A novel isoform of Cbl-associated protein that binds protein kinase A

miR-223-3p carried by cancer-associated fibroblast microvesicles targets SORBS1 to modulate the progression of gastric cancer

Background

Cancer-associated fibroblasts (CAFs) aggravate gastric cancer (GC) development.

Methods

Combined with bioinformatics analysis and literature review, miR-223-3p had high expression in microvesicles (MVs) derived from GC CAFs, and it could modulate SORBS1. miR-223-3p and SORBS1 mRNA levels were assessed by qRT-PCR. The levels of CAFs markers, MVs markers, epithelial-mesenchymal transition (EMT)-associated proteins, and SORBS1 protein were assessed by western blot. MVs isolated from fibroblasts were observed by transmission electron microscopy. Combined with immunofluorescence and co-culture experiments, GC cells were determined to absorb MVs carrying miR-223-3p. Cell functions were measured using CCK-8, transwell, flow cytometry and colony formation assays. The binding of miR-223-3p and SORBS1 was determined by dual-luciferase assay and RNA immunoprecipitation. The cancer-promoting effect of MVs carrying miR-223-3p on experimental animals was verified in vivo by tumor-bearing experiment in nude mice.

Results

miR-223-3p was upregulated in the MVs secreted by GC CAFs and could be transmitted to GC cells through MVs, to boost the malignant progression of tumor cells. Additionally, it was also revealed that miR-223-3p targeted SORBS1 and accelerated progression along with EMT in GC.

Conclusions

CAFs-derived MVs could carry miR-223-3p to GC cells to target SORBS1, thereby promoting the malignant progression of GC.

SORBS1 suppresses tumor metastasis and improves the sensitivity of cancer to chemotherapy drug

Tumor metastasis and invasion are both hallmarks of cancer malignancy and the leading cause of cancer death. Here we show that the adaptor protein SORBS1 (Sorbin and SH3 domain-containing protein 1, also known as CAP/ponsin) is expressed at low levels in clinical cancer samples. In addition, low-level expression of SORBS1 was significantly associated with poor clinical outcomes and the increased tumor cell invasive capacity in breast cancer patients. We demonstrate that depletion of SORBS1 increases protrusions and filopodium-like protrusions (FLPs) formation, as well as the migratory and invasive abilities of cancer cells, via activation of JNK/cJun. Furthermore, silencing of SORBS1 promotes the epithelial-to-mesenchymal transition (EMT) process and attenuates chemical drug sensitivity especially that to cisplatin, by inhibition of p53 in breast cancer cells. Thus, we illustrate that SORBS1 is a potential inhibitor of metastasis in cancer and may be a promising target in chemotherapy.

Ryanodine receptors are part of the myospryn complex in cardiac muscle

The Cardiomyopathy-associated gene 5 (Cmya5) encodes myospryn, a large tripartite motif (TRIM)-related protein found predominantly in cardiac and skeletal muscle. Cmya5 is an expression biomarker for a number of diseases affecting striated muscle and may also be a schizophrenia risk gene. To further understand the function of myospryn in striated muscle, we searched for additional myospryn paralogs. Here we identify a novel muscle-expressed TRIM-related protein minispryn, encoded by Fsd2, that has extensive sequence similarity with the C-terminus of myospryn. Cmya5 and Fsd2 appear to have originated by a chromosomal duplication and are found within evolutionarily-conserved gene clusters on different chromosomes. Using immunoaffinity purification and mass spectrometry we show that minispryn co-purifies with myospryn and the major cardiac ryanodine receptor (RyR2) from heart. Accordingly, myospryn, minispryn and RyR2 co-localise at the junctional sarcoplasmic reticulum of isolated cardiomyocytes. Myospryn redistributes RyR2 into clusters when co-expressed in heterologous cells whereas minispryn lacks this activity. Together these data suggest a novel role for the myospryn complex in the assembly of ryanodine receptor clusters in striated muscle.

Genome-Wide Association Study of Staphylococcus aureus Carriage in a Community-Based Sample of Mexican-Americans in Starr County, Texas

Staphylococcus aureus is the number one cause of hospital-acquired infections. Understanding host pathogen interactions is paramount to the development of more effective treatment and prevention strategies. Therefore, whole exome sequence and chip-based genotype data were used to conduct rare variant and genome-wide association analyses in a Mexican-American cohort from Starr County, Texas to identify genes and variants associated with S. aureus nasal carriage. Unlike most studies of S. aureus that are based on hospitalized populations, this study used a representative community sample. Two nasal swabs were collected from participants (n = 858) 11–17 days apart between October 2009 and December 2013, screened for the presence of S. aureus, and then classified as either persistent, intermittent, or non-carriers. The chip-based and exome sequence-based single variant association analyses identified 1 genome-wide significant region (KAT2B) for intermittent and 11 regions suggestively associated with persistent or intermittent S. aureus carriage. We also report top findings from gene-based burden analyses of rare functional variation. Notably, we observed marked differences between signals associated with persistent and intermittent carriage. In single variant analyses of persistent carriage, 7 of 9 genes in suggestively associated regions and all 5 top gene-based findings are associated with cell growth or tight junction integrity or are structural constituents of the cytoskeleton, suggesting that variation in genes associated with persistent carriage impact cellular integrity and morphology.

