The F-BAR protein PACSIN2 regulates epidermal growth factor receptor internalization

Comprehensive Analyses of the Effects of the Small-Molecule Inhibitor of the UHM Domain in the Splicing Factor U2AF1 in Leukemia Cells

Mutations in RNA splicing factor genes including SF3B1, U2AF1, SRSF2, and ZRSR2 have been reported to contribute to development of myeloid neoplasms including myelodysplastic syndrome (MDS) and secondary acute myeloid leukemia (sAML). Chemical tools targeting cells carrying these mutant genes remain limited and underdeveloped. Among the four proteins, mutant U2AF1 (U2AF1mut) acquires an altered 3' splice site selection preference and co-operates with the wild-type U2AF1 (U2AF1wt) to change various gene isoform patterns to support MDS cells survival and proliferation. U2AF1 mutations in MDS cells are always heterozygous and the cell viability is reduced when exposed to additional insult affecting U2AF1wt function. To investigate if the pharmacological inhibition of U2AF1wt function can provoke drug-induced vulnerability of cells harboring U2AF1 mut , we conducted a fragment-based library screening campaign to discover compounds targeting the U2AF homology domain (UHM) in U2AF1 that is required for the formation of the U2AF1/U2AF2 complex to define the 3' splice site. The most promising hit (SF1-8) selectively inhibited growth of leukemia cell lines overexpressingU2AF1 mut and human primary MDS cells carrying U2AF1 mut . RNA-seq analysis of K562-U2AF1mut following treatment with SF1-8 further revealed alteration of isoform patterns for a set of proteins that impair or rescue pathways associated with endocytosis, intracellular vesicle transport, and secretion. Our data suggested that further optimization of SF1-8 is warranted to obtain chemical probes that can be used to evaluate the therapeutic concept of inducing lethality to U2AF1 mut cells by inhibiting the U2AF1wt protein.

PACSIN2 as a modulator of autophagy and mercaptopurine cytotoxicity: mechanisms in lymphoid and intestinal cells

PACSIN2 variants are associated with gastrointestinal effects of thiopurines and thiopurine methyltransferase activity through an uncharacterized mechanism that is postulated to involve autophagy. This study aims to clarify the role of PACSIN2 in autophagy and in thiopurine cytotoxicity in leukemic and intestinal models. Higher autophagy and lower PACSIN2 levels were observed in inflamed compared with non-inflamed colon biopsies of inflammatory bowel disease pediatric patients at diagnosis. PACSIN2 was identified as an inhibitor of autophagy, putatively through inhibition of autophagosome formation by a protein-protein interaction with LC3-II, mediated by a LIR motif. Moreover, PACSIN2 resulted a modulator of mercaptopurine-induced cytotoxicity in intestinal cells, suggesting that PACSIN2-regulated autophagy levels might influence thiopurine sensitivity. However, PACSIN2 modulates cellular thiopurine methyltransferase activity via mechanisms distinct from its modulation of autophagy.

Reciprocal interactions among Cobll1, PACSIN2, and SH3BP1 regulate drug resistance in chronic myeloid leukemia

Cobll1 affects blast crisis (BC) progression and tyrosine kinase inhibitor (TKI) resistance in chronic myeloid leukemia (CML). PACSIN2, a novel Cobll1 binding protein, activates TKI‐induced apoptosis in K562 cells, and this activation is suppressed by Cobll1 through the interaction between PACSIN2 and Cobll1. PACSIN2 also binds and inhibits SH3BP1 which activates the downstream Rac1 pathway and induces TKI resistance. PACSIN2 competitively interacts with Cobll1 or SH3BP1 with a higher affinity for Cobll1. Cobll1 preferentially binds to PACSIN2, releasing SH3BP1 to promote the SH3BP1/Rac1 pathway and suppress TKI‐mediated apoptosis and eventually leading to TKI resistance. Similar interactions among Cobll1, PACSIN2, and SH3BP1 control hematopoiesis during vertebrate embryogenesis. Clinical analysis showed that most patients with CML have Cobll1 and SH3BP1 expression at the BC phase and BC patients with Cobll1 and SH3BP1 expression showed severe progression with a higher blast percentage than those without any Cobll1, PACSIN2, or SH3BP1 expression. Our study details the molecular mechanism of the Cobll1/PACSIN2/SH3BP1 pathway in regulating drug resistance and BC progression in CML.

