Pathways of protein secretion in eukaryotes

Molecular insights of exercise therapy in disease prevention and treatment

Despite substantial evidence emphasizing the pleiotropic benefits of exercise for the prevention and treatment of various diseases, the underlying biological mechanisms have not been fully elucidated. Several exercise benefits have been attributed to signaling molecules that are released in response to exercise by different tissues such as skeletal muscle, cardiac muscle, adipose, and liver tissue. These signaling molecules, which are collectively termed exerkines, form a heterogenous group of bioactive substances, mediating inter-organ crosstalk as well as structural and functional tissue adaption. Numerous scientific endeavors have focused on identifying and characterizing new biological mediators with such properties. Additionally, some investigations have focused on the molecular targets of exerkines and the cellular signaling cascades that trigger adaption processes. A detailed understanding of the tissue-specific downstream effects of exerkines is crucial to harness the health-related benefits mediated by exercise and improve targeted exercise programs in health and disease. Herein, we review the current in vivo evidence on exerkine-induced signal transduction across multiple target tissues and highlight the preventive and therapeutic value of exerkine signaling in various diseases. By emphasizing different aspects of exerkine research, we provide a comprehensive overview of (i) the molecular underpinnings of exerkine secretion, (ii) the receptor-dependent and receptor-independent signaling cascades mediating tissue adaption, and (iii) the clinical implications of these mechanisms in disease prevention and treatment.

A programmable protease-based protein secretion platform for therapeutic applications

Cell-based therapies represent potent enabling technologies in biomedical science. However, current genetic control systems for engineered-cell therapies are predominantly based on the transcription or translation of therapeutic outputs. Here we report a protease-based rapid protein secretion system (PASS) that regulates the secretion of pretranslated proteins retained in the endoplasmic reticulum (ER) owing to an ER-retrieval signal. Upon cleavage by inducible proteases, these proteins are secreted. Three PASS variants (chemPASS, antigenPASS and optoPASS) are developed. With chemPASS, we demonstrate the reversal of hyperglycemia in diabetic mice within minutes via drug-induced insulin secretion. AntigenPASS-equipped cells recognize the tumor antigen and secrete granzyme B and perforin, inducing targeted cell apoptosis. Finally, results from mouse models of diabetes, hypertension and inflammatory pain demonstrate light-induced, optoPASS-mediated therapeutic peptide secretion within minutes, conferring anticipated therapeutic benefits. PASS is a flexible platform for rapid delivery of therapeutic proteins that can facilitate the development and adoption of cell-based precision therapies.

Calcium flow at ER-TGN contact sites facilitates secretory cargo export

Ca2+ influx into the trans-Golgi Network (TGN) promotes secretory cargo sorting by the Ca2+-ATPase SPCA1 and the luminal Ca2+ binding protein Cab45. Cab45 oligomerizes upon local Ca2+ influx, and Cab45 oligomers sequester and separate soluble secretory cargo from the bulk flow of proteins in the TGN. However, how this Ca2+ flux into the lumen of the TGN is achieved remains mysterious, as the cytosol has a nanomolar steady-state Ca2+ concentration. The TGN forms membrane contact sites (MCS) with the Endoplasmic Reticulum (ER), allowing protein-mediated exchange of molecular species such as lipids. Here, we show that the TGN export of secretory proteins requires the integrity of ER-TGN MCS and inositol 3 phosphate receptor (IP3R)-dependent Ca2+ fluxes in the MCS, suggesting Ca2+ transfer between these organelles. Using an MCS-targeted Ca2+ FRET sensor module, we measure the Ca2+ flow in these sites in real time. These data show that ER-TGN MCS facilitates the Ca2+ transfer required for Ca2+-dependent cargo sorting and export from the TGN, thus solving a fundamental question in cell biology.

Cell-specific secretory granule sorting mechanisms: the role of MAGEL2 and retromer in hypothalamic regulated secretion

Intracellular protein trafficking and sorting are extremely arduous in endocrine and neuroendocrine cells, which synthesize and secrete on-demand substantial quantities of proteins. To ensure that neuroendocrine secretion operates correctly, each step in the secretion pathways is tightly regulated and coordinated both spatially and temporally. At the trans-Golgi network (TGN), intrinsic structural features of proteins and several sorting mechanisms and distinct signals direct newly synthesized proteins into proper membrane vesicles that enter either constitutive or regulated secretion pathways. Furthermore, this anterograde transport is counterbalanced by retrograde transport, which not only maintains membrane homeostasis but also recycles various proteins that function in the sorting of secretory cargo, formation of transport intermediates, or retrieval of resident proteins of secretory organelles. The retromer complex recycles proteins from the endocytic pathway back to the plasma membrane or TGN and was recently identified as a critical player in regulated secretion in the hypothalamus. Furthermore, melanoma antigen protein L2 (MAGEL2) was discovered to act as a tissue-specific regulator of the retromer-dependent endosomal protein recycling pathway and, by doing so, ensures proper secretory granule formation and maturation. MAGEL2 is a mammalian-specific and maternally imprinted gene implicated in Prader-Willi and Schaaf-Yang neurodevelopmental syndromes. In this review, we will briefly discuss the current understanding of the regulated secretion pathway, encompassing anterograde and retrograde traffic. Although our understanding of the retrograde trafficking and sorting in regulated secretion is not yet complete, we will review recent insights into the molecular role of MAGEL2 in hypothalamic neuroendocrine secretion and how its dysregulation contributes to the symptoms of Prader-Willi and Schaaf-Yang patients. Given that the activation of many secreted proteins occurs after they enter secretory granules, modulation of the sorting efficiency in a tissue-specific manner may represent an evolutionary adaptation to environmental cues.

Calcium-binding Cab45 regulates the polarized apical secretion of soluble proteins in epithelial cells

Protein secretion is essential for epithelial tissue homoeostasis and therefore has to be tightly regulated. However, while the mechanisms regulating polarized protein sorting and trafficking have been widely studied in the past decade, those governing polarized secretion remain elusive. The calcium manganese pump SPCA1 and the calcium-binding protein Cab45 were recently shown to regulate the secretion of a subset of soluble cargoes in nonpolarized HeLa cells. Interestingly, we demonstrated that in polarized epithelial cells calcium levels in the trans-Golgi network (TGN), controlled by SPCA1, and Cab45 are critical for the apical sorting of glycosylphosphatidylinositol-anchored proteins (GPI-APs), a class of integral membrane proteins containing a soluble protein attached to the membrane by the GPI anchor, prompting us to investigate the mechanism regulating the polarized secretion of soluble cargoes. By reducing Cab45 expression level or overexpressing an inactive mutant of SPCA1, we found that Cab45 and calcium levels in the TGN drive the polarized apical secretion of a secretory form of placental alkaline phosphatase, exogenously expressed, and the endogenous soluble protein clusterin/Gp80 in Madin-Darby canine kidney (MDCK) cells. These data highlight the critical role of a calcium-dependent Cab45 mechanism regulating apical exocytosis in polarized MDCK cells.

