Symmetric arrangement of mitochondria:plasma membrane contacts between adjacent photoreceptor cells regulated by Opa1

Mitochondria are known to play an essential role in photoreceptor function and survival that enables normal vision. Within photoreceptors, mitochondria are elongated and extend most of the inner-segment length, where they supply energy for protein synthesis and the phototransduction machinery in the outer segment, as well as acting as a calcium store. Here, we examined the arrangement of the mitochondria within the inner segment in detail using three-dimensional (3D) electron microscopy techniques and show they are tethered to the plasma membrane in a highly specialized arrangement. Remarkably, mitochondria and their cristae openings align with those of neighboring inner segments. The pathway by which photoreceptors meet their high energy demands is not fully understood. We propose this to be a mechanism to share metabolites and assist in maintaining homeostasis across the photoreceptor cell layer. In the extracellular space between photoreceptors, Müller glial processes were identified. Due to the often close proximity to the inner-segment mitochondria, they may, too, play a role in the inner-segment mitochondrial arrangement as well as metabolite shuttling. OPA1 is an important factor in mitochondrial homeostasis, including cristae remodeling; therefore, we examined the photoreceptors of a heterozygous Opa1 knockout mouse model. The cristae structure in the Opa1+/- photoreceptors was not greatly affected, but the mitochondria were enlarged and had reduced alignment to neighboring inner-segment mitochondria. This indicates the importance of key regulators in maintaining this specialized photoreceptor mitochondrial arrangement.

Remodeling of the Basal Labyrinth of Retinal Pigment Epithelial Cells With Osmotic Challenge, Age, and Disease

Purpose

The basal surface of the retinal pigment epithelium (RPE) is folded into a complex basal labyrinth thought to facilitate solute and water transport. We aimed to analyze and define the structural organization of the basal labyrinth of the RPE to enable quantitative analysis of structural changes in age and disease and to better understand the relationship between basal labyrinth structure and efficiency of transepithelial transport.

Methods

Conventional transmission and serial block-face scanning electron microscopy and electron tomography were used to examine the structure of the basal labyrinth in mouse eyes of different ages and genotypes and with and without osmotic shock before fixation.

Results

We identified structurally distinct zones (stacked and ribbon-like) within the RPE basal labyrinth that are largely organelle free and cisternal elements that make contact with the endoplasmic reticulum (ER) and mitochondria. These zones are lost in a hierarchic fashion with age and prematurely in a model of the progressive retinal degenerative disease, choroideremia. Junctional complexes crosslink closely opposed infoldings. Spacing between the basal infoldings was affected by subtle osmotic changes while osmotic shock induced dramatic remodeling of the infoldings.

Conclusions

The basal labyrinth has complex but ordered structural elements that break down with age and in choroideremia. The geometry of these elements and site of contact with ER and mitochondria likely facilitate the ion transport that drives water transport across the basal RPE surface. Changes in structure in response to local osmotic variation may allow transport to be modulated in order to maintain RPE volume.

Agonist-induced membrane nanodomain clustering drives GLP-1 receptor responses in pancreatic beta cells

The glucagon-like peptide-1 receptor (GLP-1R), a key pharmacological target in type 2 diabetes (T2D) and obesity, undergoes rapid endocytosis after stimulation by endogenous and therapeutic agonists. We have previously highlighted the relevance of this process in fine-tuning GLP-1R responses in pancreatic beta cells to control insulin secretion. In the present study, we demonstrate an important role for the translocation of active GLP-1Rs into liquid-ordered plasma membrane nanodomains, which act as hotspots for optimal coordination of intracellular signaling and clathrin-mediated endocytosis. This process is dynamically regulated by agonist binding through palmitoylation of the GLP-1R at its carboxyl-terminal tail. Biased GLP-1R agonists and small molecule allosteric modulation both influence GLP-1R palmitoylation, clustering, nanodomain signaling, and internalization. Downstream effects on insulin secretion from pancreatic beta cells indicate that these processes are relevant to GLP-1R physiological actions and might be therapeutically targetable.

Nanodomain segregation and clustering of the glucagon-like peptide-1 receptor, a key target for type 2 diabetes therapy, is regulated by agonist binding, leading to compartmentalization of downstream signaling and clathrin-dependent internalization and impacting pancreatic beta cell responses.