PACSIN proteins in vivo: Roles in development and physiology

Protein kinase C and casein kinase substrate in neurons (PACSINs), or syndapins (synaptic dynamin‐associated proteins), are a family of proteins involved in the regulation of cell cytoskeleton, intracellular trafficking and signalling. Over the last twenty years, PACSINs have been mostly studied in the in vitro and ex vivo settings, and only in the last decade reports on their function in vivo have emerged. We first summarize the identification, structure and cellular functions of PACSINs, and then focus on the relevance of PACSINs in vivo. During development in various model organisms, PACSINs participate in diverse processes, such as neural crest cell development, gastrulation, laterality development and neuromuscular junction formation. In mouse, PACSIN2 regulates angiogenesis during retinal development and in human, PACSIN2 associates with monosomy and embryonic implantation. In adulthood, PACSIN1 has been extensively studied in the brain and shown to regulate neuromorphogenesis, receptor trafficking and synaptic plasticity. Several genetic studies suggest a role for PACSIN1 in the development of schizophrenia, which is also supported by the phenotype of mice depleted of PACSIN1. PACSIN2 plays an essential role in the maintenance of intestinal homeostasis and participates in kidney repair processes after injury. PACSIN3 is abundant in muscle tissue and necessary for caveolar biogenesis to create membrane reservoirs, thus controlling muscle function, and has been linked to certain genetic muscular disorders. The above examples illustrate the importance of PACSINs in diverse physiological or tissue repair processes in various organs, and associations to diseases when their functions are disturbed.

Syndapin-2 mediated transcytosis of amyloid-ß across the blood-brain barrier

A deficient transport of amyloid-β across the blood–brain barrier, and its diminished clearance from the brain, contribute to neurodegenerative and vascular pathologies, such as Alzheimer’s disease and cerebral amyloid angiopathy, respectively. At the blood–brain barrier, amyloid-β efflux transport is associated with the low-density lipoprotein receptor-related protein 1. However, the precise mechanisms governing amyloid-β transport across the blood–brain barrier, in health and disease, remain to be fully understood. Recent evidence indicates that the low-density lipoprotein receptor-related protein 1 transcytosis occurs through a tubulation-mediated mechanism stabilized by syndapin-2. Here, we show that syndapin-2 is associated with amyloid-β clearance via low-density lipoprotein receptor-related protein 1 across the blood–brain barrier. We further demonstrate that risk factors for Alzheimer’s disease, amyloid-β expression and ageing, are associated with a decline in the native expression of syndapin-2 within the brain endothelium. Our data reveals that syndapin-2-mediated pathway, and its balance with the endosomal sorting, are important for amyloid-β clearance proposing a measure to evaluate Alzheimer’s disease and ageing, as well as a target for counteracting amyloid-β build-up. Moreover, we provide evidence for the impact of the avidity of amyloid-β assemblies in their trafficking across the brain endothelium and in low-density lipoprotein receptor-related protein 1 expression levels, which may affect the overall clearance of amyloid-β across the blood–brain barrier.

Proteomic Signature of Extracellular Vesicles for Lung Cancer Recognition

The proteins of extracellular vesicles (EVs) that originate from tumors reflect the producer cells' proteomes and can be detected in biological fluids. Thus, EVs provide proteomic signatures that are of great interest for screening and predictive cancer diagnostics. By applying targeted mass spectrometry with stable isotope-labeled peptide standards, we assessed the levels of 28 EV-associated proteins, including the conventional exosome markers CD9, CD63, CD81, CD82, and HSPA8, in vesicles derived from the lung cancer cell lines NCI-H23 and A549. Furthermore, we evaluated the detectability of these proteins and their abundance in plasma samples from 34 lung cancer patients and 23 healthy volunteers. The abundance of TLN1, TUBA4A, HSPA8, ITGB3, TSG101, and PACSIN2 in the plasma of lung cancer patients was measured using targeted mass spectrometry and compared to that in plasma from healthy volunteers. The most diagnostically potent markers were TLN1 (AUC, 0.95), TUBA4A (AUC, 0.91), and HSPA8 (AUC, 0.88). The obtained EV proteomic signature allowed us to distinguish between the lung adenocarcinoma and squamous cell carcinoma histological types. The proteomic cargo of the extracellular vesicles represents a promising source of potential biomarkers.

