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Ming Wei Zhao, Man Lin Jin, Shikun He, Christine Spee, Stephen J. Ryan, David R. Hinton; A Distinct Integrin-Mediated Phagocytic Pathway for Extracellular Matrix Remodeling by RPE Cells. Invest. Ophthalmol. Vis. Sci. 1999;40(11):2713-2723.
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© 2017 Association for Research in Vision and Ophthalmology.
purpose. To characterize the phagocytosis of extracellular matrix components by
retinal pigment epithelial cells and to determine which receptors and
signal transduction pathways are involved.
methods. Fluorescent latex beads were coated with fibronectin (FN), collagen
type I or IV, or thrombospondin and incubated with human retinal
pigment epithelial cells for 3 hours. Phagocytosis was quantified by
flow cytometry. The effects of adhesion blocking antibodies to cell
surface receptors (α1, α3, α5, β1, α5β1, ανβ3,ανβ
5 integrins and CD36) and inhibitors of specific intracellular
signaling pathways (tyrosine kinase phosphatidylinositol 3-kinase[
PI3-kinase], protein kinase C [PKC], and mitogen-activated protein
kinase) were determined using FN-coated beads.
results. Phagocytosis of FN-coated beads was greater than phagocytosis of beads
coated with collagen type I, collagen type IV, or thrombospondin or
uncoated controls (P < 0.0005). Anti-α5, -β1, and
-α5β1 antibodies markedly inhibited FN phagocytosis
(P < 0.0005); the inhibitory effects of anti-α5
antibody were stronger in the initial stages (binding) than in the
later stages (internalization) of phagocytosis. There was no
significant effect on phagocytosis when anti-α1, -α3, -αvβ5,
-αvβ3 or -CD36 antibodies were used. Fibronectin phagocytosis was
decreased by inhibitors of tyrosine kinase (genistein, 100 μg/ml, P < 0.005) and PI3-kinase (wortmannin, 5 μM, P < 0.01), but these reagents did not affect the
uncoated controls. The PKC inhibitor calphostin C (400 nM)
nonspecifically increased the phagocytosis of FN-coated
(P < 0.05) and uncoated beads
(P < 0.01).
conclusions. Subconfluent retinal pigment epithelial cells preferentially
phagocytose FN over other extracellular matrix components. Phagocytosis
of FN utilizes the α5β1 integrin, is mediated in part through
tyrosine kinase and PI3-kinase signaling pathways, and is modulated by
PKC. Phagocytosis of extracellular matrix by retinal pigment epithelial
cells may represent a novel mechanism for remodeling of the provisional
extracellular matrix during outer retinal wound
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