PDZ Motif Research Articles

LPS-induced systemic inflammation is suppressed by the PDZ motif peptide of ZO-1 via regulation of macrophage M1/M2 polarization.

The gram-negative bacterium lipopolysaccharide (LPS) is frequently administered to generate models of systemic inflammation. However, there are several side effects and no effective treatment for LPS-induced systemic inflammation. PEGylated PDZ peptide based on zonula occludens-1 (ZO-1) was analyzed for its effects on systemic inflammation induced by LPS. PDZ peptide administration led to the restoration of tissue injuries (kidney, liver, and lung) and prevented alterations in biochemical plasma markers. The production of pro-inflammatory cytokines was significantly decreased in the plasma and lung BALF in the PDZ-administered mice. Flow cytometry analysis revealed the PDZ peptide significantly inhibited inflammation, mainly by decreasing the population of M1 macrophages, and neutrophils (immature and mature), and increasing M2 macrophages. Using RNA sequencing analysis, the expression levels of the NF-κB-related proteins were lower in PDZ-treated cells than in LPS-treated cells. In addition, wild-type PDZ peptide significantly increased mitochondrial membrane integrity and decreased LPS-induced mitochondria fission. Interestingly, PDZ peptide dramatically could reduce LPS-induced NF-κB signaling, ROS production, and the expression of M1 macrophage marker proteins, but increased the expression of M2 macrophage marker proteins. These results indicated that PEGylated PDZ peptide inhibits LPS-induced systemic inflammation, reducing tissue injuries and reestablishing homeostasis, and may be a therapeutic candidate against systemic inflammation.

LPS-induced systemic inflammation is suppressed by the PDZ motif peptide of ZO-1 via regulation of macrophage M1/M2 polarization

The gram-negative bacterium lipopolysaccharide (LPS) is frequently administered to generate models of systemic inflammation. However, there are several side effects and no effective treatment for LPS-induced systemic inflammation. PEGylated PDZ peptide based on zonula occludens-1 (ZO-1) was analyzed for its effects on systemic inflammation induced by LPS. PDZ peptide administration led to the restoration of tissue injuries (kidney, liver, and lung) and prevented alterations in biochemical plasma markers. The production of pro-inflammatory cytokines was significantly decreased in the plasma and lung BALF in the PDZ-administered mice. Flow cytometry analysis revealed the PDZ peptide significantly inhibited inflammation, mainly by decreasing the population of M1 macrophages, and neutrophils (immature and mature), and increasing M2 macrophages. Using RNA sequencing analysis, the expression levels of the NF-κB-related proteins were lower in PDZ-treated cells than in LPS-treated cells. In addition, wild-type PDZ peptide significantly increased mitochondrial membrane integrity and decreased LPS-induced mitochondria fission. Interestingly, PDZ peptide dramatically could reduce LPS-induced NF-κB signaling, ROS production, and the expression of M1 macrophage marker proteins, but increased the expression of M2 macrophage marker proteins. These results indicated that PEGylated PDZ peptide inhibits LPS-induced systemic inflammation, reducing tissue injuries and reestablishing homeostasis, and may be a therapeutic candidate against systemic inflammation.

Identification of Vasopressin-Regulated Aquaporin-2 Traffcking Mechanism with Proximity-Labeling Proteomics