The Role of BAR Proteins and the Glycocalyx in Brain Endothelium Transcytosis

Within the brain, endothelial cells lining the blood vessels meticulously coordinate the transport of nutrients, energy metabolites and other macromolecules essential in maintaining an appropriate activity of the brain. While small molecules are pumped across specialised molecular transporters, large macromolecular cargos are shuttled from one side to the other through membrane-bound carriers formed by endocytosis on one side, trafficked to the other side and released by exocytosis. Such a process is collectively known as transcytosis. The brain endothelium is recognised to possess an intricate vesicular endosomal network that mediates the transcellular transport of cargos from blood-to-brain and brain-to-blood. However, mounting evidence suggests that brain endothelial cells (BECs) employ a more direct route via tubular carriers for a fast and efficient transport from the blood to the brain. Here, we compile the mechanism of transcytosis in BECs, in which we highlight intracellular trafficking mediated by tubulation, and emphasise the possible role in transcytosis of the Bin/Amphiphysin/Rvs (BAR) proteins and glycocalyx (GC)-a layer of sugars covering BECs, in transcytosis. Both BAR proteins and the GC are intrinsically associated with cell membranes and involved in the modulation and shaping of these membranes. Hence, we aim to summarise the machinery involved in transcytosis in BECs and highlight an uncovered role of BAR proteins and the GC at the brain endothelium.

The membrane-associated form of cyclin D1 enhances cellular invasion

The essential G₁-cyclin, CCND1, is a collaborative nuclear oncogene that is frequently overexpressed in cancer. D-type cyclins bind and activate CDK4 and CDK6 thereby contributing to G₁–S cell-cycle progression. In addition to the nucleus, herein cyclin D1 was also located in the cytoplasmic membrane. In contrast with the nuclear-localized form of cyclin D1 (cyclin D1^NL), the cytoplasmic membrane-localized form of cyclin D1 (cyclin D1^MEM) induced transwell migration and the velocity of cellular migration. The cyclin D1^MEM was sufficient to induce G₁–S cell-cycle progression, cellular proliferation, and colony formation. The cyclin D1^MEM was sufficient to induce phosphorylation of the serine threonine kinase Akt (Ser473) and augmented extranuclear localized 17β-estradiol dendrimer conjugate (EDC)-mediated phosphorylation of Akt (Ser473). These studies suggest distinct subcellular compartments of cell cycle proteins may convey distinct functions.

PACSIN2 Interacts with Nonstructural Protein 5A and Regulates Hepatitis C Virus Assembly

Hepatitis C virus (HCV) is a major etiologic agent of chronic liver diseases. HCV is highly dependent on cellular machinery for viral propagation. Using protein microarray analysis, we previously identified 90 cellular proteins as nonstructural 5A (NS5A) interacting partners. Of these, protein kinase C and casein kinase substrate in neurons protein 2 (PACSIN2) was selected for further study. PACSIN2 belongs to the PACSIN family, which is involved in the formation of caveolae. Protein interaction between NS5A and PACSIN2 was confirmed by pulldown assay and further verified by both coimmunoprecipitation and immunofluorescence assays. We showed that PACSIN2 interacted with domain I of NS5A and the Fer-CIP4 homology (FCH)-Bin/amphiphysin/Rvs (F-BAR) region of PACSIN2. Interestingly, NS5A specifically attenuated protein kinase C alpha (PKCα)-mediated phosphorylation of PACSIN2 at serine 313 by interrupting PACSIN2 and PKCα interaction. In fact, mutation of the serine 313 to alanine (S313A) of PACSIN2 increased protein interaction with NS5A. Silencing of PACSIN2 decreased both viral RNA and protein expression levels of HCV. Ectopic expression of the small interfering RNA (siRNA)-resistant PACSIN2 recovered the viral infectivity, suggesting that PACSIN2 was specifically required for HCV propagation. PACSIN2 was involved in viral assembly without affecting other steps of the HCV life cycle. Indeed, overexpression of PACSIN2 promoted NS5A and core protein (core) interaction. We further showed that inhibition of PKCα increased NS5A and core interaction, suggesting that phosphorylation of PACSIN2 might influence HCV assembly. Moreover, PACSIN2 was required for lipid droplet formation via modulating extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation. Taken together, these data indicate that HCV modulates PACSIN2 via NS5A to promote virion assembly.IMPORTANCE PACSIN2 is a lipid-binding protein that triggers the tubulation of the phosphatidic acid-containing membranes. The functional involvement of PACSIN2 in the virus life cycle has not yet been demonstrated. We showed that phosphorylation of PACSIN2 displayed a negative effect on NS5A and core interaction. The most significant finding is that NS5A prevents PKCα from binding to PACSIN2. Therefore, the phosphorylation level of PACSIN2 is decreased in HCV-infected cells. We showed that HCV NS5A interrupted PKCα-mediated PACSIN2 phosphorylation at serine 313, thereby promoting NS5A-PACSIN2 interaction. We further demonstrated that PACSIN2 modulated lipid droplet formation through ERK1/2 phosphorylation. These data provide evidence that PACSIN2 is a proviral cellular factor required for viral propagation.

