) solubility and its subcellular localization.
Full-text · Article · Feb 2015 · Frontiers in Cellular Neuroscience
[Show abstract][Hide abstract] ABSTRACT: Glioblastomas (GBMs) are resistant to current therapy protocols and identification of molecules that target these tumors is crucial. Interaction of secreted heat-shock protein 70 (Hsp70)-Hsp90-organizing protein (HOP) with cellular prion protein (PrP(C)) triggers a large number of trophic effects in the nervous system. We found that both PrP(C) and HOP are highly expressed in human GBM samples relative to non-tumoral tissue or astrocytoma grades I-III. High levels of PrP(C) and HOP were associated with greater GBM proliferation and lower patient survival. HOP-PrP(C) binding increased GBM proliferation in vitro via phosphatidylinositide 3-kinase and extracellular-signal-regulated kinase pathways, and a HOP peptide mimicking the PrP(C) binding site (HOP230-245) abrogates this effect. PrP(C) knockdown impaired tumor growth and increased survival of mice with tumors. In mice, intratumor delivery of HOP230-245 peptide impaired proliferation and promoted apoptosis of GBM cells. In addition, treatment with HOP230-245 peptide inhibited tumor growth, maintained cognitive performance and improved survival. Thus, together, the present results indicate that interfering with PrP(C)-HOP engagement is a promising approach for GBM therapy.Oncogene advance online publication, 25 August 2014; doi:10.1038/onc.2014.261.
[Show abstract][Hide abstract] ABSTRACT: Rnd proteins comprise a branch of the Rho family of small GTP-binding proteins, which have been implicated in rearrangements of the actin cytoskeleton and microtubule dynamics. Particularly in the nervous system, Rnd family proteins regulate neurite formation, dendrite development and axonal branching. A secreted form of the co-chaperone stress-inducible protein 1 (STI1) has been described as a prion protein partner that is involved in several processes of the nervous system, such as neurite outgrowth, neuroprotection, astrocyte development, and the self-renewal of neural progenitor cells. We show that cytoplasmic STI1 directly interacts with the GTPase Rnd1. This interaction is specific for the Rnd1 member of the Rnd family. In the COS collapse assay, overexpression of STI1 prevents Rnd1-plexin-A1-mediated cytoskeleton retraction. In PC-12 cells, overexpression of STI1 enhances neurite outgrowth in cellular processes initially established by Rnd1. Therefore, we propose that STI1 participates in Rnd1-induced signal transduction pathways that are involved in the dynamics of the actin cytoskeleton.
No preview · Article · May 2014 · Experimental Cell Research
[Show abstract][Hide abstract] ABSTRACT: In Alzheimer's disease (AD), soluble amyloid-β oligomers (AβOs) trigger neurotoxic signaling, at least partially, via the cellular prion protein (PrP(C)). However, it is unknown whether other ligands of PrP(C) can regulate this potentially toxic interaction. Stress-inducible phosphoprotein 1 (STI1), an Hsp90 cochaperone secreted by astrocytes, binds to PrP(C) in the vicinity of the AβO binding site to protect neurons against toxic stimuli. Here, we investigated a potential role of STI1 in AβO toxicity. We confirmed the specific binding of AβOs and STI1 to the PrP and showed that STI1 efficiently inhibited AβO binding to PrP in vitro (IC50 of ∼70 nm) and also decreased AβO binding to cultured mouse primary hippocampal neurons. Treatment with STI1 prevented AβO-induced synaptic loss and neuronal death in mouse cultured neurons and long-term potentiation inhibition in mouse hippocampal slices. Interestingly, STI1-haploinsufficient neurons were more sensitive to AβO-induced cell death and could be rescued by treatment with recombinant STI1. Noteworthy, both AβO binding to PrP(C) and PrP(C)-dependent AβO toxicity were inhibited by TPR2A, the PrP(C)-interacting domain of STI1. Additionally, PrP(C)-STI1 engagement activated α7 nicotinic acetylcholine receptors, which participated in neuroprotection against AβO-induced toxicity. We found an age-dependent upregulation of cortical STI1 in the APPswe/PS1dE9 mouse model of AD and in the brains of AD-affected individuals, suggesting a compensatory response. Our findings reveal a previously unrecognized role of the PrP(C) ligand STI1 in protecting neurons in AD and suggest a novel pathway that may help to offset AβO-induced toxicity.
Full-text · Article · Oct 2013 · The Journal of Neuroscience : The Official Journal of the Society for Neuroscience