Vasopressin controls collecting duct water permeability in part by regulating traffcking of aquaporin-2 to and from the apical plasma membrane in the principal cells. Evidence have shown that aquaporin-2 resides in Rab11-positive recycling endosomes where its PDZ motif is phosphorylated at serine 269, leading to apical aquaporin-2 localization in response to vasopressin. Here, we employed Rab11-conjugated biotin ligase (TurboID) to biotinylate kinases and traffcking machineries recruited to Rab11-positive endosomes in the mpkCCD cells in response to vasopressin vs. vehicle. The biotin-labeled proteins were purified with streptavidin-affnity chromatography and identified with protein mass spectrometry. A total of 2,948 proteins were quantified in three independent repeats of which 119 proteins showed increases in the Rab11-positive endosomes in response to vasopressin while 104 proteins showed decreases. GO term analysis of the 119 increased proteins showed enriched biological processes including transport, protein transport, and vesicle-mediated transport. Microtubule affnity regulating kinase 2 stood out from our Bayes theorem probability analysis as a candidate kinase for aquaporin-2 serine 269 phosphorylation. Purified microtubule affnity regulating kinase 2 phosphorylated a synthetic aquaporin-2 peptide at serine 269 in vitro. Among the 119 proteins is the PDZ-domain containing Rho GTPase-activating protein 21 involved in F-actin dynamics. Switching between GTP- and GDP-bound state, Rho GTPase-activating protein 21 promotes F-actin polymerization and depolymerization, respectively. Our preliminary observations are indicative of a hypothetical model where vasopressin recruits microtubule affnity regulating kinase 2 to the Rab11-positive endosomes where it phosphorylates aquaporin-2 PDZ motif at serine 269. The phosphorylated PDZ motif recruits and activates Rho GTPase-activating protein 21, resulting in the GDP-bound state that promotes F-actin depolymerization. The depolymerized F-actin would facilitate fusion of the aquaporin-2 vesicles with the apical plasma membrane. National Science and Technology Council, TAIWAN, MOST 111-2320-B-002-084-MY3. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

G protein-coupled estrogen receptor (GPER)/GPR30 forms a complex with the β1-adrenergic receptor, a membrane-associated guanylate kinase (MAGUK) scaffold protein, and protein kinase A anchoring protein (AKAP) 5 in MCF7 breast cancer cells

G protein-coupled receptor 30 (GPR30), also named G protein-coupled estrogen receptor (GPER), and the β1-adrenergic receptor (β1AR) are G protein-coupled receptors (GPCR) that are implicated in breast cancer progression. Both receptors contain PSD-95/Discs-large/ZO-1 homology (PDZ) motifs in their C-terminal tails through which they interact in the plasma membrane with membrane-associated guanylate kinase (MAGUK) scaffold proteins, and in turn protein kinase A anchoring protein (AKAP) 5. GPR30 constitutively and PDZ-dependently inhibits β1AR-mediated cAMP production. We hypothesized that this inhibition is a consequence of a plasma membrane complex of these receptors. Using co-immunoprecipitation, confocal immunofluorescence microscopy, and bioluminescence resonance energy transfer (BRET), we show that GPR30 and β1AR reside in close proximity in a plasma membrane complex when transiently expressed in HEK293. Deleting the GPR30 C-terminal PDZ motif (-SSAV) does not interfere with the receptor complex, indicating that the complex is not PDZ-dependent. MCF7 breast cancer cells express GPR30, β1AR, MAGUKs, and AKAP5 in the plasma membrane, and co-immunoprecipitation revealed that these proteins exist in close proximity also under native conditions. Furthermore, expression of GPR30 in MCF7 cells constitutively and PDZ-dependently inhibits β1AR-mediated cAMP production. AKAP5 also inhibits β1AR-mediated cAMP production, which is not additive with GPR30-promoted inhibition. These results argue that GPR30 and β1AR form a PDZ-independent complex in MCF7 cells through which GPR30 constitutively and PDZ-dependently inhibits β1AR signaling via receptor interaction with MAGUKs and AKAP5.

THU393 An Internal NPT2A Cryptic PDZ Motif Is A Novel Regulator of PTH- And FGF23-sensitive Phosphate Transport