PACSIN2-dependent apical endocytosis regulates the morphology of epithelial microvilli

Apical microvilli are critical for the homeostasis of transporting epithelia, yet mechanisms that control the assembly and morphology of these protrusions remain poorly understood. Previous studies in intestinal epithelial cell lines suggested a role for the F-BAR domain protein PACSIN2 in normal microvillar assembly. Here we report the phenotype of PACSIN2 KO mice and provide evidence that through its role in promoting apical endocytosis, this molecule plays a role in controlling microvillar morphology. PACSIN2 KO enterocytes exhibit reduced numbers of microvilli and defects in the microvillar ultrastructure, with membranes lifting away from rootlets of core bundles. Dynamin2, a PACSIN2 binding partner, and other endocytic factors were also lost from their normal localization near microvillar rootlets. To determine whether loss of endocytic machinery could explain defects in microvillar morphology, we examined the impact of PACSIN2 KD and endocytosis inhibition on live intestinal epithelial cells. These assays revealed that when endocytic vesicle scission fails, tubules are pulled into the cytoplasm and this, in turn, leads to a membrane-lifting phenomenon reminiscent of that observed at PACSIN2 KO brush borders. These findings lead to a new model where inward forces generated by endocytic machinery on the plasma membrane control the membrane wrapping of cell surface protrusions.

Diverse Papillomavirus Types Induce Endosomal Tubulation

Previous studies have shown that the endoplasmic reticulum (ER)-anchored protein VAP is strictly required by human papillomavirus type 16 (HPV-16) for successful infectious entry. Entry appeared to be mediated in part through the induction of endosomal tubulation and subsequent transport of the virion to the trans-Golgi network (TGN). In this study, we were interested in investigating whether this mechanism of infectious entry is conserved across multiple Papillomavirus types. To do this, we analyzed the role of VAP and endosomal tubulation following infection with Pseudovirions (PsVs) derived from the alpha, beta, delta, kappa, and pi papillomavirus genera, reflecting viruses that are important human and animal pathogens. We demonstrate that VAP is essential for infection with all PV types analyzed. Furthermore, we find that VAP and EGFR-dependent endosomal tubulation is also induced by all these different Papillomaviruses. These results indicate an evolutionarily conserved requirement for VAP-induced endocytic tubulation during Papillomavirus infectious entry.

Novel activating BRAF fusion identifies a recurrent alternative mechanism for ERK activation in pediatric Langerhans cell histiocytosis

Langerhans cell histiocytosis (LCH) is an inflammatory myeloid neoplasm characterized by constitutive activation of extracellular signal-regulated kinase (ERK). Genomic characterization has identified activating point mutations including mutually exclusive BRAFV600E and activating MAP2K1 mutations to be responsible for ERK activation in a majority of pediatric LCH patients. Here, we report the discovery of a novel BRAF kinase fusion, PACSIN2-BRAF, in a child with multisystem LCH. This is the second reported case of an activating BRAF kinase fusion and indicates a recurrent pathologic mechanism. Genomic evaluation for activating kinase fusions should be strongly considered in pediatric LCH patients lacking more common mutations.

