Integrin adhesion receptors can act as signaling receptors that transmit information from the extracellular environment to the interior of the cell, affecting many fundamental cellular processes, such as cell motility, proliferation, differentiation, and survival. Integrin signaling depends on the formation of organized sub-membrane complexes that comprise cytoskeletal, adapter, and signaling molecules. The identification of molecules that interact with the cytoplasmic domain of integrins has been the focus of research aimed to elucidating the mechanistic basis of integrin signal transduction. We have identified RanBPM as a novel interactor of the  2 integrin LFA-1 in a yeast-two-hybrid screen. In the same assay, RanBPM also interacted with the  1 integrin cytoplasmic domain. We demonstrate that Ran-BPM is a peripheral membrane protein and that integrins and RanBPM interact in vitro and in vivo and co-localize at the cell membrane. We find that RanBPM is phosphorylated on serine residues; phosphorylation of RanBPM is increased by stress stimuli and decreased by treatment with the p38 kinase inhibitor SB203580. Transfection of RanBPM synergizes with LFA-1-mediated adhesion in the transcriptional activation of an AP-1-dependent promoter, indicating that the two proteins interact functionally as well. We suggest that RanBPM may constitute a molecular scaffold that contributes to coupling LFA-1 and other integrins with intracellular signaling pathways.
Receptor recycling plays a critical role in the regulation of cellular responsiveness to environmental stimuli. Agonist-promoted phosphorylation of G protein-coupled receptors has been related to their desensitization, internalization, and sequestration. Dephosphorylation of internalized G protein-coupled receptors by cytoplasmic phosphatases has been shown to be pH-dependent, and it has been postulated to be necessary for receptors to recycle to the cell surface. The internalized V2 vasopressin receptor (V2R) expressed in HEK 293 cells is an exception to this hypothesis because it does not recycle to the plasma membrane for hours after removal of the ligand. Because this receptor is phosphorylated only by G protein-coupled receptor kinases (GRKs), the relationship between recycling and GRK-mediated phosphorylation was examined. A nonphosphorylated V2R, truncated upstream of the GRK phosphorylation sites, rapidly returned to the cell surface after removal of vasopressin. Less-drastic truncations of V2R revealed the presence of multiple phosphorylation sites and suggested a key role for a serine cluster present at the C terminus. Replacement of any one of Ser-362, Ser-363, or Ser-364 with Ala allowed quantitative recycling of full-length V2R without affecting the extent of internalization. Examination of the stability of phosphate groups incorporated into the recycling S363A mutant V2Rs revealed that the recycling receptor was dephosphorylated after hormone withdrawal, whereas the wild-type V2R was not, providing molecular evidence for the hypothesis that GRK sites must be dephosphorylated prior to receptor recycling. These experiments uncovered a role for GRK phosphorylation in intracellular sorting and revealed a GRK-dependent anchoring domain that blocks V2R recycling.The V1a and V2 vasopressin receptors (V1aR and V2R) are members of the G protein-coupled receptor family and both become phosphorylated upon activation by agonist (1, 2). For several receptors of this family phosphorylation and internalization have been shown to be a consequence of activation by ligand and seem to play a role in reducing the cellular responses to repeated exposure to hormones. Phosphorylation of G protein-coupled receptors enhances their ability to bind arrestin, which uncouples the receptors from G proteins, and helps recruit them to the clathrin-coated pits, which mediate the internalization process (3-7). Although phosphorylation and internalization of G protein-coupled receptors have been known to play a role in receptor desensitization for several years, the biochemical steps involved are not fully known and are still the subject of intense investigation.It has previously been observed that after removal of arginine vasopressin (AVP) from the medium and from the surface receptors with an acid wash, almost all of the internalized V1aR expressed in HEK 293 cells returns to the plasma membrane very rapidly (2), similar to what had been observed with isolated hepatocytes and smooth muscle vascular cells (8, 9). The human...
Cbfa1/Runx2 is a bone transcription factor homologous to the Drosophila protein, Runt. Runx2 is a master gene that encodes for a protein involved in the osteogenic differentiation process from mesenchymal precursors. It is known that in Cbfa1 deficient mice (Cbfa1(-/-)) the lack of mature osteoblasts is associated to incomplete bone mineralization. An important aim of modern biology is the development of new molecular tools for identification of therapeutic approaches. Recent discoveries in cell and molecular biology enabled researchers in the bone tissue-engineering field to develop new strategies for gene and cell-based therapies. This review summarizes the process of osteogenic differentiation from mesenchymal stem cells and the importance of bone regeneration is discussed. In particular, given the increasing interest in the study of the transcription factor Runx2, this review highlights the role of this target gene and addresses recent strategies using Runx2 for bone regeneration.
The protein product of the ocular albinism type 1 gene, named OA1, is a pigment cell-specific G protein-coupled receptor exclusively localized to intracellular organelles, namely lysosomes and melanosomes. Loss of OA1 function leads to the formation of macromelanosomes, suggesting that this receptor is implicated in organelle biogenesis, however the mechanism involved in the pathogenesis of the disease remains obscure. We report here the identification of an unexpected abnormality in melanosome distribution both in retinal pigment epithelium (RPE) and skin melanocytes of Oa1-knock-out (KO) mice, consisting in a displacement of the organelles from the central cytoplasm towards the cell periphery. Despite their depletion from the microtubule (MT)-enriched perinuclear region, Oa1-KO melanosomes were able to aggregate at the centrosome upon disruption of the actin cytoskeleton or expression of a dominant-negative construct of myosin Va. Consistently, quantification of organelle transport in living cells revealed that Oa1-KO melanosomes displayed a severe reduction in MT-based motility; however, this defect was rescued to normal following inhibition of actin-dependent capture at the cell periphery. Together, these data point to a defective regulation of organelle transport in the absence of OA1 and imply that the cytoskeleton might represent a downstream effector of this receptor. Furthermore, our results enlighten a novel function for OA1 in pigment cells and suggest that ocular albinism type 1 might result from a different pathogenetic mechanism than previously thought, based on an organelle-autonomous signalling pathway implicated in the regulation of both membrane traffic and transport.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.