A circuit for secretion-coupled cellular autonomy in multicellular eukaryotic cells

Cancers represent complex autonomous systems, displaying self-sufficiency in growth signaling. Autonomous growth is fueled by a cancer cell's ability to "secrete-and-sense" growth factors (GFs): a poorly understood phenomenon. Using an integrated computational and experimental approach, here we dissect the impact of a feedback-coupled GTPase circuit within the secretory pathway that imparts secretion-coupled autonomy. The circuit is assembled when the Ras-superfamily monomeric GTPase Arf1, and the heterotrimeric GTPase Giαβγ and their corresponding GAPs and GEFs are coupled by GIV/Girdin, a protein that is known to fuel aggressive traits in diverse cancers. One forward and two key negative feedback loops within the circuit create closed-loop control, allow the two GTPases to coregulate each other, and convert the expected switch-like behavior of Arf1-dependent secretion into an unexpected dose-response alignment behavior of sensing and secretion. Such behavior translates into cell survival that is self-sustained by stimulus-proportionate secretion. Proteomic studies and protein-protein interaction network analyses pinpoint GFs (e.g., the epidermal GF) as key stimuli for such self-sustenance. Findings highlight how the enhanced coupling of two biological switches in cancer cells is critical for multiscale feedback control to achieve secretion-coupled autonomy of growth factors.

Different pKa Shifts of Internal GLU8 in Human β-Endorphin Amyloid Revealing a Coupling of Internal Ionization and Stepwise Fibril Disassembly

As a functional amyloid, human β-endorphin amyloid fibril features a β-solenoid conformation and store peptide hormones within acidic secretory granules, which would be released into the blood through fibril disassembly when the cellular milieu pH increases from acidic to neutral level on exocytosis. To gain detailed atomic mechanism of β-endorphin amyloid fibrils' pH-responsive disassembly, we conduct constant pH molecular dynamics simulations to investigate the structural and dynamical properties of β-endorphin amyloid fibrils in experiencing the environmental pH changes. Our results demonstrate a clear pK_a shift of the internal ionizable residue of GLU8, and this shift becomes even more pronounced when it is buried more deeply in the amyloid fibrils. The unusual pK_a of GLU8 reveals that its protonation state changes from the protonated state in the acidic secretory granule to the deprotonated state in the neutral pH conditions in the blood, where the deprotonation of GLU8 leads to unfavorable interactions within the hydrophobic core of the amyloid and subsequent fibril disassembly. The different pK_a shifts of GLU8 relative to its positions in the amyloid fibril indicate that the β-endorphin amyloid fibril disassembly is a stepwise process, accounting for the experimental observation that the disassembly always initiates from the outermost layer. This study reveals the critical role of the protonation state of GLU8 in amyloid fibrils' pH-responsive disassembly, and provides clear insights for understanding the structural transitions of amyloids in hormone secretion. This study also provides theoretical basis for designing pH-sensitive biological tools for specific use with precise positioning of ionizable residues into the hydrophobic interior of proteins.

Exploring the role of secretory proteins in the human infectious diseases diagnosis and therapeutics

Secretory proteins are playing important role during the host-pathogen interaction to develop the infection or protection into the cell. Pathogens developing infectious disease to human being are taken up by host macrophages or number of immune cells, play an important role in physiological, developmental and immunological function. At the same time, infectious agents are also secreting various proteins to neutralize the resistance caused by host cells and also helping the pathogens to develop the infection. Secretory proteins (secretome) are only developed at the time of host-pathogen interaction, therefore they become very important to develop the targeted and potential therapeutic strategies. Pathogen specific secretory proteins released during interaction with host cell provide opportunity to develop point of care and rapid diagnostic kits. Proteins secreted by pathogens at the time of interaction with host cell have also been found as immunogenic in nature and numbers of vaccines have been developed to control the spread of human infectious diseases. This chapter highlights the importance of secretory proteins in the development of diagnostic and therapeutic strategies to fight against human infectious diseases.

The Role of Phospholipase Activity of Peroxiredoxin 6 in Its Transmembrane Transport and Protective Properties

Peroxiredoxin 6 (Prdx6) is a multifunctional eukaryotic antioxidant enzyme. Mammalian Prdx6 possesses peroxidase activity against a wide range of organic and inorganic hydroperoxides, as well as exhibits phospholipase A2 (aiPLA2) activity, which plays an important role in the reduction of oxidized phospholipids and cell membrane remodeling. Exogenous Prdx6 has recently been shown to be able to penetrate inside the cell. We hypothesized that this entry may be due to the phospholipase activity of Prdx6. Experiments using exogenous Prdx6 in three cell lines (3T3, A549, RAW 264.7) demonstrated that it is the phospholipase activity that promotes its penetration into the cell. Overoxidation of Prdx6 led to a suppression of the peroxidase activity and a 3-to-4-fold growth of aiPLA2, which enhanced the efficiency of its transmembrane transport into the cells by up to 15 times. A mutant form of Prdx6-S32A with an inactivated phospholipase center turned out to be unable to enter the cells in both the reduced and oxidized state of the peroxidase active center. Previously, we have shown that exogenous Prdx6 has a significant radioprotective action. However, the role of phospholipase activity in the radioprotective effects of Prdx6 remained unstudied. Trials with the mutant Prdx6-S32A form, with the use of a total irradiation model in mice, showed a nearly 50% reduction of the radioprotective effect upon aiPLA2 loss. Such a significant decrease in the radioprotective action may be due to the inability of Prdx6-S32A to penetrate animal cells, which prevents its reduction by the natural intracellular reducing agent glutathione S-transferase (πGST) and lowers the efficiency of elimination of peroxides formed from the effect of ionizing radiation. Thus, phospholipase activity may play an important role in the reduction of oxidized Prdx6 and manifestation of its antioxidant properties.

A buried glutamate in the cross-β core renders β-endorphin fibrils reversible

Functional amyloids are abundant in living organisms from prokaryotes to eukaryotes playing diverse biological roles. In contrast to the irreversible aggregation of most known pathological amyloids, we postulate that naturally-occurring functional amyloids are reversible under evolutionary pressure to be able to modulate the fibrillization process, reuse the composite peptides, or perform their biological functions. β-Endorphin, an endogenous opioid peptide hormone, forms such kinds of reversible amyloid fibrils in secretory granules for efficient storage and returns to the functional state of monomers upon release into the blood. The environmental change between low pH in secretory granules and neutral pH in extracellular spaces is believed to drive the reversible fibrillization of β-endorphin. Here, we investigate the critical role of a buried glutamate, Glu8, in the pH-responsive disassembly of β-endorphin fibrils using all-atom molecular dynamics simulations along with structure-based pKa prediction. The fibril was stable at pH 5.5 or lower with all the buried Glu8 residues protonated and neutrally charged. After switching to neutral pH, the Glu8 residues of peptides at the outer layers of the ordered fibrils became deprotonated due to partial solvent exposure, causing sheet-to-coil conformational changes and subsequent exposure of adjacent Glu8 residues in the inner chains. Via iterative deprotonation of Glu8 and induced structural disruption, all Glu8 residues would be progressively deprotonated. Electrostatic repulsion between deprotonated Glu8 residues along with their high solvation tendency disrupted the hydrogen bonding between the β1 strands and increased the solvent exposure of those otherwise buried residues in the cross-β core. Overall, our computational study reveals that the strategic positioning of ionizable residues into the cross-β core is a potential approach for designing reversible amyloid fibrils as pH-responsive smart bio-nanomaterials.

How Viruses Hijack and Modify the Secretory Transport Pathway

Eukaryotic cells contain dynamic membrane-bound organelles that are constantly remodeled in response to physiological and environmental cues. Key organelles are the endoplasmic reticulum, the Golgi apparatus and the plasma membrane, which are interconnected by vesicular traffic through the secretory transport route. Numerous viruses, especially enveloped viruses, use and modify compartments of the secretory pathway to promote their replication, assembly and cell egression by hijacking the host cell machinery. In some cases, the subversion mechanism has been uncovered. In this review, we summarize our current understanding of how the secretory pathway is subverted and exploited by viruses belonging to Picornaviridae, Coronaviridae, Flaviviridae,Poxviridae, Parvoviridae and Herpesviridae families.