Endocytosis and membrane receptor internalization: implication of F-BAR protein Carom

Endocytosis is a cellular process mostly responsible for membrane receptor internalization. Cell membrane receptors bind to their ligands and form a complex which can be internalized. We previously proposed that F-BAR protein initiates membrane curvature and mediates endocytosis via its binding partners. However, F-BAR protein partners involved in membrane receptor endocytosis and the regulatory mechanism remain unknown. In this study, we established database mining strategies to explore mechanisms underlying receptor-related endocytosis. We identified 34 endocytic membrane receptors and 10 regulating proteins in clathrin-dependent endocytosis (CDE), a major process of membrane receptor internalization. We found that F-BAR protein FCHSD2 (Carom) may facilitate endocytosis via 9 endocytic partners. Carom is highly expressed, along with highly expressed endocytic membrane receptors and partners, in endothelial cells and macrophages. We established 3 models of Carom-receptor complexes and their intracellular trafficking based on protein interaction and subcellular localization. We conclude that Carom may mediate receptor endocytosis and transport endocytic receptors to the cytoplasm for receptor signaling and lysosome/proteasome degradation, or to the nucleus for RNA processing, gene transcription and DNA repair.

Syndapin bridges the membrane-cytoskeleton divide during furrow extension

BAR domain proteins can regulate ‘membrane reservoirs’ that provide surface area and buffer membrane tension. Syndapin is an F-BAR and SH3 domain containing protein involved in cytoskeletal remodelling and endocytosis. The Syndapin F-BAR domain is uniquely versatile compared to others in the family and can bend phospholipid membranes into tubules of various diameters and directly bind actin. The Syndapin SH3 domain can also interact with actin remodelling proteins and modulate cytoskeletal contractility. Pseudocleavage furrow extension in the syncytial division cycles of Drosophila embryos requires the homeostatic control of conserved processes that control plasma membrane tension and actin contractility. We find that Syndapin plays an important role in promoting pseudocleavage furrow extension. We propose a model involving roles for Syndapin in membrane dynamics and direct or indirect effect on the cytoskeleton to explain how it affects pseudocleavage furrow growth, independent of its role in endocytosis.

Clostridium difficile Toxin A Undergoes Clathrin-Independent, PACSIN2-Dependent Endocytosis

Clostridium difficile infection affects a significant number of hospitalized patients in the United States. Two homologous exotoxins, TcdA and TcdB, are the major virulence factors in C. difficile pathogenesis. The toxins are glucosyltransferases that inactivate Rho family-GTPases to disrupt host cellular function and cause fluid secretion, inflammation, and cell death. Toxicity depends on receptor binding and subsequent endocytosis. TcdB has been shown to enter cells by clathrin-dependent endocytosis, but the mechanism of TcdA uptake is still unclear. Here, we utilize a combination of RNAi-based knockdown, pharmacological inhibition, and cell imaging approaches to investigate the endocytic mechanism(s) that contribute to TcdA uptake and subsequent cytopathic and cytotoxic effects. We show that TcdA uptake and cellular intoxication is dynamin-dependent but does not involve clathrin- or caveolae-mediated endocytosis. Confocal microscopy using fluorescently labeled TcdA shows significant colocalization of the toxin with PACSIN2-positive structures in cells during entry. Disruption of PACSIN2 function by RNAi-based knockdown approaches inhibits TcdA uptake and toxin-induced downstream effects in cells indicating that TcdA entry is PACSIN2-dependent. We conclude that TcdA and TcdB utilize distinct endocytic mechanisms to intoxicate host cells.

Clostridium difficile is a bacterial pathogen that causes nearly half a million infections each year in the United States. It infects the human colon and causes diarrhea, colitis and, in some cases, death. C. difficile infection is mediated by the action of two large homologous toxins, TcdA and TcdB. Disruption of host cell function by these toxins requires entry into cells. There are multiple ways for pathogens and virulence factors such as viruses and toxins to enter host cells. The entry mechanism is often directed by a cell surface receptor and can impact the trafficking and virulence properties of the pathogenic factor. Investigating the internalization strategy can provide critical insight into the mechanism of action for specific pathogens and virulence factors. In our current study, we sought to determine the strategy utilized by TcdA to enter host cells. We show that TcdA uptake occurs by a clathrin- and caveolae-independent endocytic mechanism that is mediated by PACSIN2 and dynamin. We also show that TcdA and TcdB can utilize different routes of entry, which may have implications regarding their cytotoxic mechanisms. In summary, our results provide new insights into the mechanism of cellular intoxication by TcdA and the role of PACSIN2 in endocytosis.

