The serine/threonine kinase Ndr2 controls integrin trafficking and integrin-dependent neurite growth

The NDR family of kinases: essential regulators of aging

Aging is defined as a progressive decline of cognitive and physiological functions over lifetime. Since the definition of the nine hallmarks of aging in 2013 by López-Otin, numerous studies have attempted to identify the main regulators and contributors in the aging process. One interesting group of proteins whose participation has been implicated in several aging hallmarks are the nuclear DBF2-related (NDR) family of serine-threonine AGC kinases. They are one of the core components of the Hippo signaling pathway and include NDR1, NDR2, LATS1 and LATS2 in mammals, along with its highly conserved metazoan orthologs; Trc in Drosophila melanogaster, SAX-1 in Caenorhabditis elegans, CBK1, DBF20 in Saccharomyces cerevisiae and orb6 in Saccharomyces pombe. These kinases have been independently linked to the regulation of widely diverse cellular processes disrupted during aging such as the cell cycle progression, transcription, intercellular communication, nutrient homeostasis, autophagy, apoptosis, and stem cell differentiation. However, a comprehensive overview of the state-of-the-art knowledge regarding the post-translational modifications of and by NDR kinases in aging has not been conducted. In this review, we summarize the current understanding of the NDR family of kinases, focusing on their relevance to various aging hallmarks, and emphasize the growing body of evidence that suggests NDR kinases are essential regulators of aging across species.

De novo variants in FRYL are associated with developmental delay, intellectual disability, and dysmorphic features

FRY-like transcription coactivator (FRYL) belongs to a Furry protein family that is evolutionarily conserved from yeast to humans. The functions of FRYL in mammals are largely unknown, and variants in FRYL have not previously been associated with a Mendelian disease. Here, we report fourteen individuals with heterozygous variants in FRYL who present with developmental delay, intellectual disability, dysmorphic features, and other congenital anomalies in multiple systems. The variants are confirmed de novo in all individuals except one. Human genetic data suggest that FRYL is intolerant to loss of function (LoF). We find that the fly FRYL ortholog, furry (fry), is expressed in multiple tissues, including the central nervous system where it is present in neurons but not in glia. Homozygous fry LoF mutation is lethal at various developmental stages, and loss of fry in mutant clones causes defects in wings and compound eyes. We next modeled four out of the five missense variants found in affected individuals using fry knockin alleles. One variant behaves as a severe LoF variant, whereas two others behave as partial LoF variants. One variant does not cause any observable defect in flies, and the corresponding human variant is not confirmed to be de novo, suggesting that this is a variant of uncertain significance. In summary, our findings support that fry is required for proper development in flies and that the LoF variants in FRYL cause a dominant disorder with developmental and neurological symptoms due to haploinsufficiency.

A cryptic microdeletion del(12)(p11.21p11.23) within an unbalanced translocation t(7;12)(q21.13;q23.1) implicates new candidate loci for intellectual disability and Kallmann syndrome

In a patient diagnosed with both Kallmann syndrome (KS) and intellectual disability (ID), who carried an apparently balanced translocation t(7;12)(q22;q24)dn, array comparative genomic hybridization (aCGH) disclosed a cryptic heterozygous 4.7 Mb deletion del(12)(p11.21p11.23), unrelated to the translocation breakpoint. This novel discovery prompted us to consider the possibility that the combination of KS and neurological disorder in this patient could be attributed to gene(s) within this specific deletion at 12p11.21-12p11.23, rather than disrupted or dysregulated genes at the translocation breakpoints. To further support this hypothesis, we expanded our study by screening five candidate genes at both breakpoints of the chromosomal translocation in a cohort of 48 KS patients. However, no mutations were found, thus reinforcing our supposition. In order to delve deeper into the characterization of the 12p11.21-12p11.23 region, we enlisted six additional patients with small copy number variations (CNVs) and analyzed eight individuals carrying small CNVs in this region from the DECIPHER database. Our investigation utilized a combination of complementary approaches. Firstly, we conducted a comprehensive phenotypic-genotypic comparison of reported CNV cases. Additionally, we reviewed knockout animal models that exhibit phenotypic similarities to human conditions. Moreover, we analyzed reported variants in candidate genes and explored their association with corresponding phenotypes. Lastly, we examined the interacting genes associated with these phenotypes to gain further insights. As a result, we identified a dozen candidate genes: TSPAN11 as a potential KS candidate gene, TM7SF3, STK38L, ARNTL2, ERGIC2, TMTC1, DENND5B, and ETFBKMT as candidate genes for the neurodevelopmental disorder, and INTS13, REP15, PPFIBP1, and FAR2 as candidate genes for KS with ID. Notably, the high-level expression pattern of these genes in relevant human tissues further supported their candidacy. Based on our findings, we propose that dosage alterations of these candidate genes may contribute to sexual and/or cognitive impairments observed in patients with KS and/or ID. However, the confirmation of their causal roles necessitates further identification of point mutations in these candidate genes through next-generation sequencing.

TOR complex 1 negatively regulates NDR kinase Cbk1 to control cell separation in budding yeast

The target of rapamycin (TOR) signalling pathway plays a key role in the coordination between cellular growth and the cell cycle machinery in eukaryotes. The underlying molecular mechanisms by which TOR might regulate events after anaphase remain unknown. We show for the first time that one of the 2 TOR complexes in budding yeast, TORC1, blocks the separation of cells following cytokinesis by phosphorylation of a member of the NDR (nuclear Dbf2-related) protein-kinase family, the protein Cbk1. We observe that TORC1 alters the phosphorylation pattern of Cbk1 and we identify a residue within Cbk1 activation loop, T574, for which a phosphomimetic substitution makes Cbk1 catalytically inactive and, indeed, reproduces TORC1 control over cell separation. In addition, we identify the exocyst component Sec3 as a key substrate of Cbk1, since Sec3 activates the SNARE complex to promote membrane fusion. TORC1 activity ultimately compromises the interaction between Sec3 and a t-SNARE component. Our data indicate that TORC1 negatively regulates cell separation in budding yeast by participating in Cbk1 phosphorylation, which in turn controls the fusion of secretory vesicles transporting hydrolase at the site of division.

