Armadillo motifs involved in vesicular transport

The lysosomal trafficking regulator "LYST": an 80-year traffic jam

Lysosomes and lysosome related organelles (LROs) are dynamic organelles at the intersection of various pathways involved in maintaining cellular hemostasis and regulating cellular functions. Vesicle trafficking of lysosomes and LROs are critical to maintain their functions. The lysosomal trafficking regulator (LYST) is an elusive protein important for the regulation of membrane dynamics and intracellular trafficking of lysosomes and LROs. Mutations to the LYST gene result in Chédiak-Higashi syndrome, an autosomal recessive immunodeficiency characterized by defective granule exocytosis, cytotoxicity, etc. Despite eight decades passing since its initial discovery, a comprehensive understanding of LYST's function in cellular biology remains unresolved. Accumulating evidence suggests that dysregulation of LYST function also manifests in other disease states. Here, we review the available literature to consolidate available scientific endeavors in relation to LYST and discuss its relevance for immunomodulatory therapies, regenerative medicine and cancer applications.

Roles of syntaphilin and armadillo repeat-containing X-linked protein 1 in brain injury after experimental intracerebral hemorrhage

Studies have indicated that neuronal mitochondrial injury may be involved in the brain injury caused by intracerebral hemorrhage (ICH). Syntaphilin (SNPH) is associated with mitochondrial anchoring and Armadillo repeat-containing X-linked protein 1 (Armcx1) is linked to mitochondrial transport. This study aimed to analyze the contribution of SNPH and Armcx1 to the neuronal damage resulting from ICH. Primary cultured neuron cells were exposed to oxygenated hemoglobin to replicate the effects of ICH stimulation, while a mouse model of ICH was established by injecting autoblood into the basal ganglia. Specific SNPH knockout or Armcx1 overexpression in neurons is achieved by stereolocalization injection of adeno-associated virus vectors carrying hsyn specific promoters. First, it was confirmed that there is a correlation between SNPH/Armcx1 and ICH pathology, as evidenced by the rise of SNPH and the decrease of Armcx1 in neurons exposed to ICH both in vitro and in vivo. Second, our research revealed the protective effects of SNPH knockdown and Armcx1 overexpression on brain cell death around the hematoma in mice. In addition, the efficacy of SNPH knockdown and Armcx1 overexpression in improving neurobehavioral deficits was also demonstrated in mouse ICH model. Thus, moderate adjusting the levels of SNPH and Armcx1 may be an effective way to improve the outcome of ICH.

The curious case of SARM1: Dr. Jekyll and Mr. Hyde in cell death and immunity?

Sterile alpha and toll/interleukin-1 receptor motif-containing protein 1 (SARM1) was first identified as a novel ortholog of Drosophila protein CG7915 and was subsequently placed as the fifth member of the human TIR-containing adaptor protein. SARM1 holds a unique position in this family where, unlike other members, it downregulates NFκB activity in response to immunogenic stimulation, interacts with another member of the family, TRIF, to negatively regulate its function, and it also mediates cell death responses. Over the past decade, SARM1 has emerged as one of the primary mediators of programmed axonal degeneration and this robust regulation of axonal degeneration-especially in models of peripheral neuropathy and traumatic injury-makes it an attractive target for therapeutic intervention. The TIR domain of SARM1 possesses an intrinsic NADase activity resulting in cellular energy deficits within the axons, a striking deviation from its other family members of human TLR adaptors. Interestingly, the TIR NADase activity, as seen in SARM1, is also observed in several prokaryotic TIR-containing proteins where they are involved in immune evasion once within the host. Although the immune function of SARM1 is yet to be conclusively discerned, this closeness in function with the prokaryotic TIR-domain containing proteins, places it at an interesting juncture of evolution raising questions about its origin and function in cell death and immunity. In this review, we discuss how a conserved immune adaptor protein like SARM1 switches to a pro-neurodegenerative function and the evolutionarily significance of the process.

Proteasomal Degradation of Zn-Dependent Hdacs: The E3-Ligases Implicated and the Designed Protacs That Enable Degradation

Protein degradation by the Ubiquitin-Proteasome System is one of the main mechanisms of the regulation of cellular proteostasis, and the E3 ligases are the key effectors for the protein recognition and degradation. Many E3 ligases have key roles in cell cycle regulation, acting as checkpoints and checkpoint regulators. One of the many important proteins involved in the regulation of the cell cycle are the members of the Histone Deacetylase (HDAC) family. The importance of zinc dependent HDACs in the regulation of chromatin packing and, therefore, gene expression, has made them targets for the design and synthesis of HDAC inhibitors. However, achieving potency and selectivity has proven to be a challenge due to the homology between the zinc dependent HDACs. PROteolysis TArgeting Chimaera (PROTAC) design has been demonstrated to be a useful strategy to inhibit and selectively degrade protein targets. In this review, we attempt to summarize the E3 ligases that naturally ubiquitinate HDACs, analyze their structure, and list the known ligands that can bind to these E3 ligases and be used for PROTAC design, as well as the already described HDAC-targeted PROTACs.

