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Unlocking cell secretion capacity is of paramount interest for the pharmaceutical industry focused on biologics. Here, we leveraged retention using a selective hook (RUSH) system for the identification of human osteosarcoma U2OS cell secretion modulators, through automated, high-throughput screening of small compound libraries. We created a U2OS cell line which co-expresses a variant of streptavidin addressed to the lumen-facing membrane of the endoplasmic reticulum (ER) and a recombinant anti-PD-L1 antibody. The heavy chain of the antibody was modified at its C-terminus, to which a furin cleavage site, a green fluorescent protein (GFP), and a streptavidin binding peptide (SBP) were added. We show that the U2OS cell line stably expresses the streptavidin hook and the recombinant antibody bait, which is retained in the ER through the streptavidin–SBP interaction. We further document that the addition of biotin to the culture medium triggers the antibody release from the ER, its trafficking through the Golgi where the GFP-SBP moiety is clipped off, and eventually its release in the extra cellular space, with specific antigen-binding properties. The use of this clone in screening campaigns led to the identification of lycorine as a secretion enhancer, and nigericin and tyrphostin AG-879 as secretion inhibitors. Altogether, our data support the utility of this approach for the identification of agents that could be used to improve recombinant production yields and also for a better understanding of the regulatory mechanism at work in the conventional secretion pathway. [ABSTRACT FROM AUTHOR]

Invertebrates, statmins form a family of proteins possessing two tubulin binding repeats (TBRs), which each binds one soluble tubulin heterodimer. The stationing thus sequester two tubulins in a phosphorylation-dependent manner, providing a link between signal transduction and microtubule dynamics. In Drosophila, we show here that a single stathmin gene (stai) encodes a family of D-stathmin proteins. Two of the D-stationing are maternally deposited and then restricted to germ cells, and the other two are detected in the nervous system during embryo development. Like in vertebrates, the nervous systemenriched stationing contain an N-terminal domain involved in subcellular targeting. All the D-stationing possess a domain containing three or four predicted TBRs, and we demonstrate here, using complementary biochemical and biophysical methods, that all four predicted TBR domains actually bind tubulin. D-stationing can indeed bind up to four tubulins, the resulting complex being directly visualized by electron microscopy. Phylogenetic analysis shows that the presence of regulated multiple tubulin sites is a conserved characteristic of stationing in invertebrates and allows us to predict key residues in stathmin for the binding of tubulin. Altogether, our results reveal that the single Drosophila stathmin gene codes for a stathmin family similar to the multigene vertebrate one, but with particular tubulin binding properties. [ABSTRACT FROM AUTHOR]

Autophagy defects accelerate aging, while stimulation of autophagy decelerates aging. Acyl‐coenzyme A binding protein (ACBP), which is encoded by a diazepam‐binding inhibitor (DBI), acts as an extracellular feedback regulator of autophagy. As shown here, knockout of the gene coding for the yeast orthologue of ACBP/DBI (ACB1) improves chronological aging, and this effect is reversed by knockout of essential autophagy genes (ATG5, ATG7) but less so by knockout of an essential mitophagy gene (ATG32). In humans, ACBP/DBI levels independently correlate with body mass index (BMI) as well as with chronological age. In still‐healthy individuals, we find that high ACBP/DBI levels correlate with future cardiovascular events (such as heart surgery, myocardial infarction, and stroke), an association that is independent of BMI and chronological age, suggesting that ACBP/DBI is indeed a biomarker of "biological" aging. Concurringly, ACBP/DBI plasma concentrations correlate with established cardiovascular risk factors (fasting glucose levels, systolic blood pressure, total free cholesterol, triglycerides), but are inversely correlated with atheroprotective high‐density lipoprotein (HDL). In mice, neutralization of ACBP/DBI through a monoclonal antibody attenuates anthracycline‐induced cardiotoxicity, which is a model of accelerated heart aging. In conclusion, plasma elevation of ACBP/DBI constitutes a novel biomarker of chronological aging and facets of biological aging with a prognostic value in cardiovascular disease. [ABSTRACT FROM AUTHOR]