The NDR/LATS protein kinases in neurobiology: Key regulators of cell proliferation, differentiation and migration in the ocular and central nervous system

Nuclear Dbf2-related (NDR) kinases are a subgroup of evolutionarily conserved AGC protein kinases that regulate various aspects of cell growth and morphogenesis. There are 4 NDR protein kinases in mammals, LATS1, LATS2 and STTK8/NDR1, STK38L/NDR2 protein kinases. LATS1 and 2 are core components of the well-studied Hippo pathway, which play a critical role in the regulation of cell proliferation, differentiation, and cell migration via YAP/TAZ transcription factor. The Hippo pathways play an important role in nervous tissue development and homeostasis, especially with regard to the central nervous system (CNS) and the ocular system. The ocular system is a very complex system generated by the interaction in a very tightly coordinated manner of numerous and diverse developing tissues, such as, but not limited to choroidal and retinal blood vessels, the retinal pigmented epithelium and the retina, a highly polarized neuronal tissue. The retina development and maintenance require precise and coordinated regulation of cell proliferation, cell death, migration, morphogenesis, synaptic connectivity, and balanced homeostasis. This review highlights the emerging roles of NDR1 and NDR2 kinases in the regulation of retinal/neuronal function and homeostasis via a noncanonical branch of the Hippo pathway. We highlight a potential role of NDR1 and NDR2 kinases in regulating neuronal inflammation and as potential therapeutic targets for the treatment of neuronal diseases.

A microdeletion del(12)(p11.21p11.23) with a cryptic unbalanced translocation t(7;12)(q21.13;q23.1) implicates new candidate loci for intellectual disability and Kallmann syndrome

In an apparently balanced translocation t(7;12)(q22;q24)dn exhibiting both Kallmann syndrome (KS) and intellectual disability (ID), we detected a cryptic heterozygous 4.7 Mb del(12)(p11.21p11.23) unrelated to the translocation breakpoint. This new finding raised the possibility that KS combined with neurological disorder in this patient could be caused by gene(s) within this deletion at 12p11.21-12p11.23 instead of disrupted or dysregulated genes at the genomic breakpoints. Screening of five candidate genes at both breakpoints in 48 KS patients we recruited found no mutation, corroborating our supposition. To substantiate this hypothesis further, we recruited six additional subjects with small CNVs and analyzed eight individuals carrying small CNVs in this region from DECIPHER to dissect 12p11.21-12p11.23. We used multiple complementary approaches including a phenotypic-genotypic comparison of reported cases, a review of knockout animal models recapitulating the human phenotypes, and analyses of reported variants in the interacting genes with corresponding phenotypes. The results identified one potential KS candidate gene ( TSPAN11 ), seven candidate genes for the neurodevelopmental disorder ( TM7SF3 , STK38L , ARNTL2 , ERGIC2 , TMTC1 , DENND5B , and ETFBKMT ), and four candidate genes for KS with ID ( INTS13 , REP15 , PPFIBP1 , and FAR2 ). The high-level expression pattern in the relevant human tissues further suggested the candidacy of these genes. We propose that the dosage alterations of the candidate genes may contribute to sexual and/or cognitive impairment in patients with KS and/or ID. Further identification of point mutations through next generation sequencing will be necessary to confirm their causal roles.

Loss of NDR1/2 kinases impairs endomembrane trafficking and autophagy leading to neurodegeneration

Autophagy is essential for neuronal development and its deregulation contributes to neurodegenerative diseases. NDR1 and NDR2 are highly conserved kinases, implicated in neuronal development, mitochondrial health and autophagy, but how they affect mammalian brain development in vivo is not known. Using single and double Ndr1/2 knockout mouse models, we show that only dual loss of Ndr1/2 in neurons causes neurodegeneration. This phenotype was present when NDR kinases were deleted both during embryonic development, as well as in adult mice. Proteomic and phosphoproteomic comparisons between Ndr1/2 knockout and control brains revealed novel kinase substrates and indicated that endocytosis is significantly affected in the absence of NDR1/2. We validated the endocytic protein Raph1/Lpd1, as a novel NDR1/2 substrate, and showed that both NDR1/2 and Raph1 are critical for endocytosis and membrane recycling. In NDR1/2 knockout brains, we observed prominent accumulation of transferrin receptor, p62 and ubiquitinated proteins, indicative of a major impairment of protein homeostasis. Furthermore, the levels of LC3-positive autophagosomes were reduced in knockout neurons, implying that reduced autophagy efficiency mediates p62 accumulation and neurotoxicity. Mechanistically, pronounced mislocalisation of the transmembrane autophagy protein ATG9A at the neuronal periphery, impaired axonal ATG9A trafficking and increased ATG9A surface levels further confirm defects in membrane trafficking, and could underlie the impairment in autophagy. We provide novel insight into the roles of NDR1/2 kinases in maintaining neuronal health.

DNA methylation signatures of Alzheimer's disease neuropathology in the cortex are primarily driven by variation in non-neuronal cell-types

Alzheimer's disease (AD) is a chronic neurodegenerative disease characterized by the progressive accumulation of amyloid-beta and neurofibrillary tangles of tau in the neocortex. We profiled DNA methylation in two regions of the cortex from 631 donors, performing an epigenome-wide association study of multiple measures of AD neuropathology. We meta-analyzed our results with those from previous studies of DNA methylation in AD cortex (total n = 2013 donors), identifying 334 cortical differentially methylated positions (DMPs) associated with AD pathology including methylomic variation at loci not previously implicated in dementia. We subsequently profiled DNA methylation in NeuN+ (neuronal-enriched), SOX10+ (oligodendrocyte-enriched) and NeuN-/SOX10- (microglia- and astrocyte-enriched) nuclei, finding that the majority of DMPs identified in 'bulk' cortex tissue reflect DNA methylation differences occurring in non-neuronal cells. Our study highlights the power of utilizing multiple measures of neuropathology to identify epigenetic signatures of AD and the importance of characterizing disease-associated variation in purified cell-types.