Abstract Disclosure: B.W. Sneddon: None. P.A. Friedman: None. T. Mamonova: None. The Na+-dependent NPT2A (SLC34A1) phosphate co-transporter is a major regulator of phosphate homeostasis. Its most notable structural element is a carboxy-terminal PDZ ligand that binds Na+/H+ Exchanger Regulatory Factor-1 (NHERF1, SLC9A3R1), a multidomain PDZ protein that determines apical NPT2A localization and is required for phosphate transport. NPT2A also possesses an uncharacterized internal PDZ ligand. Two recent clinical reports describe congenital hypophosphatemia in children harboring Arg495His or Arg495Cys variants within the internal PDZ motif. Wild-type internal 494TRL496 PDZ binds NHERF1 PDZ2, which we consider a regulatory domain. Ablating the internal PDZ ligand with a 494AAA496 variant blocked hormone-sensitive phosphate transport. Complementary approaches, including CRISPR/Cas9 technology, side-directed mutagenesis, confocal microscopy, and modeling, showed that NPT2A Arg495 His or Arg495Cys variants do not support PTH or FGF23 action on phosphate transport. CoIP experiments indicate that both variants bound NHERF1 similarly to WT NPT2A. However, in contrast to WT NPT2A, NPT2A Arg495His or Arg495Cys variants remain at the apical membrane and are not internalized in response to PTH. We predict that His or Cys substitution of the charged Arg495 changes the electrostatics, preventing phosphorylation of the upstream Thr494, interfering with phosphate uptake in response to hormone action, and inhibiting NPT2A trafficking. We advance a model where the carboxy-terminal PDZ ligand defines apical localization of NPT2A, while the internal PDZ ligand is essential for hormone-triggered phosphate transport. Presentation: Thursday, June 15, 2023

Mutations in an unrecognized internal NPT2A PDZ motif disrupt phosphate transport and cause congenital hypophosphatemia.

The Na+-dependent phosphate cotransporter-2A (NPT2A, SLC34A1) is a primary regulator of extracellular phosphate homeostasis. Its most prominent structural element is a carboxy-terminal PDZ ligand that binds Na+/H+ Exchanger Regulatory Factor-1 (NHERF1, SLC9A3R1). NHERF1, a multidomain PDZ protein, establishes NPT2A membrane localization and is required for hormone-inhibitable phosphate transport. NPT2A also possesses an uncharacterized internal PDZ ligand. Two recent clinical reports describe congenital hypophosphatemia in children harboring Arg495His or Arg495Cys variants within the internal PDZ motif. The wild-type internal 494TRL496 PDZ ligand binds NHERF1 PDZ2, which we consider a regulatory domain. Ablating the internal PDZ ligand with a 494AAA496 substitution blocked hormone-inhibitable phosphate transport. Complementary approaches, including CRISPR/Cas9 technology, site-directed mutagenesis, confocal microscopy, and modeling, showed that NPT2A Arg495His or Arg495Cys variants do not support PTH or FGF23 action on phosphate transport. Coimmunoprecipitation experiments indicate that both variants bind NHERF1 similarly to WT NPT2A. However, in contrast with WT NPT2A, NPT2A Arg495His, or Arg495Cys variants remain at the apical membrane and are not internalized in response to PTH. We predict that Cys or His substitution of the charged Arg495 changes the electrostatics, preventing phosphorylation of the upstream Thr494, interfering with phosphate uptake in response to hormone action, and inhibiting NPT2A trafficking. We advance a model wherein the carboxy-terminal PDZ ligand defines apical localization NPT2A, while the internal PDZ ligand is essential for hormone-triggered phosphate transport.

PDZ interaction of the GABA transporter GAT1 with the syntenin-1 in Neuro-2a cells

The GABA transporter GAT1 regulates brain inhibitory neurotransmission and it is considered a potential therapeutic target for the treatment of wide spectrum of neurological diseases including epilepsy, stroke and autism. Syntenin-1 binds to syntaxin 1A, which is known to regulate the plasma membrane insertion of several neurotransmitter transporters. Previously, a direct interaction of syntenin-1 with the glycine transporter GlyT2 was reported. Here, we show that the GABA transporter GAT1 also directly interacts with syntenin-1, involving both unidentified protein interaction interface and the GAT1 C-terminal PDZ binding motif interacting mainly with syntenin-1 PDZ domain 1. The PDZ interaction was eliminated by the mutation of GAT1 isoleucine 599 and tyrosine 598 located in PDZ positions 0 and -1, respectively. This indicates an unconventional PDZ interaction and possible regulation of the transporter PDZ motif via tyrosine phosphorylation. Whole syntenin-1 protein fused to GST protein and immobilised on glutathione resin coprecipitated intact GAT1 transporter from an extract of GAT1 transfected neuroblastoma N2a cells. This coprecipitation was inhibited by tyrosine phosphatases inhibitor pervanadate. The fluorescence tagged GAT1 and syntenin-1 colocalized upon coexpression in N2a cells. The above results show that syntenin-1 might be, in addition to GlyT2, directly involved in the trafficking of GAT1 transporter.

