Alzheimer's Disease-Related Loss of Pin1 Function Influences the Intracellular Localization and the Processing of A beta PP
ABSTRACT Increased amyloidogenic processing of the amyloid-β protein precursor (AβPP) is a characteristic of Alzheimer's disease (AD). We previously observed that the prolyl isomerase Pin1, which is down-regulated in AD, regulates AβPP conformation accelerating cis/trans isomerization of the phospho-Thr668-Pro669 peptide bond, and that Pin1 knockout in mice increases the amyloidogenic processing of AβPP, although the underlying mechanism is still unknown. Since the intracellular localization of AβPP determines whether the processing will be amyloidogenic or non-amyloidogenic, here we addressed the question whether loss of Pin1 function affects the intracellular localization of AβPP, influencing AβPP processing. Using cellular models of Pin1 knockout and Pin1 knockdown, we have demonstrated that lowering Pin1 levels changed the intracellular localization and the processing of AβPP. Under these conditions, less AβPP was retained at the plasma membrane favoring the amyloidogenic processing, and the kinetics of AβPP internalization increased as well as the nuclear trafficking of AβPP C-terminal fragment AICD. In addition, AβPPThr668Ala mutant, which cannot bind to Pin1 and retains more trans conformation, rescued the levels of AβPP at the plasma membrane in Pin1 knockout cells. Thus, loss of Pin1 function contributes to amyloidogenic pathways, by facilitating both the removal of AβPP from compartments where it is mostly non-amyloidogenic and its internalization to more amyloidogenic compartments. These data suggest that physiological levels of Pin1 are important to control the intracellular localization and metabolic fate of Thr668-phosphorylated AβPP, and regulation of AβPP conformation is especially important in pathologic conditions of AβPP hyperphosphorylation and/or loss of Pin1 function, associated with AD.
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ABSTRACT: The Wnt/β-catenin pathway promotes proliferation of neural progenitor cells (NPCs) at early stages and induces neuronal differentiation from NPCs at late stages, but the molecular mechanisms that control this stage-specific response are unclear. Pin1 is a prolyl isomerase that regulates cell signaling uniquely by controlling protein conformation after phosphorylation, but its role in neuronal differentiation is not known. Here we found that whereas Pin1 depletion suppresses neuronal differentiation, Pin1 overexpression enhances it, without any effects on gliogenesis from NPCs in vitro. Consequently, Pin1-null mice have significantly fewer upper layer neurons in the motor cortex and severely impaired motor activity during the neonatal stage. A proteomic approach identified β-catenin as a major substrate for Pin1 in NPCs, in which Pin1 stabilizes β-catenin. As a result, Pin1 knockout leads to reduced β-catenin during differentiation but not proliferation of NPCs in developing brains. Importantly, defective neuronal differentiation in Pin1 knockout NPCs is fully rescued in vitro by overexpression of β-catenin but not a β-catenin mutant that fails to act as a Pin1 substrate. These results show that Pin1 is a novel regulator of NPC differentiation by acting on β-catenin and provides a new postphosphorylation signaling mechanism to regulate developmental stage-specific functioning of β-catenin signaling in neuronal differentiation.Molecular and Cellular Biology 05/2012; 32(15):2966-78. DOI:10.1128/MCB.05688-11 · 5.04 Impact Factor
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ABSTRACT: Peptidyl prolyl cis-trans isomerization acts as an effective molecular timer that plays significant roles in biological and pathological processes. Enzymes such as Pin1 catalyze cis-trans isomerization, accelerating the otherwise slow isomerization rate into time scales relevant for cellular signaling. Here we have combined NMR line shape analysis, fluorescence spectroscopy, and isothermal titration calorimetry to determine the kinetic and thermodynamic parameters describing the trans-specific interaction between the binding domain of Pin1 (WW domain) and a key cis-trans molecular switch in the amyloid precursor protein cytoplasmic tail. A three-state model, in which the cis-trans isomerization equilibrium is coupled to the binding equilibrium through the trans isomer, was found to fit the data well. The trans isomer binds the WW domain with ∼22 μM affinity via very fast association (approaching the diffusion limit) and dissociation rates. The common structural and electrostatic characteristics of Pin1 substrates, which contain a phosphorylated serine/threonine-proline motif, suggest that very rapid binding kinetics are a general feature of Pin1 interactions with other substrates. The fast binding kinetics of the WW domain allows rapid response of Pin1 to the dynamic events of phosphorylation and dephosphorylation in the cell that alter the relative populations of diverse Pin1 substrates. Furthermore, our results also highlight the vastly different rates at which slow uncatalyzed cis-trans isomerization and fast isomer-specific binding events occur. These results, along with the experimental methods presented herein, should guide future experiments aimed at the thermodynamic and kinetic characterization of cis-trans molecular switches and isomer-specific interactions involved in various biological processes.Biochemistry 10/2012; 51(43). DOI:10.1021/bi3008214 · 3.19 Impact Factor
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ABSTRACT: The enzyme peptidyl-prolyl cis-trans isomerase (Pin1) may play an important role in preventing the development of Alzheimer's disease (AD). The structural and functional stability of Pin1 is extremely important. Previously, we have determined the stability of Pin1 under stressed conditions, such as thermal treatment and acidic-pH. Considering that aluminum (Al(III)) is well known for its potential neurotoxicity in the pathogenesis of AD, we examined whether Al(III) affects the structure and function of Pin1, by means of a PPIase activity assay, intrinsic fluorescence, circular dichroism (CD) spectroscopy, FTIR, and differential scanning calorimetry (DSC). The intrinsic tryptophan fluorescence measurements mainly show that Al(III) may bind to the clusters nearby W11 and W34 in the WW domain of Pin1, quenching the intrinsic fluorescence of the two tryptophan residues, which possibly results in the decreased binding affinity of Pin1 to substrates. The secondary structural analysis as revealed by FTIR and CD measurements indicate that Al(III) induces the increase in β-sheet and the decrease in α-helix in Pin1. Furthermore, the changes of the thermodynamic parameters for Pin1 as monitored by DSC confirm that the thermal stability of Pin1 significantly increases in the presence of Al(III). The Al(III)-induced structural changes of Pin1 result in a sharp decrease of the PPIase activity of Pin1. To some extent, our research is suggestive that Al(III) may inhibit the isomerization activity of Pin1 in vivo, which may contribute to the pathogenesis of AD.Journal of inorganic biochemistry 06/2013; 126C:111-117. DOI:10.1016/j.jinorgbio.2013.05.017 · 3.27 Impact Factor