Primary Cilium Identifies a Quiescent Cell Population in the Human Intestinal Crypt

Primary cilia are sensory antennae located at the cell surface which mediate a variety of extracellular signals involved in development, tissue homeostasis, stem cells and cancer. Primary cilia are found in an extensive array of vertebrae cells but can only be generated when cells become quiescent. The small intestinal epithelium is a rapidly self-renewing tissue organized into a functional unit called the crypt–villus axis, containing progenitor and differentiated cells, respectively. Terminally differentiated villus cells are notoriously devoid of primary cilia. We sought to determine if intestinal crypts contain a quiescent cell population that could be identified by the presence of primary cilia. Here we show that primary cilia are detected in a subset of cells located deep in the crypts slightly above a Paneth cell population. Using a normal epithelial proliferative crypt cell model, we show that primary cilia assembly and activity correlate with a quiescent state. These results provide further evidence for the existence of a quiescent cell population in the human small intestine and suggest the potential for new modes of regulation in stem cell dynamics.

Characterization of PGua4, a Guanidinium-Rich Peptoid that Delivers IgGs to the Cytosol via Macropinocytosis

To investigate the structure-cellular penetration relationship of guanidinium-rich transporters (GRTs), we previously designed PGua4, a five-amino acid peptoid containing a conformationally restricted pattern of eight guanidines, which showed high cell-penetrating abilities and low cell toxicity. Herein, we characterized the cellular uptake selectivity, internalization pathway, and intracellular distribution of PGua4, as well as its capacity to deliver cargo. PGua4 exhibits higher penetration efficiency in HeLa cells than in six other cell lines (A549, Caco-2, fibroblast, HEK293, Mia-PaCa2, and MCF7) and is mainly internalized by clathrin-mediated endocytosis and macropinocytosis. Confocal microscopy showed that it remained trapped in endosomes at low concentrations but induced pH-dependent endosomal membrane destabilization at concentrations ≥10 μM, allowing its diffusion into the cytoplasm. Importantly, PGua4 significantly enhanced macropinocytosis and the cellular uptake and cytosolic delivery of large IgGs following noncovalent complexation. Therefore, in addition to its peptoid nature conferring high resistance to proteolysis, PGua4 presents characteristics of a promising tool for IgG delivery and therapeutic applications.

Peptides Derived from Growth Factors to Treat Alzheimer's Disease

Alzheimer's disease (AD) is a devastating neurodegenerative disease characterized by progressive neuron losses in memory-related brain structures. The classical features of AD are a dysregulation of the cholinergic system, the accumulation of amyloid plaques, and neurofibrillary tangles. Unfortunately, current treatments are unable to cure or even delay the progression of the disease. Therefore, new therapeutic strategies have emerged, such as the exogenous administration of neurotrophic factors (e.g., NGF and BDNF) that are deficient or dysregulated in AD. However, their low capacity to cross the blood-brain barrier and their exorbitant cost currently limit their use. To overcome these limitations, short peptides mimicking the binding receptor sites of these growth factors have been developed. Such peptides can target selective signaling pathways involved in neuron survival, differentiation, and/or maintenance. This review focuses on growth factors and their derived peptides as potential treatment for AD. It describes (1) the physiological functions of growth factors in the brain, their neuronal signaling pathways, and alteration in AD; (2) the strategies to develop peptides derived from growth factor and their capacity to mimic the role of native proteins; and (3) new advancements and potential in using these molecules as therapeutic treatments for AD, as well as their limitations.

Matriptase processing of APLP1 ectodomain alters its homodimerization

The amyloid beta peptide (Aβ) is derived from the amyloid precursor protein (APP) by secretase processing. APP is also cleaved by numerous other proteases, such as the type II transmembrane serine protease matriptase, with consequences on the production of Aβ. Because the APP homolog protein amyloid-like protein 1 (APLP1) shares similarities with APP, we sought to determine if matriptase also plays a role in its processing. Here, we demonstrate that matriptase directly interacts with APLP1 and that APLP1 is cleaved in cellulo by matriptase in its E1 ectodomains at arginine 124. Replacing Arg124 with Ala abolished APLP1 processing by matriptase. Using a bioluminescence resonance energy transfer (BRET) assay we found that matriptase reduces APLP1 homodimeric interactions. This study identifies matriptase as the first protease cleaving APLP1 in its dimerization domain, potentially altering the multiple functions associated with dimer formation.