Linking up at the BAR: Oligomerization and F-BAR protein function

As cells grow, move, and divide, they must reorganize and rearrange their membranes and cytoskeleton. The F-BAR protein family links cellular membranes with actin cytoskeletal rearrangements in processes including endocytosis, cytokinesis, and cell motility. Here we review emerging information on mechanisms of F-BAR domain oligomerization and membrane binding, and how these activities are coordinated with additional domains to accomplish scaffolding and signaling functions.

Rab8b Regulates Transport of West Nile Virus Particles from Recycling Endosomes

West Nile virus (WNV) particles assemble at and bud into the endoplasmic reticulum (ER) and are secreted from infected cells through the secretory pathway. However, the host factor related to these steps is not fully understood. Rab proteins, belonging to the Ras superfamily, play essential roles in regulating many aspects of vesicular trafficking. In this study, we sought to determine which Rab proteins are involved in intracellular trafficking of nascent WNV particles. RNAi analysis revealed that Rab8b plays a role in WNV particle release. We found that Rab8 and WNV antigen were colocalized in WNV-infected human neuroblastoma cells, and that WNV infection enhanced Rab8 expression in the cells. In addition, the amount of WNV particles in the supernatant of Rab8b-deficient cells was significantly decreased compared with that of wild-type cells. We also demonstrated that WNV particles accumulated in the recycling endosomes in WNV-infected cells. In summary, these results suggest that Rab8b is involved in trafficking of WNV particles from recycling endosomes to the plasma membrane.

OCRL1 engages with the F-BAR protein pacsin 2 to promote biogenesis of membrane-trafficking intermediates

Mutation of the inositol 5-phosphatase OCRL1 causes Lowe syndrome and Dent-2 disease. Loss of OCRL1 function perturbs several cellular processes, including membrane traffic, but the underlying mechanisms remain poorly defined. Here we show that OCRL1 is part of the membrane-trafficking machinery operating at the trans-Golgi network (TGN)/endosome interface. OCRL1 interacts via IPIP27A with the F-BAR protein pacsin 2. OCRL1 and IPIP27A localize to mannose 6-phosphate receptor (MPR)-containing trafficking intermediates, and loss of either protein leads to defective MPR carrier biogenesis at the TGN and endosomes. OCRL1 5-phosphatase activity, which is membrane curvature sensitive, is stimulated by IPIP27A-mediated engagement of OCRL1 with pacsin 2 and promotes scission of MPR-containing carriers. Our data indicate a role for OCRL1, via IPIP27A, in regulating the formation of pacsin 2-dependent trafficking intermediates and reveal a mechanism for coupling PtdIns(4,5)P2 hydrolysis with carrier biogenesis on endomembranes.

Characterization of the Tyrosine Kinase-Regulated Proteome in Breast Cancer by Combined use of RNA interference (RNAi) and Stable Isotope Labeling with Amino Acids in Cell Culture (SILAC) Quantitative Proteomics

Tyrosine kinases (TKs) are central regulators in cellular activities and perturbations of TK signaling contribute to oncogenesis. However, less than half of the TKs have been thoroughly studied and a global functional analysis of their proteomic portrait is lacking. Here we conducted a combined approach of RNA interference (RNAi) and stable isotope labeling with amino acids in cell culture (SILAC)-based quantitative proteomics to decode the TK-regulated proteome and associated signaling dynamics. As a result, a broad proteomic repertoire modulated by TKs was revealed, upon silencing of the 65 TKs expressed in MCF7 breast cancer cells. This yielded 10 new distinctive TK clusters according to similarity in TK-regulated proteome, each characterized by a unique signaling signature in contrast to previous classifications. We provide functional analyses and identify critical pathways for each cluster based on their common downstream targets. Analysis of different breast cancer subtypes showed distinct correlations of each cluster with clinical outcome. From the significantly up- and down-regulated proteins, we identified a number of markers of drug sensitivity and resistance. These data supports the role of TKs in regulating major aspects of cellular activity, but also reveals redundancy in signaling, explaining why kinase inhibitors alone often fail to achieve their clinical aims. The TK-SILACepedia provides a comprehensive resource for studying the global function of TKs in cancer.

