Metabolic interplay between Proteus mirabilis and Enterococcus faecalis facilitates polymicrobial biofilm formation and invasive disease.

Biofilms play an important role in the development and pathogenesis of catheter-associated urinary tract infection (CAUTI). Proteus mirabilis and Enterococcus faecalis are common CAUTI pathogens that persistently co-colonize the catheterized urinary tract and form biofilms with increased biomass and antibiotic resistance. In this study, we uncover the metabolic interplay that drives biofilm enhancement and examine the contribution to CAUTI severity. Through compositional and proteomic biofilm analyses, we determined that the increase in biofilm biomass stems from an increase in the protein fraction of the polymicrobial biofilm. We further observed an enrichment in proteins associated with ornithine and arginine metabolism in polymicrobial biofilms compared with single-species biofilms. We show that arginine/ornithine antiport by E. faecalis promotes arginine biosynthesis and metabolism in P. mirabilis, ultimately driving the increase in polymicrobial biofilm protein content without affecting viability of either species. We further show that disrupting E. faecalis ornithine antiport alters the metabolic profile of polymicrobial biofilms and prevents enhancement, and this defect was complemented by supplementation with exogenous ornithine. In a murine model of CAUTI, ornithine antiport did not contribute to E. faecalis colonization but was required for the increased incidence of urinary stone formation and bacteremia that occurs during polymicrobial CAUTI with P. mirabilis. Thus, disrupting metabolic interplay between common co-colonizing species may represent a viable strategy for reducing risk of bacteremia.IMPORTANCEChronic infections often involve the formation of antibiotic-resistant biofilm communities that include multiple different microbes, which pose a challenge for effective treatment. In the catheterized urinary tract, potential pathogens persistently co-colonize for long periods of time and the interactions between them can lead to more severe disease outcomes. In this study, we identified the metabolite L-ornithine as a key mediator of disease-enhancing interactions between two common and challenging pathogens, Enterococcus faecalis and Proteus mirabilis. Disrupting ornithine-mediated interactions may therefore represent a strategy to prevent polymicrobial biofilm formation and decrease risk of severe disease.

Loss of prohibitin 2 in Schwann cells dysregulates key transcription factors controlling developmental myelination.

Schwann cells are critical for the proper development and function of the peripheral nervous system (PNS), where they form a collaborative relationship with axons. Past studies highlighted that a pair of proteins called the prohibitins play major roles in Schwann cell biology. Prohibitins are ubiquitously expressed and versatile proteins. We have previously shown that while prohibitins play a crucial role in Schwann cell mitochondria for long-term myelin maintenance and axon health, they may also be present at the Schwann cell-axon interface during development. Here, we expand on this, showing that drug-mediated modulation of prohibitins in vitro disrupts myelination and confirming that Schwann cell-specific ablation of prohibitin 2 (Phb2) in vivo results in severe defects in radial sorting and myelination. We show in vivo that Phb2-null Schwann cells cannot effectively proliferate and the transcription factors EGR2 (KROX20), POU3F1 (OCT6), and POU3F2 (BRN2), necessary for proper Schwann cell maturation, are dysregulated. Schwann cell-specific deletion of Jun, a transcription factor associated with negative regulation of myelination, confers partial rescue of the developmental defect seen in mice lacking Schwann cell Phb2. Finally, we identify a pool of candidate PHB2 interactors that change their interaction with PHB2 depending on neuronal signals, and thus are potential mediators of PHB2-associated developmental defects. This work develops our understanding of Schwann cell biology, revealing that Phb2 may modulate the timely expression of transcription factors necessary for proper PNS development, and proposing candidates that may play a role in PHB2-mediated integration of axon signals in the Schwann cell.

DNA damage-induced phosphorylation of a replicative DNA helicase results in inhibition of DNA replication through attenuation of helicase function.

