CREB-dependent gene regulation by prion protein: Impact on MMP-9 and β-dystroglycan
Introduction
The cellular prion protein (PrPC) is a ubiquitous glycosyl-phosphatidylinositol (GPI)-anchored membrane protein, whose conversion into an abnormal isoform, the scrapie prion protein (PrPSc), lies at the root of transmissible spongiform encephalopathies (TSE) pathogenesis [1]. While it is well established that PrPC is absolutely necessary for the development of TSE [2], its physiological function remains enigmatic. PrP-deficient mice are viable and exhibit but minor phenotypic or behavioural alterations at baseline and hence did not permit to assign any specific function to PrPC [3]. Unravelling PrPC normal function is all the more challenging since it may present as multiple glycoforms [4] and may serve promiscuous functions depending on the cell type or tissue considered. Increasing evidence actually favors the notion that PrPC combines a ubiquitous role in cell homeostasis [5], [6] as well as some neurospecific function(s). Elucidating the latter may notably provide some clues as to how the PrPSc-induced deviation of PrPC function in neurons leads to neuronal cell demise in TSE [7], [8].
A substantial body of recent research favors the view that PrPC acts as a gatekeeper against cellular insults in neuronal cells [9]. Indeed, neuronal cells derived from PrP-deficient mice undergo apoptosis following oxidative stress or serum deprivation more readily than those from wild-type mice [10], [11], [12]. From a mechanistic point of view, it is proposed that PrPC exerts an anti-apoptotic action through interference in the mitochondrial apoptotic pathways, by mimicking the inhibitory effect of Bcl-2 on the pro-apoptotic Bax protein [13], [14]. In line with in vitro observations, taking a closer look at PrPC-deficient mice allowed to reveal an enhanced susceptibility to various brain injuries as compared to wild-type animals [15]. For instance, ischemia induces larger brain infarcts in PrP-null mice than in their wild-type counterparts [16], [17], [18]. Interestingly, in wild-type animals, PrPC accumulates in the injured area following cerebral ischemia, suggesting that PrPC could participate to posttrauma recovery by counteracting neurodegeneration [19].
The neuroprotective role of PrPC has to be considered in light of its involvement in cell adhesion, neurite outgrowth and signal transduction. By forming a complex with the stress inducible protein 1 (STI1), PrPC was indeed reported to promote either neuroprotection or neuritogenesis by distinct signaling pathways involving the cAMP-dependent protein kinase (PKA) or the mitogen activated protein kinases ERK1/2 [20], [21]. Besides, PrPC interacts with various adhesion proteins including, the extracellular matrix glycoprotein laminin, the 37-kDa laminin receptor precursor (LRP) and its mature form, the 67-kDa laminin receptor (LR) [22], [23], [24]. The binding of PrPC to laminin was shown to promote neuritogenesis and neurite maintenance [23] and was recently proposed to mediate memory consolidation [25]. PrPC can also associate with the Neural Cell Adhesion Molecule (N-CAM) through both cis and trans interactions, which sustain neurite outgrowth via the activation of the Fyn tyrosine kinase [26], [27].
The observations by Santuccione et al. [26] actually fit in with our earlier work substantiating that PrPC is able to instruct cell signaling events [28]. In that study, we took advantage of the 1C11 neuroectodermal cell line that can differentiate into either serotonergic (1C115-HT) or noradrenergic (1C11NE) neuronal cells upon appropriate induction [29] and showed that antibody-mediated PrPC crosslinking in differentiated cells triggers the activation of Fyn, through the recruitment of the membrane protein caveolin. We further established that PrPC ligation promotes the serial activation of NADPH oxidase, a reactive oxygen species (ROS) generating enzyme, and the MEK/ERK1/2 MAP kinase module, not only in 1C11 neuronal derivatives but also in non-neuronal cells, underlying a ubiquitous involvement of PrPC in cell homeostasis [5]. In the 1C11 precursor and non-neuronal cells, the PrPC-induced ROS act as second messengers and fully mediate ERK1/2 phosphorylation. In contrast, in 1C115-HT and 1C11NE cells, the PrPC-caveolin-Fyn platform recruits multiple pathways, converging on ERK1/2, one of which involves NADPH oxidase.