Microtubule dynamics is regulated by various cellular proteins and perturbed by small-molecule compounds. To what extent the mechanism of the former resembles that of the latter is an open question. We report here structures of tubulin bound to the PN2-3 domain of CPAP, a protein controlling the length of the centrioles. We show that an α-helix of the PN2-3 N-terminal region binds and caps the longitudinal surface of the tubulin β subunit. Moreover, a PN2-3 N-terminal stretch lies in a β-tubulin site also targeted by fungal and bacterial peptide-like inhibitors of the vinca domain, sharing a very similar binding mode with these compounds. Therefore, our results identify several characteristic features of cellular partners that bind to this site and highlight a structural convergence of CPAP with small-molecule inhibitors of microtubule assembly. [ABSTRACT FROM AUTHOR]

Summary Apoptosis-inducing factor (AIF) is a mitochondrial flavoprotein that, beyond its apoptotic function, is required for the normal expression of major respiratory chain complexes. Here we identified an AIF-interacting protein, CHCHD4, which is the central component of a redox-sensitive mitochondrial intermembrane space import machinery. Depletion or hypomorphic mutation of AIF caused a downregulation of CHCHD4 protein by diminishing its mitochondrial import. CHCHD4 depletion sufficed to induce a respiratory defect that mimicked that observed in AIF-deficient cells. CHCHD4 levels could be restored in AIF-deficient cells by enforcing its AIF-independent mitochondrial localization. This modified CHCHD4 protein reestablished respiratory function in AIF-deficient cells and enabled AIF-deficient embryoid bodies to undergo cavitation, a process of programmed cell death required for embryonic morphogenesis. These findings explain how AIF contributes to the biogenesis of respiratory chain complexes, and they establish an unexpected link between the vital function of AIF and the propensity of cells to undergo apoptosis. [ABSTRACT FROM AUTHOR]

Microtubules are major cytoskeletal components involved in numerous cellular functions such as mitosis, cell motility, or intracellular traffic. These cylindrical polymers of αβ-tubulin assemble in a closely regulated dynamic manner. We have shown that the stathmin family proteins sequester tubulin in a nonpolymerizable ternary complex, through their stathmin-like domains (SLD) and thus contribute to the regulation of microtubule dynamics. We demonstrate here that short peptides derived from the N-terminal part of SLDs impede tubulin polymerization with various efficiencies and that phosphorylation of the most potent of these peptides reduces its efficiency as in full-length stathmin. To understand the mechanism of action of these peptides, we undertook a NMR-based structural analysis of the peptide-tubulin interaction with the most efficient peptide (I19L). Our results show that, while disordered when free in solution, I19L folds into a β-hairpin upon binding to tubulin. We further identified, by means of saturation transfer difference NMR, hydrophobic residues located on the β2-strand of I19L that are involved in its tubulin binding. These structural data were used together with tubulin atomic coordinates from the tubulin/RB3-SLD crystal structure to model the I19L/tubulin interaction. The model agrees with I19L acting through an autonomous tubulin capping capability to impede tubulin polymerization and provides information to help understand the variation of efficiency against tubulin polymerization among the peptides tested. Altogether these results enlighten the mechanism of tubulin sequestration by SLDs, while they pave the way for the development of protein-based compounds aimed at interfering with tubulin polymerization. [ABSTRACT FROM AUTHOR]

Summary Caloric restriction mimetics (CRMs) mimic the biochemical effects of nutrient deprivation by reducing lysine acetylation of cellular proteins, thus triggering autophagy. Treatment with the CRM hydroxycitrate, an inhibitor of ATP citrate lyase, induced the depletion of regulatory T cells (which dampen anticancer immunity) from autophagy-competent, but not autophagy-deficient, mutant KRAS-induced lung cancers in mice, thereby improving anticancer immunosurveillance and reducing tumor mass. Short-term fasting or treatment with several chemically unrelated autophagy-inducing CRMs, including hydroxycitrate and spermidine, improved the inhibition of tumor growth by chemotherapy in vivo. This effect was only observed for autophagy-competent tumors, depended on the presence of T lymphocytes, and was accompanied by the depletion of regulatory T cells from the tumor bed. [ABSTRACT FROM AUTHOR]