A major function of the DNA damage responses (DDRs) that act during the replicative phase of the cell cycle is to inhibit initiation and elongation of DNA replication. It has been shown that DNA replication of the polyomavirus, SV40, is inhibited and its replication fork is slowed by cellular DDR responses. The inhibition of SV40 DNA replication is associated with enhanced DDR kinase phosphorylation of SV40 Large T-antigen (LT), the viral DNA helicase. Mass spectroscopy was used to identify a novel highly conserved DDR kinase site, T518, on LT. In cell-based assays expression of a phosphomimetic form of LT at T518 (T518D) resulted in dramatically decreased levels of SV40 DNA replication, but LT-dependent transcriptional activation was unaffected. Purified WT and LT T518D were analyzed in vitro. In concordance with the cell-based data, reactions using SV40 LT-T518D, but not T518A, showed dramatic inhibition of SV40 DNA replication. A myriad of LT protein-protein interactions and LT's biochemical functions were unaffected by the LT T518D mutation; however, LT's DNA helicase activity was dramatically decreased on long, but not very short, DNA templates. These results suggest that DDR phosphorylation at T518 inhibits SV40 DNA replication by suppressing LT helicase activity.

RESC14 and RESC8 cooperate to mediate RESC function and dynamics during trypanosome RNA editing.

Mitochondrial transcripts in Trypanosoma brucei require extensive uridine insertion/deletion RNA editing to generate translatable open reading frames. The RNA editing substrate binding complex (RESC) serves as the scaffold that coordinates the protein-protein and protein-RNA interactions during editing. RESC broadly contains two modules termed the guide RNA binding complex (GRBC) and the RNA editing mediator complex (REMC), as well as organizer proteins. How the protein and RNA components of RESC dynamically interact to facilitate editing is not well understood. Here, we examine the roles of organizer proteins, RESC8 and RESC14, in facilitating RESC dynamics. High-throughput sequencing of editing intermediates reveals an overlapping RESC8 and RESC14 function during editing progression across multiple transcripts. Blue native PAGE analysis demonstrates that RESC14 is essential for incorporation of RESC8 into a large RNA-containing complex, while RESC8 is important in recruiting a smaller ribonucleoprotein complex (RNP) to this large complex. Proximity labeling shows that RESC14 is important for stable RESC protein-protein interactions, as well as RESC-RECC associations. Together, our data support a model in which RESC14 is necessary for assembly of editing competent RESC through recruitment of an RNP containing RESC8, GRBC and gRNA to REMC and mRNA.

Loss of prohibitin 2 in Schwann cells dysregulates key transcription factors controlling developmental myelination.

Schwann cells are critical for the proper development and function of the peripheral nervous system, where they form a mutually beneficial relationship with axons. Past studies have highlighted that a pair of proteins called the prohibitins play major roles in Schwann cell biology. Prohibitins are ubiquitously expressed and versatile proteins. We have previously shown that while prohibitins play a crucial role in Schwann cell mitochondria for long-term myelin maintenance and axon health, they may also be present at the Schwann cell-axon interface during development. Here, we expand on this work, showing that drug-mediated modulation of prohibitins in vitro disrupts myelination and confirming that Schwann cell-specific ablation of prohibitin 2 (Phb2) in vivo results in early and severe defects in peripheral nerve development. Using a proteomic approach in vitro, we identify a pool of candidate PHB2 interactors that change their interaction with PHB2 depending on the presence of axonal signals. Furthermore, we show in vivo that loss of Phb2 in mouse Schwann cells causes ineffective proliferation and dysregulation of transcription factors EGR2 (KROX20), POU3F1 (OCT6) and POU3F2 (BRN2) that are necessary for proper Schwann cell maturation. Schwann cell-specific deletion of Jun, a transcription factor associated with negative regulation of myelination, confers partial rescue of the development defect seen in mice lacking Schwann cell Phb2. This work develops our understanding of Schwann cell biology, revealing that Phb2 may directly or indirectly modulate the timely expression of transcription factors necessary for proper peripheral nervous system development, and proposing candidates that may play a role in PHB2-mediated integration of axon signals in the Schwann cell.