Combining RNAi and Immunofluorescence Approaches to Investigate Post-endocytic Sorting of GPCRs into Multivesicular Bodies

Following stimulation, G protein-coupled receptors (GPCRs) are internalized and transported to early endosomes where they are either recycled back to the plasma membrane for another round of activation or targeted to the lysosomes for degradation and long-term signal termination. This latter requires internalization of receptors into intraluminal vesicles (ILVs) of multivesicular bodies (MVBs) for complete degradation following fusion with lysosomes. This endosomal sorting step is highly regulated and has profound functional consequences. This chapter describes how RNAi and confocal microscopy methods can be combined to evaluate whether a protein of interest (herein Gαs) is involved in GPCR sorting into ILVs of MVBs.

The type II transmembrane serine protease matriptase cleaves the amyloid precursor protein and reduces its processing to β-amyloid peptide

Recent studies have reported that many proteases, besides the canonical α-, β-, and γ-secretases, cleave the amyloid precursor protein (APP) and modulate β-amyloid (Aβ) peptide production. Moreover, specific APP isoforms contain Kunitz protease-inhibitory domains, which regulate the proteolytic activity of serine proteases. This prompted us to investigate the role of matriptase, a member of the type II transmembrane serine protease family, in APP processing. Using quantitative RT-PCR, we detected matriptase mRNA in several regions of the human brain with an enrichment in neurons. RNA sequencing data of human dorsolateral prefrontal cortex revealed relatively high levels of matriptase RNA in young individuals, whereas lower levels were detected in older individuals. We further demonstrate that matriptase and APP directly interact with each other and that matriptase cleaves APP at a specific arginine residue (Arg-102) both in vitro and in cells. Site-directed (Arg-to-Ala) mutagenesis of this cleavage site abolished matriptase-mediated APP processing. Moreover, we observed that a soluble, shed matriptase form cleaves endogenous APP in SH-SY5Y cells and that this cleavage significantly reduces APP processing to Aβ40. In summary, this study identifies matriptase as an APP-cleaving enzyme, an activity that could have important consequences for the abundance of Aβ and in Alzheimer's disease pathology.

Caspases rule the intracellular trafficking cartel

During apoptosis, caspases feast on several hundreds of cellular proteins to orchestrate rapid cellular demise. Indeed, caspases are known to get a taste of every cellular process in one way or another, activating some, but most often shutting them down. Thus, it is not surprising that caspases proteolyze proteins involved in intracellular trafficking with particularly devastating consequences for this important process. This review article focuses on how caspases target the machinery responsible for smuggling goods within and outside the cell.

GTPase of the Immune-Associated Nucleotide Protein 5 Regulates the Lysosomal Calcium Compartment in T Lymphocytes

T lymphocytes from Gimap5^lyp/lyp rats carrying a recessive mutation in the GTPase of immune-associated protein 5 (Gimap5) gene undergo spontaneous apoptosis. Molecular mechanisms underlying this survival defect are not yet clear. We have shown that Gimap5^lyp/lyp T lymphocytes display reduced calcium influx following T cell antigen receptor (TCR) stimulation that was associated with impaired buffering of calcium by mitochondria. Here, we investigated the subcellular localization of GIMAP5 and its influence on Ca²⁺ response in HEK293T cells and T lymphocytes. The more abundantly expressed GIMAP5v2 localizes to the lysosome and certain endosomal vesicles. Gimap5^lyp/lyp T lymphocytes showed increased accumulation of calcium in the lysosomes as evidenced by Gly-Phe β-naphthylamide (GPN) triggered Ca²⁺ release. As a corollary, GPN-induced Ca²⁺ flux was decreased in HEK293T cells expressing GIMAP5v2. Strikingly, TCR stimulation of rat, mouse, and human T lymphocytes increased lysosomal calcium content. Overall, our findings show that lysosomes modulate cellular Ca²⁺ response during T cell activation and that GIMAP5 regulates the lysosomal Ca²⁺ compartment in T lymphocytes.

