Missense Mutations in Desmoplakin Plakin Repeat Domains Have Dramatic Effects on Domain Structure and Function

Plakin repeat domains (PRDs) are globular modules that mediate the interaction of plakin proteins with the intermediate filament (IF) cytoskeleton. These associations are vital for maintaining tissue integrity in cardiac muscle and epithelial tissues. PRDs are subject to mutations that give rise to cardiomyopathies such as arrhythmogenic right ventricular cardiomyopathy, characterised by ventricular arrhythmias and associated with an increased risk of sudden heart failure, and skin blistering diseases. Herein, we have examined the functional and structural effects of 12 disease-linked missense mutations, identified from the human gene mutation database, on the PRDs of the desmosomal protein desmoplakin. Five mutations (G2056R and E2193K in PRD-A, G2338R and G2375R in PRD-B and G2647D in PRD-C) rendered their respective PRD proteins either fully or partially insoluble following expression in bacterial cells. Each of the residues affected are conserved across plakin family members, inferring a crucial role in maintaining the structural integrity of the PRD. In transfected HeLa cells, the mutation G2375R adversely affected the targeting of a desmoplakin C-terminal construct containing all three PRDs to vimentin IFs. The deletion of PRD-B and PRD-C from the construct compromised its targeting to vimentin. Bioinformatic and structural modelling approaches provided multiple mechanisms by which the disease-causing mutations could potentially destabilise PRD structure and compromise cytoskeletal linkages. Overall, our data highlight potential molecular mechanisms underlying pathogenic missense mutations and could pave the way for informing novel curative interventions targeting cardiomyopathies and skin blistering disorders.

Mechanical Control of Cell Migration by the Metastasis Suppressor Tetraspanin CD82/KAI1

The plasma membrane is a key actor of cell migration. For instance, its tension controls persistent cell migration and cell surface caveolae integrity. Then, caveolae constituents such as caveolin-1 can initiate a mechanotransduction loop that involves actin- and focal adhesion-dependent control of the mechanosensor YAP to finely tune cell migration. Tetraspanin CD82 (also named KAI-1) is an integral membrane protein and a metastasis suppressor. Its expression is lost in many cancers including breast cancer. It is a strong inhibitor of cell migration by a little-known mechanism. We demonstrated here that CD82 controls persistent 2D migration of EGF-induced single cells, stress fibers and focal adhesion sizes and dynamics. Mechanistically, we found that CD82 regulates membrane tension, cell surface caveolae abundance and YAP nuclear translocation in a caveolin-1-dependent manner. Altogether, our data show that CD82 controls 2D cell migration using membrane-driven mechanics involving caveolin and the YAP pathway.

Consumer basket as the basis for the State guarantees of minimum monetary income of Russian citizens (Part 2)

The article provides an overview of special sources, research results, ideas and discussions in the following areas related to formation of consumer basket (CB): 1) methods of forming consumer baskets in the Russian Federation and abroad, their advantages and disadvantages; 2) composition and standards of consumption of goods and services that may be recommended to meet the basic needs of population; 3) approaches to defining the relationship between the actual consumption of goods and services by low-income population and the composition and standards of consumption of food, non-food goods and services in CB; 4) minimum State guarantees, which should be related to the cost estimation of CB; 5) advantages and disadvantages of the current method of forming a living wage CB; 6) new research directions and proposals for changing the CB composition and regulatory framework, ways to determine their cost and impact on the level of satisfaction of the population's needs for food, non-food products and paid services, their comparison; 7) comparison of the CB cost, resulting from different approaches to its definition, the size of minimum State guarantees and actual monetary income: modal, median and per capita; 8) alternative approaches to setting the limits of monetary income for determining the State guarantees of minimum monetary income, advantages and disadvantages of their use in the Russian Federation. Conclusions and recommendations are proposed that could contribute to formation and introduction of a science-based CB in 2021 in order to improve the standards and quality of life of Russian citizens. The article consists of two parts. The First part of the article addresses the first two of these areas related to formation of CB.