A Significant Difference in Core PDZ Interactivity of SARS-CoV, SARS-CoV2 and MERS-CoV Protein E Peptide PDZ Motifs In Vitro.

Small structural E protein of coronaviruses uses its C-terminal PDZ motif to compromise the cellular PDZ interactome. In this work we compared core PDZ interactivity of small (seven amino acids) peptide PDZ motifs, originating from the envelope proteins of recently transmitted coronaviruses SARS-CoV, SARS-CoV2, and MERS-CoV. As the interaction targets we used 23 domains of the largest PDZ proteins MUPP1/MPDZ and PATJ/INAD. Results revealed exceptional affinity and interaction promiscuity of MERS-CoV PDZ motif in vitro, suggesting an increased probability of potential PDZ targets in vivo. We hypothesize that together with its known ability to enter the cells from both apical and basolateral sites, this might further contribute to its elevated disruption of cellular PDZ pathways and higher virulence.

Dynamic Changes in ABCC4 Protein‐Protein Interactions during PKA Signaling: Role of the ABCC4 PDZ Motif

We recently demonstrated that a protein interaction between the PDZ motif of ABCC4 and a single PDZ‐domain‐containing protein, MPP1 had an important role in ABCC4 function in acute myeloid leukemia (Pitre et al. Nature Comm. 2017). To gain a better understanding into the role of the highly conserved ABCC4 PDZ‐motif, we performed live cell imaging using total internal reflectance fluorescence, TIRF, of ABCC4‐GFP expression constructs with or without the PDZ motif. The expression constructs were introduced into HEK293 cells where ABCC4 had been deleted by CRISPR‐Cas9 technology. ABCC4‐GFP was static at the membrane showing little movement, while deletion of the PDZ motif promoted rapid movement. Activation of PKA with forskolin and the phosphodiesterase inhibitor, iso‐butyl‐methyl xanthine increased intracellular cAMP and promoted membrane movement of ABCC4 harboring the PDZ motif. To get an unbiased understanding of the proteins interacting with ABCC4 both in cis‐ and trans‐, and under PKA activation conditions, we developed stable cell lines in the ABCC4‐null HEK293 cells. These stable cell lines harbored either an APEX2‐ABCC4 or an APEX2‐ABCC4 lacking a PDZ motif. APEX2‐derived ascorbate oxidase and biotin phenol, coupled with Avidin‐beads was used to interrogate the neighborhood of proteins within ~10 nm of ABCC4. We also developed stable cells harboring expression constructs for either Avi‐tagged ABCC4 or Avi‐ABCC4 without the PDZ motif to determine proteins that directly interacted with ABCC4 through the PDZ motif. Each Avi‐expression construct harbored a biotin ligase, thus enabling ABCC4 to be tagged by biotin and readily “pulled down” by avidin‐beads. The interacting proteins were identified by quantitative proteomics. Several PDZ specific interacting proteins were identified in these cell lines. By using analytical density gradient ultracentrifugation, we identified distinct PDZ specific ABCC4‐complexes that formed upon PKA activation. The actin‐binding cytoskeletal protein, Moesin (MSN) associated with ABCC4, requiring the PDZ‐motif. We used quantitative proteomics and APEX2 ABCC4 constructs to show that the neighborhood surrounding ABCC4 lacking the PDZ‐motif had fewer proteins, especially cytoskeletal proteins interacting with it. We propose that the ABCC4‐MSN interaction is important for tethering ABCC4 to the cytoskeletal actin network. Importantly, siRNA knockdown of MSN disrupted the association between ABCC4 and its interactors indicating the key role of MSN in the dynamic protein interactions occurring between ABCC4 and its interactors.