Three-dimensional structure of the basketweave Z-band in midshipman fish sonic muscle

Striated muscle enables movement in all animals by the contraction of myriads of sarcomeres joined end to end by the Z-bands. The contraction is due to tension generated in each sarcomere between overlapping arrays of actin and myosin filaments. At the Z-band, actin filaments from adjoining sarcomeres overlap and are cross-linked in a regular pattern mainly by the protein α-actinin. The Z-band is dynamic, reflected by the 2 regular patterns seen in transverse section electron micrographs; the so-called small-square and basketweave forms. Although these forms are attributed, respectively, to relaxed and actively contracting muscles, the basketweave form occurs in certain relaxed muscles as in the muscle studied here. We used electron tomography and subtomogram averaging to derive the 3D structure of the Z-band in the swimbladder sonic muscle of type I male plainfin midshipman fish (Porichthys notatus), into which we docked the crystallographic structures of actin and α-actinin. The α-actinin links run diagonally between connected pairs of antiparallel actin filaments and are oriented at an angle of about 25° away from the actin filament axes. The slightly curved and flattened structure of the α-actinin rod has a distinct fit into the map. The Z-band model provides a detailed understanding of the role of α-actinin in transmitting tension between actin filaments in adjoining sarcomeres.

Selective Ablation of Megalin in the Retinal Pigment Epithelium Results in Megaophthalmos, Macromelanosome Formation and Severe Retina Degeneration

Purpose

Mutations in the megalin-encoding gene, LRP2, cause high myopia as seen in patients suffering from Donnai-Barrow/facio-oculo-acoustico-renal syndrome. Megalin is present in both the nonpigmented epithelium of the ciliary body and in the RPE. In this study, we set out to establish an animal model to study the mechanisms underlying the ocular phenotype and to establish if high myopia/megaophthalmos is induced by postnatal megalin-deficiency in the RPE.

Methods

Postnatal RPE-specific deletion of megalin was generated by crossing mice bearing a homozygous loxP-flanked Lrp2 allele with transgenic mice expressing the Cre recombinase driven by the BEST1 promotor. The model was investigated by immunohistologic techniques, and transmission electron microscopy.

Results

Mice with postnatal RPE-specific loss of megalin developed a megaophthalmos phenotype with dramatic increase in ocular size and severe retinal thinning associated with compromised vision. This phenotype was present at postnatal day 14, indicating rapid development in the period from onset of BEST1 promotor activity at postnatal day 10. Additionally, RPE melanosomes exhibited abnormal size and morphology, suggested by electron tomography to be caused by fusion events between multiple melanosomes.

Conclusions

Postnatal loss of megalin in the RPE induces dramatic and rapid ocular growth and retinal degeneration compatible with the high myopia observed in Donnai-Barrow patients. The morphologic changes of RPE melanosomes, believed to be largely inert and fully differentiated at birth, suggested a continued plasticity of mature melanosomes and a requirement for megalin to maintain their number and morphology.

Phagosomal and mitochondrial alterations in RPE may contribute to KCNJ13 retinopathy

Mutations in KCNJ13 are associated with two retinal disorders; Leber congenital amaurosis (LCA) and snowflake vitreoretinal degeneration (SVD). We examined the retina of kcnj13 mutant zebrafish (obelix^td15, c.502T > C p.[Phe168Leu]) to provide new insights into the pathophysiology underlying these conditions. Detailed phenotyping of obelix^td15 fish revealed a late onset retinal degeneration at 12 months. Electron microscopy of the obelix^td15 retinal pigment epithelium (RPE) uncovered reduced phagosome clearance and increased mitochondrial number and size prior any signs of retinal degeneration. Melanosome distribution was also affected in dark-adapted 12-month obelix^td15 fish. At 6 and 12 months, ATP levels were found to be reduced along with increased expression of glial fibrillary acidic protein and heat shock protein 60. Quantitative RT-PCR of polg2, fis1, opa1, sod1/2 and bcl2a from isolated retina showed expression changes consistent with altered mitochondrial activity and retinal stress. We propose that the retinal disease in this model is primarily a failure of phagosome physiology with a secondary mitochondrial dysfunction. Our findings suggest that alterations in the RPE and photoreceptor cellular organelles may contribute to KCNJ13-related retinal degeneration and provide a therapeutic target.

