Plakoglobin is required for effective intermediate filament anchorage to desmosomes.
Desmosomes are adhesive junctions that provide mechanical coupling between cells. Plakoglobin (PG) is a major component of the intracellular plaque that serves to connect transmembrane elements to the cytoskeleton. We have used electron tomography and immunolabeling to investigate the consequences of PG knockout on the molecular architecture of the intracellular plaque in cultured keratinocytes. Although knockout keratinocytes form substantial numbers of desmosome-like junctions and have a relatively normal intercellular distribution of desmosomal cadherins, their cytoplasmic plaques are sparse and anchoring of intermediate filaments is defective. In the knockout, beta-catenin appears to substitute for PG in the clustering of cadherins, but is unable to recruit normal levels of plakophilin-1 and desmoplakin to the plaque. By comparing tomograms of wild type and knockout desmosomes, we have assigned particular densities to desmoplakin and described their interaction with intermediate filaments. Desmoplakin molecules are more extended in wild type than knockout desmosomes, as if intermediate filament connections produced tension within the plaque. On the basis of our observations, we propose a particular assembly sequence, beginning with cadherin clustering within the plasma membrane, followed by recruitment of plakophilin and desmoplakin to the plaque, and ending with anchoring of intermediate filaments, which represents the key to adhesive strength.
Acehan
Devrim
D
Skirball Institute for Biomolecular Medicine, New York University School of Medicine, New York, New York, USA.
Petzold
Christopher
C
Skirball Institute for Biomolecular Medicine, New York University School of Medicine, New York, New York, USA.
Gumper
Iwona
I
Department of Cell Biology, New York University School of Medicine, New York, New York, USA.
Sabatini
David D
DD
Department of Cell Biology, New York University School of Medicine, New York, New York, USA.
Müller
Eliane J
EJ
Vetsuisse Faculty, Institute of Animal Pathology, University of Bern, Bern, Switzerland.
Cowin
Pamela
P
Department of Cell Biology, New York University School of Medicine, New York, New York, USA; Department Dermatology, New York University School of Medicine, New York, New York, USA.
Stokes
David L
DL
Skirball Institute for Biomolecular Medicine, New York University School of Medicine, New York, New York, USA; Department of Cell Biology, New York University School of Medicine, New York, New York, USA; New York Structural Biology Center, New York, New York, USA. Electronic address: stokes@saturn.med.nyu.edu.
D000818:Animals; D002448:Cell Adhesion / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism / Q000648:ultrastructure; D002478:Cells, Cultured; D003599:Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure; D051180:Desmoplakins / Q000378:metabolism; D003896:Desmosomes / Q000378:metabolism* / Q000648:ultrastructure; D007382:Intermediate Filaments / Q000378:metabolism* / Q000648:ultrastructure; D015603:Keratinocytes / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D051379:Mice; D018345:Mice, Knockout; D051191:Plakophilins / Q000378:metabolism; D051176:beta Catenin / Q000378:metabolism; D051185:gamma Catenin / Q000235:genetics / Q000378:metabolism*
D051180:Desmoplakins; D051191:Plakophilins; D051176:beta Catenin; D051185:gamma Catenin