Cloning of a new form of EAAT2/GLT-1 from human and rodent brains

Glutamate transporter 1 is the principal transporter that mediates glutamate clearance in the mammalian brain. In rodents, it is referred to as GLT-1, whereas in humans it is referred to as EAAT2. We have cloned a novel and abundantly expressed carboxyl-terminal splice variant of this transporter in both rodents and humans, which we denote as GLT-1d/EAAT2d. The novel splice variant results from usage of internal splice sites and the splicing event leads to novel extra sequence spliced in after exon 10. The open reading frames of GLT-1d and EAAT2d encode proteins of 572 and 566 amino acids respectively; both contain a C-terminal PDZ motif. When expressed in COS7 cells, the proteins function as glutamate transporters that are inhibited by dihydrokainate (a GLT-1/EAAT2 transporter inhibitor). RT-PCR amplification using GLT-1d specific primers confirmed expression of message in all brain regions examined (forebrain, midbrain, hindbrain and cerebellum) as well as spinal cord, astrocyte cultures, retina and peripheral tissues (liver, testis, small intestine and lung). Quantitative RT-PCR analysis showed that expression of GLT-1d is developmentally regulated. In adult human brain, EAAT2d message is ∼ 30% of the level of EAAT2a message (the most abundant form), potentially making it the second most abundantly expressed form of EAAT2 in the brain. The amino terminal region of GLT-1d is also alternately spliced; the brain and testis forms contain a sequence corresponding to the amino acid sequence MASTEG whereas the corresponding liver sequence is MVS. In summary, we have cloned a novel EAAT2/GLT-1 splice variant from human and rodent brains. The splice variant is abundantly expressed in the brain, spinal cord, retina, liver and testis; it is a functional glutamate transporter; therefore, we conclude that it will likely have a functional role in glutamate homeostasis in the rodent and human nervous system, during development, adulthood, and plausibly in pathological states.

Comprehensive analysis of ALK, ROS1 and RET rearrangements in locally advanced rectal cancer

Gene rearrangements, such as anaplastic lymphoma kinase (ALK), c-ros oncogene 1 receptor tyrosine kinase (ROS1), rearranged during transfection (RET) and neurotrophic receptor tyrosine kinase 1 (NTRK1), identified in cancer have been indicated to be robust therapeutic targets in lung carcinomas. However, a few studies have focussed on locally advanced rectal cancer (LARC). The discovery of novel gene fusions is also valuable for LARC research. We used mass spectrometry-based assays and RNA sequencing to detect both known ALK, ROS1, RET and NTRK1 rearrangements and novel gene fusions in LARC patients. FusionMap was also used to find gene fusions. None of the ALK, ROS1, RET or NTRK1 gene fusions were detected by mass spectrometry-based assays or RNA sequencing. Three fusion candidates, integrin subunit beta 7 (ITGB7)-ROS1, lamin A/C (LMNA)-NTRK1 and Golgi-associated PDZ and coiled-coil motif containing (GOPC)-keratin 8 (KRT8), showed relatively high junction-spanning reads by the FusionMap algorithm, but did not pass validation. These results suggest that no ALK, ROS1 or RET rearrangements were found in LARC.

Down-regulation of diesel particulate matter-induced airway inflammation by the PDZ motif peptide of ZO-1.

Although diesel airborne particulate matter (PM2.5) has been known to play a role in many human diseases, there is no direct evidence that therapeutic drugs or proteins can diminish PM2.5‐induced diseases. Nevertheless, studies examining the negative control mechanisms of PM2.5‐induced diseases are critical to develop novel therapeutic medications. In this study, the consensus PDZ peptide of ZO‐1 inhibited PM2.5‐induced inflammatory cell infiltration, pro‐inflammatory cytokine gene expression, and TEER in bronchoalveolar lavage (BAL) fluid and AM cells. Our data indicated that the PDZ domain in ZO‐1 is critical for regulation of the PM2.5‐induced inflammatory microenvironment. Therefore, the PDZ peptide may be a potential therapeutic candidate during PM‐induced respiratory diseases.