Proteomic analysis of the secretome of equine herpesvirus-1 infected rabbit kidney cells

Herpesviruses are the main cause of abortions and respiratory or neurological disorders in horses. Various disease patterns are suspected to be associated with the A2254G point mutation in the DNA polymerase sequence (ORF30) of the herpesvirus genome, although the importance of this link is still under debate. Based on a label-free quantitative proteomic analysis, the differences in the secretion of some host proteins between rabbit kidney cells infected with A₂₂₅₄ and cells of the same line infected with G₂₂₅₄ equine herpesvirus 1 (EHV-1) strains were identified. In both groups, downregulation of proteins involved in insulin growth factor and extracellular matrix pathway regulation was observed. Among 12 proteins with increased secretion, 8 were regulated only in G₂₂₅₄ EHV-1 infection. Those were endoplasmic reticulum chaperones with calcium binding properties, related to unfolded protein response and mitochondria. It was presumed that the secretion of proteins such as calreticulin, Hspa5 or endoplasmin may contribute to the pathogenesis of EHV-1 infection.

Sending out molecules from the TGN

The sorting of secreted cargo proteins and their export from the trans-Golgi network (TGN) remains an enigma in the field of membrane trafficking; although the sorting mechanisms of many transmembrane proteins have been well described. The sorting of secreted proteins at the TGN is crucial for the release of signaling factors, as well as extracellular matrix proteins. These proteins are required for cell-cell communication and integrity of an organism. Missecretion of these factors can cause diseases such as neurological disorders, autoimmune disease, or cancer. The major open question is how soluble proteins that are not associated with the membrane are packed into TGN derived transport carriers to facilitate their transport to the plasma membrane. Recent investigations have identified novel types of protein and lipid machinery that facilitate the packing of these molecules into a TGN derived vesicle. In addition, novel research has uncovered an exciting link between cargo sorting and export in which TGN structure and dynamics, as well as TGN/endoplasmic reticulum contact sites, play a significant role. Here, we have reviewed the progress made in our understanding of these processes.

Regulated delivery controls Drosophila Hedgehog, Wingless, and Decapentaplegic signaling

Morphogen signaling proteins disperse across tissues to activate signal transduction in target cells. We investigated dispersion of Hedgehog (Hh), Wnt homolog Wingless (Wg), and Bone morphogenic protein homolog Decapentaplegic (Dpp) in the Drosophila wing imaginal disc. We discovered that delivery of Hh, Wg, and Dpp to their respective targets is regulated. We found that <5% of Hh and <25% of Wg are taken up by disc cells and activate signaling. The amount of morphogen that is taken up and initiates signaling did not change when the level of morphogen expression was varied between 50 and 200% (Hh) or 50 and 350% (Wg). Similar properties were observed for Dpp. We analyzed an area of 150 μm×150 μm that includes Hh-responding cells of the disc as well as overlying tracheal cells and myoblasts that are also activated by disc-produced Hh. We found that the extent of signaling in the disc was unaffected by the presence or absence of the tracheal and myoblast cells, suggesting that the mechanism that disperses Hh specifies its destinations to particular cells, and that target cells do not take up Hh from a common pool.

Functional amyloids in the human body

Amyloids have long been associated with a variety of human degenerative diseases. Discoveries indicate, however, that there are several amyloids that serve functional roles in the human body. These amyloids are involved in a variety of biological processes ranging from storage of peptide hormones to necroptosis of cells. Additionally, there are distinct differences between toxic amyloids and their functional counterparts including kinetics of assembly/disassembly and structural features. This digest article surveys the biological roles of functional amyloids found in the human body, key differences between functional and toxic amyloids, and potential therapeutic applications.

Maturing secretory granules: Where secretory and endocytic pathways converge

Secretory granules (SGs) are specialized organelles responsible for the storage and regulated release of various biologically active molecules from the endocrine and exocrine systems. Thus, proper SG biogenesis is critical to normal animal physiology. Biogenesis of SGs starts at the trans-Golgi network (TGN), where immature SGs (iSGs) bud off and undergo maturation before fusing with the plasma membrane (PM). How iSGs mature is unclear, but emerging studies have suggested an important role for the endocytic pathway. The requirement for endocytic machinery in SG maturation blurs the line between SGs and another class of secretory organelles called lysosome-related organelles (LROs). Therefore, it is important to re-evaluate the differences and similarities between SGs and LROs.

Peyronie's disease: pharmacological treatments and limitations

Introduction: Peyronie's disease (PD) is a disorder of the tunica albuginea from disordered and excessive deposition of collagen resulting in a palpable scar, pain, erect penile deformity and erectile dysfunction that significantly impacts patients both physically and emotionally.Areas Covered: Several treatment options have been described for PD, including shockwave therapy, traction therapy, both oral and intralesional pharmacological options, and surgery. This review seeks to examine the data for different types of non-surgical treatments for PD. We review how various treatment modalities impact several relevant clinical endpoints for Peyronie's disease, including effects on pain, penile curvature, plaque formation, and erectile function. We performed a literature search using PubMed and SCOPUS while referencing AUA, EAU, and CUA guidelines for management of Peyronie's Disease for studies published 1980-2020.Expert opinion: Intralesional collagenase injections have the strongest evidence and are the only FDA approved intralesional treatment for PD. Penile traction therapy (PTT) is low risk and may be beneficial in patients willing to invest significant time using the devices. Furthermore, oral combination therapy with other modalities may provide some benefit. Further investigation is required to better understand pathophysiology of PD and clarify the therapeutic utility of existing treatments, potentially with a multimodal strategy.

A Circuit for Secretion-coupled Cellular Autonomy in Multicellular Eukaryotes.. [DOI: 10.1101/2021.03.18.436048]

Cancers represent complex autonomous systems, displaying self-sufficiency in growth signaling. Autonomous growth is fueled by a cancer cell’s ability to ‘secrete-and-sense’ growth factors: a poorly understood phenomenon. Using an integrated systems and experimental approach, here we dissect the impact of a feedback-coupled GTPase circuit within the secretory pathway that imparts secretion-coupled autonomy. The circuit is assembled when the Ras-superfamily monomeric GTPase Arf1, and the heterotrimeric GTPase Giαβγ and their corresponding GAPs and GEFs are coupled by GIV/Girdin, a protein that is known to fuel aggressive traits in diverse cancers. One forward and two key negative feedback loops within the circuit create closed-loop control (CLC), allow the two GTPases to coregulate each other, and convert the expected switch-like behavior of Arf1-dependent secretion into an unexpected dose response alignment behavior of sensing and secretion. Such behavior translates into cell survival that is self-sustained by stimulus-proportionate secretion. Proteomic studies and protein-protein interaction network analyses pinpoint growth factors (e.g., the epidermal growth factor; EGF) as a key stimuli for such self-sustenance. Findings highlight how enhanced coupling of two biological switches in cancer cells is critical for multiscale feedback control to achieve secretion-coupled autonomy of growth factors.

SYNOPSIS IMAGE

STANDFIRST TEXT

This work defines the inner workings of a Golgi-localized molecular circuitry comprised of coupled GTPases, which empowers cells to achieve self-sufficiency in growth factor signaling by creating a secrete-and-sense autocrine loop.

HIGHLIGHTS/MAIN FINDINGS

Modeling and experimental approaches were used to dissect a coupled GTPase circuit.