Binding of the periplakin linker requires vimentin acidic residues D176 and E187

Plakin proteins form connections that link the cell membrane to the intermediate filament cytoskeleton. Their interactions are mediated by a highly conserved linker domain through an unresolved mechanism. Here analysis of the human periplakin linker domain structure reveals a bi-lobed module transected by an electropositive groove. Key basic residues within the periplakin groove are vital for co-localization with vimentin in human cells and compromise direct binding which also requires acidic residues D176 and E187 in vimentin. We propose a model whereby basic periplakin linker domain residues recognize acidic vimentin side chains and form a complementary binding groove. The model is shared amongst diverse linker domains and can be used to investigate the effects of pathogenic mutations in the desmoplakin linker associated with arrhythmogenic right ventricular cardiomyopathy. Linker modules either act solely or collaborate with adjacent plakin repeat domains to create strong and adaptable tethering within epithelia and cardiac muscle.

[THE STUDY OF PHYSICAL - CHEMICAL AND TECHNOLOGICAL PROPERTIES OF EPIMEDIUM STRELOLIST'S DRY EXTRACT TO CREATE A SOLID DOSAGE FORM FOR THE TREATMENT OF ERECTILE DYSFUNCTION]

One of the most famous aphrodisiac plants and remedy for recoveryerectile dysfunction is Estrellita Epimedium (Epimedium sagittatum). On this basis, development of the new dosage form (capsules with dry extract of Epimedium strelolist) is one of the promising directions in phytotherapy of erectile dysfunction in men. The main task in development of a new dosage form is the study of the physical-chemical and technological active pharmaceutical substance's (API) characteristics, such as crystal form, solubility, flowability, angle of repose, tap density, water. In this study, the dry extract of Epimedium strelolist is an API. Research of above characteristics will determine the choice of excipients and technology of dosage form.

T-cell number and subtype influence the disease course of primary chronic lymphocytic leukaemia xenografts in alymphoid mice

Chronic lymphocytic leukaemia (CLL) cells require microenvironmental support for their proliferation. This can be recapitulated in highly immunocompromised hosts in the presence of T cells and other supporting cells. Current primary CLL xenograft models suffer from limited duration of tumour cell engraftment coupled with gradual T-cell outgrowth. Thus, a greater understanding of the interaction between CLL and T cells could improve their utility. In this study, using two distinct mouse xenograft models, we investigated whether xenografts recapitulate CLL biology, including natural environmental interactions with B-cell receptors and T cells, and whether manipulation of autologous T cells can expand the duration of CLL engraftment. We observed that primary CLL xenografts recapitulated both the tumour phenotype and T-cell repertoire observed in patients and that engraftment was significantly shorter for progressive tumours. A reduction in the number of patient T cells that were injected into the mice to 2-5% of the initial number or specific depletion of CD8(+) cells extended the limited xenograft duration of progressive cases to that characteristic of indolent disease. We conclude that manipulation of T cells can enhance current CLL xenograft models and thus expand their utility for investigation of tumour biology and pre-clinical drug assessment.

Arginine dependence of acute myeloid leukemia blast proliferation: a novel therapeutic target

Acute myeloid leukemia (AML) is one of the most common acute leukemias in adults and children, yet significant numbers of patients relapse and die of disease. In this study, we identify the dependence of AML blasts on arginine for proliferation. We show that AML blasts constitutively express the arginine transporters CAT-1 and CAT-2B, and that the majority of newly diagnosed patients' blasts have deficiencies in the arginine-recycling pathway enzymes argininosuccinate synthase and ornithine transcarbamylase, making them arginine auxotrophic. BCT-100, a pegylated human recombinant arginase, leads to a rapid depletion in extracellular and intracellular arginine concentrations, resulting in arrest of AML blast proliferation and a reduction in AML engraftment in vivo. BCT-100 as a single agent causes significant death of AML blasts from adults and children, and acts synergistically in combination with cytarabine. Using RNA sequencing, 20 further candidate genes which correlated with resistance have been identified. Thus, AML blasts are dependent on arginine for survival and proliferation, as well as depletion of arginine with BCT-100 of clinical value in the treatment of AML.

