Septin dynamics are essential for exocytosis.

Septins are a family of 14 cytoskeletal proteins that dynamically form hetero-oligomers and organize membrane microdomains for protein complexes. The previously reported interactions with SNARE proteins suggested the involvement of septins in exocytosis. However, the contradictory results of up- or down-regulation of septin-5 in various cells and mouse models or septin-4 in mice suggested either an inhibitory or a stimulatory role for these septins in exocytosis. The involvement of the ubiquitously expressed septin-2 or general septin polymerization in exocytosis has not been explored to date. Here, by nano-LC with tandem MS and immunoblot analyses of the septin-2 interactome in mouse brain, we identified not only SNARE proteins but also Munc-18-1 (stabilizes assembled SNARE complexes), N-ethylmaleimide-sensitive factor (NSF) (disassembles SNARE complexes after each membrane fusion event), and the chaperones Hsc70 and synucleins (maintain functional conformation of SNARE proteins after complex disassembly). Importantly, α-soluble NSF attachment protein (SNAP), the adaptor protein that mediates NSF binding to the SNARE complex, did not interact with septin-2, indicating that septins undergo reorganization during each exocytosis cycle. Partial depletion of septin-2 by siRNA or impairment of septin dynamics by forchlorfenuron inhibited constitutive and stimulated exocytosis of secreted and transmembrane proteins in various cell types. Forchlorfenuron impaired the interaction between SNAP-25 and its chaperone Hsc70, decreasing SNAP-25 levels in cultured neuroendocrine cells, and inhibited both spontaneous and stimulated acetylcholine secretion in mouse motor neurons. The results demonstrate a stimulatory role of septin-2 and the dynamic reorganization of septin oligomers in exocytosis.

Phospho-Network Analysis Identifies and Quantifies Hepatitis C Virus (HCV)-induced Hepatocellular Carcinoma (HCC) Proteins Regulating Viral-mediated Tumor Growth.

BACKGROUND: Patients with chronic hepatitis C virus (HCV) infection are at risk of serious complications of cirrhosis and hepatocellular carcinoma (HCC). Mass spectrometry (MS) is a versatile methodology that produces a global proteomic landscape for analysis of cancer mechanisms. MATERIALS AND METHODS: Using multiplex peptide stable isotopic labeling and immobilized metal affinity chromatography (IMAC), we enriched and quantified the phosphoproteome of HCC, with and without HCV. While raw data identified protein targets based on expression alone, we also used abundance groups for comprehensive functional analysis. RESULTS: Analysis of functional differences highlighted deregulated phosphoprotein networks. This uncovered additional candidates that could be directly derived from the MS data. Cellular processes and pathways that may differ with HCV infection include: cytoskeletal dynamics, insulin response, gene expression, and PI3K/AKT oncogenesis. CONCLUSION: This function-focused workflow provides a simple framework to analyze MS data. Phosphoproteome quantitation with inclusive functional analysis can generate hypotheses for liver cancer research to improve early screening and identification of molecular targets for therapy.

The Structure and Interactions of Periplasmic Domains of Crucial MmpL Membrane Proteins from Mycobacterium tuberculosis.

Mycobacterium tuberculosis mycobacterial membrane protein large (MmpL) proteins are important in substrate transport across the inner membrane. Here, we show that MmpL proteins are classified into two phylogenetic clusters, where MmpL cluster II contains three soluble domains (D1, D2, and D3) and has two full-length members, MmpL3 and MmpL11. Significantly, MmpL3 is currently the most druggable M. tuberculosis target. We have solved the 2.4-Å MmpL11-D2 crystal structure, revealing structural homology to periplasmic porter subdomains of RND (multidrug) transporters. The resulting predicted cluster II MmpL membrane topology has D1 and D2 residing, and possibly interacting, within the periplasm. Crosslinking and biolayer interferometry experiments confirm that cluster II D1 and D2 bind with weak affinities, and guided D1-D2 heterodimeric model assemblies. The predicted full-length MmpL3 and MmpL11 structural models reveal key substrate binding and transport residues, and may serve as templates to set the stage for in silico anti-tuberculosis drug development.

Combined phosphoproteomics and bioinformatics strategy in deciphering drug resistant related pathways in triple negative breast cancer.

Because of the absence of a clear therapeutic target for triple negative breast cancer (TNBC), conventional chemotherapy is the only available systemic treatment option for these patients. Despite chemotherapy treatment, TNBC patients still have worse prognosis when compared with other breast cancer patients. The study is to investigate unique phosphorylated proteins expressed in chemoresistant TNBC cell lines. In the current study, twelve TNBC cell lines were subjected to drug sensitivity assays against chemotherapy drugs docetaxel, doxorubicin, gemcitabine, and cisplatin. Based on their half maximal inhibitory concentrations, four resistant and two sensitive cell lines were selected for further analysis. The phosphopeptides from these cells were enriched with TiO2 beads and fractionated using strong cation exchange. 1,645 phosphoprotein groups and 9,585 unique phosphopeptides were identified by a high throughput LC-MS/MS system LTQ-Orbitrap. The phosphopeptides were further filtered with Ascore system and 1,340 phosphoprotein groups, 2,760 unique phosphopeptides, and 4,549 unique phosphosites were identified. Our study suggested that differentially phosphorylated Cdk5, PML, AP-1, and HSF-1 might work together to promote vimentin induced epithelial to mesenchymal transition (EMT) in the drug resistant cells. EGFR and HGF were also shown to be involved in this process.

Drip, Ship, and Grip, then Slice and Dice: Comprehensive Stroke Center Management of Cervical and Intracranial Emboli.

BACKGROUND AND PURPOSE: Tandem acute thrombotic emboli in the cervical and intracranial arteries are an unusual cause of stroke presenting unique management challenges. In regional systems of acute stroke care anchored by Comprehensive Stroke Centers (CSC), combined fibrinolytic, endovascular, and open surgical intervention is a new therapeutic option. SUMMARY OF CASE: A 28-year-old male underwent retinal surgery, including post-operative neck compression and the next day presented to a primary stroke center with aphasia and right hemiplegia. Intravenous tissue plasminogen activator therapy was initiated and the patient was transferred to a CSC for higher level of care (drip and ship). Imaging at the CSC demonstrated tandem thrombi: a near occlusive lesion at the origin of the left cervical internal carotid artery and a total occlusion of the M1 segment of the left middle cerebral artery. Endovascular thrombectomy with the Solitaire stent retriever resulted in intracranial recanalization (grip). Immediately after the endovascular procedure, open carotid thrombectomy was performed to achieve cervical carotid revascularization without systemic heparinization (slice). Both cervical carotid and intracranial thrombi were processed for proteomic analysis via mass spectrometry (dice). CONCLUSION: Combined fibrinolytic, endovascular, and open surgical intervention can yield revascularization and good clinical outcome in cases of tandem lesions.