Coupling enables closed loop feedback and mutual control of GTPases.

Coupling generates dose response alignment behavior of sensing and secretion of growth factors.

Coupling is critical for multiscale feedback control to achieve secretion-coupled autonomy.

COPII genes SEC31A/B are essential for gametogenesis and interchangeable in pollen development in Arabidopsis

In eukaryotes, coat protein complex II (COPII) vesicles mediate anterograde traffic from the endoplasmic reticulum to the Golgi apparatus. Compared to yeasts, plants have multiple COPII coat proteins; however, the functional diversity among them is less well understood. SEC31A and SEC31B are outer coat proteins found in COPII vesicles in Arabidopsis. In this study, we explored the function of SEC31A and compared it with that of SEC31B from various perspectives. SEC31A was widely expressed, but at a significantly lower level than SEC31B. SEC31A-mCherry and SEC31B-GFP exhibited a high co-localization rate in pollen, but a lower rate in growing pollen tubes. The sec31a single mutant exhibited normal growth. SEC31A expression driven by the SEC31B promoter rescued the pollen abortion and infertility observed in sec31b. A sec31asec31b double mutant was unavailable due to lethality of the sec31asec31b gametophyte. Transmission electron microscopy revealed that one quarter of male gametogenesis was arrested at the uninuclear microspore stage, while confocal laser scanning microscopy showed that 1/4 female gametophyte development was suspended at the functional megaspore stage in sec31a-1/+sec31b-3/+ plants. Our study highlights the essential role of SEC31A/B in gametogenesis and their interchangeable functions in pollen development.

Inactivation of parathyroid hormone: perspectives of drug discovery to combating hyperparathyroidism

Hormonal coordination is tightly regulated within the human body and thus regulates human physiology. The parathyroid hormone (PTH), a member of the endocrine system, regulates the calcium and phosphate level within the human body. Under non-physiological conditions, PTH levels get upregulated (hyperparathyroidism) or downregulated (hypoparathyroidism) due to external or internal factors. In the case of hyperparathyroidism, elevated PTH stimulates cellular receptors present in the bones, kidneys, and intestines to increase the blood calcium level, leading to calcium deposition. This eventually causes various symptoms including kidney stones. Currently, there is no known medication that directly targets PTH in order to suppress its function. Therefore, it is of great interest to find novel small molecules or any other means that can modulate PTH function. The molecular signaling of PTH starts by binding of its N-terminus to the G-protein coupled PTH1/2 receptor. Therefore, any intervention that affects the N-terminus of PTH could be a lead candidate for treating hyperparathyroidism. As a proof-of-concept, there are various possibilities to inhibit molecular PTH function by (i) a small molecule, (ii) N-terminal PTH phosphorylation, (iii) fibril formation and (iv) residue-specific mutations. These modifications put PTH into an inactive state, which will be discussed in detail in this review article. We anticipate that exploring small molecules or other means that affect the N-terminus of PTH could be lead candidates in combating hyperparathyroidism.

Rab7-harboring vesicles are carriers of the transferrin receptor through the biosynthetic secretory pathway

The biosynthetic secretory pathway is particularly challenging to investigate as it is underrepresented compared to the abundance of the other intracellular trafficking routes. Here, we combined the retention using selective hook (RUSH) to a CRISPR-Cas9 gene editing approach (eRUSH) and identified Rab7-harboring vesicles as an important intermediate compartment of the Golgi-to-plasma membrane transport of neosynthesized transferrin receptor (TfR). These vesicles did not exhibit degradative properties and were not associated to Rab6A-harboring vesicles. Rab7A was transiently associated to neosynthetic TfR-containing post-Golgi vesicles but dissociated before fusion with the plasma membrane. Together, our study reveals a role for Rab7 in the biosynthetic secretory pathway of the TfR, highlighting the diversity of the secretory vesicles' nature.

The three-dimensional structure of human β-endorphin amyloid fibrils

In the pituitary gland, hormones are stored in a functional amyloid state within acidic secretory granules before they are released into the blood. To gain a detailed understanding of the structure-function relationship of amyloids in hormone secretion, the three-dimensional (3D) structure of the amyloid fibril of the human hormone β-endorphin was determined by solid-state NMR. We find that β-endorphin fibrils are in a β-solenoid conformation with a protonated glutamate residue in their fibrillar core. During exocytosis of the hormone amyloid the pH increases from acidic in the secretory granule to neutral level in the blood, thus it is suggested-and supported with mutagenesis data-that the pH change in the cellular milieu acts through the deprotonation of glutamate 8 to release the hormone from the amyloid. For amyloid disassembly in the blood, it is proposed that the pH change acts together with a buffer composition change and hormone dilution. In the pituitary gland, peptide hormones can be stored as amyloid fibrils within acidic secretory granules before release into the blood stream. Here, we use solid-state NMR to determine the 3D structure of the amyloid fiber formed by the human hormone β-endorphin. We find that β-endorphin fibrils are in a β-solenoid conformation that is generally reminiscent of other functional amyloids. In the β-endorphin amyloid, every layer of the β-solenoid is composed of a single peptide and protonated Glu8 is located in the fibrillar core. The secretory granule has an acidic pH but, on exocytosis, the β-endorphin fibril would encounter neutral pH conditions (pH 7.4) in the blood; this pH change would result in deprotonation of Glu8 to release the hormone peptide from the amyloid. Analyses of β-endorphin variants carrying mutations in Glu8 support the role of the protonation state of this residue in fibril disassembly, among other environmental changes.

Intralesional injection of the calcium channel blocker Verapamil in Peyronie's disease: A critical review

OBJECTIVE

To assess the effectiveness of an intralesional injection of verapamil in men with Peyronie's disease (PD).

MATERIALS AND METHODS

The data provided in the current review are based on a thorough review of the available original articles on PD retrieved with a systematic literature search using PubMed- Medline, and the Cochrane Central Register of Controlled Trials, up to December 2019, to identify studies dealing with Peyronie's disease and its treatment. Included were only original articles, that we thoroughly evaluated. We searched for the primary and secondary terms of: "Peyronie's disease," "Penile curvature," "Erectile dysfunction," "Verapamil and Peyronie's disease," "Calcium channel blocker," and "Intralesional injection."

RESULTS

The initial search of the databases yielded a total of 1240 studies (PubMed: 1058; Cochrane: 182), as of December 2019. Seventy studies were removed due to duplication. Further 986 studies were removed due to not being in English (except for one study by Arena F. for which we got a translation form Italian), being about animal experimentations, not being full-text, and not being clinical trials. Likewise, studies not referring at all to verapamil were excluded (148). From the remaining 36 full-text articles we focused on 13 studies which met the inclusion criteria, mainly being deemed relevant to the context of this study.

CONCLUSIONS

Calcium channel blockers have been shown in both in vitro and in vivo studies to inhibit the synthesis and secretion of extracellular matrix molecules, as well as to increase collagenase activity. Patients with localised plaque are the best candidates for intralesional injections of verapamil. The beneficial effects of intralesional verapamil are apparent within the first three months. For patients who respond to treatment, the injections should be continued for six months. Patients who fail to respond to intralesional verapamil or whose angulation is greater than 30° at presentation should be considered candidates for surgery. Injection of verapamil is clinically safe for patients with Peyronie's disease, and it appears to induce a rapid, beneficial effect in patients for the reduction of plaque size. Intralesional verapamil injection for Peyronie's disease could reduce pain, decrease penile curvature, and improve sexual function.

