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Omics score: 50
FLNc Calpain GluC SRM Analysis
ABSTRACT: Human filamin C (FLNc) is a target of the protease calpain at Y2625. To confirm the dependency of calpain cleavage from FLNc phosphorylation at position S2623/S2624 by PKCa, FLNc was overexpressed in HEK293 cells and cells were treated with PMA to stimulated kinase activity, with Gö6976 to inhibit kinase activity or mock-treated with DMSO. Subsequently, recombinant calpain-1 and GluC were used and the resulting peptide TVTSSSSRGSSY was monitored by SRM analyses.
Project description:Human filamin C (FLNc) is a target of the protease calpain at Y2625. To confirm the dependency of calpain cleavage from FLNc phosphorylation at position S2623/S2624 by PKCa, FLNc was overexpressed in HEK293 cells and cells were treated with PMA to stimulated kinase activity, with Gö6976 to inhibit kinase activity or mock-treated with DMSO. Subsequently, recombinant calpain-1 and GluC were used and the resulting peptide TVTSSSSRGSSY was monitored by SRM analyses.
Project description:FLNc, the muscle-specific isoform of the filamin family, is a multi-adaptor protein, comprising 1 amino-terminal actin-binding (ABD) domain followed by 24 immunoglobulin-like (Ig) domains. While FLNc can form homodimers via the last Ig-like domain and thus function as an actin-crosslinker like the other filamins, it features a unique insertion of 82 amino acids (aa) in domain 20. This insert was not only shown to mediate the interaction to several FLNc binding partners, but also to contain an Akt-mediated phosphorylation site at S2234 of mouse FLNc (mFLNc). To reveal novel proteins in the nano-environment of FLNc within myotubes under mild electrical pulse stimulation conditions, we applied a quantitative BioID appraoch.
Project description:The Z-disc is a protein-rich structure critically important for myofibril development and integrity. Since a role of the Z-disc for signal integration and transduction was recently suggested, its precise phosphorylation landscape warranted in-depth analysis. We therefore established a site-resolved protein phosphorylation map of the Z-disc in skeletal myocytes and found that it is a phosphorylation hotspot in living cells, underscoring its functions in signalling and disease-related processes. In an exemplary fashion, we analysed the actin-binding multi-adaptor protein filamin C (FLNc), which is essential for Z-disc assembly and maintenance, and found that PKC phosphorylation at distinct serine residues in its hinge 2 region prevents its cleavage at an adjacent tyrosine residue by calpain 1. With this quantitative in vivo kinase assay, we show that the phosphorylation site S2625 in mouse FLNc is significantly down-regulated upon treatment of C2C12 myotubes with the PKCα inhibitor Gö6976.
Project description:Skeletal muscle is known to adapt dynamically to changes in workload by regulatory processes of the phosphatidylinositide 3-kinase (PI3K)/Akt pathway. We performed a global quantitative phosphoproteomics analysis of contracting mouse C2 myotubes treated with insulin growth factor 1 (IGF-1) or LY294002 to activate or inhibit PI3K/Akt signaling, respectively. Among the significantly regulated phosphopeptides we identified the novel extended basophilic motif RxRxxp[S/T]xxp[S] to be enriched in the set of down-regulated phosphopeptides following inhibition of PI3K/Akt signaling. Using literature-based text mining we identified the kinases Akt, serum and glucocorticoid-regulated kinase 1 (SGK1) and p70S6 kinase to be potentially involved in the phosphorylation of the first serine in the RxRxxp[S/T]xxp[S] motif, whereas no kinase targeting the serine in the +3 position was revealed. In the signaling adapter protein filamin c (FLNc) we found this novel motif in immunoglobulin (Ig)-like domain 20 which is involved in various protein interactions. Through in vitro and in cellulo kinase assays we identified Akt and protein kinase C alpha as the responsible kinases phosphorylating FLNc in this motif at the first and the second serine, respectively.
Project description:Filamin C (FLNC) variants are associated with cardiac and muscular phenotypes. Originally, FLNC variants were described in myofibrillar myopathy (MFM) patients. Later, high-throughput screening in cardiomyopathy cohorts determined a prominent role for FLNC in isolated hypertrophic and dilated cardiomyopathies (HCM and DCM). FLNC variants are now among the more prevalent causes of genetic DCM. FLNC-associated DCM is associated with a malignant clinical course and a high risk of sudden cardiac death. The clinical spectrum of FLNC suggests different pathomechanisms related to variant types and their location in the gene. The appropriate functioning of FLNC is crucial for structural integrity and cell signaling of the sarcomere. The secondary protein structure of FLNC is critical to ensure this function. Truncating variants with subsequent haploinsufficiency are associated with DCM and cardiac arrhythmias. Interference with the dimerization and folding of the protein leads to aggregate formation detrimental for muscle function, as found in HCM and MFM. Variants associated with HCM are predominantly missense variants, which cluster in the ROD2 domain. This domain is important for binding to the sarcomere and to ensure appropriate cell signaling. We here review FLNC genotype-phenotype correlations based on available evidence.