With the aim of shedding further light on PrPC signaling function, we looked for PrPC intracellular targets recruited downstream from ERK1/2, focusing on transcription factors. In the present study, we identify the cyclic AMP-responsive element binding protein (CREB) transcription factor as a target of PrPC signaling, in both the 1C11 precursor and its neuronal progenies. In response to PrPC ligation, CREB triggers the transcription of two immediate early genes, Egr-1 and c-fos. In 1C115-HT and 1C11NE neuronal cells, CREB activation induces a transcriptional regulation of the MMP-9/TIMP-1 metalloproteinase system, which impacts on β-dystroglycan processing.
Section snippets
Material
All tissue culture reagents were from Invitrogen (Carlsbad, CA, USA). Monoclonal PrP-targeted antibodies (SAF61, SAF32, and Sha31, all IgG) with distinct binding epitopes [30] were obtained from the Service de Pharmacologie et d'Immunologie, Commissariat à l'Energie Atomique (Saclay, France). Polyclonal rabbit IgG antibodies against phospho-Ser133 CREB and total CREB were from Upstate Biotechnology (Lake Placid, NY, USA). Monoclonal rabbit antibodies against Egr-1 and c-fos were purchased from
PrPC stimulation induces CREB phosphorylation in 1C11 precursor cells and their neuronal progenies
Antibody-mediated ligation of PrPC, as a means to mimic its interaction with an extracellular ligand, triggers intracellular signaling events [5], [28], [31]. In the 1C11 cell line and other cell systems, PrP antibodies lead to the activation of ERK1/2, two MAP kinases that broadly mediate survival, mitogenic or differentiation signals. Here, we sought to build upon our previous findings and search for transcription factors downstream from the PrPC–ERK coupling. We chose to probe a recruitment
Discussion
Over the past few years, a wealth of data from several laboratories, including ours, have exemplified an involvement of PrPC in cell signaling. Despite the diverse array of strategies and cellular models employed in the different studies, most point to several common intracellular targets. At a proximal level, Src kinases have repeatedly been associated to PrPC-mediated signals. We indeed initially depicted a neurospecific recruitment of the Fyn kinase upon PrPC crosslinking in 1C115-HT and 1C11
Acknowledgements
We are grateful to Dr. J. Grassi for the kind gift of the Sha31 anti-PrP antibody. We thank Sylvette Reposo for technical assistance. This work was supported by grants from the Groupement d'Intérêt Scientifique “Infections à Prions”, the ANR and the Centre National de la Recherche Scientifique.
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2017, Biochemical and Biophysical Research CommunicationsCitation Excerpt :Another protein is caveolin, the principal component of non-clatrin coated membrane invaginations and a recognized regulator of signal transduction [88]. After crosslinking of PrPC with antibodies to mimic natural ligands, the essential requirement for caveolin in PrPC-dependent activation of non-receptor Tyr kinases (see below) was firstly demonstrated in the 1C11 cell line [89] and subsequently confirmed in other model cells [90–92]. Among intracellular proteins implicated in bridging PrPC to downstream signaling, members of Src family kinases (SFK) have been frequently advocated following the notion that SFK non-receptor Tyr-kinases are highly expressed in the central nervous system (CNS) [93], and that the acyl-mediated insertion to the plasma membrane [94] position them to PSD [41,95], and/or close to raft-containing PrPC.
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2017, Progress in Molecular Biology and Translational ScienceCitation Excerpt :A second member of the cadherin family, namely, N-cadherin, may also be influenced by PrPC, in terms of trafficking to the neuronal cell surface196 or distribution in the developing neuroepithelium.133 Finally, PrPC may impact on the composition of the ECM itself, as described in astrocytes83 or neuronal progenitor cells,65 or on its remodeling, for instance by controlling the activity of the metalloprotease MMP9.197 Another context where we may suspect PrPC to act on the ECM composition is in dental tissue in view of the defects in dentin structure reported in Prnp-knockout mice.198
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2014, BiochimieCitation Excerpt :Noteworthy, like Fyn, the activation of Lyn driven by PrPC is transduced via caveolin [27], further supporting a central role for caveolin in PrPC-dependent signalling. Other reported intracellular effectors of PrPC signalling include the phosphoinositide 3 kinase (PI3K) [27,46], Akt [27,47], protein kinase A (PKA) [48–50], the reactive oxygen species (ROS) generating enzyme NADPH oxidase [51], the MAP kinases ERK1/2 [49–52], the glycogen synthase kinase GSK3β [27], the TNFα-converting enzyme (TACE) metalloprotease [53], the mammalian target of rapamycin mTOR [47], as well as several transcription factors: CREB, Egr-1 and c-fos [54]. Links with sphingolipid [55] and calcium signalling [56–59] have also been depicted.
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