A minimal self-organisation model of the Golgi apparatus

The design principles dictating the spatio-temporal organisation of eukaryotic cells, and in particular the mechanisms controlling the self-organisation and dynamics of membrane-bound organelles such as the Golgi apparatus, remain elusive. Although this organelle was discovered 120 years ago, such basic questions as whether vesicular transport through the Golgi occurs in an anterograde (from entry to exit) or retrograde fashion are still strongly debated. Here, we address these issues by studying a quantitative model of organelle dynamics that includes: de-novo compartment generation, inter-compartment vesicular exchange, and biochemical conversion of membrane components. We show that anterograde or retrograde vesicular transports are asymptotic behaviors of a much richer dynamical system. Indeed, the structure and composition of cellular compartments and the directionality of vesicular exchange are intimately linked. They are emergent properties that can be tuned by varying the relative rates of vesicle budding, fusion and biochemical conversion.

Direct trafficking pathways from the Golgi apparatus to the plasma membrane

In eukaryotic cells, protein sorting is a highly regulated mechanism important for many physiological events. After synthesis in the endoplasmic reticulum and trafficking to the Golgi apparatus, proteins sort to many different cellular destinations including the endolysosomal system and the extracellular space. Secreted proteins need to be delivered directly to the cell surface. Sorting of secreted proteins from the Golgi apparatus has been a topic of interest for over thirty years, yet there is still no clear understanding of the machinery that forms the post-Golgi carriers. Most evidence points to these post-Golgi carriers being tubular pleomorphic structures that bud from the trans-face of the Golgi. In this review, we present the background studies and highlight the key components of this pathway, we then discuss the machinery implicated in the formation of these carriers, their translocation across the cytosol, and their fusion at the plasma membrane.

ATF6 as a Nodal Regulator of Proteostasis in the Heart

Proteostasis encompasses a homeostatic cellular network in all cells that maintains the integrity of the proteome, which is critical for optimal cellular function. The components of the proteostasis network include protein synthesis, folding, trafficking, and degradation. Cardiac myocytes have a specialized endoplasmic reticulum (ER) called the sarcoplasmic reticulum that is well known for its role in contractile calcium handling. However, less studied is the proteostasis network associated with the ER, which is of particular importance in cardiac myocytes because it ensures the integrity of proteins that are critical for cardiac contraction, e.g., ion channels, as well as proteins necessary for maintaining myocyte viability and interaction with other cell types, e.g., secreted hormones and growth factors. A major aspect of the ER proteostasis network is the ER unfolded protein response (UPR), which is initiated when misfolded proteins in the ER activate a group of three ER transmembrane proteins, one of which is the transcription factor, ATF6. Prior to studies in the heart, ATF6 had been shown in model cell lines to be primarily adaptive, exerting protective effects by inducing genes that encode ER proteins that fortify protein-folding in this organelle, thus establishing the canonical role for ATF6. Subsequent studies in isolated cardiac myocytes and in the myocardium, in vivo, have expanded roles for ATF6 beyond the canonical functions to include the induction of genes that encode proteins outside of the ER that do not have known functions that are obviously related to ER protein-folding. The identification of such non-canonical roles for ATF6, as well as findings that the gene programs induced by ATF6 differ depending on the stimulus, have piqued interest in further research on ATF6 as an adaptive effector in cardiac myocytes, underscoring the therapeutic potential of activating ATF6 in the heart. Moreover, discoveries of small molecule activators of ATF6 that adaptively affect the heart, as well as other organs, in vivo, have expanded the potential for development of ATF6-based therapeutics. This review focuses on the ATF6 arm of the ER UPR and its effects on the proteostasis network in the myocardium.

Molecular evolution of gland cell types and chemical interactions in animals

Across the Metazoa, the emergence of new ecological interactions has been enabled by the repeated evolution of exocrine glands. Specialized glands have arisen recurrently and with great frequency, even in single genera or species, transforming how animals interact with their environment through trophic resource exploitation, pheromonal communication, chemical defense and parental care. The widespread convergent evolution of animal glands implies that exocrine secretory cells are a hotspot of metazoan cell type innovation. Each evolutionary origin of a novel gland involves a process of 'gland cell type assembly': the stitching together of unique biosynthesis pathways; coordinated changes in secretory systems to enable efficient chemical release; and transcriptional deployment of these machineries into cells constituting the gland. This molecular evolutionary process influences what types of compound a given species is capable of secreting, and, consequently, the kinds of ecological interactions that species can display. Here, we discuss what is known about the evolutionary assembly of gland cell types and propose a framework for how it may happen. We posit the existence of 'terminal selector' transcription factors that program gland function via regulatory recruitment of biosynthetic enzymes and secretory proteins. We suggest ancestral enzymes are initially co-opted into the novel gland, fostering pleiotropic conflict that drives enzyme duplication. This process has yielded the observed pattern of modular, gland-specific biosynthesis pathways optimized for manufacturing specific secretions. We anticipate that single-cell technologies and gene editing methods applicable in diverse species will transform the study of animal chemical interactions, revealing how gland cell types are assembled and functionally configured at a molecular level.

Gastric Peptides-Gastrin and Somatostatin

Gastric acid secretion (i) facilitates digestion of protein as well as absorption of micronutrients and certain medications, (ii) kills ingested microorganisms, including Helicobacter pylori, and (iii) prevents bacterial overgrowth and enteric infection. The principal regulators of acid secretion are the gastric peptides gastrin and somatostatin. Gastrin, the major hormonal stimulant for acid secretion, is synthesized in pyloric mucosal G cells as a 101-amino acid precursor (preprogastrin) that is processed to yield biologically active amidated gastrin-17 and gastrin-34. The C-terminal active site of gastrin (Trp-Met-Asp-Phe-NH₂ ) binds to gastrin/CCK₂ receptors on parietal and, more importantly, histamine-containing enterochromaffin-like (ECL) cells, located in oxyntic mucosa, to induce acid secretion. Histamine diffuses to the neighboring parietal cells where it binds to histamine H₂ -receptors coupled to hydrochloric acid secretion. Gastrin is also a trophic hormone that maintains the integrity of gastric mucosa, induces proliferation of parietal and ECL cells, and is thought to play a role in carcinogenesis. Somatostatin, present in D cells of the gastric pyloric and oxyntic mucosa, is the main inhibitor of acid secretion, particularly during the interdigestive period. Somatostatin exerts a tonic paracrine restraint on gastrin secretion from G cells, histamine secretion from ECL cells, and acid secretion from parietal cells. Removal of this restraint, for example by activation of cholinergic neurons during ingestion of food, initiates and maximizes acid secretion. Knowledge regarding the structure and function of gastrin, somatostatin, and their respective receptors is providing novel avenues to better diagnose and manage acid-peptic disorders and certain cancers. Published 2020. Compr Physiol 10:197-228, 2020.

Functional Amyloids

When protein/peptides aggregate, they usually form the amyloid state consisting of cross β-sheet structure built by repetitively stacked β-strands forming long fibrils. Amyloids are usually associated with disease including Alzheimer's. However, amyloid has many useful features. It efficiently transforms protein from the soluble to the insoluble state in an essentially two-state process, while its repetitive structure provides high stability and a robust prion-like replication mechanism. Accordingly, amyloid is used by nature in multifaceted and ingenious ways of life, ranging from bacteria and fungi to mammals. These include (1) Structure: Templating for small chemical molecules (Pmel17), biofilm formation in bacteria (curli), assisting aerial hyphae formation in streptomycetes (chaplins) or monolayer formation at a surface (hydrophobins). (2) Reservoirs: A storage state for peptide/proteins to protect them from their surroundings or vice versa (storage of peptide hormones in mammalian secretory granules or major basic protein in eosinophils). (3) Information carriers: The fungal immune system (HET-s prion in Podospora anserina, yeast prions) or long-term memory (e.g., mnemons in yeast, cytoplasmic polyadenylation element-binding protein in aplysia). Aggregation is also used to (4) "suppress" the function of the soluble protein (e.g., Cdc19 in yeast stress granules), or (5) "signaling" through formation of oligomers (e.g., HET-s prion, necroptosis-related proteins RIP1/RIP3). This review summarizes current knowledge on functional amyloids with a focus on the amyloid systems curli in bacteria, HET-s prion in P. anserina, and peptide hormone storage in mammals together with an attempt to highlight differences between functional and disease-associated amyloids.

