The Type I Keratin 19 Possesses Distinct and Context-Dependent Assembly Properties

The study investigated the assembly properties of type I keratin 19 (K19) compared to keratin 14 (K14) when paired with type II keratin 5 (K5) in vitro and in various cell lines. It was found that K5–K19 filaments were shorter and less stable than K5–K14 filaments, with K19 showing a lower affinity for K5. In transfected BHK-21 cells, K5–K19 did not form a filamentous array, unlike K5–K14, which formed a network of filaments. However, K19 could integrate into pre-existing keratin networks in epithelial cell lines without disrupting them. In PtK2 cells, K19 expression led to the collapse of the keratin network, but co-expression with K8, a natural partner for K19, restored filament formation. These findings highlighted the distinct and context-dependent assembly properties of K19, suggesting its limited ability to form stable filaments with K5 compared to K14.