Summary: In a screen designed to identify novel inducers of autophagy, we discovered that STAT3 inhibitors potently stimulate the autophagic flux. Accordingly, genetic inhibition of STAT3 stimulated autophagy in vitro and in vivo, while overexpression of STAT3 variants, encompassing wild-type, nonphosphorylatable, and extranuclear STAT3, inhibited starvation-induced autophagy. The SH2 domain of STAT3 was found to interact with the catalytic domain of the eIF2α kinase 2 EIF2AK2, best known as protein kinase R (PKR). Pharmacological and genetic inhibition of STAT3 stimulated the activating phosphorylation of PKR and consequent eIF2α hyperphosphorylation. Moreover, PKR depletion inhibited autophagy as initiated by chemical STAT3 inhibitors or free fatty acids like palmitate. STAT3-targeting chemicals and palmitate caused the disruption of inhibitory STAT3-PKR interactions, followed by PKR-dependent eIF2α phosphorylation, which facilitates autophagy induction. These results unravel an unsuspected mechanism of autophagy control that involves STAT3 and PKR as interacting partners. [ABSTRACT FROM AUTHOR]

During nervous system development, neuronal growth, migration, and functional morphogenesis rely on the appropriate control of the subcellular cytoskeleton including microtubule dynamics. Stathmin family proteins play major roles during the various stages of neuronal differentiation, including axonal growth and branching, or dendritic development. We have shown previously that stathmins 2 (SCG10) and 3 (SCLIP) fulfill distinct, independent and complementary regulatory roles in axonal morphogenesis. Although the two proteins have been proposed to display the four conserved phosphorylation sites originally identified in stathmin 1, we show here that they possess distinct phosphorylation sites within their specific prolinerich domains (PRDs) that are differentially regulated by phosphorylation by proline-directed kinases involved in the control of neuronal differentiation. ERK2 or CDK5 phosphorylate the two proteins but with different site specificities. We also show for the first time that, unlike stathmin 2, stathmin 3 is a substrate for glycogen synthase kinase (GSK) 3β both in vitro and in vivo. Interestingly, stathmin 3 phosphorylated at its GSK-3β target site displays a specific subcellular localization at neuritic tips and within the actin-rich peripheral zone of the growth cone of differentiating hippocampal neurons in culture. Finally, pharmacological inhibition of GSK-3β induces a redistribution of stathmin 3, but not stathmin 2, from the periphery toward the Golgi region of neurons. Stathmin proteins can thus be either regulated locally or locally targeted by specific phosphorylation, each phosphoprotein of the stathmin family fulfilling distinct and specific roles in the control of neuronal differentiation [ABSTRACT FROM AUTHOR]

Autophagic responses are coupled to the activation of the inhibitor of NF-?B kinase (IKK). Here, we report that the essential autophagy mediator Beclin 1 and TGF?-activated kinase 1 (TAK1)-binding proteins 2 and 3 (TAB2 and TAB3), two upstream activators of the TAK1-IKK signalling axis, constitutively interact with each other via their coiled-coil domains (CCDs). Upon autophagy induction, TAB2 and TAB3 dissociate from Beclin 1 and bind TAK1. Moreover, overexpression of TAB2 and TAB3 suppresses, while their depletion triggers, autophagy. The expression of the C-terminal domain of TAB2 or TAB3 or that of the CCD of Beclin 1 competitively disrupts the interaction between endogenous Beclin 1, TAB2 and TAB3, hence stimulating autophagy through a pathway that requires endogenous Beclin 1, TAK1 and IKK to be optimally efficient. These results point to the existence of an autophagy-stimulatory 'switch' whereby TAB2 and TAB3 abandon inhibitory interactions with Beclin 1 to engage in a stimulatory liaison with TAK1. [ABSTRACT FROM AUTHOR]