Proteomics Analysis of the Polyomavirus DNA Replication Initiation Complex Reveals Novel Functional Phosphorylated Residues and Associated Proteins.

Polyomavirus (PyV) Large T-antigen (LT) is the major viral regulatory protein that targets numerous cellular pathways for cellular transformation and viral replication. LT directly recruits the cellular replication factors involved in initiation of viral DNA replication through mutual interactions between LT, DNA polymerase alpha-primase (Polprim), and single-stranded DNA binding complex, (RPA). Activities and interactions of these complexes are known to be modulated by post-translational modifications; however, high-sensitivity proteomic analyses of the PTMs and proteins associated have been lacking. High-resolution liquid chromatography tandem mass spectrometry (LC-MS/MS) of the immunoprecipitated factors (IPMS) identified 479 novel phosphorylated amino acid residues (PAARs) on the three factors; the function of one has been validated. IPMS revealed 374, 453, and 183 novel proteins associated with the three, respectively. A significant transcription-related process network identified by Gene Ontology (GO) enrichment analysis was unique to LT. Although unidentified by IPMS, the ETS protooncogene 1, transcription factor (ETS1) was significantly overconnected to our dataset indicating its involvement in PyV processes. This result was validated by demonstrating that ETS1 coimmunoprecipitates with LT. Identification of a novel PAAR that regulates PyV replication and LT's association with the protooncogenic Ets1 transcription factor demonstrates the value of these results for studies in PyV biology.

Systems pharmacodynamic model of combined gemcitabine and trabectedin in pancreatic cancer cells. Part I.Çô Effects on signal transduction pathways related to tumor growth.

Pancreatic ductal adenocarcinoma (PDAC) is often chemotherapy-resistant, and novel drug combinations would fill an unmet clinical need. Previously we reported synergistic cytotoxic effects of gemcitabine and trabectedin on pancreatic cancer cells, but underlying protein-level interaction mechanisms remained unclear. We employed a reliable, sensitive, comprehensive, quantitative, high-throughput IonStar proteomic workflow to investigate the time course of gemcitabine and trabectedin effects, alone and combined, upon pancreatic cancer cells. MiaPaCa-2 cells were incubated with vehicle (controls), gemcitabine, trabectedin, and their combinations over 72 hours. Samples were collected at intervals and analyzed using the label-free IonStar liquid chromatography-mass spectrometry (LC-MS/MS) workflow to provide temporal quantification of protein expression for 4,829 proteins in four experimental groups. To characterize diverse signal transduction pathways, a comprehensive systems pharmacodynamic (SPD) model was developed. The analysis is presented in two parts. Here, Part I describes drug responses in cancer cell growth and migration pathways included in the full model: receptor tyrosine kinase- (RTK), integrin-, G-protein coupled receptor- (GPCR), and calcium-signaling pathways. The developed model revealed multiple underlying mechanisms of drug actions, provides insight into the basis of drug interaction synergism, and offers a scientific rationale for potential drug combination strategies.

Fibroblast growth factor receptor 1 inhibition suppresses pancreatic cancer chemoresistance and chemotherapy-driven aggressiveness.

