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Intracellular Movements (intracellular + movement)
Selected AbstractsSalt-inducible kinase-1 represses cAMP response element-binding protein activity both in the nucleus and in the cytoplasmFEBS JOURNAL, Issue 21 2004Yoshiko Katoh Salt-inducible kinase-1 (SIK1) is phosphorylated at Ser577 by protein kinase A in adrenocorticotropic hormone-stimulated Y1 cells, and the phospho-SIK1 translocates from the nucleus to the cytoplasm. The phospho-SIK1 is dephosphorylated in the cytoplasm and re-enters the nucleus several hours later. By using green-fluorescent protein-tagged SIK1 fragments, we found that a peptide region (586,612) was responsible for the nuclear localization of SIK1. The region was named the ,RK-rich region' because of its Arg- and Lys-rich nature. SIK1s mutated in the RK-rich region were localized mainly in the cytoplasm. Because SIK1 represses cAMP-response element (CRE)-mediated transcription of steroidogenic genes, the mutants were examined for their effect on transcription. To our surprise, the cytoplasmic mutants strongly repressed the CRE-binding protein (CREB) activity, the extent of repression being similar to that of SIK1(S577A), a mutant localized exclusively in the nucleus. Several chimeras were constructed from SIK1 and from its isoform SIK2, which was localized mainly in the cytoplasm, and they were examined for intracellular localization as well as CREB-repression activity. A SIK1-derived chimera, where the RK-rich region had been replaced with the corresponding region of SIK2, was found in the cytoplasm, its CREB-modulating activity being similar to that of wild-type SIK1. On the other hand, a SIK2-derived chimera with the RK-rich region of SIK1 was localized in both the nucleus and the cytoplasm, and had a CREB-repressing activity similar to that of the wild-type SIK2. Green fluorescent protein-fused transducer of regulated CREB activity 2 (TORC2), a CREB-specific co-activator, was localized in the cytoplasm and nucleus of Y1 cells, and, after treatment with adrenocorticotropic hormone, cytoplasmic TORC2 entered the nucleus, activating CREB. The SIK1 mutants, having a strong CRE-repressing activity, completely inhibited the adrenocorticotropic hormone-induced nuclear entry of green fluorescent protein-fused TORC2. This suggests that SIK1 may regulate the intracellular movement of TORC2, and as a result modulates the CREB-dependent transcription activity. Together, these results indicate that the RK-rich region of SIK1 is important for determining the nuclear localization and attenuating CREB-repressing activity, but the degree of the nuclear localization of SIK1 itself does not necessarily reflect the degree of SIK1-mediated CREB repression. [source] The translocation of signaling molecules in dark adapting mammalian rod photoreceptor cells is dependent on the cytoskeletonCYTOSKELETON, Issue 10 2008Boris Reidel Abstract In vertebrate rod photoreceptor cells, arrestin and the visual G-protein transducin move between the inner segment and outer segment in response to changes in light. This stimulus dependent translocation of signalling molecules is assumed to participate in long term light adaptation of photoreceptors. So far the cellular basis for the transport mechanisms underlying these intracellular movements remains largely elusive. Here we investigated the dependency of these movements on actin filaments and the microtubule cytoskeleton of photoreceptor cells. Co-cultures of mouse retina and retinal pigment epithelium were incubated with drugs stabilizing and destabilizing the cytoskeleton. The actin and microtubule cytoskeleton and the light dependent distribution of signaling molecules were subsequently analyzed by light and electron microscopy. The application of cytoskeletal drugs differentially affected the cytoskeleton in photoreceptor compartments. During dark adaptation the depolymerization of microtubules as well as actin filaments disrupted the translocation of arrestin and transducin in rod photoreceptor cells. During light adaptation only the delivery of arrestin within the outer segment was impaired after destabilization of microtubules. Movements of transducin and arrestin required intact cytoskeletal elements in dark adapting cells. However, diffusion might be sufficient for the fast molecular movements observed as cells adapt to light. These findings indicate that different molecular translocation mechanisms are responsible for the dark and light associated translocations of arrestin and transducin in rod photoreceptor cells. Cell Motil. Cytoskeleton 65: 785,800, 2008. © 2008 Wiley-Liss, Inc. [source] Melanophores: A model system for neuronal transport and exocytosis?JOURNAL OF NEUROSCIENCE RESEARCH, Issue 12 2007Sara Aspengren Abstract Black pigment cells, melanophores, from lower vertebrates are specialized in bidirectional and coordinated translocation of pigment granules, melanosomes, in the cytoplasm. Melanophores develop from the neuronal crest and are most abundant in the dermal and epidermal layers of the skin, where the intracellular distribution of the pigment significantly influences the color of the animal. The transport of pigment is dependent on an intact cytoskeleton and motor proteins associated with cytoskeletal components. The easily cultured melanophores have proved to be excellent models for organelle transport because the intracellular movements of pigment can be visualized via light microscopy, and the granules move in response to defined chemical signals. The ease of achieving a combination of morphological and functional transport studies is the advantage of the melanophore system, and studies on pigment cells have revealed new components of the transport machinery, including molecular motors, their adapters, and transfer of vesicles to other cells. Many cellular components are transported with a combination of the actin- and microtubule-based transport systems, and, since all eukaryotic organisms rely on functional intracellular transport and an intact cytoskeleton, studies on melanophores are important for many aspects of cell biology, including axonal transport. In this review, we present an overview of the research on the pigment transport system and the potential use of pigment cells as a model system. © 2006 Wiley-Liss, Inc. [source] Effects of isoflurane on measurements of delayed lumininescence in Acetabularia acetabulumLUMINESCENCE: THE JOURNAL OF BIOLOGICAL AND CHEMICAL LUMINESCENCE, Issue 1 2005Wen Li Chen Abstract The volatile halogenated methyl ethyl ether, isoflurane, used as an anaesthetic, inhibits actin-based dynamics directly or indirectly in animal cells. In plant cells, most intracellular movements are related to actin pathways. We have used isoflurane in a unicellular alga, Acetabularia acetabulum, to test the dynamics of choloroplast organization. By measuring the delayed luminescence, we found that isoflurane worked efficiently in the unicellular organism and showed dose- and time-course-dependent actin-inhibition patterns. When A. acetabulum was treated with saturated solutions of isoflurane in artificial seawater (defined as 100% isoflurane) for 3 or 6 min, the delayed luminescence (DL) was decreased and was never recovered. In contrast, if treated with 75% diluted isoflurane, the DL was firstly inhibited and then recovered several hours later, and if treated with 50% diluted isoflurane, the change of DL was small. Our work proved that isoflurane can affect actin-related pathways in both animals and plants. Copyright © 2005 John Wiley & Sons, Ltd. [source] | |||||||||||||