Chromogranins as molecular coordinators at the crossroads between hormone aggregation and secretory granule biogenesis

International audienc

The long coiled-coil protein NECC2 is associated to caveolae and modulates NGF/TrkA signaling in PC12 cells [corrected].

TrkA-mediated NGF signaling in PC12 cells has been shown to be compartimentalized in specialized microdomains of the plasma membrane, the caveolae, which are organized by scaffold proteins including the member of the caveolin family of proteins, caveolin-1. Here, we characterize the intracellular distribution as well as the biochemical and functional properties of the neuroendocrine long coiled-coil protein 2 (NECC2), a novel long coiled-coil protein selectively expressed in neuroendocrine tissues that contains a predicted caveolin-binding domain and displays structural characteristics of a scaffolding factor. NECC2 distributes in caveolae, wherein it colocalizes with the TrkA receptor, and behaves as a caveolae-associated protein in neuroendocrine PC12 cells. In addition, stimulation of PC12 cells with nerve growth factor (NGF) increased the expression and regulated the distribution of NECC2. Interestingly, knockdown as well as overexpression of NECC2 resulted in a reduction of NGF-induced phosphorylation of the TrkA downstream effector extracellular signal-regulated kinases 1 and 2 (ERK1/ERK2) but not of Akt. Altogether, our results identify NECC2 as a novel component of caveolae in PC12 cells and support the contribution of this protein in the maintenance of TrkA-mediated NGF signaling.journal articleresearch support, non-u.s. gov't20132013 09 06importe

Binary Switching of Calendar Cells in the Pituitary Defines the Phase of the Circannual Cycle in Mammals

Persistent free-running circannual (approximately year-long) rhythms have evolved in animals to regulate hormone cycles, drive metabolic rhythms (including hibernation), and time annual reproduction. Recent studies have defined the photoperiodic input to this rhythm, wherein melatonin acts on thyrotroph cells of the pituitary pars tuberalis (PT), leading to seasonal changes in the control of thyroid hormone metabolism in the hypothalamus. However, seasonal rhythms persist in constant conditions in many species in the absence of a changing photoperiod signal, leading to the generation of circannual cycles. It is not known which cells, tissues, and pathways generate these remarkable long-term rhythmic processes. We show that individual PT thyrotrophs can be in one of two binary states reflecting either a long (EYA3+) or short (CHGA+) photoperiod, with the relative proportion in each state defining the phase of the circannual cycle. We also show that a morphogenic cycle driven by the PT leads to extensive re-modeling of the PT and hypothalamus over the circannual cycle. We propose that the PT may employ a recapitulated developmental pathway to drive changes in morphology of tissues and cells. Our data are consistent with the hypothesis that the circannual timer may reside within the PT thyrotroph and is encoded by a binary switch timing mechanism, which may regulate the generation of circannual neuroendocrine rhythms, leading to dynamic re-modeling of the hypothalamic interface. In summary, the PT-ventral hypothalamus now appears to be a prime structure involved in long-term rhythm generation

Contribution à l'étude du rôle de la Chromogranine A dans la sécrétion neuroendocrine : identification de ses partenaires moléculaires impliqués dans la biogenèse des granules de sécrétion

ROUEN-BU Sciences (764512102) / SudocSudocFranceF

Contribution à la caractérisation des mécanismes moléculaires impliquant la chromogranine A dans l'établissement de la voie de sécrétion régulée dans les cellules neuroendocrines