Involvement of the coatomer protein complex I in the intracellular traffic of the delta opioid receptor

The delta opioid receptor (DOPr) is known to be mainly expressed in intracellular compartments. It remains unknown why DOPr is barely exported to the cell surface, but it seems that a substantial proportion of the immature receptor is trapped within the endoplasmic reticulum (ER) and the Golgi network. In the present study, we performed LC-MS/MS analysis to identify putative protein partners involved in the retention of DOPr. Analysis of the proteins co-immunoprecipitating with Flag-DOPr in transfected HEK293 cells revealed the presence of numerous subunits of the coatomer protein complex I (COPI), a vesicle-coating complex involved in recycling resident proteins from the Golgi back to the ER. Further analysis of the amino acid sequence of DOPr identified multiple consensus di-lysine and di-arginine motifs within the intracellular segments of DOPr. Using cell-surface ELISA and GST pulldown assays, we showed that DOPr interacts with COPI through its intracellular loops 2 and 3 (ICL2 and ICL3, respectively) and that the mutation of the K¹⁶⁴AK¹⁶⁶ (ICL2) or K²⁵⁰EK²⁵² (ICL3) putative COPI binding sites increased the cell-surface expression of DOPr in transfected cells. Altogether, our results indicate that COPI is a binding partner of DOPr and provide a putative mechanism to explain why DOPr is highly retained inside the cells.

GGA3 mediates TrkA endocytic recycling to promote sustained Akt phosphorylation and cell survival

GGA3 binds directly to the TrkA internal DXXLL motif and mediates TrkA endocytic recycling. This effect is dependent on the activation of Arf6. GGA3 is a key player in a novel DXXLL-mediated recycling machinery for TrkA, where it prolongs the activation of Akt signaling and survival responses.

Although TrkA postendocytic sorting significantly influences neuronal cell survival and differentiation, the molecular mechanism underlying TrkA receptor sorting in the recycling or degradation pathways remains poorly understood. Here we demonstrate that Golgi-localized, γ adaptin-ear–containing ADP ribosylation factor-binding protein 3 (GGA3) interacts directly with the TrkA cytoplasmic tail through an internal DXXLL motif and mediates the functional recycling of TrkA to the plasma membrane. We find that GGA3 depletion by siRNA delays TrkA recycling, accelerates TrkA degradation, attenuates sustained NGF-induced Akt activation, and reduces cell survival. We also show that GGA3’s effect on TrkA recycling is dependent on the activation of Arf6. This work identifies GGA3 as a key player in a novel DXXLL-mediated endosomal sorting machinery that targets TrkA to the plasma membrane, where it prolongs the activation of Akt signaling and survival responses.

Regulation of μ and δ opioid receptor functions: involvement of cyclin-dependent kinase 5

Background and Purpose

Phosphorylation of δ opioid receptors (DOP receptors) by cyclin-dependent kinase 5 (CDK5) was shown to regulate the trafficking of this receptor. Therefore, we aimed to determine the role of CDK5 in regulating DOP receptors in rats treated with morphine or with complete Freund's adjuvant (CFA). As μ (MOP) and DOP receptors are known to be co-regulated, we also sought to determine if CDK5-mediated regulation of DOP receptors also affects MOP receptor functions.

Experimental Approach

The role of CDK5 in regulating opioid receptors in CFA- and morphine-treated rats was studied using roscovitine as a CDK inhibitor and a cell-penetrant peptide mimicking the second intracellular loop of DOP receptors (C11-DOPri2). Opioid receptor functions were assessed in vivo in a series of behavioural experiments and correlated by measuring ERK1/2 activity in dorsal root ganglia homogenates.

