A null mutation in TNIK defines a novel locus for intellectual disability

Intellectual disability (ID) is one of the most common disabilities and, although many genes have been implicated in its etiology, the genetic heterogeneity of ID continues to expand. The purpose of the study was to describe a novel autosomal recessive non-syndromic ID locus. Autozygome and linkage analysis, and exome sequencing followed by RNA and protein analysis of the candidate disease gene were performed. We describe two multiplex consanguineous families with non-syndromic ID phenotype, which maps to a critical linkage locus on 3q26. Exome sequencing of the index in each family revealed the same homozygous truncating mutation in TNIK that results in complete loss of the protein. TNIK is a kinase with a well-established role in dendrite development and synaptic transmission. The phenotype we observe in human patients who lack TNIK is consistent with the previously published Tnik ^?/? phenotype in the murine model. Our data strongly implicate TNIK deficiency in the causation of ID in humans.     

Rce1: mechanism and inhibition

Ras converting enzyme 1 (Rce1) is an integral membrane endoprotease localized to the endoplasmic reticulum that mediates the cleavage of the carboxyl-terminal three amino acids from CaaX proteins, whose members play important roles in cell signaling processes. Examples include the Ras family of small GTPases, the γ-subunit of heterotrimeric GTPases, nuclear lamins, and protein kinases and phosphatases. CaaX proteins, especially Ras, have been implicated in cancer, and understanding the post-translational modifications of CaaX proteins would provide insight into their biological function and regulation. Many proteolytic mechanisms have been proposed for Rce1, but sequence alignment, mutational studies, topology, and recent crystallographic data point to a novel mechanism involving a glutamate-activated water and an oxyanion hole. Studies using in vivo and in vitro reporters of Rce1 activity have revealed that the enzyme cleaves only prenylated substrates and the identity of the a₂ amino residue in the Ca₁a₂X sequence is most critical for recognition, preferring Ile, Leu, or Val. Substrate mimetics can be somewhat effective inhibitors of Rce1 in vitro. Small-molecule inhibitor discovery is currently limited by the lack of structural information on a eukaryotic enzyme, but a set of 8-hydroxyquinoline derivatives has demonstrated an ability to mislocalize all three mammalian Ras isoforms, giving optimism that potent, selective inhibitors might be developed. Much remains to be discovered regarding cleavage specificity, the impact of chemical inhibition, and the potential of Rce1 as a therapeutic target, not only for cancer, but also for other diseases.     

Different susceptibility of prefrontal cortex and hippocampus to oxidative stress following chronic social isolation stress

Chronic oxidative stress plays an important role in depression. The aim of present study was to examine the stress-induced changes in serum corticosterone (CORT) levels, cytosolic protein carbonyl groups, malondialdehyde (MDA), reduced glutathione (GSH), nitric oxide (NO) and total superoxide dismutase (SOD) activity in the prefrontal cortex versus hippocampus of male Wistar rats exposed to acute (2 h of immobilization or cold), chronic (21d of social isolation) stress, and their combination (chronic + acute stress). The subcellular distribution of nuclear factor-κB (NF-κB) and cytosolic cyclooxygenase 2 (COX-2) protein expressions were also examined. Depressive- and anxiety-like behaviors were assessed via the forced swim, sucrose preference, and marble burying tests in chronically isolated rats. Although both acute stressors resulted in elevated CORT, increased MDA in the prefrontal cortex and NF-κB activation accompanied by increased NO in the hippocampus were detected only following acute cold stress. Chronic isolation resulted in no change in CORT levels, but disabled appropriate response to novel acute stress and led to depressive- and anxiety-like behaviors. Increased oxidative/nitrosative stress markers, likely by NF-κB nuclear translocation and concomitant COX-2 upregulation, associated with decreased SOD activity and GSH levels, suggested the existence of oxidative stress in the prefrontal cortex. In contrast, hippocampus was less susceptible to oxidative damage showing only increase in protein carbonyl groups and depleted GSH. Taken together, the prefrontal cortex seems to be more sensitive to oxidative stress than the hippocampus following chronic isolation stress, which may be relevant for further research related to stress-induced depressive-like behavior.     

Rho GTPase signaling at the synapse: Implications for intellectual disability

Intellectual disability (ID) imposes a major medical and social–economical problem in our society. It is defined as a global reduction in cognitive and intellectual abilities, associated with impaired social adaptation. The causes of ID are extremely heterogeneous and include non-genetic and genetic changes. Great progress has been made over recent years towards the identification of ID-related genes, resulting in a list of approximately 450 genes. A prominent neuropathological feature of patients with ID is altered dendritic spine morphogenesis. These structural abnormalities, in part, reflect impaired cytoskeleton remodeling and are associated with synaptic dysfunction. The dynamic, actin-rich nature of dendritic spines points to the Rho GTPase family as a central contributor, since they are key regulators of actin dynamics and organization. It is therefore not surprising that mutations in genes encoding regulators and effectors of the Rho GTPases have been associated with ID. This review will focus on the role of Rho GTPase signaling in synaptic structure/function and ID.     