AIMS: Pancreatic ductal adenocarcinoma (PDAC) is often intrinsically-resistant to standard-of-care chemotherapies such as gemcitabine. Acquired gemcitabine resistance (GemR) can arise from treatment of initially-sensitive tumors, and chemotherapy can increase tumor aggressiveness. We investigated the molecular mechanisms of chemoresistance and chemotherapy-driven tumor aggressiveness, which are understood incompletely. METHODS: Differential proteomic analysis was employed to investigate chemotherapy-driven chemoresistance drivers and responses of PDAC cells and patient-derived tumor xenografts (PDX) having different chemosensitivities. We also investigated the prognostic value of FGFR1 expression in the efficacy of selective pan-FGFR inhibitor (FGFRi)-gemcitabine combinations. RESULTS: Quantitative proteomic analysis of a highly-GemR cell line revealed fibroblast growth factor receptor 1 (FGFR1) as the highest-expressed receptor tyrosine kinase. FGFR1 knockdown or FGFRi co-treatment enhanced gemcitabine efficacy and decreased GemR marker expression, implicating FGFR1 in augmentation of GemR. FGFRi treatment reduced PDX tumor progression and prolonged survival significantly, even in highly-resistant tumors in which neither single-agent showed efficacy. Gemcitabine exacerbated aggressiveness of highly-GemR tumors, based upon proliferation and metastatic markers. Combining FGFRi with gemcitabine or gemcitabine+nab-paclitaxel reversed tumor aggressiveness and progression, and prolonged survival significantly. In multiple PDAC PDXs, FGFR1 expression correlated with intrinsic tumor gemcitabine sensitivity. CONCLUSION: FGFR1 drives chemoresistance and tumor aggressiveness, which FGFRi can reverse.

Proteomics analysis reveals novel phosphorylated residues and associated proteins of the polyomavirus DNA replication initiation complex.

Polyomavirus ( PyV ) Large T-antigen ( LT ) is the major viral regulatory protein that targets numerous cellular factors/pathways: tumor suppressors, cell cycle regulators, transcription and chromatin regulators, as well as other factors for viral replication. LT directly recruits the cellular replication factors involved in LT's recognition of the viral origin, origin unwinding, and primer synthesis which is carried out by mutual interactions between LT, DNA polymerase alpha-primase ( Polprim ), and single strand (ss) DNA binding replication protein A ( RPA ). The activities as well as interactions of these three with each other as well as other factors, are known to be modulated by post-translational modifications (PTMs); however, modern high-sensitivity proteomic analyses of the PTMs as well as proteins associated with the three have been lacking. Elution from immunoprecipitation (IP) of the three factors were subjected to high-resolution liquid chromatography tandem mass spectrometry (LC-MS/MS). We identified 479 novel phosphorylated amino acid residues (PAARs) on the three factors: 82 PAARs on SV40 LT, 305 on the Polprim heterotetrametric complex and 92 on the RPA heterotrimeric complex. LC-MS/MS analysis also identified proteins that co-immunoprecipitated (coIP-ed) with the three factors that were not previously reported: 374 with LT, 453 with Polprim and 183 with RPA. We used a bioinformatic-based approach to analyze the proteomics data and demonstrate a highly significant "enrichment" of transcription-related process associated uniquely with LT, consistent with its role as a transcriptional regulator, as opposed to Polprim and RPA associated proteins which showed no such enrichment. The most significant cell cycle related network was regulated by ETS proto-oncogene 1 (ETS1), indicating its involvement in regulatory control of DNA replication, repair, and metabolism. The interaction between LT and ETS1 is validated and shown to be independent of nucleic acids. One of the novel phosphorylated aa residues detected on LT from this study, has been demonstrated by us to affect DNA replication activities of SV40 Large T-antigen. Our data provide substantial additional novel information on PAARs, and proteins associated with PyV LT, and the cellular Polprim-, RPA- complexes which will benefit research in DNA replication, transformation, transcription, and other viral and host cellular processes.

Systems Pharmacodynamic Model of Combined Gemcitabine and Trabectedin in Pancreatic Cancer Cells. Part II: Cell Cycle, DNA Damage Response, and Apoptosis Pathways.