USO1 isoforms differentially promote liver cancer progression by dysregulating the ER-Golgi network

Alternative splicing of RNA transcripts plays an important role in cancer development and progression. Recent advances in RNA-seq technology have made it possible to identify alternately spliced events in various types of cancer; however, research on hepatocellular carcinoma (HCC) is still limited. Here, by performing RNA-Seq profiling of HCC transcripts at isoform level, we identified tumor-specific and molecular subtype-dependent expression of the USO1 isoforms, which we designated as a normal form USO1-N (XM_001290049) and a tumor form USO1-T (NM_003715). The expression of USO1-T, but not USO1-N, was associated with worse prognostic outcomes of HCC patients. We confirmed that the expression of USO1-T promoted an aggressive phenotype of HCC, both in vitro and in vivo. In addition, structural modeling analyses revealed that USO1-T lacks an ARM10 loop encoded by exon 15, which may weaken the dimerization of USO1 and its tethering to GM130. We demonstrated that USO1-T ensured unstacking of the Golgi and accelerated the trafficking from ER to Golgi and plasma membrane in multiple liver cancer cells. ERK and GRASP65 were found to be involved in the USO1-T mediated Golgi dysfunction. Conclusively, we provide new mechanophysical insights into the USO1 isoforms that differentially regulate the ER-Golgi network, promoting the heterogeneous HCC progression.

ARMCX Family Gene Expression Analysis and Potential Prognostic Biomarkers for Prediction of Clinical Outcome in Patients with Gastric Carcinoma

Armadillo gene subfamily members (ARMCX1-6) are well-known to regulate protein-protein interaction involved in nuclear transport, cellular connection, and transcription activation. Moreover, ARMCX signals on cell pathways also implicated in carcinogenesis and tumor progression. However, little is known about the associations of the ARMCX subfamily members with gastric carcinoma. This study investigated the prognostic value of ARMCX subfamily mRNA expression levels with the prognosis of gastric carcinoma (GC). We retrieved the data of a total of 351 GC patients from TCGA database. Survival and gene set enrichment analyses were employed to explore the predictive value and underlying mechanism of ARMCX genes in GC. The multivariate survival analysis revealed that individually low expressions of ARMCX1 (adjusted P = 0.006, HR = 0.620, CI = 0.440 - 0.874) and ARMCX2 (adjusted P = 0.005, HR = 0.610, 95%CI = 0.432-0.861) were related to preferable overall survival (OS). The joint-effects analysis shown that combinations of low level expression of ARMCX1 and ARMCX2 were correlated with favorable OS (adjusted P = 0.003, HR = 0.563, 95%CI = 0.384-0.825). ARMCX1 and ARMCX2 were implicated in WNT and NF-kappaB pathways, and biological processes including cell cycle, apoptosis, RNA modification, DNA replication, and damage response. Our results suggest that mRNA expression levels of ARMCX subfamily are potential prognostic markers of GC.

Ventricular Zone Expressed PH Domain Containing 1 (VEPH1): an adaptor protein capable of modulating multiple signaling transduction pathways during normal and pathological development

Ventricular Zone Expressed PH Domain-Containing 1 (VEPH1) is an 833-amino acid protein encoded by an evolutionarily conserved single-copy gene that emerged with pseudocoelomates. This gene has no paralog in any species identified to date and few studies have investigated the function of its encoded protein. Loss of expression of its ortholog, melted, in Drosophila results in a severe neural phenotype and impacts TOR, FoxO, and Hippo signaling. Studies in mammals indicate a role for VEPH1 in modulating TGFβ signaling and AKT activation, while numerous studies indicate VEPH1 expression is altered in several pathological conditions, including cancer. Although often referred to as an uncharacterized protein, available evidence supports VEPH1 as an adaptor protein capable of modulating multiple signal transduction networks. Further studies are required to define these adaptor functions and the role of VEPH1 in development and disease progression.

The LRRK2 signalling system

The LRRK2 gene is a major contributor to genetic risk for Parkinson's disease and understanding the biology of the leucine-rich repeat kinase 2 (LRRK2, the protein product of this gene) is an important goal in Parkinson's research. LRRK2 is a multi-domain, multi-activity enzyme and has been implicated in a wide range of signalling events within the cell. Because of the complexities of the signal transduction pathways in which LRRK2 is involved, it has been challenging to generate a clear idea as to how mutations and disease associated variants in this gene are altered in disease. Understanding the events in which LRRK2 is involved at a systems level is therefore critical to fully understand the biology and pathobiology of this protein and is the subject of this review.