Key Results

Chronic roscovitine treatment reduced the antinociceptive and antihyperalgesic effects of deltorphin II (Dlt II) in morphine- and CFA-treated rats respectively. Repeated administrations of C11-DOPri2 also robustly decreased Dlt II-induced analgesia. Interestingly, DAMGO-induced analgesia was significantly increased by roscovitine and C11-DOPri2. Concomitantly, in roscovitine-treated rats the Dlt II-induced ERK1/2 activation was decreased, whereas the DAMGO-induced ERK1/2 activation was increased. An acute roscovitine treatment had no effect on Dlt II- or DAMGO-induced analgesia.

Conclusions and Implications

Together, our results demonstrate that CDK5 is a key player in the regulation of DOP receptors in morphine- and CFA-treated rats and that the regulation of DOP receptors by CDK5 is sufficient to modulate MOP receptor functions through an indirect process.

Gαs regulates the post-endocytic sorting of G protein-coupled receptors

The role of Gαs in G protein-coupled receptor (GPCR) signalling at the cell surface is well established. Recent evidence has revealed the presence of Gαs on endosomes and its capacity to elicit GPCR-promoted signalling from this intracellular compartment. Here, we report an unconventional role for Gαs in the endocytic sorting of GPCRs to lysosomes. Cellular depletion of Gαs specifically delays the lysosomal degradation of GPCRs by disrupting the transfer of GPCRs into the intraluminal vesicles (ILVs) of multivesicular bodies. We show that Gαs interacts with GPCR-associated binding protein-1 (GASP1) and dysbindin, two key proteins that serve as linkers between GPCRs and the endosomal-sorting complex required for transport (ESCRT) machinery involved in receptor sorting into ILVs. Our findings reveal that Gαs plays a role in both GPCR signalling and trafficking pathways, providing another piece in the intertwining molecular network between these processes.

Topology and membrane anchoring of the lysosomal storage disease-related protein CLN5

One late infantile variant of the neurodegenerative disease neuronal ceroid lipofuscinosis (NCL) is caused by a mutation in the CLN5 gene. CLN5 encodes a lysosomal glycoprotein whose structure and function have not yet been clearly defined. In the present study, we used epitope-tagged CLN5 to determine the topology and solubility of the CLN5 protein. Our results indicated that CLN5 is synthesized as a type II transmembrane (TM) glycoprotein with a cytoplasmic N-terminus, one TM segment, and a large luminal C-terminal domain containing an amphipathic helix (AH). The cytoplasmic and TM domains were rapidly removed following signal-peptide cleavage, and the resulting mature CLN5 was tightly associated with the lumen of the membrane through the AH. CLN5 pathological mutants deprived of AH lose their membrane association, are retained in the endoplasmic reticulum, and are rapidly degraded by the proteasomal machinery. We experimentally define the topology of CLN5 and demonstrate the existence of an AH that anchors the protein to the membrane. Our work sheds light on the basic properties of CLN5 required to better understand its biological functions and involvement in NCL pathogenesis.

Liver glucagon receptors (GluR): effect of exercise and fasting on binding characteristics, GluR-mRNA, and GluR protein content in rats

The purpose of the study was to investigate the effects of acute exercise and fasting on glucagon receptor (GluR) binding characteristics, GluR-mRNA, and protein content in rat liver. Liver homogenates were prepared and plasma membranes were purified by aqueous 2-phase affinity partitioning in rats fed at rest (control) and after 180 min of swimming exercise and 24 h of fasting (7 rats/group). Saturation curve of plasma membranes incubated with [125I]-glucagon showed significant higher GluR density following exercise and fasting than in the control group (8.19±0.29 and 8.01±0.65 vs. 3.09±0.12 pmol/mg of proteins, respectively). When compared to control rats, GluR Kd was also higher following exercise and fasting (0.46±0.05 and 0.56±0.13 vs. 0.33±0.05 nM, respectively; significantly different for fasting only). Expression of GluR-mRNA and protein content were both significantly higher (~100% and ~90%, respectively) following the 24-h fast than in the control rats, but not following exercise. These results, in line with the literature showing an increased sensitivity of the liver to glucagon following exercise and fasting, indicate that an increased density of GluR on plasma membranes can be obtained by 2 complementary mechanisms: externalization of pre-existing GluR from intracellular pools operative in response to the prolonged exercise, and de novo synthesis of GluR operative only in response to fasting. The reduction in plasma insulin concentration and/or depletion of liver glycogen stores, which results from both prolonged exercise and fasting, could be involved in the control of these mechanisms.