A snapshot of intralesional verapamil injection in the treatment of Peyronie's disease today

Studies assessing the efficacy of intralesional verapamil injection in the treatment of Peyronie's disease have yielded mixed results. The purpose of this meta-analysis is to systematise the existing literature on the efficacy of intralesional verapamil injection when used in the treatment of Peyronie's disease. The treatment outcomes of seven different study groups identified by computerised literature search were compared with natural history outcomes and data from control groups of three studies involving placebo saline injection. An exploratory meta-analysis was performed on the data due to differing patient populations, treatment protocols, and inconsistent selection and reporting of outcomes. Intralesional verapamil injection significantly improved sexual function (p < .0005) and penile curvature (p < .005) in individuals with Peyronie's disease. Decreases in pain may be significant after therapy but are questionable. The effect of verapamil on plaque size remains less impressive (p > .05). Intralesional verapamil injection has promise to positively impact a number of clinical outcomes of Peyronie's disease; however, a large, multicentre, randomised, controlled study with reliable protocols is needed to confirm the efficacy of treatment.

Characterization of molecular mechanisms of extracellular acidification-induced intracellular Ca2+ increase in LβT2 cells

Extracellular acidification regulates endocrine cell functions. Ovarian cancer G protein-coupled receptor 1 (OGR1), also known as GPR68, is a proton-sensing G protein-coupled receptor and is activated by extracellular acidification, resulting in the activation of multiple intracellular signaling pathways. In the present study, we found that OGR1 was expressed in some gonadotropic cells in rat anterior pituitary and in LβΤ2 cells, which are used as a model of gonadotropic cells. When we reduced extracellular pH, a transient intracellular Ca²⁺ increase was detected in LβT2 cells. The Ca²⁺ increase was inhibited by a G_q/11 inhibitor and Cu²⁺, which is known as an OGR1 antagonist. We also found that extracellular acidification enhanced GnRH-induced Gaussia luciferase secretion from LβT2 cells. These results suggest that OGR1 may play a role in the regulation of gonadotropic cell function such as its hormone secretion.

Protein Nanofibrils as Storage Forms of Peptide Drugs and Hormones

Amyloids are highly organized cross β-sheet protein nanofibrils that are associated with both diseases and functions. Thermodynamically amyloids are stable structures as they represent the lowest free energy state that proteins can attain. However, recent studies suggest that amyloid fibrils can be dissociated by a change in environmental parameters such as pH and ionic strength. This reversibility of amyloids can not only be associated with disease, but function as well. In disease-associated amyloids, fibrils can act as reservoirs of cytotoxic oligomers. Recently, in higher organisms such as mammals, hormones were found to be stored in amyloid-like state, where these were reported to act as a reservoir of functional monomers. These hormone amyloids can dissociate to monomers upon release from the secretory granules, and subsequently bind to their respective receptors and perform their functions. In this book chapter, we describe in detail how these protein nanofibrils represent the densest possible peptide packing and are suitable for long-term storage. Thus, mimicking the feature of amyloids to release functional monomers, it is possible to formulate amyloid-based peptide/protein drugs, which can be used for sustained release.

PACS-1 and adaptor protein-1 mediate ACTH trafficking to the regulated secretory pathway

The regulated secretory pathway is a specialized form of protein secretion found in endocrine and neuroendocrine cell types. Pro-opiomelanocortin (POMC) is a pro-hormone that utilizes this pathway to be trafficked to dense core secretory granules (DCSGs). Within this organelle, POMC is processed to multiple bioactive hormones that play key roles in cellular physiology. However, the complete set of cellular membrane trafficking proteins that mediate the correct sorting of POMC to DCSGs remain unknown. Here, we report the roles of the phosphofurin acidic cluster sorting protein - 1 (PACS-1) and the clathrin adaptor protein 1 (AP-1) in the targeting of POMC to DCSGs. Upon knockdown of PACS-1 and AP-1, POMC is readily secreted into the extracellular milieu and fails to be targeted to DCSGs.

Cancer Cell-Derived, Drug-Loaded Nanovesicles Induced by Sulfhydryl-Blocking for Effective and Safe Cancer Therapy

Extracellular vesicles (EVs) pose great promise as therapeutic carriers due to their ideal size range and intrinsic biocompatibility. Limited scalability, poor quality control during production, and cumbersome isolation and purification processes have caused major setbacks in the progression of EV therapeutics to the clinic. Here, we overcome these setbacks by preparing cell-derived nanovesicles induced by sulfhydryl-blocking (NIbS), in the desirable size range for therapeutic delivery, that can be further loaded with the chemotherapeutic drug, doxorubicin (DOX), resulting in NIbS/DOX. Applicable to most cell types, this chemical blebbing approach enables efficient, quick, and simple harvest and purification as well as easily scalable production. Cellular uptake and intracellular release of DOX was improved using NIbS/DOX compared to a liposomal formulation. We also confirmed that in tumor-challenged C57BL/6 mice NIbS/DOX significantly slowed tumor growth and led to improved survival compared to treatment with free drug or liposomal drug. NIbS are a promising therapeutic carrier for improving cancer treatment outcomes since they are easy to prepare at a large scale, good candidates for drug loading, and capable of efficient administration of therapeutic agents with avoided nonspecific major distribution in vital organs. In addition, the utility of NIbS can be easily expanded to immunotherapy, gene therapy, and cell therapy when they are derived from applicable cell types.

New insight into the mechanism underlying the silk gland biological process by knocking out fibroin heavy chain in the silkworm

BACKGROUND

Exploring whether and how mutation of silk protein contributes to subsequent re-allocation of nitrogen, and impacts on the timing of silk gland degradation, is important to understand silk gland biology. Rapid development and wide application of genome editing approach in the silkworm provide us an opportunity to address these issues.

RESULTS

Using CRISPR/Cas9 system, we successfully performed genome editing of Bmfib-H. The loss-of-function mutations caused naked pupa and thin cocoon mutant phenotypes. Compared with the wild type, the posterior silk gland of mutant showed obviously degraded into fragments in advance of programmed cell death of silk gland cells. Comparative transcriptomic analyses of silk gland at the fourth day of the fifth instar larval stage(L5D4)identified 1456 differential expressed genes (DEGs) between posterior silk gland (PSG) and mid silk gland (MSG) and 1388 DEGs between the mutant and the wild type. Hierarchical clustering of all the DEGs indicated a remarkable down-regulated and an up-regulated gene clade in the mutant silk glands, respectively. Down-regulated genes were overrepresented in the pathways involved in cancer, DNA replication and cell proliferation. Intriguingly, up-regulated DEGs are significantly enriched in the proteasome. By further comparison on the transcriptome of MSG and PSG between the wild type and the mutant, we consistently observed that up-regulated DEGs in the mutant PSG were enriched in protein degrading activity and proteasome. Meantime, we observed a series of up-regulated genes involved in autophagy. Since these protein degradation processes would be normally occur after the spinning time, the results suggesting that these progresses were activated remarkably ahead of schedule in the mutant.