Chediak-Higashi syndrome: Lysosomal trafficking regulator domains regulate exocytosis of lytic granules but not cytokine secretion by natural killer cells

BACKGROUND

Mutations in lysosomal trafficking regulator (LYST) cause Chediak-Higashi syndrome (CHS), a rare immunodeficiency with impaired cytotoxic lymphocyte function, mainly that of natural killer (NK) cells. Our understanding of NK cell function deficiency in patients with CHS and how LYST regulates lytic granule exocytosis is very limited.

OBJECTIVE

We sought to delineate cellular defects associated with LYST mutations responsible for the impaired NK cell function seen in patients with CHS.

METHODS

We analyzed NK cells from patients with CHS with missense mutations in the LYST ARM/HEAT (armadillo/huntingtin, elongation factor 3, protein phosphatase 2A, and the yeast kinase TOR1) or BEACH (beige and Chediak-Higashi) domains.

RESULTS

NK cells from patients with CHS displayed severely reduced cytotoxicity. Mutations in the ARM/HEAT domain led to a reduced number of perforin-containing granules, which were significantly increased in size but able to polarize to the immunologic synapse; however, they were unable to properly fuse with the plasma membrane. Mutations in the BEACH domain resulted in formation of normal or slightly enlarged granules that had markedly impaired polarization to the IS but could be exocytosed on reaching the immunologic synapse. Perforin-containing granules in NK cells from patients with CHS did not acquire certain lysosomal markers (lysosome-associated membrane protein 1/2) but were positive for markers of transport vesicles (cation-independent mannose 6-phosphate receptor), late endosomes (Ras-associated binding protein 27a), and, to some extent, early endosomes (early endosome antigen 1), indicating a lack of integrity in the endolysosomal compartments. NK cells from patients with CHS had normal cytokine compartments and cytokine secretion.

CONCLUSION

LYST is involved in regulation of multiple aspects of NK cell lytic activity, ranging from governance of lytic granule size to control of their polarization and exocytosis, as well as regulation of endolysosomal compartment identity. LYST functions in the regulated exocytosis but not in the constitutive secretion pathway.

ALEX1 may be a novel biomarker for human cervical squamous cell carcinoma

The armadillo repeat proteins were first found in armadillo gene of Drosophila. Since then a number of proteins containing armadillo repeats have been noticed and studied. These proteins that consist of 6 to 13 armadillo repeat domains are classified as family of armadillo repeat proteins. Recently, several studies indicated that armadillo repeat family of proteins play an important role in the tumorigenesis and maintenance of tissue integrity. ALEX1 (Arm protein lost in epithelial cancers, on chromosome X), contains two armadillo repeats domains, is expressed different in normal and carcinomas tissues. Several studies have found that ALEX1 protein lost in tumors that originated in epithelial tissues. We evaluated the ALEX1 protein expression in 53 cervical cancers and in 53 non-cancerous cervical tissues from patients and adjacent non-cancerous tissues using immunohistochemistry

RESULTS

ALEX1 protein expression is significantly increased in 53 cervical cancers tissues compared with non-cancerous tissues. We found, for the first time, that ALEX1 protein expression in cervical cancers tissues is higher than non-cancerous tissues. It is suggested that the ALEX1 protein is associated with tumorigenesis in cervical cancer and we speculate that the ALEX1 may plays a role as an oncogene in cervical cancer. Moreover, ALEX1 may serve as a novel potential diagnostic biomarker in identifying cervical cancer.

Gudu, an Armadillo repeat-containing protein, is required for spermatogenesis in Drosophila

The Drosophila annotated gene CG5155 encodes a protein that contains 10 Armadillo-repeats and has an unknown function. To fill this gap, we performed loss-of-function studies using RNAi. By analysis of four independent Drosophila RNAi lines targeting two non-overlapping regions of the CG5155 transcript, we demonstrate that this gene is required for male fertility. Therefore, we have named this gene Gudu. The transcript of Gudu is highly enriched in adult testes. Knockdown of Gudu by a ubiquitous driver leads to defects in the formation of the individualization complex that is required for spermatid maturation, thereby impairing spermatogenesis. Furthermore, testis-specific knockdown of Gudu by crossing the RNAi lines with the bam-Gal4 driver is sufficient to cause the infertility and defective spermatogenesis. Since Gudu is highly homologous to vertebrate ARMC4, also an Armadillo-repeat-containing protein enriched in testes, our results suggest that Gudu and ARMC4 are a subfamily of Armadillo-repeat containing proteins that may have an evolutionarily conserved function in spermatogenesis.