Despite decades of research efforts, pancreatic adenocarcinoma (PDAC) continues to present a formidable clinical challenge, demanding innovative therapeutic approaches. In a prior study, we reported the synergistic cytotoxic effects of gemcitabine and trabectedin on pancreatic cancer cells. To investigate potential mechanisms underlying this synergistic pharmacodynamic interaction, liquid chromatography-mass spectrometry-based proteomic analysis was performed, and a systems pharmacodynamics model (SPD) was developed to capture pancreatic cancer cell responses to gemcitabine and trabectedin, alone and combined, at the proteome level. Companion report Part I describes the proteomic workflow and drug effects on the upstream portion of the SPD model related to cell growth and migration, specifically the RTK-, integrin-, GPCR-, and calcium-signaling pathways. This report presents Part II of the SPD model. Here we describe drug effects on pathways associated with cell cycle, DNA damage response (DDR), and apoptosis, and provide insights into underlying mechanisms. Drug combination effects on protein changes in the cell cycle- and apoptosis pathways contribute to the synergistic effects observed between gemcitabine and trabectedin. The SPD model was subsequently incorporated into our previously-established cell cycle model, forming a comprehensive, multi-scale quantification platform for evaluating drug effects across multiple scales, spanning the proteomic-, cellular-, and subcellular levels. This approach provides a quantitative mechanistic framework for evaluating drug-drug interactions in combination chemotherapy, and could potentially serve as a tool to predict combinatorial efficacy and assist in target selection.

Highly Reproducible Quantitative Proteomics Analysis of Pancreatic Cancer Cells Reveals Proteome-Level Effects of a Novel Combination Drug Therapy That Induces Cancer Cell Death via Metabolic Remodeling and Activation of the Extrinsic Apoptosis Pathway.

Pancreatic cancer patients have poor survival rates and are frequently treated using gemcitabine (Gem). However, initial tumor sensitivity often gives way to rapid development of resistance. Gem-based drug combinations are employed to increase efficacy and mitigate resistance, but our understanding of molecular-level drug interactions, which could assist in the development of more effective therapeutic regimens, is limited. Global quantitative proteomic analysis could provide novel mechanistic insights into drug combination interactions, but it is challenging to achieve high-quality quantitative proteomics analysis of the large sample sets that are typically required for drug combination studies. Here, we investigated molecular-level temporal interactions of Gem with BGJ398 (infigratinib), a recently approved pan-FGFR inhibitor, in multiple treatment groups (N = 42 samples) using IonStar, a robust large-scale proteomics method that employs well-controlled, ultrahigh-resolution MS1 quantification. A total of 5514 proteins in the sample set were quantified without missing data, requiring >2 unique peptides/protein, <1% protein false discovery rate (FDR), <0.1% peptide FDR, and CV < 10%. Functional analysis of the differentially altered proteins revealed drug-dysregulated processes such as metabolism, apoptosis, and antigen presentation pathways. These changes were validated experimentally using Seahorse metabolic assays and immunoassays. Overall, in-depth analysis of large-scale proteomics data provided novel insights into possible mechanisms by which FGFR inhibitors complement and enhance Gem activity in pancreatic cancers.

Translational control by Trypanosoma brucei DRBD18 contributes to the maintenance of the procyclic state.

Trypanosoma brucei occupies distinct niches throughout its life cycle, within both the mammalian and tsetse fly hosts. The immunological and biochemical complexity and variability of each of these environments require a reshaping of the protein landscape of the parasite both to evade surveillance and face changing metabolic demands. In kinetoplastid protozoa, including T. brucei, posttranscriptional control mechanisms are the primary means of gene regulation, and these are often mediated by RNA-binding proteins. DRBD18 is a T. brucei RNA-binding protein that reportedly interacts with ribosomal proteins and translation factors. Here, we tested a role for DRBD18 in translational control. We validate the DRBD18 interaction with translating ribosomes and the translation initiation factor, eIF3a. We further show that DRBD18 depletion by RNA interference leads to altered polysomal profiles with a specific depletion of heavy polysomes. Ribosome profiling analysis reveals that 101 transcripts change in translational efficiency (TE) upon DRBD18 depletion: 41 exhibit decreased TE and 60 exhibit increased TE. A further 66 transcripts are buffered, that is, changes in transcript abundance are compensated by changes in TE such that the total translational output is expected not to change. In DRBD18-depleted cells, a set of transcripts that codes for procyclic form-specific proteins is translationally repressed while, conversely, transcripts that code for bloodstream form- and metacyclic form-specific proteins are translationally enhanced. RNA immunoprecipitation/qRT-PCR indicates that DRBD18 associates with members of both repressed and enhanced cohorts. These data suggest that DRBD18 contributes to the maintenance of the procyclic state through both positive and negative translational control of specific mRNAs.