Mutations in Outer Dynein Arm Heavy Chain DNAH9 Cause Motile Cilia Defects and Situs Inversus

Motile cilia move body fluids and gametes and the beating of cilia lining the airway epithelial surfaces ensures that they are kept clear and protected from inhaled pathogens and consequent respiratory infections. Dynein motor proteins provide mechanical force for cilia beating. Dynein mutations are a common cause of primary ciliary dyskinesia (PCD), an inherited condition characterized by deficient mucociliary clearance and chronic respiratory disease coupled with laterality disturbances and subfertility. Using next-generation sequencing, we detected mutations in the ciliary outer dynein arm (ODA) heavy chain gene DNAH9 in individuals from PCD clinics with situs inversus and in one case male infertility. DNAH9 and its partner heavy chain DNAH5 localize to type 2 ODAs of the distal cilium and in DNAH9-mutated nasal respiratory epithelial cilia we found a loss of DNAH9/DNAH5-containing type 2 ODAs that was restricted to the distal cilia region. This confers a reduced beating frequency with a subtle beating pattern defect affecting the motility of the distal cilia portion. 3D electron tomography ultrastructural studies confirmed regional loss of ODAs from the distal cilium, manifesting as either loss of whole ODA or partial loss of ODA volume. Paramecium DNAH9 knockdown confirms an evolutionarily conserved function for DNAH9 in cilia motility and ODA stability. We find that DNAH9 is widely expressed in the airways, despite DNAH9 mutations appearing to confer symptoms restricted to the upper respiratory tract. In summary, DNAH9 mutations reduce cilia function but some respiratory mucociliary clearance potential may be retained, widening the PCD disease spectrum.

ALIX Regulates Tumor-Mediated Immunosuppression by Controlling EGFR Activity and PD-L1 Presentation

The immunosuppressive transmembrane protein PD-L1 was shown to traffic via the multivesicular body (MVB) and to be released on exosomes. A high-content siRNA screen identified the endosomal sorting complexes required for transport (ESCRT)-associated protein ALIX as a regulator of both EGFR activity and PD-L1 surface presentation in basal-like breast cancer (BLBC) cells. ALIX depletion results in prolonged and enhanced stimulation-induced EGFR activity as well as defective PD-L1 trafficking through the MVB, reduced exosomal secretion, and its redistribution to the cell surface. Increased surface PD-L1 expression confers an EGFR-dependent immunosuppressive phenotype on ALIX-depleted cells. An inverse association between ALIX and PD-L1 expression was observed in human breast cancer tissues, while an immunocompetent mouse model of breast cancer revealed that ALIX-deficient tumors are larger and show an increased immunosuppressive environment. Our data suggest that ALIX modulates immunosuppression through regulation of PD-L1 and EGFR and may, therefore, present a diagnostic and therapeutic target for BLBC.

Primary Cilia Mediate Diverse Kinase Inhibitor Resistance Mechanisms in Cancer

Primary cilia are microtubule-based organelles that detect mechanical and chemical stimuli. Although cilia house a number of oncogenic molecules (including Smoothened, KRAS, EGFR, and PDGFR), their precise role in cancer remains unclear. We have interrogated the role of cilia in acquired and de novo resistance to a variety of kinase inhibitors, and found that, in several examples, resistant cells are distinctly characterized by an increase in the number and/or length of cilia with altered structural features. Changes in ciliation seem to be linked to differences in the molecular composition of cilia and result in enhanced Hedgehog pathway activation. Notably, manipulating cilia length via Kif7 knockdown is sufficient to confer drug resistance in drug-sensitive cells. Conversely, targeting of cilia length or integrity through genetic and pharmacological approaches overcomes kinase inhibitor resistance. Our work establishes a role for ciliogenesis and cilia length in promoting cancer drug resistance and has significant translational implications.