Myeloid cell-restricted insulin receptor deficiency protects against obesity-induced inflammation and systemic insulin resistance

A major component of obesity-related insulin resistance is the establishment of a chronic inflammatory state with invasion of white adipose tissue by mononuclear cells. This results in the release of pro-inflammatory cytokines, which in turn leads to insulin resistance in target tissues such as skeletal muscle and liver. To determine the role of insulin action in macrophages and monocytes in obesity-associated insulin resistance, we conditionally inactivated the insulin receptor (IR) gene in myeloid lineage cells in mice (IR(Deltamyel)-mice). While these animals exhibit unaltered glucose metabolism on a normal diet, they are protected from the development of obesity-associated insulin resistance upon high fat feeding. Euglycemic, hyperinsulinemic clamp studies demonstrate that this results from decreased basal hepatic glucose production and from increased insulin-stimulated glucose disposal in skeletal muscle. Furthermore, IR(Deltamyel)-mice exhibit decreased concentrations of circulating tumor necrosis factor (TNF) alpha and thus reduced c-Jun N-terminal kinase (JNK) activity in skeletal muscle upon high fat feeding, reflecting a dramatic reduction of the chronic and systemic low-grade inflammatory state associated with obesity. This is paralleled by a reduced accumulation of macrophages in white adipose tissue due to a pronounced impairment of matrix metalloproteinase (MMP) 9 expression and activity in these cells. These data indicate that insulin action in myeloid cells plays an unexpected, critical role in the regulation of macrophage invasion into white adipose tissue and in the development of obesity-associated insulin resistance.

Ponsin interacts with Nck adapter proteins: implications for a role in cytoskeletal remodelling during differentiation of skeletal muscle cells

Skeletal muscle differentiation is a complex process: It is characterised by changes in gene expression and protein composition. Simultaneously, a dramatic remodelling of the cytoskeleton and associated cell-matrix contacts, the costameres, occurs. The expression and localisation of the protein ponsin at cell-matrix contacts marks the establishment of costameres. In this report we show that skeletal muscle cells are characterised by a novel ponsin isoform, which contains a large insertion in its carboxy-terminus. This skeletal muscle-specific module binds the adapter proteins Nck1 and Nck2, and increased co-localisation of ponsin with Nck2 is observed at remodelling cell-matrix contacts of differentiating skeletal muscle cells. Since this ponsin insertion can be phosphorylated, it may adjust the interaction affinity with Nck adapter proteins. The novel ponsin isoform and its interaction with Nck1/2 provide exciting insight into the convergence of signalling pathways at the costameres, and its crucial role for skeletal muscle differentiation and re-generation.

BmCAP, a silkmoth gene encoding multiple protein isoforms characterized by SoHo and SH3 domains: expression analysis during ovarian follicular development

CAP/ArgBP2/vinexin family proteins, adaptor proteins characterized by three SH3 domains at their C-termini and a SoHo domain towards their N-termini, are known to regulate cell adhesion, cytoskeletal organization, and growth factor signaling. Here we present the isolation and ovarian expression of the BmCAP gene which encodes CAP/ArgBP2/vinexin family proteins in the silkmoth, Bombyx mori. Screening for full-length cDNA clones identified three mRNA isoforms, BmCAP-A1, BmCAP-A2 and BmCAP-B, which show expression throughout ovarian follicular development. Using an antibody raised against a unique region between the SoHo and SH3 domains, BmCAP-A protein isoforms were identified that show specific expression in different compartments of the ovarian follicles. Immunofluorescence staining of the cells of the follicular epithelium establishes a dynamic pattern of BmCAP-A protein localization during choriogenesis. During early choriogenesis, BmCAP-A has a diffuse localization in the cytoplasm but could also be found concentrated at the apical and basal sides at the cell-cell junctions. During late choriogenesis, the diffuse cytoplasmic staining of BmCAP-A disappears while the staining pattern at the apical side resembles a blueprint for the eggshell surface structure. We suggest that BmCAP-A isoforms have important functions during ovarian development, which involve not only the traditional roles in actin organization or cell-cell adhesion but also the regulation of secretion of chorion proteins and the sculpting of the chorion surface.