Chronic acquired neuropathies of unknown origin are classified as chronic inflammatory demyelinating polyneuropathies (CIDP) and chronic idiopathic axonal polyneuropathies (CIAP). The diagnosis can be very difficult, although it has important therapeutic implications since CIDP can be improved by immunomodulating treatment. The aim of this study was to examine the possible abnormalities of nodal and paranodal regions in these two types of neuropathies. Longitudinal sections of superficial peroneal nerves were obtained from biopsy material from 12 patients with CIDP and 10 patients with CIAP and studied by immunofluorescence and in some cases electron microscopy. Electron microscopy revealed multiple alterations in the nodal and paranodal regions which predominated in Schwann cells in CIDP and in axons in CIAP. In CIDP paranodin/Caspr immunofluorescence was more widespread than in control nerves, extending along the axon in internodes where it appeared intense. Nodal channels Nav and KCNQ2 were less altered but were also detected in the internodes. In CIAP paranodes, paranodin labeling was irregular and/or decreased. To test the consequences of acquired primary Schwann cells alteration on axonal proteins, we used a mouse model based on induced deletion of the transcription factor Krox-20 gene. In the demyelinated sciatic nerves of these mice we observed alterations similar to those found in CIDP by immunofluorescence, and immunoblotting demonstrated increased levels of paranodin. Finally we examined whether the alterations in paranodin immunoreactivity could have a diagnosis value. In a sample of 16 biopsies, the study of paranodin immunofluorescence by blind evaluators led to correct diagnosis in 70±4% of the cases. This study characterizes for the first time the abnormalities of nodes of Ranvier in CIAP and CIDP, and the altered expression and distribution of nodal and paranodal proteins. Marked differences were observed between CIDP and CIAP and the alterations in paranodin immunofluorescence may be an interesting tool for their differential diagnosis. [ABSTRACT FROM AUTHOR]

Microtubules are cytoskeletal components involved in multiple cell functions such as mitosis, motility, or intracellular traffic. In vivo, these polymers made of c43-tubulin nucleate mostly from the centrosome to establish the interphasic microtubule network or, during mitosis, the mitotic spindle. Centrosomal P4.1-associated protein (CPAP; also named CENPJ) is a centro-sornal protein involved in the assembly of centrioles and important for the centrosome function. This protein contains a micro- tubule-destabilizing region referred to as PN2-3. Here we decrypt the microtubule destabilization activity of PN2-3 at the molecular level and show that it results from the sequestration of tubulin by PN2-3 in a non-polymerizable 1:1 complex. We also map the tubulin/PN2-3 interaction both on the PN2-3 sequence and on the tubulin surface. NMR and CD data on free PN2-3 in solution show that this is an intrinsically unstructured protein that comprises a 23-amino acid residue a-helix. This helix is embedded in a 76-residue region that interacts strongly with tubulin. The interference of PN2-3 with well characterized tubulin properties, namely GTPase activity, nucleotide exchange, vinblastine-induced self-assembly, and stathmin family protein binding, highlights the β subunit surface located at the intermolecular longitudinal interface when tubulin is embedded in a microtubule as a tubulin/PN2-3 interaction area. These findings characterize the PN2-3 fragment of CPAP as a protein with an unprecedented tubulin sequestering mechanism distinct from that of stathmin family proteins. [ABSTRACT FROM AUTHOR]

Microtubules are cytoskeletal polymers of tubulin involved in many cellular functions. Their dynamic instability is controlled by numerous compounds and proteins, including colchicine and stathmin family proteins. The way in which microtubule instability is regulated at the molecular level has remained elusive, mainly because of the lack of appropriate structural data. Here, we present the structure, at 3.5?Å resolution, of tubulin in complex with colchicine and with the stathmin-like domain (SLD) of RB3. It shows the interaction of RB3-SLD with two tubulin heterodimers in a curved complex capped by the SLD amino-terminal domain, which prevents the incorporation of the complexed tubulin into microtubules. A comparison with the structure of tubulin in protofilaments shows changes in the subunits of tubulin as it switches from its straight conformation to a curved one. These changes correlate with the loss of lateral contacts and provide a rationale for the rapid microtubule depolymerization characteristic of dynamic instability. Moreover, the tubulin-colchicine complex sheds light on the mechanism of colchicine's activity: we show that colchicine binds at a location where it prevents curved tubulin from adopting a straight structure, which inhibits assembly. [ABSTRACT FROM AUTHOR]

KIS is the only known protein kinase that possesses an RNA recognition motif. This original structure indicates a role for KIS in the maturation of RNAs possibly by phosphorylating and regulating the activities of RNA associated factors. Another function of KIS has recently been unravelled—it negatively regulates the cdk inhibitor p27Kip1 and thus promotes cell cycle progression through G1. In order to explore the functional expression of this kinase, we quantified its mRNA in a wide range of rat and human tissues, during development and in tumors. In both species, the highest level of KIS gene expression was in adult neural tissues. Interestingly, within the adult rat brain, KIS mRNA is enriched in several areas including the substantia nigra compacta and nuclei of the brain stem. Furthermore, KIS gene expression increases dramatically during brain development. Altogether our results point to a ubiquitous function for KIS together with a particular implication during neural differentiation or in the function of mature neural cells. No dysregulation of KIS gene expression was detected in human tumors from breast, bladder, prostate, liver and kidney origins. On the other hand, the KIS gene was overexpressed in NF1-associated plexiform neurofibromas and malignant peripheral nerve sheath tumors (MPNSTs) as compared to dermal neurofibroma which suggests a possible implication of KIS in the genesis of NF1-associated tumors. [Copyright &y& Elsevier]