A high‐affinity, bivalent PDZ domain inhibitor complexes PICK1 to alleviate neuropathic pain

Maladaptive plasticity involving increased expression of AMPA‐type glutamate receptors is involved in several pathologies, including neuropathic pain, but direct inhibition of AMPARs is associated with side effects. As an alternative, we developed a cell‐permeable, high‐affinity (~2 nM) peptide inhibitor, Tat‐P4‐(C5)2, of the PDZ domain protein PICK1 to interfere with increased AMPAR expression. The affinity is obtained partly from the Tat peptide and partly from the bivalency of the PDZ motif, engaging PDZ domains from two separate PICK1 dimers to form a tetrameric complex. Bivalent Tat‐P4‐(C5)2 disrupts PICK1 interaction with membrane proteins on supported cell membrane sheets and reduce the interaction of AMPARs with PICK1 and AMPA‐receptor surface expression in vivo. Moreover, Tat‐P4‐(C5)2 administration reduces spinal cord transmission and alleviates mechanical hyperalgesia in the spared nerve injury model of neuropathic pain. Taken together, our data reveal Tat‐P4‐(C5)2 as a novel promising lead for neuropathic pain treatment and expand the therapeutic potential of bivalent inhibitors to non‐tandem protein–protein interaction domains.

Comparison of SynCAM1/CADM1 PDZ interactions with MUPP1 using mammalian and bacterial pull-down systems.

BackgroundSynaptic cell adhesion molecule 1 (SynCAM1) also known as cell adhesion molecule 1 (CADM1) is a transmembrane cell adhesion protein that operates in a variety of physiological and pathological cellular contexts, and its interaction with the PDZ signalling protein MUPP1 have been previously implicated in autism spectrum disorder (ASD).MethodsWe used in vitro pull‐down systems based on the bacterial and mammalian extracts to study SynCAM1/CADM1 PDZ interactions with MUPP1 at various conditions.ResultsSo far, the investigated interaction of SynCAM1/CADM1 with MUPP1 has been mostly attributed to an unspecified region of MUPP1 PDZ domains 1–5 or exclusively to domain 2, using a yeast two‐hybrid system. We also confirmed the single interaction of native synaptosomal CADM1 with PDZ domain 2. However, in this work, using recombinant proteins overexpressed in bacteria, we found an in vitro pull‐down conditions in which all first five domains and, to a much lesser extent, MUPP1 domains 7 and 11 significantly interacted with the whole C‐terminal domain of SynCAM1/CADM1. These PDZ interactions were confirmed by a pull‐down assay using the last seven amino acids of the SynCAM1/CADM1 PDZ motif and using two fusion partners. Multiple interactions were additionally replicated using the continuous N‐terminal MUPP1 protein fragment, which included first five PDZ domains, containing either intact or mutated domain 2.ConclusionsWe hypothesize that multiple interactions might exist in vivo, representing transient low‐affinity interactions or alternative binding sites on MUPP1 when domain 2 is occupied or occluded by the interaction with other ligands. This newly identified interactions extend the potential genetic mutations, possibly affecting SynCAM1/CADM1/MUPP1 function. Possible reasons for the absence of some of the identified CADM1 PDZ interactions in mammalian extracts are discussed.

Hippo Signal Transduction Mechanisms in T Cell Immunity.

Hippo signaling pathways are evolutionarily conserved signal transduction mechanisms mainly involved in organ size control, tissue regeneration, and tumor suppression. However, in mammals, the primary role of Hippo signaling seems to be regulation of immunity. As such, humans with null mutations in STK4 (mammalian homologue of Drosophila Hippo; also known as MST1) suffer from recurrent infections and autoimmune symptoms. Although dysregulated T cell homeostasis and functions have been identified in MST1-deficient human patients and mouse models, detailed cellular and molecular bases of the immune dysfunction remain to be elucidated. Although the canonical Hippo signaling pathway involves transcriptional co-activator Yes-associated protein (YAP) or transcriptional coactivator with PDZ motif (TAZ), the major Hippo downstream signaling pathways in T cells are YAP/TAZ-independent and they widely differ between T cell subsets. Here we will review Hippo signaling mechanisms in T cell immunity and describe their implications for immune defects found in MST1-deficient patients and animals. Further, we propose that mutual inhibition of Mst and Akt kinases and their opposing roles on the stability and function of forkhead box O and β-catenin may explain various immune defects discovered in mutant mice lacking Hippo signaling components. Understanding these diverse Hippo signaling pathways and their interplay with other evolutionarily-conserved signaling components in T cells may uncover molecular targets relevant to vaccination, autoimmune diseases, and cancer immunotherapies.

