avb5 integrin recruits the CrkII-DOCK180-rac1 complex for phagocytosis of apoptotic cells
ABSTRACT Integrin receptors are important for the phagocytosis of apoptotic cells. However, little is known about their function in mediating internalization, as previous studies used blocking antibodies for the inhibition of binding. Here we show that the alphavbeta5 receptor mediates both binding and internalization of apoptotic cells. Internalization is dependent upon signalling through the beta5 cytoplasmic tail, and engagement of the alphavbeta5 heterodimer results in recruitment of the p130cas-CrkII-Dock180 molecular complex, which in turn triggers Rac1 activation and phagosome formation. In addition to defining integrin-receptor signalling as critical for the internalization of apoptotic material, our results also constitute the first evidence in human cells that the CED-2-CED-5-CED-10 complex defined in Caenorhabditis elegans is functionally analagous to the CrkII-Dock180-Rac1 molecular complex in mammalian cells. By linking the alphavbeta 5 receptor to this molecular switch, we reveal an evolutionarily conserved signalling pathway that is responsible for the recognition and internalization of apoptotic cells by both professional and non-professional phagocytes.
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- "Thus far, a few receptors that bind directly to this aminophospholipid have been identified (Miyanishi et al., 2007; Park et al., 2007; 2008). Upon recognition, apoptotic cells trigger intracellular signaling pathways, thereby stimulating cytoskeletal rearrangement to draw apoptotic cells into phagocytes (Albert et al., 2000; Lee et al., 2014; Park et al., 2007). Finally, ingested apoptotic cells within phagocytes are degraded in phagolysosomes by digestive enzymes derived from lysosomes. "
ABSTRACT: Rapid and efficient engulfment of apoptotic cells is an essential property of phagocytes for removal of the large number of apoptotic cells generated in multicellular organisms. To achieve this, phagocytes need to be able to continuously uptake apoptotic cells. It was recently reported that uncoupling protein 2 (Ucp2) promotes engulfment of apoptotic cells by increasing the phagocytic capacity, thereby allowing cells to continuously ingest apoptotic cells. However, the functions of Ucp2, beyond its possible role in dissipating the mitochondrial membrane potential, that contribute to elevation of the phagocytic capacity have not been determined. Here, we report that the anion transfer or nucleotide binding activity of Ucp2, as well as its dissipation of the mitochondrial membrane potential, is necessary for Ucp2-mediated engulfment of apoptotic cells. To study these properties, we generated Ucp2 mutations that affected three different functions of Ucp2, namely, dissipation of the mitochondrial membrane potential, transfer of anions, and binding of purine nucleotides. Mutations of Ucp2 that affected the proton leak did not enhance the engulfment of apoptotic cells. Although anion transfer and nucleotide binding mutations did not affect the mitochondrial membrane potential, they exerted a dominant-negative effect on Ucp2-mediated engulfment. Furthermore, none of our Ucp2 mutations increased the phagocytic capacity. We conclude that dissipation of the proton gradient by Ucp2 is not the only determinant of the phagocytic capacity and that anion transfer or nucleotide binding by Ucp2 is also essential for Ucp2-mediated engulfment of apoptotic cells.Moleculer Cells 06/2015; DOI:10.14348/molcells.2015.0083 · 2.24 Impact Factor
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- "Macrophages are capable of both expressing the cell surface receptors and releasing their bridging molecules for the recognition and engulfment of apoptotic cells. CD14  or Tim4  phagocytosis receptors mediate tethering, while other receptors, such as CD36 , integrin β 3 , integrin β 5 , Mer tyrosine kinase (MERTK) , stabilin-2  and CD91  activate two evolutionally conserved parallel signaling pathways which promote cytoskeletal reorganization via the activation of the low molecular weight GTPase Rac1 . Macrophages are exposed to varying numbers of apoptotic cells in vivo, and therefore they need a sensing mechanism that prepares Biochimica et Biophysica Acta 1853 (2015) 573–582 Abbreviations: BMDM, bone marrow derived macrophage; C1qb, complement 1qb; C/EBP, CCAAT/enhancer binding protein; CFDA, carboxyfluorescein diacetate succinimidyl ester; CHX, cycloheximide; CMTMR, 5-(and-6)-(((4-chloromethyl) benzoylamino)tetramethylrhodamine); CYP27, a mitochondrial sterol 27-hydroxylase; DEAB, 4-diethylaminobenzaldehyde; Dex, dexamethasone acetate; GAPDH, glyceralde- hyde-3-phosphate dehydrogenase; LXR, liver X receptor; MERTK, c-Mertk proto-oncogene tyrosine kinase; MFG-E8, milk fat globule EGF-factor 8; PPAR, peroxisome proliferatoractivated receptor; RAR, retinoic acid receptor; RALDH, retinaldehyde dehydrogenase; RXR, retinoid X receptor; SREBP, c1 sterol response element binding protein; UCP2, uncoupling protein 2 ⁎ Corresponding author at: Department of Biochemistry and Molecular Biology, "