Regulation of Dynamic Cell Adhesion by Integrin-Integrin Crosstalk

Most cells express several integrins. The integrins are able to respond to various cellular functions and needs by modifying their own activation state, but in addition by their ability to regulate each other by activation or inhibition. This crosstalk or transdominant regulation is strictly controlled. The mechanisms resulting in integrin crosstalk are incompletely understood, but they often involve intracellular signalling routes also used by other cell surface receptors. Several studies show that the integrin cytoplasmic tails bind to a number of cytoskeletal and adaptor molecules in a regulated manner. Recent work has shown that phosphorylations of integrins and key intracellular molecules are of pivotal importance in integrin-cytoplasmic interactions, and these in turn affect integrin activity and crosstalk. The integrin β-chains play a central role in regulating crosstalk. In addition to Integrin-integrin crosstalk, crosstalk may also occur between integrins and related receptors, including other adhesion receptors, growth factor and SARS-CoV-2 receptors.

Pathways of integrins in the endo-lysosomal system

In this review, we present recent scientific advances about integrin trafficking in the endo-lysosomal system. In the last few years, plenty of new information has emerged about the endo-lysosomal system, integrins, and the mechanism, how exactly the intracellular trafficking of integrins is regulated. We review the internalization and recycling pathways of integrins, and we provide information about the possible ways of lysosomal degradation through the endosomal and autophagic system. The regulation of integrin internalization and recycling proved to be a complex process worth studying. Trafficking of integrins, together with the regulation of their gene expression, defines cellular adhesion and cellular migration through bidirectional signalization and ligand binding. Thus, any malfunction in this system can potentially (but not necessarily) lead to tumorigenesis or metastasis. Hence, extensive examinations of integrins in the endo-lysosomal system raise the possibility to identify potential new medical targets. Furthermore, this knowledge can also serve as a basis for further determination of integrin signaling- and adhesion-related processes.

New insights into the phosphorylation of the threonine motif of the β1 integrin cytoplasmic domain

Integrins require an activation step before ligand binding and signaling that is mediated by talin and kindlin binding to the β integrin cytosolic domain (β-tail). Conflicting reports exist about the contribution of phosphorylation of a conserved threonine motif in the β1-tail (β1-pT788/pT789) to integrin activation. We show that widely used and commercially available antibodies against β1-pT788/pT789 integrin do not detect specific β1-pT788/pT789 integrin signals in immunoblots of several human and mouse cell lysates but bind bi-phosphorylated threonine residues in numerous proteins, which were identified by mass spectrometry experiments. Furthermore, we found that fibroblasts and epithelial cells expressing the phospho-mimicking β1-TT788/789DD integrin failed to activate β1 integrins and displayed reduced integrin ligand binding, adhesion initiation and cell spreading. These cellular defects are specifically caused by the inability of kindlin to bind β1-tail polypeptides carrying a phosphorylated threonine motif or phospho-mimicking TT788/789DD substitutions. Our findings indicate that the double-threonine motif in β1-class integrins is not a major phosphorylation site but if phosphorylated would curb integrin function.

Neuromechanobiology: An Expanding Field Driven by the Force of Greater Focus

The brain processes information by transmitting signals through highly connected and dynamic networks of neurons. Neurons use specific cellular structures, including axons, dendrites and synapses, and specific molecules, including cell adhesion molecules, ion channels and chemical receptors to form, maintain and communicate among cells in the networks. These cellular and molecular processes take place in environments rich of mechanical cues, thus offering ample opportunities for mechanical regulation of neural development and function. Recent studies have suggested the importance of mechanical cues and their potential regulatory roles in the development and maintenance of these neuronal structures. Also suggested are the importance of mechanical cues and their potential regulatory roles in the interaction and function of molecules mediating the interneuronal communications. In this review, the current understanding is integrated and promising future directions of neuromechanobiology are suggested at the cellular and molecular levels. Several neuronal processes where mechanics likely plays a role are examined and how forces affect ligand binding, conformational change, and signal induction of molecules key to these neuronal processes are indicated, especially at the synapse. The disease relevance of neuromechanobiology as well as therapies and engineering solutions to neurological disorders stemmed from this emergent field of study are also discussed.

Transgenic modeling of Ndr2 gene amplification reveals disturbance of hippocampus circuitry and function

Duplications and deletions of short chromosomal fragments are increasingly recognized as the cause for rare neurodevelopmental conditions and disorders. The NDR2 gene encodes a protein kinase important for neuronal development and is part of a microduplication region on chromosome 12 that is associated with intellectual disabilities, autism, and epilepsy. We developed a conditional transgenic mouse with increased Ndr2 expression in postmigratory forebrain neurons to study the consequences of an increased gene dosage of this Hippo pathway kinase on brain circuitry and cognitive functions. Our analysis reveals reduced terminal fields and synaptic transmission of hippocampal mossy fibers, altered hippocampal network activity, and deficits in mossy fiber-dependent behaviors. Reduced doublecortin expression and protein interactome analysis indicate that transgenic Ndr2 disturbs the maturation of granule cells in the dentate gyrus. Together, our data suggest that increased expression of Ndr2 may critically contribute to the development of intellectual disabilities upon gene amplification.