Cancer risk in individuals with intellectual disability in Sweden: A population-based cohort study

BackgroundA knowledge gap exists about the risk of cancer in individuals with intellectual disability (ID). The primary aim of this study was to estimate the cancer risk among individuals with ID compared to individuals without ID.Methods and findingsWe conducted a population-based cohort study of all children live-born in Sweden between 1974 and 2013 and whose mothers were born in a Nordic country. All individuals were followed from birth until cancer diagnosis, emigration, death, or 31 December 2016 (up to age 43 years), whichever came first. Incident cancers were identified from the Swedish Cancer Register. We fitted Cox regression models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) as measures of cancer risk in relation to ID after adjusting for several potential confounders. We analyzed ID by severity, as well as idiopathic ID and syndromic ID separately. We performed a sibling comparison to investigate familial confounding. The study cohort included a total of 3,531,305 individuals, including 27,956 (0.8%) individuals diagnosed with ID. Compared with the reference group (individuals without ID and without a full sibling with ID), individuals with ID were in general more likely to be male. The median follow-up time was 8.9 and 23.0 years for individuals with ID and individuals without ID, respectively. A total of 188 cancer cases were identified among individuals with ID (incidence rate [IR], 62 per 1,000 person-years), and 24,960 among individuals in the reference group (IR, 31 per 1,000 person-years). A statistically significantly increased risk was observed for any cancer (HR 1.57, 95% CI 1.35–1.82; P < 0.001), as well as for several cancer types, including cancers of the esophagus (HR 28.4, 95% CI 6.2–130.6; P < 0.001), stomach (HR 6.1, 95% CI 1.5–24.9; P = 0.013), small intestine (HR 12.0, 95% CI 2.9–50.1; P < 0.001), colon (HR 2.0, 95% CI 1.0–4.1; P = 0.045), pancreas (HR 6.0, 95% CI 1.5–24.8; P = 0.013), uterus (HR 11.7, 95% CI 1.5–90.7; P = 0.019), kidney (HR 4.4, 95% CI 2.0–9.8; P < 0.001), central nervous system (HR 2.7, 95% CI 2.0–3.7; P < 0.001), and other or unspecified sites (HR 4.8, 95% CI 1.8–12.9; P = 0.002), as well as acute lymphoid leukemia (HR 2.4, 95% CI 1.3–4.4; P = 0.003) and acute myeloid leukemia (HR 3.0, 95% CI 1.4–6.4; P = 0.004). Cancer risk was not modified by ID severity or sex but was higher for syndromic ID. The sibling comparison showed little support for familial confounding. The main study limitations were the limited statistical power for the analyses of specific cancer types, and the potential for underestimation of the studied associations (e.g., due to potential underdetection or delayed diagnosis of cancer among individuals with ID).ConclusionsIn this study, we found that individuals with ID showed an increased risk of any cancer, as well as of several specific cancer types. These findings suggest that extended surveillance and early intervention for cancer among individuals with ID are warranted.

In a nationwide cohort study in Sweden, Qianwei Liu and co-workers report on cancer risk in people with intellectual disability.     

A cellular mechanism for prepulse inhibition

In prepulse inhibition (PPI), startle responses to sudden, unexpected stimuli are markedly attenuated if immediately preceded by a weak stimulus of almost any modality. This experimental paradigm exposes a potent inhibitory process, present in nervous systems from invertebrates to humans, that is widely considered to play an important role in reducing distraction during the processing of sensory input. The neural mechanisms mediating PPI are of considerable interest given evidence linking PPI deficits with some of the cognitive disorders of schizophrenia. Here, in the marine mollusk Tritonia diomedea, we describe a detailed cellular mechanism for PPI--a combination of presynaptic inhibition of startle afferent neurons together with distributed postsynaptic inhibition of several downstream interneuronal sites in the startle circuit.     

A kinetic inhibition mechanism for maintenance

To fulfil their maintenance costs, most species use mobile pools of metabolites (reserve) in favourable conditions, but can also use less mobile pools (structure) under food-limiting conditions. While some empirical models always pay maintenance costs from structure, the presence of reserve inhibits the use of structure for maintenance purposes. The standard dynamic energy budgets (DEB) model captures this by simply supplementing all costs that could not be paid from reserve with structure. This is less realistic at the biochemical level, and involves a sudden use of structure that can complicate the analysis of the model properties. We here propose a new inhibition formulation for the preferential use of reserve above structure in maintenance that avoids sudden changes in the metabolites use. It is based on the application of the theory for synthesizing units, which can easily become rather complex for demand processes, such as the maintenance. We found, however, a simple explicit expression for the use of reserve and structure for maintenance purposes and compared the numerical behaviour with that of a classical model in oscillating conditions, by using parameters values from a fit of the models to data on yeasts in a batch culture. We conclude that our model can better handle variable environments. This new inhibition formulation has a wide applicability in modelling metabolic processes.     

