The Fate of Desmosomal Proteins in Apoptotic Cells

Abstract

Activation of caspases results in the disruption of structural and signaling networks in apoptotic cells. Recent biochemical and cell biological studies have shown that components of the cadherin-catenin adhesion complex in epithelial adherens junctions are targeted by caspases during apoptosis. In epithelial cells, desmosomes represent a second type of anchoring junctions mediating strong cell-cell contacts. Using antibodies directed against a set of desmosomal proteins, we show that desmosomes are proteolytically targeted during apoptosis. Desmogleins and desmocollins, representing desmosome-specific members of the cadherin superfamily of cell adhesion molecules, are specifically cleaved after onset of apoptosis. Similar to E-cadherin, the desmoglein-3 cytoplasmic tail is cleaved by caspases. In addition the extracellular domains of desmoglein-3 and desmocollin-3 are released from the cell surface by a metalloproteinase activity. In the presence of caspase and/or metalloproteinase inhibitors, both cleavage reactions are almost completely inhibited. As reported previously, the desmosomal plaque protein plakoglobin is cleaved by caspase-3 during apoptosis. Our studies now show that plakophilin-1 and two other major plaque proteins, desmoplakin-1 and -2, are also cleaved by caspases. Immunofluorescence analysis confirmed that this cleavage results in the disruption of the desmosome structure and thus contributes to cell rounding and disintegration of the intermediate filament system. Apoptosis is a highly conserved process important for the destruction of excess or damaged cells during the development and in the homeostasis of multicellular organisms (1). Impaired regulation of programmed cell death is involved in the pathogenesis of cancer and immune and neuronal diseases (2, 3). Once the cell death program is started, dramatic changes in cell morphology can be observed such as nuclear/cytoplasmic condensation, formation of membrane protrusions, DNA fragmentation, and disruption of the structural integrity followed by fragmentation into "apoptotic bodies" that are removed by subsequent engulfment by neighboring cells or macrophages. Many of these morphological changes can be attributed to the cleavage of structural and regulatory proteins by members of the caspase family of cysteine proteinases. Caspases specifically cleave substrate proteins C-terminal to aspartate residues (for review see Refs. 4 -6). Caspase-3-mediated cleavage of inhibitor of caspase-activated DNase releases caspase-activated DNase, which is responsible for the generation of the nucleosomal ladder. Cleavage of cytoskeletal proteins and regulators such as fodrin (7), gelsolin (8), Gas2 (9), and focal adhesion kinase (10 -12) and adhesion molecules such as cadherins (13-16) results in disruption of the cyto-architecture.Desmosomes are punctate intercellular junctions located on the basolateral side primarily of epithelial cells. They provide mechanical strength to epithelial tissues by forming stable cell-cell contacts that are anchored to the...

Novel Mechanisms of Target Cell Death and Survival and of Therapeutic Action of IVIg in Pemphigus

“…46,90 In turn, caspase activation leads to proteolytic cleavage of numerous intracellular targets, including CSP, which upregulates calpain activity, 91 and the adhesion molecules desmogleins, desmocollins, and ␤-and ␥-catenins. [92][93][94] The extracellular domains of desmoglein 3 and desmocollin 3 are released from the cell surface by a metalloproteinase activity, because in the presence of caspase and/or metalloproteinase inhibitors, both cleavage reactions are almost completely inhibited. This may initiate or augment production autoantibodies to desmoglein 3 and other adhesion molecules found in PV patients (reviewed by Grando 2 ).…”

The specific fates of tight junction proteins in apoptotic epithelial cells

“…Since the anti-occludin antibody is directed against the Cterminus of occludin the apparent molecular mass of fragment 2 suggested that it is generated by cleavage within the first extracellular loop of occludin. Therefore, we assumed that, similar to the apoptotic cleavage of cadherin extracellular domains (Herren et al, 1998;Steinhusen et al, 2001;Weiske et al, 2001), occludin is cleaved by metalloproteinase(s) in the extracellular loop. To address this question cells were preincubated with metalloproteinase inhibitors before induction of apoptosis.…”

The Histidine Triad Protein Hint1 Triggers Apoptosis Independent of Its Enzymatic Activity

“…Preparation of Cell Lysate and Western Blot AnalysisHint1-transfected cells were lysed 72 h after transfection, and 50 g of total protein was analyzed by SDS-PAGE and subsequent Western blotting as described previously (38). For immunodetection, antibodies were diluted in TST (anti-Bax, 1 g/ml; anti-Bcl-2, 0.5 g/ml; anti-PARP, 1:2000; anti-p53, 1 g/ml;…”