Reducing glutamic acid decarboxylase in the dorsal dentate gyrus attenuates juvenile stress induced emotional and cognitive deficits

A high degree of regional, temporal and molecular specificity is evident in the regulation of GABAergic signaling in stress-responsive circuitry, hampering the use of systemic GABAergic modulators for the treatment of stress-related psychopathology. Here we investigated the effectiveness of local intervention with the GABA synthetic enzymes GAD65 and GAD67 in the dorsal dentate gyrus (dDG) vs ventral DG (vDG) to alleviate anxiety-like behavior and stress-induced symptoms in the rat. We induced shRNA-mediated knock down of either GAD65 or GAD67 with lentiviral vectors microinjected into the dDG or vDG of young adult male rats and examined anxiety behavior, learning and memory performance. Subsequently we tested whether reducing GAD65 expression in the dDG would also confer resilience against juvenile stress-induced behavioral and physiological symptoms in adulthood. While knock down of either isoform in the vDG increased anxiety levels in the open field and the elevated plus maze tests, the knock down of GAD65, but not GAD67, in the dDG conferred a significant reduction in anxiety levels. Strikingly, this manipulation also attenuated juvenile stress evoked anxiety behavior, cognitive and synaptic plasticity impairments. Local GABAergic circuitry in the DG plays an important and highly region-specific role in control of emotional behavior and stress responding. Reduction of GAD65 expression in the dDG appears to provide resilience to juvenile stress-induced emotional and cognitive deficits, opening a new direction towards addressing a significant risk factor for developing stress and trauma-related psychopathologies later in life.

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GAD67/65 in the dorsal/ventral dentate gyrus differentially modulate anxiety.

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Reduced GAD65 expression in the dorsal dentate gyrus supports stress resilience.

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The dorsal dentate gyrus plays a key role in stress resilience.

Transparent Touch: Insights From Model Systems on Epidermal Control of Somatosensory Innervation

Somatosensory neurons (SSNs) densely innervate our largest organ, the skin, and shape our experience of the world, mediating responses to sensory stimuli including touch, pressure, and temperature. Historically, epidermal contributions to somatosensation, including roles in shaping innervation patterns and responses to sensory stimuli, have been understudied. However, recent work demonstrates that epidermal signals dictate patterns of SSN skin innervation through a variety of mechanisms including targeting afferents to the epidermis, providing instructive cues for branching morphogenesis, growth control and structural stability of neurites, and facilitating neurite-neurite interactions. Here, we focus onstudies conducted in worms (Caenorhabditis elegans), fruit flies (Drosophila melanogaster), and zebrafish (Danio rerio): prominent model systems in which anatomical and genetic analyses have defined fundamental principles by which epidermal cells govern SSN development.

Kinase Signaling in Dendritic Development and Disease

Dendrites undergo extensive growth and remodeling during their lifetime. Specification of neurites into dendrites is followed by their arborization, maturation, and functional integration into synaptic networks. Each of these distinct developmental processes is spatially and temporally controlled in an exquisite fashion. Protein kinases through their highly specific substrate phosphorylation regulate dendritic growth and plasticity. Perturbation of kinase function results in aberrant dendritic growth and synaptic function. Not surprisingly, kinase dysfunction is strongly associated with neurodevelopmental and psychiatric disorders. Herein, we review, (a) key kinase pathways that regulate dendrite structure, function and plasticity, (b) how aberrant kinase signaling contributes to dendritic dysfunction in neurological disorders and (c) emergent technologies that can be applied to dissect the role of protein kinases in dendritic structure and function.

PPM1F controls integrin activity via a conserved phospho-switch

Control of integrin activity is vital during development and tissue homeostasis, while derailment of integrin function contributes to pathophysiological processes. Phosphorylation of a conserved threonine motif (T788/T789) in the integrin β cytoplasmic domain increases integrin activity. Here, we report that T788/T789 functions as a phospho-switch, which determines the association with either talin and kindlin-2, the major integrin activators, or filaminA, an integrin activity suppressor. A genetic screen identifies the phosphatase PPM1F as the critical enzyme, which selectively and directly dephosphorylates the T788/T789 motif. PPM1F-deficient cell lines show constitutive integrin phosphorylation, exaggerated talin binding, increased integrin activity, and enhanced cell adhesion. These gain-of-function phenotypes are reverted by reexpression of active PPM1F, but not a phosphatase-dead mutant. Disruption of the ppm1f gene in mice results in early embryonic death at day E10.5. Together, PPM1F controls the T788/T789 phospho-switch in the integrin β1 cytoplasmic tail and constitutes a novel target to modulate integrin activity.

Fission Yeast NDR/LATS Kinase Orb6 Regulates Exocytosis via Phosphorylation of the Exocyst Complex

NDR/LATS kinases regulate multiple aspects of cell polarity and morphogenesis from yeast to mammals. Fission yeast NDR/LATS kinase Orb6 has been proposed to control cell polarity by regulating the Cdc42 guanine nucleotide exchange factor Gef1. Here, we show that Orb6 regulates polarity largely independently of Gef1 and that Orb6 positively regulates exocytosis. Through Orb6 inhibition in vivo and quantitative global phosphoproteomics, we identify Orb6 targets, including proteins involved in membrane trafficking. We confirm Sec3 and Sec5, conserved components of the exocyst complex, as substrates of Orb6 both in vivo and in vitro, and we show that Orb6 kinase activity is important for exocyst localization to cell tips and for exocyst activity during septum dissolution after cytokinesis. We further find that Orb6 phosphorylation of Sec3 contributes to exocyst function in concert with exocyst protein Exo70. We propose that Orb6 contributes to polarized growth by regulating membrane trafficking at multiple levels.