Primary ciliary dyskinesia with normal ultrastructure: three-dimensional tomography detects absence of DNAH11

In primary ciliary dyskinesia (PCD), motile ciliary dysfunction arises from ciliary defects usually confirmed by transmission electron microscopy (TEM). In 30% of patients, such as those with DNAH11 mutations, apparently normal ultrastructure makes diagnosis difficult. Genetic analysis supports diagnosis, but may not identify definitive causal variants. Electron tomography, an extension of TEM, produces three-dimensional ultrastructural ciliary models with superior resolution to TEM. Our hypothesis is that tomography using existing patient samples will enable visualisation of DNAH11-associated ultrastructural defects. Dual axis tomograms from araldite-embedded nasal cilia were collected in 13 PCD patients with normal ultrastructure (DNAH11 n=7, HYDIN n=2, CCDC65 n=3 and DRC1 n=1) and six healthy controls, then analysed using IMOD and Chimera software.

DNAH11 protein is localised to the proximal ciliary region. Within this region, electron tomography indicated a deficiency of >25% of proximal outer dynein arm volume in all patients with DNAH11 mutations (n=7) compared to other patients with PCD and normal ultrastructure (n=6) and healthy controls (n=6). DNAH11 mutations cause a shared abnormality in ciliary ultrastructure previously undetectable by TEM. Advantageously, electron tomography can be used on existing diagnostic samples and establishes a structural abnormality where ultrastructural studies were previously normal.

Correlative light and immuno-electron microscopy of retinal tissue cryostat sections

Correlative light-electron microscopy (CLEM) is a powerful technique allowing localisation of specific macromolecules within fluorescence microscopy (FM) images to be mapped onto corresponding high-resolution electron microscopy (EM) images. Existing methods are applicable to limited sample types and are technically challenging. Here we describe novel methods to perform CLEM and immuno-electron microscopy (iEM) on cryostat sections utilising the popular FM embedding solution, optimal cutting temperature (OCT) compound. Utilising these approaches, we have (i) identified the same phagosomes by FM and EM in the retinal pigment epithelium (RPE) of retinal tissue (ii) shown the correct localisation of rhodopsin on photoreceptor outer segment disc like-structures in iPSC derived optic cups and (iii) identified a novel interaction between peroxisomes and melanosomes as well as phagosomes in the RPE. These data show that cryostat sections allow easy characterisation of target macromolecule localisation within tissue samples, thus providing a substantial improvement over many conventional methods that are limited to cultured cells. As OCT embedding is routinely used for FM this provides an easily accessible and robust method for further analysis of existing samples by high resolution EM.

REEP6 deficiency leads to retinal degeneration through disruption of ER homeostasis and protein trafficking

Retinitis pigmentosa (RP) is the most common form of inherited retinal dystrophy. We recently identified mutations in REEP6, which encodes the receptor expression enhancing protein 6, in several families with autosomal recessive RP. REEP6 is related to the REEP and Yop1p family of ER shaping proteins and potential receptor accessory proteins, but the role of REEP6 in the retina is unknown. Here we characterize the disease mechanisms associated with loss of REEP6 function using a Reep6 knockout mouse generated by CRISPR/Cas9 gene editing. In control mice REEP6 was localized to the inner segment and outer plexiform layer of rod photoreceptors. The Reep6-/- mice exhibited progressive photoreceptor degeneration from P20 onwards. Ultrastructural analyses at P20 by transmission electron microscopy and 3View serial block face scanning EM revealed an expansion of the distal ER in the Reep6-/- rods and an increase in their number of mitochondria. Electroretinograms revealed photoreceptor dysfunction preceded degeneration, suggesting potential defects in phototransduction. There was no effect on the traffic of rhodopsin, Rom1 or peripherin/rds; however, the retinal guanylate cyclases GC1 and GC2 were severely affected in the Reep6 knockout animals, with almost undetectable expression. These changes correlated with an increase in C/EBP homologous protein (CHOP) expression and the activation of caspase 12, suggesting that ER stress contributes to cell death. Collectively, these data suggest that REEP6 plays an essential role in maintaining cGMP homeostasis though facilitating the stability and/or trafficking of guanylate cyclases and maintaining ER and mitochondrial homeostasis.