Metastasis suppressor tetraspanin CD82/KAI1 regulates ubiquitylation of epidermal growth factor receptor

Ligand-induced ubiquitylation of EGF receptor (EGFR) is an important regulatory mechanism that controls endocytic trafficking of the receptor and its signaling potential. Here we report that tetraspanin CD82/KAI1 specifically suppresses ubiquitylation of EGFR after stimulation with heparin-binding EGF or amphiregulin and alters the rate of recruitment of the activated receptor to EEA1-positive endosomes. The suppressive effect of CD82 is dependent on the heparin-binding domain of the ligand. Deletion of the C-terminal cytoplasmic domain of CD82 (CD82ΔC mutant) inhibits endocytic trafficking of the tetraspanin and compromises its activity toward heparin-binding EGF-activated EGFR. Reduced ubiquitylation of EGFR is accompanied by PKC-dependent increase in serine phosphorylation of c-Cbl in cells expressing elevated levels of CD82. Furthermore, phosphorylation of threonine 654 (PKC phosphorylation site) in the juxtamembrane domain of the receptor is considerably increased in CD82-expressing cells. These results describe previously unsuspected links between tetraspanin proteins and ubiquitylation of their molecular partners (e.g., EGFR). Our data identify CD82 as a new regulator of c-Cbl, which discriminatively controls the activity of this E3 ubiquitin ligase toward heparin-binding ligand-EGFR pairs. Taken together, these observations provide an important new insight into the modulatory role of CD82 in endocytic trafficking of EGF receptor.

Integrin α3β1-CD151 complex regulates dimerization of ErbB2 via RhoA

Integrin α3β1 regulates adhesive interactions of cells with laminins and have a critical role in adhesion-dependent cellular responses. Here, we examined the role of α3β1-integrin in ErbB2-dependent proliferation of breast cancer cells in three-dimensional laminin-rich extracellular matrix (3D lr-ECM). Depletion of α3β1 in ErbB2-overexpressing breast cancer cells suppressed growth and restore cell polarity in 3D lr-ECM. The phenotype of α3β1-depleted cells was reproduced upon depletion of tetraspanin CD151 and mirrored that of the cells treated with Herceptin, an established ErbB2 antagonist. Breast cancer cells expressing the α3β1-CD151 complex have higher steady-state phosphorylation of ErbB2 and show enhanced dimerization of the protein when compared with α3β1-/CD151-depleted cells. Furthermore, Herceptin-dependent dephosphorylation of ErbB2 was only observed in α3β1-CD151-expressing cells. Importantly, the inhibitory activity of Herceptin was more pronounced when cells expressed both α3β1 and CD151. We also found that the level of active RhoA was increased in α3β1- and CD151-depleted cells and that Rho controls dimerization of ErbB2. Expression of α3β1 alone did not have significant prognostic value in patients with invasive ductal carcinoma of the breast. However, expression of α3β1 in combination with CD151 represented a more stringent indicator of poor survival than CD151 alone. Taken together, these results demonstrate that the α3β1-CD151 complex has a critical regulatory role in ErbB2-dependent signalling and thereby may be involved in breast cancer progression.

Binding to syntenin-1 protein defines a new mode of ubiquitin-based interactions regulated by phosphorylation

Syntenin-1 is a PDZ domain-containing adaptor that controls trafficking of transmembrane proteins including those associated with tetraspanin-enriched microdomains. We describe the interaction of syntenin-1 with ubiquitin through a novel binding site spanning the C terminus of ubiquitin, centered on Arg(72), Leu(73), and Arg(74). A conserved LYPSL sequence in the N terminus, as well as the C-terminal region of syntenin-1, are essential for binding to ubiquitin. We present evidence for the regulation of this interaction through syntenin-1 dimerization. We have also established that syntenin-1 is phosphorylated downstream of Ulk1, a serine/threonine kinase that plays a critical role in autophagy and regulates endocytic trafficking. Importantly, Ulk1-dependent phosphorylation of Ser(6) in the LYPSL prevents the interaction of syntenin-1 with ubiquitin. These results define an unprecedented ubiquitin-dependent pathway involving syntenin-1 that is regulated by Ulk1.