CONCLUSIONS

Accumulation of abnormal fib-H protein might arouse the activation of proteasomes as well as autophagy process, to promote the rapid degradation of such abnormal proteins and the silk gland cells. Our study therefore proposes a subsequent process of protein and partial cellular degradation caused by mutation of silk protein, which might be helpful for understanding its impact of the silk gland biological process, and further exploration the re-allocation of nitrogen in the silkworm.

Ångstrom-size exocytotic fusion pore: Implications for pituitary hormone secretion

In the past, vesicle content release was thought to occur immediately and completely after triggering of exocytosis. However, vesicles may merge with the plasma membrane to form an Ångstrom diameter fusion pore that prevents the exit of secretions from the vesicle lumen. The advantage of such a narrow pore is to minimize the delay between the trigger and the release. Instead of stimulating a sequence of processes, leading to vesicle merger with the plasma membrane and a formation of a fusion pore, the stimulus only widens the pre-established fusion pore. The fusion pore may be stable and may exhibit repetitive opening of the vesicle lumen to the cell exterior accompanied by a content discharge. Such release of vesicle content is partial (subquantal), and depends on fusion pore open time, diameter and the diffusibility of the cargo. Such transient mode of fusion pore opening was not confirmed until the development of the membrane capacitance patch-clamp technique, which enables high-resolution measurement of changes in membrane surface area. It allows millisecond dwell-time measurements of fusion pores with subnanometer diameters. Currently, the soluble N-ethylmaleimide-sensitive factor-attachment protein receptor (SNARE) proteins are considered to be key entities in end-stage exocytosis, and the SNARE complex assembly/disassembly may regulate the fusion pore. Moreover, lipids or other membrane constituents with anisotropic (non-axisymmetric) geometry may also favour the establishment of stable narrow fusion pores, if positioned in the neck of the fusion pore.

Stochastic Model of Maturation and Vesicular Exchange in Cellular Organelles

The dynamical organization of membrane-bound organelles along intracellular transport pathways relies on vesicular exchange between organelles and on the maturation of the organelle's composition by enzymatic reactions or exchange with the cytoplasm. The relative importance of each mechanism in controlling organelle dynamics remains controversial, in particular for transport through the Golgi apparatus. Using a stochastic model, we identify two classes of dynamical behavior that can lead to full maturation of membrane-bound compartments. In the first class, maturation corresponds to the stochastic escape from a steady state in which export is dominated by vesicular exchange, and is very unlikely for large compartments. In the second class, it occurs in a quasi-deterministic fashion and is almost size independent. Whether a system belongs to the first or second class is largely controlled by homotypic fusion.

Stochastic Model of Vesicular Sorting in Cellular Organelles

The proper sorting of membrane components by regulated exchange between cellular organelles is crucial to intracellular organization. This process relies on the budding and fusion of transport vesicles, and should be strongly influenced by stochastic fluctuations, considering the relatively small size of many organelles. We identify the perfect sorting of two membrane components initially mixed in a single compartment as a first passage process, and we show that the mean sorting time exhibits two distinct regimes as a function of the ratio of vesicle fusion to budding rates. Low ratio values lead to fast sorting but result in a broad size distribution of sorted compartments dominated by small entities. High ratio values result in two well-defined sorted compartments but sorting is exponentially slow. Our results suggest an optimal balance between vesicle budding and fusion for the rapid and efficient sorting of membrane components and highlight the importance of stochastic effects for the steady-state organization of intracellular compartments.

Secretogranin III: a diabetic retinopathy-selective angiogenic factor

Secretogranin III (Scg3) is a member of the granin protein family that regulates the biogenesis of secretory granules. Scg3 was recently discovered as an angiogenic factor, expanding its functional role to extrinsic regulation. Unlike many other known angiogenic factors, the pro-angiogenic actions of Scg3 are restricted to pathological conditions. Among thousands of quantified endothelial ligands, Scg3 has the highest binding activity ratio to diabetic vs. healthy mouse retinas and lowest background binding to normal vessels. In contrast, vascular endothelial growth factor binds to and stimulates angiogenesis of both diabetic and control vasculature. Consistent with its role in pathological angiogenesis, Scg3-neutralizing antibodies alleviate retinal vascular leakage in mouse models of diabetic retinopathy and retinal neovascularization in oxygen-induced retinopathy mice. This review summarizes our current knowledge of Scg3 as a regulatory protein of secretory granules, highlights its new role as a highly disease-selective angiogenic factor, and envisions Scg3 inhibitors as "selective angiogenesis blockers" for targeted therapy.

Impaired Processing of Prohormones in Secretogranin III-Null Mice Causes Maladaptation to an Inadequate Diet and Stress

Secretogranin III (SgIII), a member of the granin family, binds both to another granin, chromogranin A (CgA), and to a cholesterol-rich membrane that is destined for secretory granules (SGs). The knockdown of SgIII in adrenocorticotropic hormone (ACTH)-producing AtT-20 cells largely impairs the regulated secretion of CgA and ACTH. To clarify the physiological roles of SgIII in vivo, we analyzed hormone secretion and SG biogenesis in newly established SgIII-knockout (KO) mice. Although the SgIII-KO mice were viable and fertile and exhibited no overt abnormalities under ordinary rearing conditions, a high-fat/high-sucrose diet caused pronounced obesity in the mice. Furthermore, in the SgIII-KO mice compared with wild-type (WT) mice, the stimulated secretion of active insulin decreased substantially, whereas the storage of proinsulin increased in the islets. The plasma ACTH was also less elevated in the SgIII-KO mice than in the WT mice after chronic restraint stress, whereas the storage level of the precursor proopiomelanocortin in the pituitary gland was somewhat increased. These findings suggest that the lack of SgIII causes maladaptation of endocrine cells to an inadequate diet and stress by impairing the proteolytic conversion of prohormones in SGs, whereas SG biogenesis and the basal secretion of peptide hormones under ordinary conditions are ensured by the compensatory upregulation of other residual granins or factors.

Distinguishing signal from autofluorescence in cryogenic correlated light and electron microscopy of mammalian cells

In cryogenic correlated light and electron microscopy (cryo-CLEM), frozen targets of interest are identified and located on EM grids by fluorescence microscopy and then imaged at higher resolution by cryo-EM. Whilst working with these methods, we discovered that a variety of mammalian cells exhibit strong punctate autofluorescence when imaged under cryogenic conditions (80 K). Autofluorescence originated from multilamellar bodies (MLBs) and secretory granules. Here we describe a method to distinguish fluorescent protein tags from these autofluorescent sources based on the narrower emission spectrum of the former. The method is first tested on mitochondria and then applied to examine the ultrastructural variability of secretory granules within insulin-secreting pancreatic beta-cell-derived INS-1E cells.