Endothelial MAPKs Direct ICAM-1 Signaling to Divergent Inflammatory Functions

Lymphocyte transendothelial migration (TEM) is critically dependent on intraendothelial signaling triggered by adhesion to ICAM-1. Here we show that endothelial MAPKs ERK, p38, and JNK mediate diapedesis-related and diapedesis-unrelated functions of ICAM-1 in cerebral and dermal microvascular endothelial cells (MVECs). All three MAPKs were activated by ICAM-1 engagement, either through lymphocyte adhesion or Ab-mediated clustering. MAPKs were involved in ICAM-1-dependent expression of TNF-α in cerebral and dermal MVECs, and CXCL8, CCL3, CCL4, VCAM-1, and cyclooxygenase 2 (COX-2) in cerebral MVECs. Endothelial JNK and to a much lesser degree p38 were the principal MAPKs involved in facilitating diapedesis of CD4⁺ lymphocytes across both types of MVECs, whereas ERK was additionally required for TEM across dermal MVECs. JNK activity was critical for ICAM-1-induced F-actin rearrangements. Furthermore, activation of endothelial ICAM-1/JNK led to phosphorylation of paxillin, its association with VE-cadherin, and internalization of the latter. Importantly ICAM-1-induced phosphorylation of paxillin was required for lymphocyte TEM and converged functionally with VE-cadherin phosphorylation. Taken together we conclude that during lymphocyte TEM, ICAM-1 signaling diverges into pathways regulating lymphocyte diapedesis, and other pathways modulating gene expression thereby contributing to the long-term inflammatory response of the endothelium.

Probing the Heterogeneity of Protein Kinase Activation in Cells by Super-resolution Microscopy

Heterogeneity of mitogen-activated protein kinase (MAPK) activation in genetically identical cells, which occurs in response to epidermal growth factor receptor (EGFR) signaling, remains poorly understood. MAPK cascades integrate signals emanating from different EGFR spatial locations, including the plasma membrane and endocytic compartment. We previously hypothesized that in EGF-stimulated cells the MAPK phosphorylation (pMAPK) level and activity are largely determined by the spatial organization of the EGFR clusters within the cell. For experimental testing of this hypothesis, we used super-resolution microscopy to define EGFR clusters by receptor numbers (N) and average intracluster distances (d). From these data, we predicted the extent of pMAPK with 85% accuracy on a cell-to-cell basis with control data returning 54% accuracy (P < 0.001). For comparison, the prediction accuracy was only 61% (P = 0.382) when the diffraction-limited averaged fluorescence intensity/cluster was used. Large clusters (N ≥ 3) with d > 50 nm were most predictive for pMAPK level in cells. Electron microscopy revealed that these large clusters were primarily localized to the limiting membrane of multivesicular bodies (MVB). Many tighter packed dimers/multimers (d < 50 nm) were found on intraluminal vesicles within MVBs, where they were unlikely to activate MAPK because of the physical separation. Our results suggest that cell-to-cell differences in N and d contain crucial information to predict EGFR-activated cellular pMAPK levels and explain pMAPK heterogeneity in isogenic cells.

Mutations in REEP6 Cause Autosomal-Recessive Retinitis Pigmentosa

Retinitis pigmentosa (RP) is the most frequent form of inherited retinal dystrophy. RP is genetically heterogeneous and the genes identified to date encode proteins involved in a wide range of functional pathways, including photoreceptor development, phototransduction, the retinoid cycle, cilia, and outer segment development. Here we report the identification of biallelic mutations in Receptor Expression Enhancer Protein 6 (REEP6) in seven individuals with autosomal-recessive RP from five unrelated families. REEP6 is a member of the REEP/Yop1 family of proteins that influence the structure of the endoplasmic reticulum but is relatively unstudied. The six variants identified include three frameshift variants, two missense variants, and a genomic rearrangement that disrupts exon 1. Human 3D organoid optic cups were used to investigate REEP6 expression and confirmed the expression of a retina-specific isoform REEP6.1, which is specifically affected by one of the frameshift mutations. Expression of the two missense variants (c.383C>T [p.Pro128Leu] and c.404T>C [p.Leu135Pro]) and the REEP6.1 frameshift mutant in cultured cells suggest that these changes destabilize the protein. Furthermore, CRISPR-Cas9-mediated gene editing was used to produce Reep6 knock-in mice with the p.Leu135Pro RP-associated variant identified in one RP-affected individual. The homozygous knock-in mice mimic the clinical phenotypes of RP, including progressive photoreceptor degeneration and dysfunction of the rod photoreceptors. Therefore, our study implicates REEP6 in retinal homeostasis and highlights a pathway previously uncharacterized in retinal dystrophy.