Genomic architecture of adaptive color pattern divergence and convergence in Heliconius butterflies

Identifying the genetic changes driving adaptive variation in natural populations is key to understanding the origins of biodiversity. The mosaic of mimetic wing patterns in Heliconius butterflies makes an excellent system for exploring adaptive variation using next-generation sequencing. In this study, we use a combination of techniques to annotate the genomic interval modulating red color pattern variation, identify a narrow region responsible for adaptive divergence and convergence in Heliconius wing color patterns, and explore the evolutionary history of these adaptive alleles. We use whole genome resequencing from four hybrid zones between divergent color pattern races of Heliconius erato and two hybrid zones of the co-mimic Heliconius melpomene to examine genetic variation across 2.2 Mb of a partial reference sequence. In the intergenic region near optix, the gene previously shown to be responsible for the complex red pattern variation in Heliconius, population genetic analyses identify a shared 65-kb region of divergence that includes several sites perfectly associated with phenotype within each species. This region likely contains multiple cis-regulatory elements that control discrete expression domains of optix. The parallel signatures of genetic differentiation in H. erato and H. melpomene support a shared genetic architecture between the two distantly related co-mimics; however, phylogenetic analysis suggests mimetic patterns in each species evolved independently. Using a combination of next-generation sequencing analyses, we have refined our understanding of the genetic architecture of wing pattern variation in Heliconius and gained important insights into the evolution of novel adaptive phenotypes in natural populations.

LDLR-related protein 10 (LRP10) regulates amyloid precursor protein (APP) trafficking and processing: evidence for a role in Alzheimer's disease

Background

The Aβ peptide that accumulates in Alzheimer’s disease (AD) is derived from amyloid precursor protein (APP) following proteolysis by β- and γ-secretases. Substantial evidence indicates that alterations in APP trafficking within the secretory and endocytic pathways directly impact the interaction of APP with these secretases and subsequent Aβ production. Various members of the low-density lipoprotein receptor (LDLR) family have been reported to play a role in APP trafficking and processing and are important risk factors in AD. We recently characterized a distinct member of the LDLR family called LDLR-related protein 10 (LRP10) that shuttles between the trans-Golgi Network (TGN), plasma membrane (PM), and endosomes. Here we investigated whether LRP10 participates in APP intracellular trafficking and Aβ production.

Results

In this report, we provide evidence that LRP10 is a functional APP receptor involved in APP trafficking and processing. LRP10 interacts directly with the ectodomain of APP and colocalizes with APP at the TGN. Increased expression of LRP10 in human neuroblastoma SH-SY5Y cells induces the accumulation of mature APP in the Golgi and reduces its presence at the cell surface and its processing into Aβ, while knockdown of LRP10 expression increases Aβ production. Mutations of key motifs responsible for the recycling of LRP10 to the TGN results in the aberrant redistribution of APP with LRP10 to early endosomes and a concomitant increase in APP β-cleavage into Aβ. Furthermore, expression of LRP10 is significantly lower in the post-mortem brain tissues of AD patients, supporting a possible role for LRP10 in AD.

Conclusions

The present study identified LRP10 as a novel APP sorting receptor that protects APP from amyloidogenic processing, suggesting that a decrease in LRP10 function may contribute to the pathogenesis of Alzheimer’s disease.

The Barriers to Physical Activity in Type 1 Diabetes (BAPAD-1) scale: predictive validity and reliability

AIM

Perceived barriers are one determinant of physical activity. Depending on the study population, these barriers can vary. The aim of this study was to assess the reliability and predictive validity of the 'Barriers to Physical Activity in Type 1 Diabetes' (BAPAD-1) scale, developed by Dubé et al.

METHODS

A total of 77 adults (48% women; age: 43.5±10.4; body mass index: 25.2±4.3kg/m(2); HbA(1c): 7.6±1.3%) with type 1 diabetes completed the questionnaire and an evaluation of their physical activity using an accelerometer (8.4±1.2 days) and cardiorespiratory fitness assessment (VO(2)(peak)). To evaluate the temporal stability of the questionnaire, a subgroup of 17 participants answered the BAPAD-1 scale on both visits required by the protocol (10±4 days).