Capillary nano-immunoassays: advancing quantitative proteomics analysis, biomarker assessment, and molecular diagnostics

There is an emerging demand for the use of molecular profiling to facilitate biomarker identification and development, and to stratify patients for more efficient treatment decisions with reduced adverse effects. In the past decade, great strides have been made to advance genomic, transcriptomic and proteomic approaches to address these demands. While there has been much progress with these large scale approaches, profiling at the protein level still faces challenges due to limitations in clinical sample size, poor reproducibility, unreliable quantitation, and lack of assay robustness. A novel automated capillary nano-immunoassay (CNIA) technology has been developed. This technology offers precise and accurate measurement of proteins and their post-translational modifications using either charge-based or size-based separation formats. The system not only uses ultralow nanogram levels of protein but also allows multi-analyte analysis using a parallel single-analyte format for increased sensitivity and specificity. The high sensitivity and excellent reproducibility of this technology make it particularly powerful for analysis of clinical samples. Furthermore, the system can distinguish and detect specific protein post-translational modifications that conventional Western blot and other immunoassays cannot easily capture. This review will summarize and evaluate the latest progress to optimize the CNIA system for comprehensive, quantitative protein and signaling event characterization. It will also discuss how the technology has been successfully applied in both discovery research and clinical studies, for signaling pathway dissection, proteomic biomarker assessment, targeted treatment evaluation and quantitative proteomic analysis. Lastly, a comparison of this novel system with other conventional immuno-assay platforms is performed.

FlnA binding to PACSIN2 F-BAR domain regulates membrane tubulation in megakaryocytes and platelets

Bin-Amphiphysin-Rvs (BAR) and Fes-CIP4 homology BAR (F-BAR) proteins generate tubular membrane invaginations reminiscent of the megakaryocyte (MK) demarcation membrane system (DMS), which provides membranes necessary for future platelets. The F-BAR protein PACSIN2 is one of the most abundant BAR/F-BAR proteins in platelets and the only one reported to interact with the cytoskeletal and scaffold protein filamin A (FlnA), an essential regulator of platelet formation and function. The FlnA-PACSIN2 interaction was therefore investigated in MKs and platelets. PACSIN2 associated with FlnA in human platelets. The interaction required FlnA immunoglobulin-like repeat 20 and the tip of PACSIN2 F-BAR domain and enhanced PACSIN2 F-BAR domain membrane tubulation in vitro. Most human and wild-type mouse platelets had 1 to 2 distinct PACSIN2 foci associated with cell membrane GPIbα, whereas Flna-null platelets had 0 to 4 or more foci. Endogenous PACSIN2 and transfected enhanced green fluorescent protein-PACSIN2 were concentrated in midstage wild-type mouse MKs in a well-defined invagination of the plasma membrane reminiscent of the initiating DMS and dispersed in the absence of FlnA binding. The DMS appeared less well defined, and platelet territories were not readily visualized in Flna-null MKs. We conclude that the FlnA-PACSIN2 interaction regulates membrane tubulation in MKs and platelets and likely contributes to DMS formation.

Dynamic shaping of cellular membranes by phospholipids and membrane-deforming proteins

All cellular compartments are separated from the external environment by a membrane, which consists of a lipid bilayer. Subcellular structures, including clathrin-coated pits, caveolae, filopodia, lamellipodia, podosomes, and other intracellular membrane systems, are molded into their specific submicron-scale shapes through various mechanisms. Cells construct their micro-structures on plasma membrane and execute vital functions for life, such as cell migration, cell division, endocytosis, exocytosis, and cytoskeletal regulation. The plasma membrane, rich in anionic phospholipids, utilizes the electrostatic nature of the lipids, specifically the phosphoinositides, to form interactions with cytosolic proteins. These cytosolic proteins have three modes of interaction: 1) electrostatic interaction through unstructured polycationic regions, 2) through structured phosphoinositide-specific binding domains, and 3) through structured domains that bind the membrane without specificity for particular phospholipid. Among the structured domains, there are several that have membrane-deforming activity, which is essential for the formation of concave or convex membrane curvature. These domains include the amphipathic helix, which deforms the membrane by hemi-insertion of the helix with both hydrophobic and electrostatic interactions, and/or the BAR domain superfamily, known to use their positively charged, curved structural surface to deform membranes. Below the membrane, actin filaments support the micro-structures through interactions with several BAR proteins as well as other scaffold proteins, resulting in outward and inward membrane micro-structure formation. Here, we describe the characteristics of phospholipids, and the mechanisms utilized by phosphoinositides to regulate cellular events. We then summarize the precise mechanisms underlying the construction of membrane micro-structures and their involvements in physiological and pathological processes.