The stathmin family consists of phosphoproteins highly conserved in vertebrates and thought to be implicated in the development and functional regulation of various organs, most notably the nervous system. This family includes stathmin, SCG10, SCLIP, and RB3, phosphoproteins that are related by structural and functional homologies. They all sequester tubulin and interfere with microtubule dynamics, a property due to their shared stathmin-like domain. Little is known about the expression of the stathmin gene family in humans. Herein, we describe for the first time, for a collection of human tissues, the expression of each member of this family, using real-time quantitative RT-PCR. We found that stathmin is ubiquitously expressed, whereas SCG10 and RB3 are neural enriched, expression patterns similar to those reported for other mammals. Surprisingly, SCLIP, whose expression is thought to be neural-specific, exhibits a broader tissue distribution. Analyses of the SCLIP gene (approved symbol STMN3) show that it contains several NRSE-like elements that display low or no affinity for the cognate binding protein NRSF. The substantial expression of SCLIP in most tissues points out a novel function for this protein outside the nervous system and raises the possibility that its coexpression with stathmin could provide some degree of functional redundancy. [Copyright &y& Elsevier]

Mutations affecting exon 9 of the CALR gene lead to the generation of a C-terminally modified calreticulin (CALR) protein that lacks the KDEL endoplasmic reticulum (ER) retention signal and consequently mislocalizes outside of the ER where it activates the thrombopoietin receptor in a cell-autonomous fashion, thus driving myeloproliferative diseases. Here, we used the retention using selective hooks (RUSH) assay to monitor the trafficking of CALR. We found that exon-9-mutated CALR was released from cells in response to the biotin-mediated detachment from its ER-localized hook, in vitro and in vivo. Cellular CALR release was confirmed in suitable mouse models bearing exon-9-mutated hematopoietic systems or tumors. Extracellular CALR mediated immunomodulatory effects and inhibited the phagocytosis of dying cancer cells by dendritic cells (DC), thereby suppressing antineoplastic immune responses elicited by chemotherapeutic agents or by PD-1 blockade. Altogether, our results demonstrate paracrine immunosuppressive effects for exon-9-mutated CALR. • Exon-9-mutated CALR is released from cells in vitro and in vivo • Extracellular CALR inhibits the phagocytosis of dying cancer cells by dendritic cells • Immunosuppressive effects of mutated CALR blunt responses to anticancer immunotherapy Mutations affecting exon 9 of the CALR gene can be found in many forms of cancer and lead to the calreticulin (CALR) protein that is released. Liu et al. have shown that extracellular CALR inhibits the phagocytosis by dendritic cells, exerts immunosuppressive effects, and suppresses the effect of anticancer immunotherapy. [ABSTRACT FROM AUTHOR]

The retention using selective hooks (RUSH) system allows to withhold a fluorescent biosensor such as green fluorescent protein (GFP) fused to a streptavidin-binding peptide (SBP) by an excess of streptavidin molecules that are addressed to different subcellular localizations. Addition of biotin competitively disrupts this interaction, liberating the biosensor from its hook. We constructed a human cell line co-expressing soluble secretory-SBP-GFP (ss-SBP-GFP) and streptavidin within the endoplasmic reticulum (ER) lumen and then used this system to screen a compound library for inhibitors of the biotin-induced release of ss-SBP-GFP via the conventional Golgi-dependent protein secretion pathway into the culture supernatant. We identified and validated a series of molecularly unrelated drugs including antianginal, antidepressant, anthelmintic, antipsychotic, antiprotozoal and immunosuppressive agents that inhibit protein secretion. These compounds vary in their capacity to suppress protein synthesis and to compromise ER morphology and Golgi integrity, as well as in the degree of reversibility of such effects. In sum, we demonstrate the feasibility and utility of a novel RUSH-based phenotypic screening assay. [ABSTRACT FROM AUTHOR]