Rod disc renewal occurs by evagination of the ciliary plasma membrane that makes cadherin-based contacts with the inner segment

The outer segments of vertebrate rod photoreceptors are renewed every 10 d. Outer segment components are transported from the site of synthesis in the inner segment through the connecting cilium, followed by assembly of the highly ordered discs. Two models of assembly of discrete discs involving either successive fusion events between intracellular rhodopsin-bearing vesicles or the evagination of the plasma membrane followed by fusion of adjacent evaginations have been proposed. Here we use immuno-electron microscopy and electron tomography to show that rhodopsin is transported from the inner to the outer segment via the ciliary plasma membrane, subsequently forming successive evaginations that "zipper" up proximally, but at their leading edges are free to make junctions containing the protocadherin, PCDH21, with the inner segment plasma membrane. Given the physical dimensions of the evaginations, coupled with likely instability of the membrane cortex at the distal end of the connecting cilium, we propose that the evagination occurs via a process akin to blebbing and is not driven by actin polymerization. Disassembly of these junctions is accompanied by fusion of the leading edges of successive evaginations to form discrete discs. This fusion is topologically different to that mediated by the membrane fusion proteins, SNAREs, as initial fusion is between exoplasmic leaflets, and is accompanied by gain of the tetraspanin rim protein, peripherin.

Three-Dimensional Structure of Vertebrate Muscle Z-Band: The Small-Square Lattice Z-Band in Rat Cardiac Muscle

The Z-band in vertebrate striated muscle crosslinks actin filaments of opposite polarity from adjoining sarcomeres and transmits tension along myofibrils during muscular contraction. It is also the location of a number of proteins involved in signalling and myofibrillogenesis; mutations in these proteins lead to myopathies. Understanding the high-resolution structure of the Z-band will help us understand its role in muscle contraction and the role of these proteins in the function of muscle. The appearance of the Z-band in transverse-section electron micrographs typically resembles a small-square lattice or a basketweave appearance. In longitudinal sections, the Z-band width varies more with muscle type than species: slow skeletal and cardiac muscles have wider Z-bands than fast skeletal muscles. As the Z-band is periodic, Fourier methods have previously been used for three-dimensional structural analysis. To cope with variations in the periodic structure of the Z-band, we have used subtomogram averaging of tomograms of rat cardiac muscle in which subtomograms are extracted and compared and similar ones are averaged. We show that the Z-band comprises four to six layers of links, presumably α-actinin, linking antiparallel overlapping ends of the actin filaments from the adjoining sarcomeres. The reconstruction shows that the terminal 5-7nm of the actin filaments within the Z-band is devoid of any α-actinin links and is likely to be the location of capping protein CapZ.

Arum Palaestinum with isovanillin, linolenic acid and β-sitosterol inhibits prostate cancer spheroids and reduces the growth rate of prostate tumors in mice

BACKGROUND

Arum palaestinum is a plant commonly found in the Middle East that is ingested as an herbal remedy to fight cancer. However, no studies have examined the direct effect of the plant/plant extract on tumor growth in an animal model.

METHODS

Verified prostate cancer cells were plated as 3D spheroids to determine the effect of extract from boiled Arum Palaestinum Boiss roots. In addition, male NU/NU mice (8 weeks old) with xenograft tumors derived from the prostate cancer cell line were treated daily with 1000 mg/kg body weight gavage of the suspension GZ17. The tumor growth was measured repeatedly with calipers and the excised tumors were weighed at the termination of the 3 week study. Control mice (10 mice in each group) received vehicle in the same manner and volume.