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Inhibiting Orb6 leads to cessation of cell elongation and impaired exocytosis

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These and related phenotypes are independent of the Cdc42 GEF Gef1

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Phosphoproteomics reveals multiple Orb6 targets involved in membrane trafficking

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Exocyst protein Sec3 is an important Orb6 substrate for daughter-cell separation

Hypothalamic transcriptome of tame and aggressive silver foxes (Vulpes vulpes) identifies gene expression differences shared across brain regions

The underlying neurological events accompanying dog domestication remain elusive. To reconstruct the domestication process in an experimental setting, silver foxes (Vulpes vulpes) have been deliberately bred for tame vs aggressive behaviors for more than 50 generations at the Institute for Cytology and Genetics in Novosibirsk, Russia. The hypothalamus is an essential part of the hypothalamic-pituitary-adrenal axis and regulates the fight-or-flight response, and thus, we hypothesized that selective breeding for tameness/aggressiveness has shaped the hypothalamic transcriptomic profile. RNA-seq analysis identified 70 differentially expressed genes (DEGs). Seven of these genes, DKKL1, FBLN7, NPL, PRIMPOL, PTGRN, SHCBP1L and SKIV2L, showed the same direction expression differences in the hypothalamus, basal forebrain and prefrontal cortex. The genes differentially expressed across the three tissues are involved in cell division, differentiation, adhesion and carbohydrate processing, suggesting an association of these processes with selective breeding. Additionally, 159 transcripts from the hypothalamus demonstrated differences in the abundance of alternative spliced forms between the tame and aggressive foxes. Weighted gene coexpression network analyses also suggested that gene modules in hypothalamus were significantly associated with tame vs aggressive behavior. Pathways associated with these modules include signal transduction, interleukin signaling, cytokine-cytokine receptor interaction and peptide ligand-binding receptors (eg, G-protein coupled receptor [GPCR] ligand binding). Current studies show the selection for tameness vs aggressiveness in foxes is associated with unique hypothalamic gene profiles partly shared with other brain regions and highlight DEGs involved in biological processes such as development, differentiation and immunological responses. The role of these processes in fox and dog domestication remains to be determined.

SIRT1 and p300/CBP regulate the reversible acetylation of serine-threonine kinase NDR2

Nuclear Dbf2-related kinase 2 (NDR2) is a highly conserved kinase that belongs to the NDR/LATS serine-threonine kinase family. NDR2 is involved in many cellular processes as a kinase or a scaffolding protein. As a known kinase, NDR2 requires self-phosphorylation and trans-phosphorylation to become fully active. However, beside phosphorylation, little is known about other posttranslational modifications of NDR2. In this study, we found that NDR2 can be specially acetylated at K463 in cells. In addition, SIRT1 acts as the major deacetylase for NDR2, while p300 and CBP function as specific acetyltransferases for NDR2. Interestingly, in SIRT1 deficient cells HDAC6 and HDAC1/2 can deacetylate NDR2, which provides a novel insight in deacetylation regulation. Our results demonstrate that NDR2 is a reversible acetylated kinase regulated by SIRT1 and p300/CBP.

Pb exposure reduces the expression of SNX6 and Homer1 in offspring rats and PC12 cells

Lead (Pb) is a widespread environmental heavy metal toxicant and chronic Pb exposure can have irreversible effects on memory and cognitive function, which is closely related to dendritic spines. Studies have shown that SNX6 and Homer1 can regulate the growth of dendritic spines. We aimed to investigate the effect of Pb exposure on the dendritic spines in hippocampus, the expression of SNX6 and Homer1 in rats and PC12 cells. The animals were randomly divided to three groups: control group, low lead group and high lead group. PC12 cells were divided into 3 groups: 0 μM, 1 μM and 100 μM Pb acetate. The results showed that the Pb levels in blood and hippocampus of all exposure groups were significantly higher than that of the control group. The morphology of dendritic spines in hippocampus after Pb treatment was changed and the density of dendritic spines was reduced. The expression of SNX6 and Homer1 was decreased in Pb exposed groups compared with the control group. Furthermore, up-regulation of SNX6 expression could reverse the down-regulation of Pb exposure on Homer1. These results indicate that Pb exposure can reduce the expression of SNX6 and lead to a decrease in Homer1 expression, which affects the changes in dendritic spines causing learning and memory impairment.

Integrin trafficking in cells and tissues

Cell adhesion to the extracellular matrix is fundamental to metazoan multicellularity and is accomplished primarily through the integrin family of cell-surface receptors. Integrins are internalized and enter the endocytic-exocytic pathway before being recycled back to the plasma membrane. The trafficking of this extensive protein family is regulated in multiple context-dependent ways to modulate integrin function in the cell. Here, we discuss recent advances in understanding the mechanisms and cellular roles of integrin endocytic trafficking.

NDR2 promotes the antiviral immune response via facilitating TRIM25-mediated RIG-I activation in macrophages

Retinoic acid-inducible gene I (RIG-I), a pivotal cytosolic sensor, recognizes viral RNAs to initiate antiviral innate immunity. However, posttranslational regulation of RIG-I signaling is not well understood. We report here that nuclear Dbf2-related kinase 2 (NDR2) functions as a crucial positive regulator of the RIG-I-mediated antiviral immune response. Overexpression of NDR2 or its kinase-inactive mutants potentiates RNA virus-induced production of type I interferons and proinflammatory cytokines and dampens viral replication. NDR2 conditional knockout mice (Lysm+NDR2f/f) show an impaired antiviral immune response. Mechanistically, NDR2 directly associates with RIG-I and TRIM25, thus facilitating the RIG-I/TRIM25 complex and enhancing the TRIM25-mediated K63-linked polyubiquitination of RIG-I, which is required for the RIG-I-mediated antiviral immune response. Furthermore, NDR2 expression is notably down-regulated in peripheral blood from respiratory syncytial virus-infected patients and in virus-infected macrophages. Collectively, these findings provide insights into the function of NDR2 in antiviral immunity and its related clinical significance.

