Fig. 9. Model for the assembly of HDs in cultured keratinocytes. The association of the 6ß4 integrin with plectin via the ß4 subunit and their clustering is crucial for the formation of type II HDs. When BP180 is present, it will be incorporated into this complex through interactions with both ß4 and plectin. This is followed by the recruitment of additional plectin and BP180 molecules, resulting in a further increase of the size and the stability of the ternary complexes. In a final step, BP230 becomes incorporated into these complexes, and the HD-like structures containing 6ß4, BP180 and plectin are turned into type I HDs. Because both plectin and BP230 interact with the same site on BP180, it is likely that they may compete for this binding site.