ABSTRACT: Efficient phagocytic clearance of apoptotic cells (efferocytosis) is essential to prevent the development of chronic inflammation and autoimmunity. Glucocorticoids are widely used in the therapy of chronic inflammatory diseases, and increasing evidence suggests that they act partly via enhancing efferocytosis by macrophages. Glucocorticoids were previously shown to promote both protein S- and MFG-E8-dependent efferocytosis. Since previous studies in our laboratory have demonstrated that glucocorticoids induce the expression of retinaldehyde dehydrogenases in macrophages, in the present experiments the possible involvement of retinoids in the glucocorticoid-induced efferocytosis was studied in mouse bone marrow derived macrophages. Here we show that glucocorticoids promote not only short-term, but also long-term clearance of apoptotic cells. Glucocorticoids seem to directly induce the expression of the phagocytosis-related genes MERTK, C1q, UCP2, and the transcription factor C/EBPβ. C/EBPβ contributes to the further induction of the phagocytosis-related genes, and is required for the induction of lipid sensing receptors LXRs, PPARδ, RARα, RXRα and RALDH1, the latter one in an LXR- and RARα-dependent manner. Glucocorticoid-induced enhancement in long-term efferocytosis was dependent on the induction of lipid sensing receptors known to be triggered by the lipid content of the engulfed cells to enhance phagocytic capacity. Retinoids did not affect the glucocorticoid-induced short term phagocytosis of apoptotic cells, but were required for the glucocorticoid-induced enhancement of efferocytosis during prolonged clearance of apoptotic cells by promoting efficient LXR and PPARδ upregulation. Our data indicate that retinoids could be considered as potential promoters of the efficacy of glucocorticoid treatment in inflammatory diseases.Biochimica et Biophysica Acta (BBA) - Molecular Cell Research 12/2014; 1853(3). DOI:10.1016/j.bbamcr.2014.12.014 · 5.30 Impact Factor
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- "Given their recent identification , much less is known about the CZH GEF family compared with the Dbl family. Nonetheless, the CZH GEFs such as myoblast city have been shown to be involved in myoblast fusion, dorsal closure, cytoskeletal organization, and border cells migration (Erickson et al., 1997; Bianco et al., 2007), whereas Ced-5 plays a critical role in phagocytosis and cell migration (Wu and Horvitz, 1998) and Dock180 is required for cell morphogenesis (Hasegawa et al., 1996) and phagocytosis (Albert et al., 2000; Park et al., 2007). Very recently, Dock180 has been shown to have a critical role in netrin-dependent axon outgrowth and attraction (Li et al., 2008). "
ABSTRACT: Rho G proteins and their regulators are critical for cytoskeleton organization and cell morphology in all eukaryotes. In the opportunistic pathogen Candida albicans, the Rho G proteins Cdc42 and Rac1 are required for the switch from budding to filamentous growth in response to different stimuli. We show that Dck1, a protein with homology to the Ced-5, Dock180, myoblast city family of guanine nucleotide exchange factors, is necessary for filamentous growth in solid media, similar to Rac1. Our results indicate that Dck1 and Rac1 do not function in the same pathway as the transcription factor Czf1, which is also required for embedded filamentous growth. The conserved catalytic region of Dck1 is required for such filamentous growth, and in vitro this region directly binds a Rac1 mutant, which mimics the nucleotide-free state. In vivo overexpression of a constitutively active Rac1 mutant, but not wild-type Rac1, in a dck1 deletion mutant restores filamentous growth. These results indicate that the Dock180 guanine nucleotide exchange factor homologue, Dck1 activates Rac1 during invasive filamentous growth. We conclude that specific exchange factors, together with the G proteins they activate, are required for morphological changes in response to different stimuli.Molecular biology of the cell 07/2008; 19(9):3638-51. DOI:10.1091/mbc.E07-12-1272 · 5.98 Impact Factor