Filamin A Phosphorylation at Serine 2152 by the Serine/Threonine Kinase Ndr2 Controls TCR-Induced LFA-1 Activation in T Cells

The integrin LFA-1 (CD11a/CD18) plays a critical role in the interaction of T cells with antigen presenting cells (APCs) to promote lymphocyte differentiation and proliferation. This integrin can be present either in a closed or in an open active conformation and its activation upon T-cell receptor (TCR) stimulation is a critical step to allow interaction with APCs. In this study we demonstrate that the serine/threonine kinase Ndr2 is critically involved in the initiation of TCR-mediated LFA-1 activation (open conformation) in T cells. Ndr2 itself becomes activated upon TCR stimulation and phosphorylates the intracellular integrin binding partner Filamin A (FLNa) at serine 2152. This phosphorylation promotes the dissociation of FLNa from LFA-1, allowing for a subsequent association of Talin and Kindlin-3 which both stabilize the open conformation of LFA-1. Our data suggest that Ndr2 activation is a crucial step to initiate TCR-mediated LFA-1 activation in T cells.

Ndr kinases regulate retinal interneuron proliferation and homeostasis

Ndr2/Stk38l encodes a protein kinase associated with the Hippo tumor suppressor pathway and is mutated in a naturally-occurring canine early retinal degeneration (erd). To elucidate the retinal functions of Ndr2 and its paralog Ndr1/Stk38, we generated Ndr1 and Ndr2 single knockout mice. Although retinal lamination appeared normal in these mice, Ndr deletion caused a subset of Pax6-positive amacrine cells to proliferate in differentiated retinas, while concurrently decreasing the number of GABAergic, HuD and Pax6-positive amacrine cells. Retinal transcriptome analyses revealed that Ndr2 deletion increased expression of neuronal stress genes and decreased expression of synaptic organization genes. Consistent with the latter, Ndr deletion dramatically reduced levels of Aak1, an Ndr substrate that regulates vesicle trafficking. Our findings indicate that Ndr kinases are important regulators of amacrine and photoreceptor cells and suggest that Ndr kinases inhibit the proliferation of a subset of terminally differentiated cells and modulate interneuron synapse function via Aak1.

JAK2-V617F promotes venous thrombosis through β1/β2 integrin activation

JAK2-V617F-positive chronic myeloproliferative neoplasia (CMN) commonly displays dysfunction of integrins and adhesion molecules expressed on platelets, erythrocytes, and leukocytes. However, the mechanism by which the 2 major leukocyte integrin chains, β1 and β2, may contribute to CMN pathophysiology remained unclear. β1 (α4β1; VLA-4) and β2 (αLβ2; LFA-1) integrins are essential regulators for attachment of leukocytes to endothelial cells. We here showed enhanced adhesion of granulocytes from mice with JAK2-V617F knockin (JAK2+/VF mice) to vascular cell adhesion molecule 1- (VCAM1-) and intercellular adhesion molecule 1-coated (ICAM1-coated) surfaces. Soluble VCAM1 and ICAM1 ligand binding assays revealed increased affinity of β1 and β2 integrins for their respective ligands. For β1 integrins, this correlated with a structural change from the low- to the high-affinity conformation induced by JAK2-V617F. JAK2-V617F triggered constitutive activation of the integrin inside-out signaling molecule Rap1, resulting in translocation toward the cell membrane. Employing a venous thrombosis model, we demonstrated that neutralizing anti-VLA-4 and anti-β2 integrin antibodies suppress pathologic thrombosis as observed in JAK2+/VF mice. In addition, aberrant homing of JAK2+/VF leukocytes to the spleen was inhibited by neutralizing anti-β2 antibodies and by pharmacologic inhibition of Rap1. Thus, our findings identified cross-talk between JAK2-V617F and integrin activation promoting pathologic thrombosis and abnormal trafficking of leukocytes to the spleen.

Ablation of the presynaptic organizer Bassoon in excitatory neurons retards dentate gyrus maturation and enhances learning performance

Bassoon is a large scaffolding protein of the presynaptic active zone involved in the development of presynaptic terminals and in the regulation of neurotransmitter release at both excitatory and inhibitory brain synapses. Mice with constitutive ablation of the Bassoon (Bsn) gene display impaired presynaptic function, show sensory deficits and develop severe seizures. To specifically study the role of Bassoon at excitatory forebrain synapses and its relevance for control of behavior, we generated conditional knockout (Bsn cKO) mice by gene ablation through an Emx1 promoter-driven Cre recombinase. In these animals, we confirm selective loss of Bassoon from glutamatergic neurons of the forebrain. Behavioral assessment revealed that, in comparison to wild-type littermates, Bsn cKO mice display selectively enhanced contextual fear memory and increased novelty preference in a spatial discrimination/pattern separation task. These changes are accompanied by an augmentation of baseline synaptic transmission at medial perforant path to dentate gyrus (DG) synapses, as indicated by increased ratios of field excitatory postsynaptic potential slope to fiber volley amplitude. At the structural level, an increased complexity of apical dendrites of DG granule cells can be detected in Bsn cKO mice. In addition, alterations in the expression of cellular maturation markers and a lack of age-dependent decrease in excitability between juvenile and adult Bsn cKO mice are observed. Our data suggest that expression of Bassoon in excitatory forebrain neurons is required for the normal maturation of the DG and important for spatial and contextual memory.

Ndr2 Kinase Controls Neurite Outgrowth and Dendritic Branching Through α1 Integrin Expression

The serine/threonine kinase Ndr2 has been shown to control the inside-out activation of the β₁subunit of integrins and the formation of neurites in both primary neurons and neurally differentiated pheochromacytoma (PC12) cells. In this study, we demonstrate that Ndr2 kinase furthermore determines the substrate specificity of neurite extension in PC12 cells via expression of α₁β₁ integrins. We show that stable overexpression of Ndr2 in PC12 cells increases neurite growth and extension on poly-D-lysine substrate, likely involving an increased expression of active β₁ integrin in the growth tips of these cells. By contrast, the Ndr2 overexpressing cells do not show the α₁β₁ integrin-mediated enhancement of neurite growth on collagen IV substrate that can be seen in control cells. Moreover, they entirely fail to increase in response to activation of α₁β₁ integrins via a soluble KTS ligand and show a diminished accumulation of α₁ integrin in neurite tips, although the expression of this subunit is induced during differentiation to comparable levels as in control cells. Finally, we demonstrate that Ndr2 overexpression similarly inhibits the α₁β₁ integrin-dependent dendritic growth of primary hippocampal neurons on laminin 111 substrate. By contrast, lack of Ndr2 impairs the dendritic growth regardless of the substrate. Together, these results suggest that Ndr2 regulates α₁ integrin trafficking in addition to β₁ integrin subunit activation and thereby controls the neurite growth on different extracellular matrix (ECM) substrates.