New insights into the evolution of metazoan cadherins and catenins

E-Cadherin and β-catenin are the best studied representatives of the superfamilies of transmembrane cadherins and intracellular armadillo catenins, respectively. However, in over 600 million years of multicellular animal evolution, these two superfamilies have diversified remarkably both structurally and functionally. Although their basic building blocks, respectively, the cadherin repeat domain and the armadillo repeat domain, predate metazoans, the specific and complex domain compositions of the different family members and their functional roles in cell adhesion and signaling appear to be key features for the emergence of multicellular animal life. Basal animals such as placozoans and sponges have a limited number of distinct cadherins and catenins. The origin of vertebrates, in particular, coincided with a large increase in the number of cadherins and armadillo proteins, including modern "classical" cadherins, protocadherins, and plakophilins. Also, α-catenins increased. This chapter introduces the many different family members and describes the putative evolutionary relationships between them.

Molecular insights into arrhythmogenic right ventricular cardiomyopathy caused by plakophilin-2 missense mutations

BACKGROUND

Arrhythmogenic right ventricular cardiomyopathy (ARVC) is an inherited cardiac disorder mainly caused by dominant mutations in several components of the cardiac desmosome including plakophilin-2 (PKP2), the most prevalent disease gene. Little is known about the underlying genetic and molecular mechanisms of missense mutations located in the armadillo (ARM) domains of PKP2, as well as their consequences on human cardiac pathology.

METHODS AND RESULTS

We focused on in vivo and in vitro studies of the PKP2 founder mutation c.2386T>C (p.C796R), and demonstrated in cardiac tissue from 2 related mutation carriers a patchy expression pattern ranging from unchanged to totally absent immunoreactive signals of PKP2 and other desmosomal proteins. In vitro expression analysis of mutant PKP2 in cardiac derived HL-1 cells revealed unstable proteins that fail to interact with desmoplakin and are targeted by degradation involving calpain proteases. Bacterial expression, crystallization, and structural modeling of mutated proteins impacting different ARM domains and helices of PKP2 confirmed their instability and degradation, resulting in the same remaining protein fragment that was crystallized and used to model the entire ARM domain of PKP2.

CONCLUSIONS

The p.C796R and other ARVC-related PKP2 mutations indicate loss of function effects by intrinsic instability and calpain proteases mediated degradation in in vitro model systems, suggesting haploinsufficiency as the most likely cause for the genesis of dominant ARVC due to mutations in PKP2.

Molecular characterization of an elicitor-responsive Armadillo repeat gene (GhARM) from cotton (Gossypium hirsutum)

Only a few Armadillo (ARM) repeat proteins have been characterized in plants where they appear to have diverse functions, including the regulation of defence responses. In this study, the identification, cloning and characterization of a gene, encoding an ARM repeat protein (GhARM), is described. GhARM exists as multiple copies in cotton, with an 1713 bp ORF encoding 570 amino acids. The predicted protein contains three consecutive ARM repeats within an Armadillo-type fold, with no other distinguishing domains. Sequence alignments and phylogenetic analysis revealed that GhARM has a high homology with other ARM proteins in plants. The predicted three dimensional model of GhARM displayed a characteristic right-handed superhelical twist. In silico analysis of the promoter sequence revealed that it contains several defence- and hormone-responsive cis-regulatory elements. Expression of GhARM was significantly down-regulated in response to treatment with a V. dahliae elicitor suggesting that GhARM may function as a negative-regulator of cotton defence signalling against V. dahliae. To date, GhARM is the only ARM repeat gene that has been completely sequenced and characterized in cotton.

The golgin coiled-coil proteins of the Golgi apparatus

A number of long coiled-coil proteins are present on the Golgi. Often referred to as "golgins," they are well conserved in evolution and at least five are likely to have been present in the last common ancestor of all eukaryotes. Individual golgins are found in different parts of the Golgi stack, and they are typically anchored to the membrane at their carboxyl termini by a transmembrane domain or by binding a small GTPase. They appear to have roles in membrane traffic and Golgi structure, but their precise function is in most cases unclear. Many have binding sites for Rab family GTPases along their length, and this has led to the suggestion that the golgins act collectively to form a tentacular matrix that surrounds the Golgi to capture Rab-coated membranes in the vicinity of the stack. Such a collective role might explain the lack of cell lethality seen following loss of some of the genes in human familial conditions or mouse models.

Armadillo-repeat protein functions: questions for little creatures

Armadillo (ARM)-repeat proteins form a large family with diverse and fundamental functions in many eukaryotes. ARM-repeat proteins have largely been characterised in multicellular organisms and much is known about how a subset of these proteins function. The structure of ARM-repeats allows proteins containing them to be functionally very versatile. Are the ARM-repeat proteins in 'little creatures' as multifunctional as their better-studied relatives? The time is now right to start analysing ARM-repeat proteins in these new systems to better understand their cell biology. Here, we review recent advances in understanding the many cellular roles of both well-known and novel ARM-repeat proteins.