RESULTS

The BAPAD-1 scale showed good internal validity with an inter-items correlation coefficient (Cronbach's correlation) of 0.85. The intraclass correlation coefficient for the two times the scales were completed was 0.80. The BAPAD-1 score was negatively correlated with both physical activity energy expenditure (r=-0.25; P=0.03) and VO(2)(peak) adjusted for gender and age (r=-0.27; P=0.02).

CONCLUSION

The BAPAD-1 scale is a reliable and valid tool for assessing salient barriers to physical activity. In future, this scale could be used to describe the factors accounting for physical activity, and for planning interventions aimed at promoting physical activity among adults with type 1 diabetes.

Taking organelles apart, putting them back together and creating new ones: lessons from the endoplasmic reticulum

The endoplasmic reticulum (ER) is a highly dynamic organelle. It is composed of four subcompartments including nuclear envelope (NE), rough ER (rER), smooth ER (sER) and transitional ER (tER). The subcompartments are interconnected, can fragment and dissociate and are able to reassemble again. They coordinate with cell function by way of protein regulators in the surrounding cytosol. The activity of the many associated molecular machines of the ER as well as the fluid nature of the limiting membrane of the ER contribute extensively to the dynamics of the ER. This review examines the properties of the ER that permit its isolation and purification and the physiological conditions that permit reconstitution both in vitro and in vivo in normal and in disease conditions.

Surface Roughening During Titanium Silicide Formation: a Comparison Between Si(100) and Poly-Si Substrates

We demonstrate that the formation of TiSi2 for Ti films deposited on undoped Si(100) substrates leads to rougher surfaces than for Ti films deposited on undoped poly-Si substrates. The successive formations of TiSi2, C49 (high resistivity) and C54 (low resistivity) phases from titanium films deposited on either Si(100) or poly-Si substrates were monitored in situ during rapid thermal annealing using elastic light scattering, x-ray diffraction and resistance measurements. For both types of substrates, the roughening occurs only during the formation of the first TiSi2, phase (C49) by light scattered from lateral length scales of ˜0.5 μm. Atomic force microscopy (AFM) images. quantified using Fourier filtering, are consistent with the light scattering results.

Light Scattering Measurement Of Surface Topography During Formation Of Titanium Silicide

The evolution of the surface topography during the phase transformations of titanium silicide has been studied using elastic light scattering at two different collection angles. The light scattering measurements were performed simultaneously with x-ray diffraction and resistance measurements for titanium films deposited on either Si(100) or on poly-silicon substrates. At selected points during annealing, the samples were cooled rapidly to room temperature and analyzed ex situ using Nomarski microscopy. We find that, depending on the detection geometry, the in situ light scattering shows preferentially the formation of the C49 or C54 TiSi2 phase as well as differentiates between inversion and agglomeration on poly-silicon substrates.

In-Situ Studies of Silicide Formation in Ti-Ta Bilayer Thin Films on Poly-Si

We have studied the formation of titanium silicides in the presence of an ultra-thin layer of Ta, interposed between Ti and Si. In-situ x-ray diffraction (XRD), resistance measurements and elastic light scattering were used to study the thin film reactions in real time during ramp anneals to 1000°C. On poly-Si substrates the Ta thickness was varied from 0 to 1.5 nm while the Ti thickness was held constant at ∼27 nm. The time-resolved XRD shows that the volume fraction of C40 and metal-rich silicide phases grows with increasing Ta layer thickness. Increased Ta layer thicknesses also delay the growth of the C49 disilicide phase to higher temperatures. Among the Ta thicknesses we examined, 0.3 nm is the most effective in lowering the C49-C54 transformation temperature. Films with Ta layers thicker than 0.5 nm do not completely transform into the C54 phase. The texture of the C54 phase is also sensitive to the Ta thickness. The C54 disilicide film is predominantly (010) textured for the Ti / 0.3 nm Ta sample. The final C54 texture is significantly different for Ta layers thinner or thicker than the optimal 0.3 nm. This suggests that the most effective thickness for lowering the C54 formation temperature is related to the development of a strong (010) texture. The possibility of a template effect by the C40 or metal-rich Ti5Si3 phases is also discussed on the basis of texture considerations.