NDR1-Dependent Regulation of Kindlin-3 Controls High-Affinity LFA-1 Binding and Immune Synapse Organization

Antigen-specific adhesion between T cells and antigen-presenting cells (APC) during the formation of the immunological synapse (IS) is mediated by LFA-1 and ICAM-1. Here, LFA-1–ICAM-1 interactions were measured at the single-molecule level on supported lipid bilayers. High-affinity binding was detected at low frequencies in the inner peripheral supramolecular activation cluster (SMAC) zone that contained high levels of activated Rap1 and kindlin-3. Rap1 was essential for T cell attachment, whereas deficiencies of ste20-like kinases, Mst1/Mst2, diminished high-affinity binding and abrogated central SMAC (cSMAC) formation with mislocalized kindlin-3 and vesicle transport regulators involved in T cell receptor recycling/releasing machineries, resulting in impaired T cell-APC interactions. We found that NDR1 kinase, activated by the Rap1 signaling cascade through RAPL and Mst1/Mst2, associated with and recruited kindlin-3 to the IS, which was required for high-affinity LFA-1/ICAM-1 binding and cSMAC formation. Our findings reveal crucial roles for Rap1 signaling via NDR1 for recruitment of kindlin-3 and IS organization.

Integrin Activation Through the Hematopoietic Adapter Molecule ADAP Regulates Dendritic Development of Hippocampal Neurons

Integrin-mediated cell adhesion and signaling is of critical importance for neuronal differentiation. Recent evidence suggests that an “inside-out” activation of β1-integrin, similar to that observed in hematopoietic cells, contributes to the growth and branching of dendrites. In this study, we investigated the role of the hematopoietic adaptor protein adhesion and degranulation promoting adapter protein (ADAP) in these processes. We demonstrate the expression of ADAP in the developing and adult nervous hippocampus, and in outgrowing dendrites of primary hippocampal neurons. We further show that ADAP occurs in a complex with another adaptor protein signal-transducing kinase-associated phosphoprotein-homolog (SKAP-HOM), with the Rap1 effector protein RAPL and the Hippo kinase macrophage-stimulating 1 (MST1), resembling an ADAP/SKAP module that has been previously described in T-cells and is critically involved in “inside-out” activation of integrins. Knock down of ADAP resulted in reduced expression of activated β1-integrin on dendrites. It furthermore reduced the differentiation of developing neurons, as indicated by reduced dendrite growth and decreased expression of the dendritic marker microtubule-associated protein 2 (MAP2). Our data suggest that an ADAP-dependent integrin-activation similar to that described in hematopoietic cells contributes to the differentiation of neuronal cells.

The Roles of NDR Protein Kinases in Hippo Signalling

The Hippo tumour suppressor pathway has emerged as a critical regulator of tissue growth through controlling cellular processes such as cell proliferation, death, differentiation and stemness. Traditionally, the core cassette of the Hippo pathway includes the MST1/2 protein kinases, the LATS1/2 protein kinases, and the MOB1 scaffold signal transducer, which together regulate the transcriptional co-activator functions of the proto-oncoproteins YAP and TAZ through LATS1/2-mediated phosphorylation of YAP/TAZ. Recent research has identified additional kinases, such as NDR1/2 (also known as STK38/STK38L) and MAP4Ks, which should be considered as novel members of the Hippo core cassette. While these efforts helped to expand our understanding of Hippo core signalling, they also began to provide insights into the complexity and redundancy of the Hippo signalling network. Here, we focus on summarising our current knowledge of the regulation and functions of mammalian NDR kinases, discussing parallels between the NDR pathways in Drosophila and mammals. Initially, we provide a general overview of the cellular functions of NDR kinases in cell cycle progression, centrosome biology, apoptosis, autophagy, DNA damage signalling, immunology and neurobiology. Finally, we put particular emphasis on discussing NDR1/2 as YAP kinases downstream of MST1/2 and MOB1 signalling in Hippo signalling.

Epidermis-Derived Semaphorin Promotes Dendrite Self-Avoidance by Regulating Dendrite-Substrate Adhesion in Drosophila Sensory Neurons

Precise patterning of dendritic arbors is critical for the wiring and function of neural circuits. Dendrite-extracellular matrix (ECM) adhesion ensures that the dendrites of Drosophila dendritic arborization (da) sensory neurons are properly restricted in a 2D space, and thereby facilitates contact-mediated dendritic self-avoidance and tiling. However, the mechanisms regulating dendrite-ECM adhesion in vivo are poorly understood. Here, we show that mutations in the semaphorin ligand sema-2b lead to a dramatic increase in self-crossing of dendrites due to defects in dendrite-ECM adhesion, resulting in a failure to confine dendrites to a 2D plane. Furthermore, we find that Sema-2b is secreted from the epidermis and signals through the Plexin B receptor in neighboring neurons. Importantly, we find that Sema-2b/PlexB genetically and physically interacts with TORC2 complex, Tricornered (Trc) kinase, and integrins. These results reveal a novel role for semaphorins in dendrite patterning and illustrate how epidermal-derived cues regulate neural circuit assembly.