RESULTS

The number of live prostate cancer cells declined in a dose/dependent manner with a 24 h exposure to the extract at doses of 0.015 to 6.25 mg/mL. A fortified version of the extract (referred to as GZ17) that contained higher levels of isovanillin, linolenic acid and β-sitosterol had a stronger effect on the cell death rate, shifting the percentage of dead cells from 30 % to 55 % at the highest dose while the vehicle control had no effect on cell numbers. When GZ17 was applied to non-cancer tissue, in this case, human islets, there was no cell death at doses that were toxic to treated cancer cells. Preliminary toxicity studies were conducted on rats using an up-down design, with no signs of toxic effect at the highest dose. NU/NU mice with xenograft prostate tumors treated with GZ17 had a dramatic inhibition of tumor progression, while tumors in the control group grew steadily through the 3 weeks. The rate of tumor volume increase was 73 mm(3)/day for the vehicle group and 24 mm(3)/day for the GZ17 treated mice. While there was a trend towards lower excised tumor weight at study termination in the GZ17 treatment group, there was no statistical difference.

CONCLUSIONS

Fortified Arum palaestinum Boiss caused a reduction in live cells within prostate cancer spheroids and blocked tumor growth in xenografted prostate tumors in mice without signs of toxicity.

WASH and Tsg101/ALIX-dependent diversion of stress-internalized EGFR from the canonical endocytic pathway

Stress exposure triggers ligand-independent EGF receptor (EGFR) endocytosis, but its post-endocytic fate and role in regulating signalling are unclear. We show that the p38 MAP kinase-dependent, EGFR tyrosine kinase (TK)-independent EGFR internalization induced by ultraviolet light C (UVC) or the cancer therapeutic cisplatin, is followed by diversion from the canonical endocytic pathway. Instead of lysosomal degradation or plasma membrane recycling, EGFR accumulates in a subset of LBPA-rich perinuclear multivesicular bodies (MVBs) distinct from those carrying EGF-stimulated EGFR. Stress-internalized EGFR co-segregates with exogenously expressed pre-melanosomal markers OA1 and fibrillar PMEL, following early endosomal sorting by the actin polymerization-promoting WASH complex. Stress-internalized EGFR is retained intracellularly by continued p38 activity in a mechanism involving ubiquitin-independent, ESCRT/ALIX-dependent incorporation onto intraluminal vesicles (ILVs) of MVBs. In contrast to the internalization-independent EGF-stimulated activation, UVC/cisplatin-triggered EGFR activation depends on EGFR internalization and intracellular retention. EGFR signalling from this MVB subpopulation delays apoptosis and might contribute to chemoresistance.

Regulation of melanosome number, shape and movement in the zebrafish retinal pigment epithelium by OA1 and PMEL

Analysis of melanosome biogenesis in the retinal pigment epithelium (RPE) is challenging because it occurs predominantly in a short embryonic time window. Here, we show that the zebrafish provides an ideal model system for studying this process because in the RPE the timing of melanosome biogenesis facilitates molecular manipulation using morpholinos. Morpholino-mediated knockdown of OA1 (also known as GPR143), mutations in the human homologue of which cause the most common form of human ocular albinism, induces a major reduction in melanosome number, recapitulating a key feature of the mammalian disease where reduced melanosome numbers precede macromelanosome formation. We further show that PMEL, a key component of mammalian melanosome biogenesis, is required for the generation of cylindrical melanosomes in zebrafish, which in turn is required for melanosome movement into the apical processes and maintenance of photoreceptor integrity. Spherical and cylindrical melanosomes containing similar melanin volumes co-exist in the cell body but only cylindrical melanosomes enter the apical processes. Taken together, our findings indicate that melanosome number and shape are independently regulated and that melanosome shape controls a function in the RPE that depends on localisation in the apical processes.

Calcium signaling at ER membrane contact sites

Communication between organelles is a necessary consequence of intracellular compartmentalization. Membrane contact sites (MCSs) are regions where the membranes of two organelles come into close apposition allowing exchange of small molecules and ions including Ca²⁺. The ER, the cell's major Ca²⁺ store, forms an extensive and dynamic network of contacts with multiple organelles. Here we review established and emerging roles of ER contacts as platforms for Ca²⁺ exchange and further consider a potential role for Ca²⁺ in the regulation of MCS formation. We additionally discuss the challenges associated with the study of MCS biology and highlight advances in microscopy-based solutions. This article is part of a Special Issue entitled: 13th European Symposium on Calcium.