Activation, regulation, and inhibition of DYRK1A

Dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) is a protein kinase with diverse functions in neuronal development and adult brain physiology. Higher than normal levels of DYRK1A are associated with the pathology of neurodegenerative diseases and have been implicated in some neurobiological alterations of Down syndrome, such as mental retardation. It is therefore important to understand the molecular mechanisms that control the activity of DYRK1A. Here we review the current knowledge about the initial self-activation of DYRK1A by tyrosine autophosphorylation and propose that this mechanism presents an ancestral feature of the CMGC group of kinases. However, tyrosine phosphorylation does not appear to regulate the enzymatic activity of DYRK1A. Control of DYRK1A may take place on the level of gene expression, interaction with regulatory proteins and regulated nuclear translocation. Finally, we compare the properties of small molecule inhibitors that target DYRK1A and evaluate their potential application and limitations. The β-carboline alkaloid harmine is currently the most selective and potent inhibitor of DYRK1A and has proven very useful in cellular assays.     

Carboxypeptidase A: mechanism of zinc inhibition

Zinc ions competitively inhibit carboxypeptidase A from bovine pancreas. The state(s) of hydroxylation of zinc and their possible site(s) of interaction with the enzyme have been investigated by determining the strength of zinc inhibition over pH range 4.6-10.5. The inhibition kinetics were recorded under stopped-flow conditions using the alpha-Val isozyme and the peptide substrate Dns-Gly-Ala-Phe in 0.5 M NaCl at 25 degrees C. The pH dependence of pKI follows a pattern which indicates that the enzyme is selectively inhibited by zinc monohydroxide, ZnOH+ (KI = 7.1 X 10(-7) M). The formation of the inhibitory ZnOH+ complex from fully hydrated Zn2+ is characterized by an ionization constant of 9.05, and the consecutive conversion of ZnOH+ to Zn(OH)2, Zn(OH)3-, and Zn(OH)4(2-) complexes takes place with ionization constants of 9.75, 10.1, and 10.5, respectively. Ionization of a ligand, LH, in the enzyme's inhibitory site (pKLH 5.8) is obligatory for binding of the ZnOH+ complex. The enzymatic activity (kcat/Km) is influenced by three ionizable groups: pKEH2 5.78, pKEH 8.60, and pKE 10.2. Since the values of pKLH and pKEH2 are virtually identical, it is possible that the inhibitory ZnOH+ complex interacts with the group responsible for pKEH2. Previous studies have suggested that pKEH2 reflects the ionization of Glu-270 and its interaction with a water molecule coordinated to the catalytic zinc ion. It is proposed that the inhibitory zinc ion binds to the carboxylate of Glu-270 and that the inhibition process is specific for zinc monohydroxide because it allows the formation of a stabilizing hydroxide bridge between the inhibitory and catalytic zinc ions.     

Down regulation of DJ-1 enhances cell death by oxidative stress, ER stress, and proteasome inhibition

Mutations in DJ-1 gene have been linked to autosomal recessive early onset parkinsonism (AR-EOP). Although the mechanism of neuronal cell death due to DJ-1 mutation has not been fully elucidated, loss of DJ-1 function was considered to cause the phenotype. Here, we demonstrated that the down regulation of endogenous DJ-1 of the neuronal cell line by siRNA enhanced the cell death which was induced by oxidative stress, ER stress, and proteasome inhibition, but not by pro-apoptotic stimulus. The cell death with hydrogen peroxide was dramatically rescued by over-expression of wild-type DJ-1, but not by that of L166P mutant DJ-1. Furthermore, DJ-1 rescued the cell death caused by over-expression of Pael receptor, which was a substrate of Parkin, another gene product for autosomal recessive juvenile parkinsonism. These results suggest that loss of protective activity of DJ-1 from neuro-toxicity induced by these stresses contributes to neuronal cell death in AR-EOP with mutant DJ-1.     