Chronic Lead Exposure and Mixed Factors of Gender×Age×Brain Regions Interactions on Dendrite Growth, Spine Maturity and NDR Kinase

NDR1/2 kinase is essential in dendrite morphology and spine formation, which is regulated by cellular Ca²⁺. Lead (Pb) is a potent blocker of L-type calcium channel and our recent work showed Pb exposure impairs dendritic spine outgrowth in hippocampal neurons in rats. But the sensitivity of Pb-induced spine maturity with mixed factors (gender×age×brain regions) remains unknown. This study aimed to systematically investigate the effect of Pb exposure on spine maturity in rat brain with three factors (gender×age×brain regions), as well as the NDR1/2 kinase expression. Sprague–Dawley rats were exposed to Pb from parturition to postnatal day 30, 60, 90, respectively. Golgi-Cox staining was used to examine spine maturity. Western blot assay was applied to measure protein expression and real-time fluorescence quantitative PCR assay was used to examine mRNA levels. The results showed chronic Pb exposure significantly decreased dendritic length and impaired spine maturity in both rat hippocampus and medial prefrontal cortex. The impairment of dendritic length induced by Pb exposure tended to adolescence > adulthood, hippocampus > medial prefrontal cortex and female > male. Pb exposure induced significant damage in spine maturity during adolescence and early adult while little damage during adult in male rat brain and female medial prefrontal cortex. Besides, there was sustained impairment from adolescence to adulthood in female hippocampus. Interestingly, impairment of spine maturity followed by Pb exposure was correlated with NDR1/2 kinase. The reduction of NDR1/2 kinase protein expression after Pb exposure was similar to the result of spine maturity. In addition, NDR2 and their substrate Rabin3 mRNA levels were significantly decreased by Pb exposure in developmental rat brain. Taken together, Pb exposure impaired dendrite growth and maturity which was subject to gender×age×brain regions effects and related to NDR1/2 signal expression.

NDR Kinases Are Essential for Somitogenesis and Cardiac Looping during Mouse Embryonic Development

Studies of mammalian tissue culture cells indicate that the conserved and distinct NDR isoforms, NDR1 and NDR2, play essential cell biological roles. However, mice lacking either Ndr1 or Ndr2 alone develop normally. Here, we studied the physiological consequences of inactivating both NDR1 and NDR2 in mice, showing that the lack of both Ndr1/Ndr2 (called Ndr1/2-double null mutants) causes embryonic lethality. In support of compensatory roles for NDR1 and NDR2, total protein and activating phosphorylation levels of the remaining NDR isoform were elevated in mice lacking either Ndr1 or Ndr2. Mice retaining one single wild-type Ndr allele were viable and fertile. Ndr1/2-double null embryos displayed multiple phenotypes causing a developmental delay from embryonic day E8.5 onwards. While NDR kinases are not required for notochord formation, the somites of Ndr1/2-double null embryos were smaller, irregularly shaped and unevenly spaced along the anterior-posterior axis. Genes implicated in somitogenesis were down-regulated and the normally symmetric expression of Lunatic fringe, a component of the Notch pathway, showed a left-right bias in the last forming somite in 50% of all Ndr1/2-double null embryos. In addition, Ndr1/2-double null embryos developed a heart defect that manifests itself as pericardial edemas, obstructed heart tubes and arrest of cardiac looping. The resulting cardiac insufficiency is the likely cause of the lethality of Ndr1/2-double null embryos around E10. Taken together, we show that NDR kinases compensate for each other in vivo in mouse embryos, explaining why mice deficient for either Ndr1 or Ndr2 are viable. Ndr1/2-double null embryos show defects in somitogenesis and cardiac looping, which reveals their essential functions and shows that the NDR kinases are critically required during the early phase of organogenesis.

Molecular Mechanoneurobiology: An Emerging Angle to Explore Neural Synaptic Functions

Neural synapses are intercellular asymmetrical junctions that transmit biochemical and biophysical information between a neuron and a target cell. They are very tight, dynamic, and well organized by many synaptic adhesion molecules, signaling receptors, ion channels, and their associated cytoskeleton that bear forces. Mechanical forces have been an emerging factor in regulating axon guidance and growth, synapse formation and plasticity in physiological and pathological brain activity. Therefore, mechanical forces are undoubtedly exerted on those synaptic molecules and modulate their functions. Here we review current progress on how mechanical forces regulate receptor-ligand interactions, protein conformations, ion channels activation, and cytoskeleton dynamics and discuss how these regulations potentially affect synapse formation, stabilization, and plasticity.

P-selectin-mediated platelet adhesion promotes tumor growth

Blood platelets foster carcinogenesis. We found that platelets are accumulated in human tumors. P-selectin deficiency and soluble P-selectin abolish platelet deposition within tumors, decreasing secretion of vascular endothelial growth factor and angiogenesis, thereby suppressing tumor growth. Binding of the P-selectin cytoplasmic tail to talin1 triggers the talin1 N-terminal head to interact with the β3 cytoplasmic tail. This activates αIIbβ3 and recruits platelets into tumors. Platelet infiltration into solid tumors occurs through a P-selectin-dependent mechanism.

ECM receptors in neuronal structure, synaptic plasticity, and behavior

During central nervous system development, extracellular matrix (ECM) receptors and their ligands play key roles as guidance molecules, informing neurons where and when to send axonal and dendritic projections, establish connections, and form synapses between pre- and postsynaptic cells. Once stable synapses are formed, many ECM receptors transition in function to control the maintenance of stable connections between neurons and regulate synaptic plasticity. These receptors bind to and are activated by ECM ligands. In turn, ECM receptor activation modulates downstream signaling cascades that control cytoskeletal dynamics and synaptic activity to regulate neuronal structure and function and thereby impact animal behavior. The activities of cell adhesion receptors that mediate interactions between pre- and postsynaptic partners are also strongly influenced by ECM composition. This chapter highlights a number of ECM receptors, their roles in the control of synapse structure and function, and the impact of these receptors on synaptic plasticity and animal behavior.