The role of tetraspanin CD63 in antigen presentation via MHC class II

Interactions between MHC class II (MHC II)-positive APCs and CD4(+) T cells are central to adaptive immune responses. Using an Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell line (LCL) as MHC II-positive APCs and CD4(+) T-cell clones specific for two endogenously expressed EBV antigens, we found that shRNA knockdown of the tetraspanin protein CD63 in LCL cells consistently led to increased CD4(+) T-cell recognition. This effect was not due to enhanced antigen processing nor to changes in MHC II expression since CD63 knockdown did not influence the amount or dimerization of MHC II in LCL cells. We therefore investigated the possible involvement of exosomes, small MHC II- and tetraspanin-abundant vesicles which are secreted by LCL cells and which we found could themselves activate the CD4(+) T-cell clones in an MHC II-dependent manner. While equal loadings of exosomes purified from the control and CD63(low) LCLs stimulated T cells to a comparable degree, we found that exosome production significantly increased following CD63-knockdown, suggesting that this may underlie the greater T-cell stimulatory capacity of the CD63(low) LCLs. Taken together, our data reveal a new insight into the mechanisms by which tetraspanins are involved in the regulation of MHC II-dependent T-cell stimulation.

Tetraspanins as regulators of protein trafficking

Small transmembrane proteins of the tetraspanin superfamily are believed to function as the main structural blocks of specialized membrane microdomains (referred to as tetraspanin-enriched microdomains, TERM or TEM). Through a multitude of homotypic and heterotypic interactions, tetraspanins regulate lateral clustering and, consequently, signalling involving adhesion and growth factor receptors as well as costimulatory proteins. The presence of major histocompatibility complex (MHC) I and MHCII molecules in TERM led to suggestion of tetraspanins' involvement in antigen presentation. In addition, certain tetraspanins function as viral co-receptors and may be important for viral egress from infected cells. It has recently become apparent that in addition to their purely structural function as organizers of TERM, tetraspanins also regulate various aspects of trafficking and biosynthetic processing of associated receptors. Here, we review recent studies, which specifically focus on this issue.

Gangliosides play an important role in the organization of CD82-enriched microdomains

Four-transmembrane-domain proteins of the tetraspanin superfamily are the organizers of specific microdomains at the membrane [TERMs (tetraspanin-enriched microdomains)] that incorporate various transmembrane receptors and modulate their activities. The structural aspects of the organization of TERM are poorly understood. In the present study, we investigated the role of gangliosides in the assembly and stability of TERM. We demonstrated that inhibition of the glycosphingolipid biosynthetic pathway with specific inhibitors of glucosylceramide synthase [NB-DGJ (N-butyldeoxygalactonojirimycin) and PPMP (D-threo-1-phenyl-2-hexadecanoylamino-3-morpholino-1-propanol.HCl)] resulted in specific weakening of the interactions involving tetraspanin CD82. Furthermore, ectopic expression of the plasma-membrane-bound sialidase Neu3 in mammary epithelial cells also affected stability of the complexes containing CD82: its association with tetraspanin CD151 was decreased, but the association with EGFR [EGF (epidermal growth factor) receptor] was enhanced. The destabilization of the CD82-containing complexes upon ganglioside depletion correlated with the re-distribution of the proteins within plasma membrane. Importantly, depletion of gangliosides affected EGF-induced signalling only in the presence of CD82. Taken together, our results provide strong evidence that gangliosides play an important role in supporting the integrity of CD82-enriched microdomains. Furthermore, these results demonstrate that the association between different tetraspanins in TERM is controlled by distinct mechanisms and identify Neu3 as a first physiological regulator of the integrity of these microdomains.

Regulation of urokinase receptor proteolytic function by the tetraspanin CD82

The high affinity interaction between the urokinase-type plasminogen activator (uPA) and its glycolipid-anchored cellular receptor (uPAR) promotes plasminogen activation and the efficient generation of pericellular proteolytic activity. We demonstrate here that expression of the tetraspanin CD82/KAI1 (a tumor metastasis suppressor) leads to a profound effect on uPAR function. Pericellular plasminogen activation was reduced by approximately 50-fold in the presence of CD82, although levels of components of the plasminogen activation system were unchanged. uPAR was present on the cell surface and molecularly intact, but radioligand binding analysis with uPA and anti-uPAR antibodies revealed that it was in a previously undetected cryptic form unable to bind uPA. This was not due to direct interactions between uPAR and CD82, as they neither co-localized on the cell surface nor could be co-immunoprecipitated. However, expression of CD82 led to a redistribution of uPAR to focal adhesions, where it was shown by double immunofluorescence labeling to co-localize with the integrin alpha(5)beta(1), which was also redistributed in the presence of CD82. Co-immunoprecipitation experiments showed that, in the presence of CD82, uPAR preferentially formed stable associations with alpha(5)beta(1), but not with a variety of other integrins, including alpha(3)beta(1). These data suggest that CD82 inhibits the proteolytic function of uPAR indirectly, directing uPAR and alpha(5)beta(1) to focal adhesions and promoting their association with a resultant loss of uPA binding. This represents a novel mechanism whereby tetraspanins, integrins, and uPAR, systems involved in cell adhesion and migration, cooperate to regulate pericellular proteolytic activity and may suggest a mechanism for the tumor-suppressive effects of CD82/KAI1.