Species-Deconvolved Proteomics for In Situ Investigation of Tumor-Stroma Interactions after Treatment of Pancreatic Cancer Patient-Derived Xenografts with Combined Gemcitabine and Paclitaxel.

Tumor-stroma interactions are critical in pancreatic ductal adenocarcinoma (PDAC) progression and therapeutics. Patient-derived xenograft (PDX) models recapitulate tumor-stroma interactions, but the conventional antibody-based immunoassay is inadequate to discriminate tumor and stromal proteins. Here, we describe a species-deconvolved proteomics approach embedded in IonStar that can unambiguously quantify the tumor (human-derived) and stromal (mouse-derived) proteins in PDX samples, enabling unbiased investigation of tumor and stromal proteomes with excellent quantitative reproducibility. With this strategy, we studied tumor-stroma interactions in PDAC PDXs that responded differently to Gemcitabine combined with nab-Paclitaxel (GEM+PTX) treatment. By analyzing 48 PDX animals 24 h/192 h after treatment with/without GEM+PTX, we quantified 7262 species-specific proteins under stringent cutoff criteria, with high reproducibility. For the PDX sensitive to GEM+PTX, the drug-dysregulated proteins in tumor cells were involved in suppressed oxidative phosphorylation and the TCA cycle, and in the stroma, inhibition of glycolytic activity was predominant, suggesting a relieved reverse Warburg effect by the treatment. In GEM+PTX-resistant PDXs, protein changes suggested extracellular matrix deposition and activation of tumor cell proliferation. Key findings were validated by immunohistochemistry (IHC). Overall, this approach provides a species-deconvolved proteomic platform that could advance cancer therapeutic studies by enabling unbiased exploration of tumor-stroma interactions in the large number of PDX samples required for such investigations.

Metabolic interplay between Proteus mirabilis and Enterococcus faecalis facilitates polymicrobial biofilm formation and invasive disease.

Polymicrobial biofilms play an important role in the development and pathogenesis of CAUTI. Proteus mirabilis and Enterococcus faecalis are common CAUTI pathogens that persistently co-colonize the catheterized urinary tract and form biofilms with increased biomass and antibiotic resistance. In this study, we uncover the metabolic interplay that drives biofilm enhancement and examine the contribution to CAUTI severity. Through compositional and proteomic biofilm analyses, we determined that the increase in biofilm biomass stems from an increase in the protein fraction of the polymicrobial biofilm matrix. We further observed an enrichment in proteins associated with ornithine and arginine metabolism in polymicrobial biofilms compared to single-species biofilms. We show that L-ornithine secretion by E. faecalis promotes arginine biosynthesis in P. mirabilis, and that disruption of this metabolic interplay abrogates the biofilm enhancement we see in vitro and leads to significant decreases in infection severity and dissemination in a murine CAUTI model.

Quantitative Proteomics of Human Retinal Pigment Epithelium Reveals Key Regulators for the Pathogenesis of Age-Related Macular Degeneration.

Age-related macular degeneration (AMD) is the leading cause of blindness in elderly people, with limited treatment options available for most patients. AMD involves the death of retinal pigment epithelium (RPE) and photoreceptor cells, with mitochondria dysfunction being a critical early event. In the current study, we utilized our unique resource of human donor RPE graded for AMD presence and severity to investigate proteome-wide dysregulation involved in early AMD. Organelle-enriched fractions of RPE were isolated from donors with early AMD (n = 45) and healthy age-matched controls (n = 32) and were analyzed by UHR-IonStar, an integrated proteomics platform enabling reliable and in-depth proteomic quantification in large cohorts. A total of 5941 proteins were quantified with excellent analytical reproducibility, and with further informatics analysis, many biological functions and pathways were found to be significantly dysregulated in donor RPE samples with early AMD. Several of these directly pinpointed changes in mitochondrial functions, e.g., translation, ATP metabolic process, lipid homeostasis, and oxidative stress. These novel findings highlighted the value of our proteomics investigation by allowing a better understanding of the molecular mechanisms underlying early AMD onset and facilitating both treatment development and biomarker discovery.