Des études récentes d'invalidation du gène codant la chromogranine A (CgA) ont suggéré que cette protéine jouerait un rôle clé dans la biogenèse des granules de sécrétion (GS) au sein des cellules neuroendocrines. Néanmoins, les mécanismes moléculaires impliqués au cours de ce processus demeurent mal connus. Récemment, nous avons montré que l'expression de la CgA dans les cellules non-endocrines COS-7 induit la biogenèse de structures granulaires apparentées aux GS, capables de stocker et de sécréter la CgA et des hormones co-exprimées (NPY, GH), de manière calcium-dépendante. Les analyses des cellules COS-7 exprimant la CgA en microscope confocale et en vidéomicroscopie, associées à des approches biochimiques, ont permis d'établir des interactions entre les granules contenant la CgA, les microtubules et les filaments d'actine. Ces deux éléments du cytosquelette exercent des fonctions régulatrices sur le trafic intracellulaire et l'exocytose calcium-dépendante des granules contenant la CgA. Ces résultats suggèrent que la CgA est suffisante pour induire la biogenèse de GS et instaurer ainsi une voie de sécrétion régulée dans des cellules non-endocrines. Le clonage de la CgA de grenouille ayant révélé la conservation des régions N- et C-terminales au cours de l'évolution des vertébrés, nous avons émis l'hypothèse de leur implication en tant que déterminants fonctionnels de la CgA. Ainsi, nos résultats démontrent que les peptides conservés confèrent à la CgA sa capacité à former des GS et dirigent l'adressage et la libération régulée des hormones exogènes co-exprimées avec la CgA dans les cellules COS-7, ainsi que la POMC endogène dans les cellules corticotropes AtT20.The nature of the sorting signals for entry of proteins into the dense-core secretory granules (SG) and the molecular machinery required to generate SG remain unclear. Recent studies revealed that chromogranin A (CgA) deficiency is associated with hormone storage impairment, suggesting that CgA plays a major role in the formation of SG in neuroendocrine cells. The cloning of frog CgA revealed high conservation though evolution of the global acidity and of the terminal regions of the protein, suggesting that these features are essential for the biological activity of CgA. Expression of CgA in the non-endocrine COS-7 cells induced the formation of dense-core vesicles containing CgA. As SG in neuroendocrine cells, trafficking and exocytosis of CgA-containing granules required interactions with microtubules and actin filaments. These SG-like organelles were able to store hormones that could be released in a calcium-dependent manner. Deletion of the terminal regions of CgA resulted in a reorientation of the proteins from the regulated to the constitutive secretory pathway, indicating that these domains were essential for the formation of functional SG-like structures in COS-7 cells. Expression of CgA in the corticotrope AtT20 cells increased POMC levels in SG, whereas the expression of terminal deletion-mutants provoked retention of the hormone in the Golgi area. Thus, CgA, but not its truncated forms, promoted POMC sorting to the regulated secretory pathway. Our results demonstrate that CgA, through its conserved terminal domains, directs the formation of SG and the sorting and release of hormones.ROUEN-BU Sciences (764512102) / SudocSudocFranceF

Chromogranins as molecular coordinators at the crossroads between hormone aggregation and secretory granule biogenesis

International audienc

Chromogranin A as a Crucial Factor in the Sorting of Peptide Hormones to Secretory Granules

International audienc

Advanced Imaging Approaches to Reveal Molecular Mechanisms Governing Neuroendocrine Secretion

International audienceIdentification of the molecular mechanisms governing neuroendocrine secretion and resulting intercellular communication is one of the great challenges of cell biology to better understand organism physiology and neurosecretion disruption-related pathologies such as hypertension, neurodegenerative, or metabolic diseases. To visualize molecule distribution and dynamics at the nanoscale, many imaging approaches have been developed and are still emerging. In this review, we provide an overview of the pioneering studies using transmission electron microscopy, atomic force microscopy, total internal reflection microscopy, and super-resolution microscopy in neuroendocrine cells to visualize molecular mechanisms driving neurosecretion processes, including exocytosis and associated fusion pores, endocytosis and associated recycling vesicles, and protein-protein or protein-lipid interactions. Furthermore, the potential and the challenges of these different advanced imaging approaches for application in the study of neuroendocrine cell biology are discussed, aiming to guide researchers to select the best approach for their specific purpose around the crucial but not yet fully understood neurosecretion process

Chromogranins A and B and secretogranin II: evolutionary and functional aspects

International audienc