Calnuc plays a role in dynamic distribution of Galphai but not Gbeta subunits and modulates ACTH secretion in AtT-20 neuroendocrine secretory cells

In AtT-20 cells ACTH secretion is regulated by both Ca²⁺ and G proteins. We previously demonstrated that calnuc, an EF-hand Ca²⁺ binding protein which regulates Alzheimer's β-amyloid precursor protein (APP) biogenesis, binds both Ca²⁺ as well as Gα subunits. Here we investigate calnuc's role in G protein-mediated regulation of ACTH secretion in AtT-20 neuroendocrine secretory cells stably overexpressing calnuc-GFP. Similar to endogenous calnuc, calnuc-GFP is mainly found in the Golgi, on the plasma membrane (PM), and associated with regulated secretion granules (RSG). By deconvolution immunofluorescence, calnuc-GFP partially colocalizes with Gαi1/2 and Gαi3 at the PM and on RSG. Cytosolic calnuc(ΔSS)-CFP with the signal sequence deleted also partially colocalizes with RSG and partially cosediments with Gαi1/2 in fractions enriched in RSG. Overexpression of calnuc-GFP specifically increases the distribution of Gαi1/2 on the PM whereas the distribution of Gβ subunits and synaptobrevin 2 (Vamp 2) is unchanged. Overexpression of calnuc-GFP or cytosolic calnuc(ΔSS)-CFP enhances ACTH secretion two-fold triggered by mastoparan or GTPγS but does not significantly affect glycosaminoglycan (GAG) chain secretion along the constitutive pathway or basal secretion of ACTH. Calnuc's facilitating effects on ACTH secretion are decreased after introducing anti-Gαi1/2, Gαi3, Gβ or calnuc IgG into permeabilized cells but not when Gα12 or preimmune IgG is introduced. The results suggest that calnuc binds to Gα subunits on the Golgi and on RSG and that overexpression of calnuc causes redistribution of Gαi subunits to the PM and RSG, indicating that calnuc plays a role in dynamic distribution of only Gα but not Gβ subunits. Thus calnuc may connect G protein signaling and calcium signaling during regulated secretion.

Sci-Fri PM: Planning-04: Dose escalation study using anatomy-based aperture IMRT and SPECT perfusion images for lung cancer

In the case of non-small cell lung cancer, doses typically prescribed (60-66 Gy) are not sufficient to ensure a satisfactory tumor control probability. Dose escalation needs to be realized, but dose to organs at risk (OARs) must be kept under widely accepted clinical thresholds. Also, lung functionality is not homogeneously distributed over all the volume: single-photon emission computed tomography (SPECT) allows spatial characterization of perfusion, open the way to the design of treatments plans that could preferentially avoid highly-functional lung. In this study, three cases of lung cancer were retrospectively used to assess the capacity of an anatomy-based aperture inverse planning system to realize dose escalation while limiting dose to perfused lung. Plans were generated for four-beam non-coplanar configurations, mixing 6 and 23 MV photon beams. All dose calculations were performed using Pinnacle³ superposition/convolution algorithm. An increasing dose was prescribed to a subvolume of the initial planning target volume. Levels of escalation achieved for the three cases studied were 81 Gy, 111 Gy and 66 Gy to the subvolume. Escalation was limited in two cases by the dose to the esophagus and in the other case by the presence of overdosages near beam entry ports. Calculation of dose-volume parameters for OARs shows that they respect clinical thresholds. Plans generated by the system are less complex than plans generated in beamlet-based IMRT, because of the use of few, large segments. The approach used in this study allows important dose escalation, potentially improving treatment outcome.