Comparative Proteomics Analysis of Exosomes Identifies Key Pathways and Protein Markers Related to Breast Cancer Metastasis.

Proteomics analysis of circulating exosomes derived from cancer cells represents a promising approach to the elucidation of cell-cell communication and the discovery of putative biomarker candidates for cancer diagnosis and treatment. Nonetheless, the proteome of exosomes derived from cell lines with different metastatic capabilities still warrants further investigation. Here, we present a comprehensive quantitative proteomics investigation of exosomes isolated from immortalized mammary epithelial cells and matched tumor lines with different metastatic potentials in an attempt to discover exosome markers specific to breast cancer (BC) metastasis. A total of 2135 unique proteins were quantified with a high confidence level from 20 isolated exosome samples, including 94 of the TOP 100 exosome markers archived by ExoCarta. Moreover, 348 altered proteins were observed, among which several metastasis-specific markers, including cathepsin W (CATW), magnesium transporter MRS2 (MRS2), syntenin-2 (SDCB2), reticulon-4 (RTN), and UV excision repair protein RAD23 homolog (RAD23B), were also identified. Notably, the abundance of these metastasis-specific markers corresponds well with the overall survival of BC patients in clinical settings. Together, these data provide a valuable dataset for BC exosome proteomics investigation and prominently facilitate the elucidation of the molecular mechanisms underlying primary tumor development and progression.

Translational control by Trypanosoma brucei DRBD18 contributes to the maintenance of the procyclic state.

Trypanosoma brucei occupies distinct niches throughout its life cycle, within both the mammalian and tsetse fly hosts. The immunological and biochemical complexity and variability of each of these environments require a reshaping of the protein landscape of the parasite both to evade surveillance and face changing metabolic demands. Whereas most well-studied organisms rely on transcriptional control as the main regulator of gene expression, post-transcriptional control mechanisms are particularly important in T. brucei , and these are often mediated by RNA-binding proteins. DRBD18 is a T. brucei RNA-binding protein that interacts with ribosomal proteins and translation factors. Here, we tested a role for DRBD18 in translational control. We show that DRBD18 depletion by RNA interference leads to altered polysomal profiles with a specific depletion of heavy polysomes. Ribosome profiling analysis reveals that 101 transcripts change in translational efficiency (TE) upon DRBD18 depletion: 41 exhibit decreased TE and 60 exhibit increased TE. A further 66 transcripts are buffered, i.e . changes in transcript abundance are compensated by changes in TE such that the total translational output is expected not to change. Proteomic analysis validates these data. In DRBD18-depleted cells, a cohort of transcripts that codes for procyclic form-specific proteins is translationally repressed while, conversely, transcripts that code for bloodstream form- and metacyclic form-specific proteins are translationally enhanced. These data suggest that DRBD18 contributes to the maintenance of the procyclic state through both positive and negative translational control of specific mRNAs.

High-quality and robust protein quantification in large clinical/pharmaceutical cohorts with IonStar proteomics investigation.