Proteomic analysis of a membrane skeleton fraction from human liver

The cytoskeleton networks around liver cell cortex can resist Triton extraction and co-pellet with their tightly associated integral membrane proteins, forming assemblies called "membrane skeletons". Despite their important roles in determining cell shape and in signal transduction pathways, the membrane skeletons of human liver cells are uncharacterized to a great extent. In the present work, we prepared a membrane skeleton fraction by Triton extraction of human liver plasma membranes and then separated its protein components by 2-D gels. We optimized the detergent used for protein solubilization and found that 2% ASB-14 allowed the best recovery of membrane skeleton proteins. By analyzing the protein spots with MALDI-TOF and MALDI-TOF-TOF MS, we identified 104 nonredundant proteins, wherein 38 were cytoskeletal proteins that were further classified into several groups, including proteins in fodrin-based meshworks, adhesion proteins (proteins involved in adherens junctions, focal adhesions, desmosomes, hemidesmosomes and tight junctions), proteins that regulate F-actin dynamics, motor proteins, and some other cytoskeletal proteins. To the best of our knowledge, this is one of the largest data sets of membrane skeleton proteins to date. All the results suggested that the liver cells had complex actin- and cytokeratin-based membrane skeletons. This work provided a representative 2-DE map of membrane skeletons from human normal liver, for the purpose of helping to elucidate the composition and function of the membrane skeletons.

Identification and mapping of protein kinase A binding sites in the costameric protein myospryn

Recently we identified a novel target gene of MEF2A named myospryn that encodes a large, muscle-specific, costamere-restricted alpha-actinin binding protein. Myospryn belongs to the tripartite motif (TRIM) superfamily of proteins and was independently identified as a dysbindin-interacting protein. Dysbindin is associated with alpha-dystrobrevin, a component of the dystrophin-glycoprotein complex (DGC) in muscle. Apart from these initial findings little else is known regarding the potential function of myospryn in striated muscle. Here we reveal that myospryn is an anchoring protein for protein kinase A (PKA) (or AKAP) whose closest homolog is AKAP12, also known as gravin/AKAP250/SSeCKS. We demonstrate that myospryn co-localizes with RII alpha, a type II regulatory subunit of PKA, at the peripheral Z-disc/costameric region in striated muscle. Myospryn interacts with RII alpha and this scaffolding function has been evolutionarily conserved as the zebrafish ortholog also interacts with PKA. Moreover, myospryn serves as a substrate for PKA. These findings point to localized PKA signaling at the muscle costamere.

CAP interacts with cytoskeletal proteins and regulates adhesion-mediated ERK activation and motility

CAP/Ponsin belongs to the SoHo family of adaptor molecules that includes ArgBP2 and Vinexin. These proteins possess an N-terminal sorbin homology (SoHo) domain and three C-terminal SH3 domains that bind to diverse signaling molecules involved in a variety of cellular processes. Here, we show that CAP binds to the cytoskeletal proteins paxillin and vinculin. CAP localizes to cell-extracellular matrix (ECM) adhesion sites, and this process requires binding to vinculin. Overexpression of CAP induces the aggregation of paxillin, vinculin and actin at cell-ECM adhesion sites. Moreover, CAP inhibits adhesion-dependent processes such as cell spreading and focal adhesion turnover, whereas a CAP mutant that is unable to localize to cell-ECM adhesion sites is incapable of exerting these effects. Finally, depletion of CAP by siRNA-mediated knockdown leads to enhanced cell spreading, migration and the activation of the PAK/MEK/ERK pathway in REF52 cells. Taken together, these results indicate that CAP is a cytoskeletal adaptor protein involved in modulating adhesion-mediated signaling events that lead to cell migration.

Protein kinase A-dependent increase in WAVE2 expression induced by the focal adhesion protein vinexin

The focal adhesion protein vinexin is a member of a family of adaptor proteins that are thought to participate in the regulation of cell adhesion, cytoskeletal reorganization, and growth factor signaling. Here, we show that vinexin beta increases the amount of and reduces the mobility on SDS-PAGE of Wiskott-Aldrich syndrome protein family verprolin-homologous protein (WAVE) 2 protein, which is a key factor modulating actin polymerization in migrating cells. This mobility retardation disappeared after in vitro phosphatase treatment. Co-immunoprecipitation assays revealed the interaction of vinexin beta with WAVE2 as well as WAVE1 and N-WASP. Vinexin beta interacts with the proline-rich region of WAVE2 through the first and second SH3 domains of vinexin beta. Mutations disrupting the interaction impaired the ability of vinexin beta to increase the amount of WAVE2 protein. Treatments with proteasome inhibitors increased the amount of WAVE2, but did not have an additive effect with vinexin beta. Inhibition of protein kinase A (PKA) activity suppressed the vinexin-induced increase in WAVE2 protein, while activation of PKA increased WAVE2 expression without vinexin beta. These results suggest that vinexin beta regulates the proteasome-dependent degradation of WAVE2 in a PKA-dependent manner.