Tetraspanin CD82 regulates compartmentalisation and ligand-induced dimerization of EGFR

We have previously shown that CD82, a transmembrane protein of the tetraspanin superfamily is associated with EGFR and has a negative effect on EGF-induced signalling (Odintsova, E., Sugiura, T. and Berditchevski, F. (2000) Curr. Biol. 10, 1009-1012). Here we demonstrate that CD82 specifically attenuates ligand-induced dimerization of EGFR. The recombinant soluble large extracellular loop of CD82 has no effect on the dimerization thereby suggesting that other parts of the protein are required. Although CD82 is also associated with ErbB2 and ErbB3, ligand-induced assembly of the ErbB2-ErbB3 complexes is not affected in CD82-expressing cells. Furthermore, in contrast to the CD82-EGFR association, CD82-ErbB2 and CD82-ErbB3 complexes are stable in the presence of ErbB3 ligand. The effect of CD82 on the formation of EGFR dimers correlates with changes in compartmentalisation of the ErbB receptors on the plasma membrane. Expression of CD82 causes a significant increase in the amount of EGFR and ErbB2 in the light fractions of the sucrose gradient. This correlates with the increased surface expression of gangliosides GD1a and GM1 and redistribution of GD1a and EGFR on the plasma membrane. Furthermore, in CD82-expressing cells GD1a is co-localised with EGFR and the tetraspanin. Taken together our results offer a molecular mechanism of the attenuating activity of CD82 towards EGFR, whereby GD1a functions as a mediator of CD82-dependent compartmentalisation of the receptor.

The tetraspanin CD151 functions as a negative regulator in the adhesion-dependent activation of Ras

Transmembrane proteins of the tetraspanin superfamily are associated with integrins and are thought to regulate adhesion-dependent signaling. The molecular mechanisms of this regulation remain unknown. We used rat fibroblasts to analyze the contribution of the tetraspanin CD151 in the adhesion-dependent signaling. Expression of CD151 specifically attenuated adhesion-dependent activation of Ras. Furthermore, activation of PKB/c-Akt and ERK1/2, downstream targets in the Ras signaling pathway, was also diminished in cells expressing CD151. In contrast, adhesion-dependent activation of FAK and c-Src were not affected by CD151. The attenuation of Ras signaling did not correlate with phosphorylation of Tyr925-FAK, tyrosine phosphorylation of Shc, or with assembly of the p120RasGAP-p62Dok complex. Using mutants of CD151 we established that the cytoplasmic C-terminal portion is critical for activity of CD151 toward Ras. Taken together these results identify CD151 as a negative regulator of Ras and suggest a novel mechanism of adhesion-dependent regulation of Ras activity.

Expression of the palmitoylation-deficient CD151 weakens the association of alpha 3 beta 1 integrin with the tetraspanin-enriched microdomains and affects integrin-dependent signaling