Phosphomimetic Mutation of Glycine Transporter GlyT1 C-Terminal PDZ Binding Motif Inhibits its Interactions with PSD95.

Even though the abundance of GlyT1 in postsynaptic aspects of forebrain neurons is low, its previously reported interaction with postsynaptic density protein PSD95 represents a prototype of interaction, which might uncover the binding mechanism and regulation of the GlyT1 C-terminal PDZ motif. We used a phosphomimetic approach to mimic the potential phosphorylation of GlyT1 C-terminal serines 640, 643, 644, and 649 of the mouse GlyT1b subtype (mGlyT1b) (Uniprot P28571-2) and its effect on GlyT1-PSD95 PDZ interaction. Among them, only phosphomimetic mutation of serine 649 to aspartate, which resides in the minimal PDZ motif -SRI, significantly eliminated the interaction of the GlyT1 C-terminus with PSD95 PDZ domain 2. The effect was observed with recombinant fusion proteins as well as with GlyT1 and PSD95 expressed in tissue culture. Results indicate that phosphorylation of mouse GlyT1b serine 649 and equivalent serines of GlyT1a and GlyT1c subtypes might regulate the PDZ interaction of the GlyT1 C-terminal PDZ binding motif.

PTEN Activity Defines an Axis for Plasticity at Cortico-Amygdala Synapses and Influences Social Behavior.

Phosphatase and tensin homolog on chromosome 10 (PTEN) is a tumor suppressor and autism-associated gene that exerts an important influence over neuronal structure and function during development. In addition, it participates in synaptic plasticity processes in adulthood. As an attempt to assess synaptic and developmental mechanisms by which PTEN can modulate cognitive function, we studied the consequences of 2 different genetic manipulations in mice: presence of additional genomic copies of the Pten gene (Ptentg) and knock-in of a truncated Pten gene lacking its PDZ motif (Pten-ΔPDZ), which is required for interaction with synaptic proteins. Ptentg mice exhibit substantial microcephaly, structural hypoconnectivity, enhanced synaptic depression at cortico-amygdala synapses, reduced anxiety, and intensified social interactions. In contrast, Pten-ΔPDZ mice have a much more restricted phenotype, with normal synaptic connectivity, but impaired synaptic depression at cortico-amygdala synapses and virtually abolished social interactions. These results suggest that synaptic actions of PTEN in the amygdala contribute to specific behavioral traits, such as sociability. Also, PTEN appears to function as a bidirectional rheostat in the amygdala: reduction in PTEN activity at synapses is associated with less sociability, whereas enhanced PTEN activity accompanies hypersocial behavior.

Sodium-coupled monocarboxylate transporter 1 interacts with the RING finger- and PDZ domain-containing protein PDZRN3.

Sodium-coupled monocarboxylate transporter SMCT1 (SLC5A8) mediates monocarboxylate transport in the proximal tubule of the kidney. We have identified PDZK1 and PDZ domain-containing RING finger 3 (PDZRN3) as potent binding partners of SMCT1, which has a PDZ motif (Thr-Arg-Leu), by yeast two-hybrid screening and revealed that PDZK1 enhances the transport activity of SMCT1. In this study, we aimed to characterize the interaction between SMCT1 and PDZRN3 as well as to examine how PDZRN3 regulates SMCT1 function. An interaction between SMCT1 and PDZRN3 through the PDZ motif was observed in a co-immunoprecipitation assay and yeast two-hybrid assay. A transport assay showed that PDZRN3 abolished the enhancing effect of PDZK1 on nicotinate uptake via SMCT1. Our results suggest that SMCT1 interacts with PDZRN3 and that PDZRN3 may regulate SMCT1 function by interfering with the interaction between SMCT1 and PDZK1.