Project description:FilaminC (FLNc) is the muscle-specific member of a family of actin binding proteins. Although it interacts with many proteins involved in muscular dystrophies, its unique role in muscle is poorly understood. To address this, two models were developed. First, FLNc expression was stably reduced in C2C12 myoblasts by RNA interference. While these cells start differentiation normally, they display defects in differentiation and fusion ability and ultimately form multinucleated "myoballs" rather than maintain elongated morphology. Second, a mouse model carrying a deletion of last 8 exons of Flnc was developed. FLNc-deficient mice die shortly after birth, due to respiratory failure, and have severely reduced birth weights, with fewer muscle fibers and primary myotubes, indicating defects in primary myogenesis. They exhibit variation in fiber size, fibers with centrally located nuclei, and some rounded fibers resembling the in vitro phenotype. The similarity of the phenotype of FLNc-deficient mice to the filamin-interacting TRIO null mice was further confirmed by comparing FLNc-deficient C2C12 cells to TRIO-deficient cells. These data provide the first evidence that FLNc has a crucial role in muscle development and maintenance of muscle structural integrity and suggest the presence of a TRIO-FLNc-dependent pathway in maintaining proper myotube structure.
Project description:OBJECTIVE:To identify novel dilated cardiomyopathy (DCM) causing genes, and to elucidate the pathological mechanism leading to DCM by utilizing zebrafish as a model organism. BACKGROUND:DCM, a major cause of heart failure, is frequently familial and caused by a genetic defect. However, only 50% of DCM cases can be attributed to a known DCM gene variant, motivating the ongoing search for novel disease genes. METHODS:We performed whole exome sequencing (WES) in two multigenerational Italian families and one US family with arrhythmogenic DCM without skeletal muscle defects, in whom prior genetic testing had been unrevealing. Pathogenic variants were sought by a combination of bioinformatic filtering and cosegregation testing among affected individuals within the families. We performed function assays and generated a zebrafish morpholino knockdown model. RESULTS:A novel filamin C gene splicing variant (FLNC c.7251+1 G>A) was identified by WES in all affected family members in the two Italian families. A separate novel splicing mutation (FLNC c.5669-1delG) was identified in the US family. Western blot analysis of cardiac heart tissue from an affected individual showed decreased FLNC protein, supporting a haploinsufficiency model of pathogenesis. To further analyze this model, a morpholino knockdown of the ortholog filamin Cb in zebrafish was created which resulted in abnormal cardiac function and ultrastructure. CONCLUSIONS:Using WES, we identified two novel FLNC splicing variants as the likely cause of DCM in three families. We provided protein expression and in vivo zebrafish data supporting haploinsufficiency as the pathogenic mechanism leading to DCM.
Project description:Filamin C (FLNC) is one of three filamin proteins (Filamin A (FLNA), Filamin B (FLNB), and FLNC) that cross-link actin filaments and interact with numerous binding partners. FLNC consists of a N-terminal actin-binding domain followed by 24 immunoglobulin-like repeats with two intervening calpain-sensitive hinges separating R15 and R16 (hinge 1) and R23 and R24 (hinge-2). The FLNC subunit is dimerized through R24 and calpain cleaves off the dimerization domain to regulate mobility of the FLNC subunit. FLNC is localized in the Z-disc due to the unique insertion of 82 amino acid residues in repeat 20 and necessary for normal Z-disc formation that connect sarcomeres. Since phosphorylation of FLNC by PKC diminishes the calpain sensitivity, assembly, and disassembly of the Z-disc may be regulated by phosphorylation of FLNC. Mutations of FLNC result in cardiomyopathy and muscle weakness. Although this review will focus on the current understanding of FLNC structure and functions in muscle, we will also discuss other filamins because they share high sequence similarity and are better characterized. We will also discuss a possible role of FLNC as a mechanosensor during muscle contraction.
Project description:BACKGROUND:Filamin C (FLNC) mutation was reported as a cause of HCM, with a high probability of sudden cardiac death. However, the mutation profile of FLNC, and its relationship with phenotypic expression in HCM, remains to be elucidated. METHODS:In this study, FLNC gene was sequenced in 540 HCM patients and 307 healthy controls. RESULTS:We found that 39 (7.2%) patients carried FLNC mutations, with a similar frequency to that of controls (4.2%, p = 0.101). Pedigree analysis showed that mutations were not well segregated with HCM. The baseline characteristics between HCM patients, with and without mutations, were comparable. FLNC mutations did not increase the risk for either all-cause mortality (HR 0.746, 95% CI 0.222-2.295, p = 0.575) or cardiac mortality (HR 0.615, 95% CI 0.153-1.947, p = 0.354) in HCM patients during a follow-up of 4.7 ± 3.2 years. Moreover, there was no significant difference in survival free from sudden cardiac arrest (HR 0.721, 95% CI 0.128-3.667, p = 0.660) and heart failure (HR 0.757, 95% CI 0.318-1.642, p = 0.447). CONCLUSIONS:FLNC mutations were common in both HCM patients and healthy population. The pathogenicity of FLNC mutations detected in HCM patients and its association with the clinical outcomes should be cautiously interpreted.