Angiogenic growth factors augment K-Cl cotransporter expression in erythroid cells via hypoxia-inducible factor-1α

The potassium chloride cotransporters (KCC) family of proteins are widely expressed and are involved in the transepithelial movement of potassium and chloride ions and the regulation of cell volume. KCC activity is high in reticulocytes, and contributes to the dehydration of sickle red blood cells. Because plasma levels of both vascular endothelial growth factor (VEGF) and placental growth factor (PlGF) are elevated in sickle cell individuals, and VEGF has been shown to increase KCC expression in other cells, we hypothesized that VEGF and PlGF influence KCC expression in erythroid cells. Both VEGF and PlGF treatment of human erythroid K562 cells increased both mRNA and protein levels of KCC1, KCC3b, and KCC4. VEGF- and PlGF-mediated cellular signaling involved VEGF-R1 and downstream effectors, specifically, PI-3 kinase, p38 MAP kinase, mTOR, NADPH-oxidase, JNK kinase, and HIF-1α. VEGF and PlGF-mediated transcription of KCC3b and KCC4 involved hypoxia response element (HRE) motifs in their promoters, as demonstrated by promoter analysis, EMSA and ChiP. These results were corroborated in vivo by adenoviral-mediated overexpression of PlGF in normal mice, which led to increased expression of mKCC3 and mKCC4 in erythroid precursors. Our studies show that VEGF and PlGF regulate transcription of KCC3b and KCC4 in erythroid cells via activation of HIF-1α, independent of hypoxia. These studies provide novel therapeutic targets for regulation of cell volume in RBC precursors, and thus, amelioration of dehydration in RBCs in sickle cell disease.

Real-time nanoscale proteomic analysis of the novel multi-kinase pathway inhibitor rigosertib to measure the response to treatment of cancer

INTRODUCTION

Rigosertib (ON01910.Na), is a targeted therapeutic that inhibits multiple kinases, including PI3K and PIk-1. Rigosertib has been found to induce the proliferative arrest and apoptosis of myeloblasts but not of other normal hematopoietic cells. Rigosertib has significant clinical activity as a therapy for patients with high-risk myelodysplastic syndrome who are otherwise refractory to DNA methyltransferase inhibitors. Moreover, rigosertib has potential clinical activity in a multitude of solid tumors.

AREAS COVERED

The objective of this review is to evaluate the mechanism of activity, efficacy and dosing of rigosertib. Furthermore, the challenge in the clinical development of rigosertib, to identify the specific patients that are most likely to benefit from this therapeutic agent, is discussed. A PubMed search was performed using the following key words: rigosertib and ON01910.Na.

EXPERT OPINION

We describe the application of a novel nanoscale proteomic assay, the nanoimmunoassay, a tractable approach for measuring the activity and predicting the efficacy of rigosertib, in real-time, using limited human clinical specimens. Our strategy suggests a possible paradigm where proteomic analysis during the pre-clinical and clinical development of a therapy can be used to uncover biomarkers for the analysis and prediction of efficacy in human patients.

Tip-to-tip interaction in the crystal packing of PACSIN 2 is important in regulating tubulation activity

The F-BAR domain containing proteins PACSINs are cytoplasmic phosphoproteins involved in various membrane deformations, such as actin reorganization, vesicle transport and microtubule movement. Our previous study shows that all PACSINs are composed of crescent shaped dimers with two wedge loops, and the wedge loop-mediated lateral interaction between neighboring dimers is important for protein packing and tubulation activity. Here, from the crystal packing of PACSIN 2, we observed a tight tip-to-tip interaction, in addition to the wedge loop-mediated lateral interaction. With this tip-to-tip interaction, the whole packing of PACSIN 2 shows a spiral-like assembly with a central hole from the top view. Elimination of this tip-to-tip connection inhibited the tubulation function of PACSIN 2, indicating that tip-to-tip interaction plays an important role in membrane deformation activity. Together with our previous study, we proposed a packing model for the assembly of PACSIN 2 on membrane, where the proteins are connected by tip-to-tip and wedge loop-mediated lateral interactions on the surface of membrane to generate various diameter tubules.