Robust, reliable quantification of large sample cohorts is often essential for meaningful clinical or pharmaceutical proteomics investigations, but it is technically challenging. When analyzing very large numbers of samples, isotope labeling approaches may suffer from substantial batch effects, and even with label-free methods, it becomes evident that low-abundance proteins are not reliably measured owing to unsufficient reproducibility for quantification. The MS1-based quantitative proteomics pipeline IonStar was designed to address these challenges. IonStar is a label-free approach that takes advantage of the high sensitivity/selectivity attainable by ultrahigh-resolution (UHR)-MS1 acquisition (e.g., 120-240k full width at half maximum at m/z = 200) which is now widely available on ultrahigh-field Orbitrap instruments. By selectively and accurately procuring quantitative features of peptides within precisely defined, very narrow m/z windows corresponding to the UHR-MS1 resolution, the method minimizes co-eluted interferences and substantially enhances signal-to-noise ratio of low-abundance species by decreasing noise level. This feature results in high sensitivity, selectivity, accuracy and precision for quantification of low-abundance proteins, as well as fewer missing data and fewer false positives. This protocol also emphasizes the importance of well-controlled, robust experimental procedures to achieve high-quality quantification across a large cohort. It includes a surfactant cocktail-aided sample preparation procedure that achieves high/reproducible protein/peptide recoveries among many samples, and a trapping nano-liquid chromatography-mass spectrometry strategy for sensitive and reproducible acquisition of UHR-MS1 peptide signal robustly across a large cohort. Data processing and quality evaluation are illustrated using an example dataset ( http://proteomecentral.proteomexchange.org ), and example results from pharmaceutical project and one clinical project (patients with acute respiratory distress syndrome) are shown. The complete IonStar pipeline takes ~1-2 weeks for a sample cohort containing ~50-100 samples.

In-depth mapping of protein localizations in whole tissue by micro-scaffold assisted spatial proteomics (MASP).

Accurate, in-depth mapping of proteins on whole-tissue levels provides comprehensive insights into the spatially-organized regulatory processes/networks in tissues, but is challenging. Here we describe a micro-scaffold assisted spatial proteomics (MASP) strategy, based on spatially-resolved micro-compartmentalization of tissue using a 3D-printed micro-scaffold, capable of mapping thousands of proteins across a whole-tissue slice with excellent quantitative accuracy/precision. The pipeline includes robust tissue micro-compartmentalization with precisely-preserved spatial information, reproducible procurement and preparation of the micro-specimens, followed by sensitive LC-MS analysis and map generation by a MAsP app. The mapping accuracy was validated by comparing the MASP-generated maps of spiked-in peptides and brain-region-specific markers with known patterns, and by correlating the maps of the two protein components of the same heterodimer. The MASP was applied in mapping >5000 cerebral proteins in the mouse brain, encompassing numerous important brain markers, regulators, and transporters, where many of these proteins had not previously been mapped on the whole-tissue level.

Identification of Potential Megalin/Cubilin Substrates Using Extensive Proteomics Quantification from Kidney Megalin-Knockdown Mice.

Megalin and cubilin, endocytic proteins present in the proximal tubule of the kidney, are responsible for reabsorbing filtered proteins from urine. Our hypothesis was that potential substrates of megalin/cubilin could be identified by examining urinary protein differences between control (WT) mice and kidney-specific megalin knockdown (KD) mice. Using the IonStar proteomics approach, 877 potential megalin/cubilin substrates were discovered, with 23 of these compounds representing known megalin/cubilin substrates. Some of the proteins with the largest fold changes in the urine between KD and WT included the known megalin substrates retinol-binding protein and vitamin D-binding protein. Of the total proteins identified as novel substrates, about three-quarters of compounds had molecular weights (MWs) below 69 kDa, the MW of albumin, and the remaining had higher MWs, with about 5% of the proteins having MWs greater than 150 kDa. Sex differences in the number of identified substrates occurred, but this may be due to differences in kidney megalin expression between both male and female megalin KD and WT animals, with the ratio of megalin between WT and KD being 2.76 and 2.14 for female and male mice, respectively. The top three ingenuity canonical pathways based on the urinary proteins in both female and male KD mice were acute phase response signaling, liver X receptor/retinoid X receptor activation, and intrinsic prothrombin activation pathways. In conclusion, analysis of urine samples from kidney-specific megalin KD and WT mice was found to be useful for the identification of potential endogenous substrates for megalin and cubilin.