Intracellular trafficking of LRP9 is dependent on two acidic cluster/dileucine motifs

LDL receptor-related protein 9 (LRP9) is a distant member of the low-density lipoprotein receptor (LDLR) superfamily. To date, there are no reports on the cellular distribution of LRP9 or the signals responsible for its localization. Here, we investigated the intracellular localization and trafficking of LRP9. Using confocal microscopy, we demonstrated that LRP9 was not present at the plasma membrane but co-localized with various markers of the trans-Golgi network (TGN) and endosomes. This co-localization was dependent on the presence of two acidic cluster/dileucine (DXXLL) motifs in the cytoplasmic tail of LRP9, which interact with GGA proteins, clathrin adaptors involved in transport between the TGN and endosomes. LRP9 is the first example of a transmembrane protein with an internal GGA-binding sequence in addition to the usual C-terminal motif. An inactivating mutation (LL --> AA) in both DXXLL motifs, which completely inhibited the interaction of LRP9 with GGA proteins, led to an intracellular redistribution of LRP9 from the TGN to early endosomes and the cell surface, indicating that the two DXXLL motifs are essential sorting determinants of LRP9. In conclusion, our results suggest that LRP9 cycles between the TGN, endosomes and the plasma membrane through a GGA dependent-trafficking mechanism.

Topology of molecular machines of the endoplasmic reticulum: a compilation of proteomics and cytological data

The endoplasmic reticulum (ER) is a key organelle of the secretion pathway involved in the synthesis of both proteins and lipids destined for multiple sites within and without the cell. The ER functions to both co- and post-translationally modify newly synthesized proteins and lipids and sort them for housekeeping within the ER and for transport to their sites of function away from the ER. In addition, the ER is involved in the metabolism and degradation of specific xenobiotics and endogenous biosynthetic products. A variety of proteomics studies have been reported on different subcompartments of the ER providing an ER protein dictionary with new data being made available on many protein complexes of relevance to the biology of the ER including the ribosome, the translocon, coatomer proteins, cytoskeletal proteins, folding proteins, the antigen-processing machinery, signaling proteins and proteins involved in membrane traffic. This review examines proteomics and cytological data in support of the presence of specific molecular machines at specific sites or subcompartments of the ER.

Substrate source utilization during moderate intensity exercise with glucose ingestion in Type 1 diabetic patients

Substrate oxidation and the respective contributions of exogenous glucose, glucose released from the liver, and muscle glycogen oxidation were measured by indirect respiratory calorimetry combined with tracer technique in eight control subjects and eight diabetic patients (5 men and 3 women in both groups) of similar age, height, body mass, and maximal oxygen uptake, over a 60-min exercise period on cycle ergometer at 50.8% (SD 4.0) maximal oxygen uptake [131.0 W (SD 38.2)]. The subjects and patients ingested a breakfast (containing ∼80 g of carbohydrates) 3 h before and 30 g of glucose (labeled with 13C) 15 min before the beginning of exercise. The diabetic patients also received their usual insulin dose [Humalog = 9.1 U (SD 0.9); Humulin N = 13.9 U (SD 4.4)] immediately before the breakfast. Over the last 30 min of exercise, the oxidation of carbohydrate [1.32 g/min (SD 0.48) and 1.42 g/min (SD 0.63)] and fat [0.33 g/min (SD 0.10) and 0.30 g/min (SD 0.10)] and their contribution to the energy yield were not significantly different in the control subjects and diabetic patients. Exogenous glucose oxidation was also not significantly different in the control subjects and diabetic patients [6.3 g/30 min (SD 1.3) and 5.2 g/30 min (SD 1.6), respectively]. In contrast, the oxidation of plasma glucose and oxidation of glucose released from the liver were significantly lower in the diabetic patients than in control subjects [14.5 g/30 min (SD 4.3) and 9.3 g/30 min (SD 2.8) vs. 27.9 g/30 min (SD 13.3) and 21.6 g/30 min (SD 12.8), respectively], whereas that of muscle glycogen was significantly higher [28.1 g/30 min (SD 15.5) vs. 11.6 g/30 min (SD 8.1)]. These data indicate that, compared with control subjects, in diabetic patients fed glucose before exercise, substrate oxidation and exogenous glucose oxidation overall are similar but plasma glucose oxidation is lower; this is associated with a compensatory higher utilization of muscle glycogen.