Tetraspanin CD81 is required for the αvβ5-integrin-dependent particle-binding step of RPE phagocytosis

Chang, Ying; Finnemann, Silvia C.

doi:10.1242/jcs.006361

Cited by 77 publications

(56 citation statements)

References 37 publications

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“…RPE cells like non-elicited macrophages and immature dendritic cells utilize a pathway dependent on ␣v␤5 integrin whereas elicited macrophages do not. We have shown previously that the particle recognition mechanism used by RPE cells requires activation of the particle recognition/binding receptor ␣v␤5 integrin by interaction with the tetraspanin CD81 (50). We speculate that tetraspanin and caveolin-1 may play similar roles in particle recognition/binding/engulfment in RPE cells and macrophages, respectively.…”

Section: Discussionmentioning

confidence: 73%

Regulation of Phagolysosomal Digestion by Caveolin-1 of the Retinal Pigment Epithelium Is Essential for Vision

Sethna

Chamakkala

et al. 2016

Journal of Biological Chemistry

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Caveolin-1 associates with the endo/lysosomal machinery of cells in culture, suggesting that it functions at these organelles independently of its contribution to cell surface caveolae. Here we explored mice lacking caveolin-1 specifically in the retinal pigment epithelium (RPE Support of the neural retina generally and of adjacent photoreceptor neurons specifically by the retinal pigment epithelium (RPE) 5 is essential for vision (1). A major function of the RPE is its contribution to photoreceptor outer segment renewal, a continuous and life-long rejuvenation process that involves the formation of new membrane disks at the proximal end of the outer segment and diurnal shedding of distal spent outer segment tips (2). Outer segment renewal is critical for photoreceptor function and survival, and any abnormality is thought to impair vision. RPE cells participate in outer segment renewal by clearing shed photoreceptor outer segment fragments (POS) by receptor-mediated phagocytosis (3).Mechanistically, RPE phagocytosis belongs to a family of conserved non-inflammatory clearance phagocytosis pathways that other cell types use to remove apoptotic cells and debris. These pathways have in common that their failure to efficiently clear debris contributes to human disease. However, unlike other forms of phagocytosis, RPE clearance of POS occurs in a strict diurnal rhythm that is regulated by light and circadian mechanisms (4). This is a unique advantage for RPE phagocytosis studies because all steps of the synchronized phagocytic process may be quantified precisely in situ in the intact, undisturbed retinas of experimental animals. Content in the RPE of engulfed rod POS phagosomes peaks shortly after light onset and declines characteristically within several hours as RPE cells complete digestion of their phagocytic load before the next burst of intake (5).Like other phagocytic pathways, ingested phagosomes in the RPE fuse with lysosomal vesicles to form phagolysosomes. In POS phagolysosomes, degradation of opsin, which constitutes ϳ85% of POS protein, requires the aspartic protease cathepsin D and phagosomal acidification (6, 7). Because RPE cells are post-mitotic in the mammalian eye and ingest numerous POS daily, prompt and complete POS engulfment is essential to prevent gradual buildup of undigested debris in the RPE (8). Inefficient RPE lysosomal function causes accumulation of debris in human and experimental animal RPE that can be toxic and

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Section: Discussionmentioning

confidence: 73%

Regulation of Phagolysosomal Digestion by Caveolin-1 of the Retinal Pigment Epithelium Is Essential for Vision

Sethna

Chamakkala

et al. 2016

Journal of Biological Chemistry

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“…Ezrin is a member of the ERM family (ezrin, radixin, moesin) of actin-binding proteins (Bretscher et al, 2002;Tsukita and Yonemura, 1997). This finding was of great interest because CD81 has recently been shown to interact directly with ERM family members (Chang and Finnemann, 2007;Pan et al, 2007;Sala-Valdes et al, 2006).…”

Section: Resultsmentioning

confidence: 99%

“…The ability of CD81 to activate ezrin is probably due to their direct interaction. Indeed, CD81 coimmunoprecipitated with ezrin in rat retinal pigment epithelial cells (Chang and Finnemann, 2007;Pan et al, 2007) and a peptide derived from the cytoplasmic C-terminal tail of CD81 bound the N-terminal domain of ezrin (Sala-Valdes et al, 2006). Moreover, ezrin contains an ITAM motif, which could enable its direct interaction with Syk (Rozsnyay et al, 1996;Urzainqui et al, 2002).…”

Section: Discussionmentioning

confidence: 99%

Engagement of CD81 induces ezrin tyrosine phosphorylation and its cellular redistribution with filamentous actin

Coffey

Rajapaksa

Liu

et al. 2009

Journal of Cell Science

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CD81 is a tetraspanin family member involved in diverse cellular interactions in the immune and nervous systems and in cell fusion events. However, the mechanism of action of CD81 and of other tetraspanins has not been defined. We reasoned that identifying signaling molecules downstream of CD81 would provide mechanistic clues. We engaged CD81 on the surface of B-lymphocytes and identified the induced tyrosine-phosphorylated proteins by mass spectrometry. This analysis showed that the most prominent tyrosine phosphorylated protein was ezrin, an actin-binding protein and a member of the ezrin-radixin-moesin family. We also found that CD81 engagement induces spleen tyrosine kinase (Syk) and that Syk was involved in tyrosine phosphorylation of ezrin. After engagement of CD81, it colocalized with ezrin and F-actin, and this association was disrupted when Syk activation was blocked. Taken together, these studies suggest a model in which CD81 interfaces between the plasma membrane and the cytoskeleton by activating Syk, mobilizing ezrin, and recruiting F-actin to facilitate cytoskeletal reorganization and cell signaling. This mechanism might explain the pleiotropic effects induced in response to stimulation of cells by anti-CD81 antibodies or by the hepatitis C virus, which uses this molecule as its key receptor.

