Abstract
Epiplakin is a member of the plakin family with multiple copies of the plakin repeat domain (PRD). We studied the subcellular distribution and interactions of human epiplakin by immunostaining, overlay assays and RNAi knockdown. Epiplakin decorated the keratin intermediate filaments (IF) network and partially that of vimentin. In the binding assays, the repeat unit (PRD plus linker) showed strong binding and preferentially associated with assembled IF over keratin monomers. Epiplakin knockdown revealed disruption of IF networks in simple epithelial but not in epidermal cells. In rescue experiments, the repeat unit was necessary to prevent the collapse of IF networks in transient knockdown; however, it could only partially restore the keratin but not the vimentin IF network in stably knocked down HeLa cells. We suggest that epiplakin is a cytolinker involved in maintaining the integrity of IF networks in simple epithelial cells. Furthermore, we observed an increase of epiplakin expression in keratinocytes after the calcium switch, suggesting the involvement of epiplakin in the process of keratinocyte differentiation.
Highlights
Epiplakin was first discovered as an autoantigen in a patient with subepidermal blistering skin disease (Fujiwara et al, 1996)
We suggest that epiplakin is a cytolinker involved in maintaining the integrity of intermediate filaments (IF) networks in simple epithelial cells
We observed an increase of epiplakin expression in keratinocytes after the calcium switch, suggesting the involvement of epiplakin in the process of keratinocyte differentiation
Summary
Epiplakin was first discovered as an autoantigen in a patient with subepidermal blistering skin disease (Fujiwara et al, 1996). Depending on the type of tissue, each isoform has a distinct interaction with the cytoskeletal networks (Yang et al, 1996; Yang et al, 1999). The importance of these cytolinkers is further highlighted by the impairment of plakins found in patients with autoimmune or inherited diseases. These disorders usually lead to tissue fragility such as that displayed in muscular dystrophy and the skin disease epidemolysis bullosa simplex (Fuchs and Cleveland, 1998)
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