Functional Amyloids and their Possible Influence on Alzheimer Disease

Amyloids play critical roles in human diseases but have increasingly been recognized to also exist naturally. Shared physicochemical characteristics of amyloids and of their smaller oligomeric building blocks offer the prospect of molecular interactions and crosstalk amongst these assemblies, including the propensity to mutually influence aggregation. A case in point might be the recent discovery of an interaction between the amyloid β peptide (Aβ) and somatostatin (SST). Whereas Aβ is best known for its role in Alzheimer disease (AD) as the main constituent of amyloid plaques, SST is intermittently stored in amyloid-form in dense core granules before its regulated release into the synaptic cleft. This review was written to introduce to readers a large body of literature that surrounds these two peptides. After introducing general concepts and recent progress related to our understanding of amyloids and their aggregation, the review focuses separately on the biogenesis and interactions of Aβ and SST, before attempting to assess the likelihood of encounters of the two peptides in the brain, and summarizing key observations linking SST to the pathobiology of AD. While the review focuses on Aβ and SST, it is to be anticipated that crosstalk amongst functional and disease-associated amyloids will emerge as a general theme with much broader significance in the etiology of dementias and other amyloidosis.

The dynamic plasticity of insulin production in β-cells

BACKGROUND

Although the insulin-producing pancreatic β-cells are quite capable of adapting to both acute and chronic changes in metabolic demand, persistently high demand for insulin will ultimately lead to their progressive dysfunction and eventual loss. Recent and historical studies highlight the importance of 'resting' the β-cell as a means of preserving functional β-cell mass.

SCOPE OF REVIEW

We provide experimental evidence to highlight the remarkable plasticity for insulin production and secretion by the pancreatic β-cell alongside some clinical evidence that supports leveraging this unique ability to preserve β-cell function.

MAJOR CONCLUSIONS

Treatment strategies for type 2 diabetes mellitus (T2DM) targeted towards reducing the systemic metabolic burden, rather than demanding greater insulin production from an already beleaguered β-cell, should be emphasized to maintain endogenous insulin secretory function and delay the progression of T2DM.

Human protein secretory pathway genes are expressed in a tissue-specific pattern to match processing demands of the secretome

Protein secretory pathway in eukaryal cells is responsible for delivering functional secretory proteins. The dysfunction of this pathway causes a range of important human diseases from congenital disorders to cancer. Despite the piled-up knowledge on the molecular biology and biochemistry level, the tissue-specific expression of the secretory pathway genes has not been analyzed on the transcriptome level. Based on the recent RNA-sequencing studies, the largest fraction of tissue-specific transcriptome encodes for the secretome (secretory proteins). Here, the question arises that if the expression levels of the secretory pathway genes have a tissue-specific tuning. In this study, we tackled this question by performing a meta-analysis of the recently published transcriptome data on human tissues. As a result, we detected 68 as called “extreme genes” which show an unusual expression pattern in specific gene families of the secretory pathway. We also inspected the potential functional link between detected extreme genes and the corresponding tissues enriched secretome. As a result, the detected extreme genes showed correlation with the enrichment of the nature and number of specific post-translational modifications in each tissue’s secretome. Our findings conciliate both the housekeeping and tissue-specific nature of the protein secretory pathway, which we attribute to a fine-tuned regulation of defined gene families to support the diversity of secreted proteins and their modifications.

The secretory pathway, an ubiquitous cellular machinery in human cells, is here shown to have tissue-specific characteristics. A research team led by Prof. Jens Nielsen at the Chalmers University of Technology performed a meta-analysis of the gene expressions of the secretory pathway’ component. They detected that even though most of these components are expressed in all tissues, there exist distinct components with fine-tuned expression. They further evaluated the functional link between the detected tuning and the processes that are demanded to make a set of tissue-specific proteins such as endocrine system hormones or their receptors. These findings open up a new avenue to understand the function of the secretion pathway in human tissues with possible applications for improving production of pharmaceutical proteins and getting more insight into the mechanisms underlying diseases such as diabetes that are connected with the endocrine system.

Easy detection of hormone secretion from LβT2 cells by using Gaussia luciferase

Reproduction is regulated by gonadotropins secreted from gonadotrophs. The production and secretion of gonadotropins are mainly regulated by gonadotropin-releasing hormone (GnRH). Agonists or antagonists that influence GnRH action on gonadotrophs are important to regulate reproduction; however, these factors have not been fully characterized due to the lack of simple and easy-to-use techniques to detect gonadotropin secretion from gonadotropin-producing cells. In the present study, we found that Gaussia luciferase (Gluc), which was expressed in LβT2 cells, can be secreted like a luteinizing-hormone (LH) upon stimulation with GnRH. The Gluc secreted into the medium was easily monitored as luminescence signals. The detection range of the GnRH-induced Gluc activity was comparable to that of the enzyme-linked immunosorbent assay for LH. In addition, when the Gluc was expressed in AtT20 cells, which produce adrenocorticotropic hormone (ACTH), the Gluc activity in the medium increased in parallel with the ACTH secretion upon stimulation with corticotropin-releasing hormone. Thus, the Gluc assay in the present study can be easily used for high-throughput screening of factors that influence LH or ACTH secretion from LβT2 or AtT20 cells, respectively.

VAMP3/Syb and YKT6 are required for the fusion of constitutive secretory carriers with the plasma membrane

The cellular machinery required for the fusion of constitutive secretory vesicles with the plasma membrane in metazoans remains poorly defined. To address this problem we have developed a powerful, quantitative assay for measuring secretion and used it in combination with combinatorial gene depletion studies in Drosophila cells. This has allowed us to identify at least three SNARE complexes mediating Golgi to PM transport (STX1, SNAP24/29 and Syb; STX1, SNAP24/29 and YKT6; STX4, SNAP24 and Syb). RNAi mediated depletion of YKT6 and VAMP3 in mammalian cells also blocks constitutive secretion suggesting that YKT6 has an evolutionarily conserved role in this process. The unexpected role of YKT6 in plasma membrane fusion may in part explain why RNAi and gene disruption studies have failed to produce the expected phenotypes in higher eukaryotes.

Prorenin receptor in kidney development

Prorenin receptor (PRR), a receptor for renin and prorenin and an accessory subunit of the vacuolar proton pump H⁺-ATPase, is expressed in the developing kidney. Global loss of PRR is lethal in mice, and PRR mutations are associated with a high blood pressure, left ventricular hypertrophy and X-linked mental retardation in humans. With the advent of modern gene targeting techniques, including conditional knockout approaches, several recent studies have demonstrated critical roles for the PRR in several lineages of the developing kidney. PRR signaling has been shown to be essential for branching morphogenesis of the ureteric bud (UB), nephron progenitor survival and nephrogenesis. PRR regulates these developmental events through interactions with other transcription and growth factors. Several targeted PRR knockout animal models have structural defects mimicking congenital anomalies of the kidney and urinary tract observed in humans. The aim of this review, is to highlight new insights into the cellular and molecular mechanisms by which PRR may regulate UB branching, terminal differentiation and function of UB-derived collecting ducts, nephron progenitor maintenance, progression of nephrogenesis and normal structural kidney development and function.

Protein Production and Secretion in Exocrine Cells

Acinar cells of exocrine glands are highly specialized for producing, storing, and discharging secretory proteins for use on surfaces that represent interfaces between the organism and the surrounding environment. These functions are achieved through the secretory pathway that includes a series of functionally distinct intracellular compartments — the endoplasmic reticulum, subcompartments of the Golgi complex, and the secretion granule in which exportable macromolecules are stored at high concentrations. Most secretion occurs by granule exocytosis in response to external hormonal or neural stimuli. Although these processes have been traced in a variety of morphological and biochemical studies, very Utile is known about the mechanisms involved in facilitating and maintaining secretory storage, orchestrating discharge at the apical cell surface, and in ensuring conservation and re-internalization of the granule membrane. Recent studies initiated on cell fractions obtained from the rat parotid gland have provided significant insight into the protein storage conditions that prevail in the granule interior and the components of the granule membrane that are likely to be involved in general secretory function such as exocytosis.