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“…RPE cell lines rat RPE-J (ATCC) and human d407 (a gift from Dr. R. C. Hunt, University of South Carolina, Columbia, SC), and d407 RPE-derived cybrid clones were routinely grown to confluence in Dulbecco's modified Eagle's medium containing 4.5 g/liter glucose supplemented with 4 and 3% fetal bovine serum, respectively, as described previously (26). The day prior to an experiment, cells on coverslips or on chamber slides received 50 M (RPE-J) or 10 M (cybrids) A2E for 6 h followed by incubation with regular growth medium overnight.…”

Section: Methodsmentioning

confidence: 99%

“…Samples with and without trypan blue treatment were mounted on glass slides, scanned using a Typhoon Trioϩ scanner, and quantified using ImageQuaNT v1.2 yielding relative fluorescence values representing total (bound plus internal) and internal OS, respectively. Bound OS were calculated by subtracting internal from total OS (26).…”

Section: Methodsmentioning

confidence: 99%

The Age Lipid A2E and Mitochondrial Dysfunction Synergistically Impair Phagocytosis by Retinal Pigment Epithelial Cells

Vives-Bauzà

Anand

Shirazi

et al. 2008

Journal of Biological Chemistry

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141

110

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Accumulation of indigestible lipofuscin and decreased mitochondrial energy production are characteristic age-related changes of post-mitotic retinal pigment epithelial (RPE) cells in the human eye. To test whether these two forms of age-related impairment have interdependent effects, we quantified the ATPdependent phagocytic function of RPE cells loaded or not with the lipofuscin component A2E and inhibiting or not mitochondrial ATP synthesis either pharmacologically or genetically. We found that physiological levels of lysosomal A2E reduced mitochondrial membrane potential and inhibited oxidative phosphorylation (OXPHOS) of RPE cells. Furthermore, in media with physiological concentrations of glucose or pyruvate, A2E significantly inhibited phagocytosis. Antioxidants reversed these effects of A2E, suggesting that A2E damage is mediated by oxidative processes. Because mitochondrial mutations accumulate with aging, we generated novel genetic cellular models of RPE carrying mitochondrial DNA point mutations causing either moderate or severe mitochondrial dysfunction. Exploring these mutant RPE cells we found that, by itself, only the severe but not the moderate OXPHOS defect reduces phagocytosis. However, sub-toxic levels of lysosomal A2E are sufficient to reduce phagocytic activity of RPE with moderate OXPHOS defect and cause cell death of RPE with severe OXPHOS defect. Taken together, RPE cells rely on OXPHOS for phagocytosis when the carbon energy source is limited. Our results demonstrate that A2E accumulation exacerbates the effects of moderate mitochondrial dysfunction. They suggest that synergy of sub-toxic lysosomal and mitochondrial changes in RPE cells with age may cause RPE dysfunction that is known to contribute to human retinal diseases like agerelated macular degeneration. Retinal pigment epithelial (RPE)5 cells form a polarized monolayer epithelium between the photoreceptors of the neurosensory retina and the choroidal capillary bed. Daily phagocytosis of outer segment (OS) tips shed by adjacent photoreceptors is a vital task of the RPE (recently reviewed by Strauss (1)). RPE cells are post-mitotic and face each ϳ30 photoreceptor outer segments in the human eye, all of which shed their distal tip containing stacked membrane disks once a day. Diurnal phagocytosis and digestion of thousands of OS disks for life renders RPE cells the most active phagocytes in the body. Photoreceptor function strictly depends on efficient RPE phagocytosis of spent OS. Complete failure of RPE cells to engulf OS causes rapid photoreceptor degeneration in the Royal College of Surgeons rat (2-4). Impaired RPE phagocytosis also contributes to human retinal disease such as retinitis pigmentosa and, likely, age-related macular degeneration (5, 6).The continuous nature of outer segment renewal implies that any delay in OS removal by aged or damaged RPE will gradually cause OS components to accumulate. RPE cells are at risk for oxidative damage due to their location in the highly oxygenated environment of the outer retina and th...

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Tetraspanin CD81 is required for the αvβ5-integrin-dependent particle-binding step of RPE phagocytosis

Cited by 77 publications

References 37 publications

Regulation of Phagolysosomal Digestion by Caveolin-1 of the Retinal Pigment Epithelium Is Essential for Vision

Regulation of Phagolysosomal Digestion by Caveolin-1 of the Retinal Pigment Epithelium Is Essential for Vision

Engagement of CD81 induces ezrin tyrosine phosphorylation and its cellular redistribution with filamentous actin

The Age Lipid A2E and Mitochondrial Dysfunction Synergistically Impair Phagocytosis by Retinal Pigment Epithelial Cells

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