衣原体抗宿主细胞凋亡调控机制研究进展

衣原体为完成发育周期以及逃避宿主免疫,进化形成一整套机制以实现持续性感染并对宿主细胞进行调控,抑制宿主细胞凋亡。细胞感染衣原体后,早期可以抑制Caspase酶系,抑制相关信号转导途径,且胞内线粒体发生一系列结构和功能的变化,抑制凋亡因子释放,一系列因子协同作用,抑制宿主细胞凋亡。本文从凋亡途径、凋亡蛋白、凋亡信号通路三个主要方面作了衣原体抑制宿主细胞凋亡机制概述,对进一步了解衣原体发育及其致病机制提供了新的研究思路。     

Novel mechanism for regulation of epidermal growth factor receptor endocytosis revealed by protein kinase A inhibition

Current models put forward that the epidermal growth factor receptor (EGFR) is efficiently internalized via clathrin-coated pits only in response to ligand-induced activation of its intrinsic tyrosine kinase and is subsequently directed into a lysosomal-proteasomal degradation pathway by mechanisms that include receptor tyrosine phosphorylation and ubiquitylation. Herein, we report a novel mechanism of EGFR internalization that does not require ligand binding, receptor kinase activity, or ubiquitylation and does not direct the receptor into a degradative pathway. Inhibition of basal protein kinase A (PKA) activity by H89 and the cell-permeable substrate peptide Myr-PKI induced internalization of 40-60% unoccupied, inactive EGFR, and its accumulation into early endosomes without affecting endocytosis of transferrin and mu-opioid receptors. This effect was abrogated by interfering with clathrin function. Thus, the predominant distribution of inactive EGFR at the plasma membrane is not simply by default but involves a PKA-dependent restrictive condition resulting in receptor avoidance of endocytosis until it is stimulated by ligand. Furthermore, PKA inhibition may contribute to ligand-induced EGFR endocytosis because epidermal growth factor inhibited 26% of PKA basal activity. On the other hand, H89 did not alter ligand-induced internalization of EGFR but doubled its half-time of down-regulation by retarding its segregation into degradative compartments, seemingly due to a delay in the receptor tyrosine phosphorylation and ubiquitylation. Our results reveal that PKA basal activity controls EGFR function at two levels: 1) residence time of inactive EGFR at the cell surface by a process of "endocytic evasion," modulating the accessibility of receptors to stimuli; and 2) sorting events leading to the down-regulation pathway of ligand-activated EGFR, determining the length of its intracellular signaling. They add a new dimension to the fine-tuning of EGFR function in response to cellular demands and cross talk with other signaling receptors.     

A cost of reproduction in Drosophila melanogaster: stress susceptibility

Little is known about physiological mechanisms that underlie the cost of reproduction. We tested the hypothesis that stress susceptibility is a cost of reproduction. In one test of our hypothesis, Drosophila melanogaster females were exposed to a juvenile hormone analog (methoprene) to stimulate egg production followed by stress assays. A sterile stock of D. melanogaster was employed as a control for reproduction. Exposure of fertile females to methoprene resulted in an increase in female reproduction and increased susceptibility to oxidative stress and starvation (compared to solvent controls). Sterile females did not exhibit a decrease in stress resistance. Mating also stimulated egg production. As a second test of our hypothesis, mated females were compared to virgin females. Mated fertile females were relatively susceptible to oxidative stress, but this relationship was not evident when mated and virgin sterile females were compared. The results of the present study support the hypothesis that stress susceptibility is a cost of reproduction.     

A molecular mechanism for bacterial susceptibility to zinc

Transition row metal ions are both essential and toxic to microorganisms. Zinc in excess has significant toxicity to bacteria, and host release of Zn(II) at mucosal surfaces is an important innate defence mechanism. However, the molecular mechanisms by which Zn(II) affords protection have not been defined. We show that in Streptococcus pneumoniae extracellular Zn(II) inhibits the acquisition of the essential metal Mn(II) by competing for binding to the solute binding protein PsaA. We show that, although Mn(II) is the high-affinity substrate for PsaA, Zn(II) can still bind, albeit with a difference in affinity of nearly two orders of magnitude. Despite the difference in metal ion affinities, high-resolution structures of PsaA in complex with Mn(II) or Zn(II) showed almost no difference. However, Zn(II)-PsaA is significantly more thermally stable than Mn(II)-PsaA, suggesting that Zn(II) binding may be irreversible. In vitro growth analyses show that extracellular Zn(II) is able to inhibit Mn(II) intracellular accumulation with little effect on intracellular Zn(II). The phenotype of S. pneumoniae grown at high Zn(II):Mn(II) ratios, i.e. induced Mn(II) starvation, closely mimicked a ΔpsaA mutant, which is unable to accumulate Mn(II). S. pneumoniae infection in vivo elicits massive elevation of the Zn(II):Mn(II) ratio and, in vitro, these Zn(II):Mn(II) ratios inhibited growth due to Mn(II) starvation, resulting in heightened sensitivity to oxidative stress and polymorphonuclear leucocyte killing. These results demonstrate that microbial susceptibility to Zn(II) toxicity is mediated by extracellular cation competition and that this can be harnessed by the innate immune response.