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Original Article

: Apoptotic Cells and Photoreceptors Compete for vβ3 and vβ5 Integrins, and Protein Kinase C Regulates vβ5 Binding and Cytoskeletal Linkage

Silvia C. Finnemann^a and Enrique Rodriguez-Boulan^a

^a Department of Ophthalmology and Department of Cell Biology, Margaret M. Dyson Vision Institute, Weill Medical College of Cornell University, New York, New York 10021
Margaret M. Dyson Vision Research Institute, Box 233, Department of Ophthalmology, Weill Medical College of Cornell University, 1300 York Ave., New York, NY 10021.212-746-8101212-746-2271

sfinne{at}mail.med.cornell.edu

Noninflammatory monocyte macrophages use vβ3 integrin to selectively bind apoptotic cells, initiating their phagocytic removal. In a related process, the retinal pigment epithelium (RPE) employs vβ5 integrin to recognize spent photoreceptor outer segment particles (OS). Here, we show that apoptotic cells and OS compete for binding to these receptors, indicating that OS and apoptotic cells expose surface signals recognizable by vβ3 and vβ5. Particle binding to vβ5 required protein kinase C (PKC) activation. In RPE, vβ5 binding was maximally activated even before any phagocytic challenge and was reduced by PKC inhibitors. In macrophages, it was dormant but became activated upon PKC stimulation. PKC-activated vβ5-mediated binding in macrophages differed from constitutive binding to the same integrin receptor in RPE cells in that the former followed much faster kinetics, similar to particle binding mediated by vβ3. Activation of vβ5 for particle binding correlated with its recruitment into a detergent-insoluble fraction, a process sensitive to pharmacological modulation of PKC in both types of phagocytes. Furthermore, vβ5 but not vβ3 particle binding required actin microfilaments. These data constitute the first evidence that noninflammatory phagocytes actively regulate the earliest phase of phagocytic clearance, particle binding, by controlling receptor activity.

Key Words: phagocytosis • recognition • integrins • macrophages • retinal pigment epithelium

© 1999 The Rockefeller University Press

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