Recent studies with patients suffering from
epidermolysis bullosa simplex associated with
muscular dystrophy and the targeted gene disruption in mice suggested that
plectin, a versatile cytoskeletal linker and intermediate filament-
binding protein, may play an essential role in hemidesmosome integrity and stabilization. To define
plectin's interactions with hemidesmosomal
proteins on the molecular level, we studied its interaction with the uniquely long cytoplasmic tail domain of the beta4 subunit of the basement membrane
laminin receptor integrin alpha6beta4 that has been implicated in connecting the transmembrane
integrin complex with hemidesmosome-anchored
cytokeratin filaments. In vitro binding and in vivo cotransfection assays, using recombinant mutant forms of both
proteins, revealed their direct interaction via multiple molecular domains. Furthermore, we show in vitro self-interaction of
integrin beta4 cytoplasmic domains, as well as disruption of intermediate filament network arrays and dislocation of hemidesmosome-associated endogenous
plectin upon ectopic overexpression of this domain in PtK2 and/or 804G cells. The close association of
plectin molecules with hemidesmosomal structures and their apparent random orientation was indicated by
gold immunoelectron microscopy using domain-specific
antibodies. Our data support a model in which
plectin stabilizes hemidesmosomes, via directly interlinking
integrin beta4 subunits and
cytokeratin filaments.