Transmembrane proteins of the tetraspanin superfamily are assembled in multimeric complexes on the cell surface. Spatial orientation of tetraspanins within these complexes may affect signaling functions of the associated transmembrane receptors (e.g. integrins, receptor-type tyrosine kinases). The structural determinants that control assembly of the tetraspanin complexes are unknown. We have found that various tetraspanins and the alpha(3) integrin subunit are palmitoylated. The stability and molecular composition of the palmitoylated alpha(3)beta(1)-tetraspanin complexes are not affected by adhesion. To assess the significance of palmitoylation in the function of the alpha(3)beta(1)-tetraspanin complexes we mapped the sites of palmitoylation for CD151. Mutation of six cysteines, Cys(11), Cys(15), Cys(79), Cys(80), Cys(242), and Cys(243) was necessary to completely abolish palmitoylation of CD151. The association of the palmitoylation-deficient mutant of CD151 (CD151Cys8) with CD81 and CD63 was markedly decreased, but the interaction of the alpha(3)beta(1)-CD151Cys8 complex with phosphatidylinositol 4-kinase was not affected. Ectopic expression of CD151Cys8 in Rat-1 cells impaired the interactions of the endogenous CD63 and CD81 with the alpha(3)beta(1) integrin. Although the expression of the palmitoylation-deficient CD151 does not change cell spreading on the extracellular matrix, the number of focal adhesions increased. Adhesion-induced phosphorylation of PKB/c-Akt is markedly increased in cells expressing a palmitoylation-deficient mutant, thereby providing direct evidence for the role of the tetraspanin microdomains in regulation of the integrin-dependent phosphatidylinositol 3-kinase signaling pathway. In contrast, activation of FAK and ERK1/2 were not affected by the expression of CD151Cys8. Our results demonstrate that palmitoylation of tetraspanins is critical not only for the organization of the integrin-tetraspanin microdomains but also has a specific role in modulation of adhesion-dependent signaling.

Attenuation of EGF receptor signaling by a metastasis suppressor, the tetraspanin CD82/KAI-1

The 'metastasis suppressor' CD82/KAI-1, a member of the tetraspanin superfamily of transmembrane proteins, is widely distributed in normal tissues [1], and has been shown to be suppressed in the advanced stages of various epithelial malignancies [2-6]. Although the physiological relevance of this change is unknown, in vitro data show that ectopically expressed CD82/KAI-1 can suppress tumor cell migration, a process underlying the dissemination of tumor cells in vivo [5]. The function of CD82/KAI-1 is not known and it has been proposed that association of CD82/KAI-1 with other cell-surface proteins may be pivotal in directing its biological activities [7,8]. We show here that the CD82/KAI-1 tetraspanin is directly associated with the EGF receptor (EGFR), and that ectopic expression of CD82/KAI-1 in epithelial cells specifically suppresses EGF-induced lamellipodial extensions and cell migration. In cells expressing CD82/KAI-1, the initial activation of EGFR is not affected, but subsequent desensitization of EGF-induced signaling occurs more rapidly. This attenuation is correlated with an increased rate of receptor endocytosis. These results identify CD82/KAI-1 as a new regulator of EGF-induced signaling and show that the association of EGFR with the tetraspanin is critical in EGFR desensitization.

Characterization of integrin-tetraspanin adhesion complexes: role of tetraspanins in integrin signaling

Tetraspanins (or proteins from the transmembrane 4 superfamily, TM4SF) form membrane complexes with integrin receptors and are implicated in integrin-mediated cell migration. Here we characterized cellular localization, structural composition, and signaling properties of alpha3beta1-TM4SF adhesion complexes. Double-immunofluorescence staining showed that various TM4SF proteins, including CD9, CD63, CD81, CD82, and CD151 are colocalized within dot-like structures that are particularly abundant at the cell periphery. Differential extraction in conjunction with chemical cross-linking indicated that the cell surface fraction of alpha3beta1-TM4SF protein complexes may not be directly linked to the cytoskeleton. However, in cells treated with cytochalasin B alpha3beta1-TM4SF protein complexes are relocated into intracellular vesicles suggesting that actin cytoskeleton plays an important role in the distribution of tetraspanins into adhesion structures. Talin and MARCKS are partially codistributed with TM4SF proteins, whereas vinculin is not detected within the tetraspanin-containing adhesion structures. Attachment of serum-starved cells to the immobilized anti-TM4SF mAbs induced dephosphorylation of focal adhesion kinase (FAK). On the other hand, clustering of tetraspanins in cells attached to collagen enhanced tyrosine phosphorylation of FAK. Furthermore, ectopic expression of CD9 in fibrosarcoma cells affected adhesion-induced tyrosine phosphorylation of FAK, that correlated with the reorganization of the cortical actin cytoskeleton. These results show that tetraspanins can modulate integrin signaling, and point to a mechanism by which TM4SF proteins regulate cell motility.