Making a connection: direct binding between keratin intermediate filaments and desmosomal proteins.

Abstract

Abstract. In epidermal cells, keratin intermediate filaments connect with desmosomes to form extensive cadherin-mediated cytoskeletal architectures. Desmoplakin (DPI), a desmosomal component lacking a transmembrane domain, has been implicated in this interaction, although most studies have been conducted with cells that contain few or no desmosomes, and efforts to demonstrate direct interactions between desmoplaldn and intermediate filaments have not been successful. In this report, we explore the biochemical nature of the connections between keratin filaments and desmosomes in epidermal keratinocytes. We show that the carboxy terminal "tail" of DPI associates directly with the amino terminal "head" of type II epidermal keratins, including K1, K2, K5, and K6. We have engineered and purified recombinant K5 head and DPI tail, and we demonstrate direct interaction in vitro by solution-binding assays and by ligand blot assays. This marked association is not seen with simple epithelial type II keratins, vimentin, or with type I keratins, providing a possible explanation for the greater stability of the epidermal keratin filament architecture over that of other cell types. We have identified an 18-amino acid residue stretch in the K5 head that is conserved only among type II epidermal keratins and that appears to play some role in DPI tail binding. This finding might have important implications for understanding a recent point mutation found within this binding site in a family with a blistering skin disorder.

Cytokeratin 8: The Dominant Type II Intermediate Filament Protein in Lung Cancer

“…Indeed, loss of desmosomal proteins has been shown to increase epithelial cell migration (Rieger-Christ et al, 2005;South et al, 2003). CKs connect with desmosomes to form extensive cadherin-mediated cytoskeletal structures (Buhler & Schaller, 2005;Kouklis et al, 1994;Smith & Fuchs, 1998). These data would therefore be consistent with the idea that the loss of CK expression can promote an invasive phenotype through a mechanism that elevates migratory ability by down-regulating desmosomal proteins.…”

iASPP, a previously unidentified regulator of desmosomes, prevents arrhythmogenic right ventricular cardiomyopathy (ARVC)-induced sudden death

“…Keratin 5 is an intermediate filament (IF) protein that binds specifically to desmoplakin in keratinocytes (32). Immunoprecipitation of keratin 5 on IMOK cells in the presence or absence of a desmoplakin siRNA revealed that immunoprecipitated keratin 5 bound much less to iASPP in the presence of a desmoplakin siRNA compared with scrambled siRNA control (Fig.…”

Complete Cytolysis and Neonatal Lethality in Keratin 5 Knockout Mice Reveal Its Fundamental Role in Skin Integrity and in Epidermolysis Bullosa Simplex

“…E-mail address: t.magin@uni-bonn. and yeast 2 hybrid assays demonstrated that the amino terminal head domain of type II keratins (e.g., K5) binds to the C-terminal tail of desmoplakin I, whereas no association was seen with type I keratins (Kouklis et al, 1994;Meng et al, 1997). More recently, it was shown that the major hemidesmosomal plaque protein plectin interacts with K14 but not with K5 (Geerts et al, 1999).…”