SAT-283 A Mutation In Ccdc53 Affects Pth1r Trafficking And Causes Disproportionate Short Stature With Noonan-like Facies

In many children with short stature, the genetic etiology remains unknown. Short stature due to defects in trafficking of membrane-associated proteins, such as receptors, has not been reported. A mother and two daughters presented with disproportionate short stature and Noonan-like facies. Exome sequencing, confirmed by Sanger sequencing, identified a de novo dominant mutation (L69F) in CCDC53. CCDC53 normally binds to WASH1 within a protein complex termed the WASH complex. To study the effect of the mutation on this interaction, CCDC53 was first ablated in HEK293 cells (CCDC53KO-HEK) by CRISPER-Cas9 and then wild-type (WT) or mutant (mut) CCDC53 or empty vector (EV) was expressed in these cells. The identified mutation impaired CCDC53 interaction with WASH1 as assessed by co-immunoprecipitation. CCDC53 and the WASH complex are involved in trafficking of cell-surface proteins that have undergone endocytosis, including G-coupled protein receptors that contain a PDZ motif, such as PTH1R. We therefore hypothesized that the mutation would affect PTH1R endocytic trafficking. CCDC53KO-HEK cells were transfected with vectors to express PTH1R and either EV, WT or mut CCDC53 and treated with PTH, after which endosomes were extracted and PTH1R was detected by western blot. Compared to WT, EV and mut CCDC53 showed decreased PTH1R localization in endosomes. In this system, the mutation also decreased generation of cAMP by extracellular PTH (P=0.001 vs WT), indicating that the mutation interferes with PTH1R signal transduction. PTH1R acts as the receptor for PTHrP and prevents premature hypertrophy of growth plate chondrocytes. We therefore hypothesized that the CCDC53 mutation would allow premature hypertrophy of growth plate chondrocytes. Primary rat epiphyseal chondrocytes were transfected with siRNA against Ccdc53 and with vectors to express either WT or mut Ccdc53. Compared to WT, mut Ccdc53 led to increased expression of hypertrophy-associated genes: Col10a1 (P=0.001), Ihh (P=0.031), and Mmp13 (P=0.003), consistent with the hypothesized effect on hypertrophic differentiation. In conclusion, a mutation in CCDC53 was identified in a family with disproportionate short stature and Noonan-like facies. The mutation interfered with the ability of CCDC53 to participate in the WASH complex, affecting endosomal localization of PTH1R, PTH1R signal transduction, and chondrocyte hypertrophy. Because the timing of growth plate chondrocyte hypertrophy is critical for linear growth, the findings provide a potential explanation for the short stature in this disorder. More generally, the findings also indicate that endocytic trafficking of PTH1R by the WASH complex plays an important role in the regulation of human linear growth.

Lipopolysaccharide from Escherichia coli stimulates osteogenic differentiation of human periodontal ligament stem cells through Wnt/β‐catenin–induced TAZ elevation

Human periodontal ligament stem cells (PDLSCs), a type of dental tissue-derived mesenchymal stem cells (MSCs), can be clinically applied in periodontal tissue regeneration to treat periodontitis, which is initiated and sustained by bacteria. Lipopolysaccharide (LPS), the major component of the outer membrane of gram-negative bacteria, is a pertinent deleterious factor in the oral microenvironment. The aim of this study was to investigate the effect of LPS on the proliferation and osteogenic differentiation of PDLSCs, as well as the mechanisms involved. Proliferation and osteogenic differentiation of PDLSCs were detected under the stimulation of Escherichia coli-derived LPS. The data showed that E. coli-derived LPS did not affect the proliferation, viability, and cell cycle of PDLSCs. Furthermore, it promoted osteogenic differentiation with the activation of TAZ. Lentivirus-mediated depletion of TAZ (transcriptional activator with a PDZ motif) was used to determine the role of TAZ on LPS-induced enhancement of osteogenesis. PDLSCs cultured in osteogenic media with or without LPS and DKK1 (Wnt/β-catenin pathway inhibitor) were used to determine the regulatory effect of Wnt signaling. We found that TAZ depletion offset LPS-induced enhancement of osteogenesis. Moreover, treatment with DKK1 offset LPS-induced TAZ elevation and osteogenic promotion. In conclusion, E. coli-derived LPS promoted osteogenic differentiation of PDLSCs by fortifying TAZ activity. The elevation and activation of TAZ were mostly mediated by the Wnt/β-catenin pathway. PDLSC-governed alveolar bone tissue regeneration was not necessarily reduced under bacterial conditions and could be modulated by Wnt and TAZ.