Actin-containing microfilaments control cell shape, adhesion, and contracti
on. In striated muscle, a-actinin and other Z-disk proteins coordinate the
organization and functions of actin filaments. In smooth muscle and nonmusc
le cells, periodic structures termed dense bodies and dense regions, respec
tively, are thought to serve functions analogous to Z-discs. We describe he
re identification and characterization of human palladin, a protein express
ed mainly in smooth muscle and nonmuscle and distributed along microfilamen
ts iri a periodic manner consistent with dense regions/bodies. Palladin con
tains three Ig-domains most homologous to the sarcomeric Z-disk protein myo
tilin. The N terminus includes an FPPPP motif recognized by the Ena-Vasp ho
mology domain I domain in Ena/vasodilatator-stimulated phosphoprotein (VASP
)/WiscottAldrich syndrome protein (WASP) protein family. Cytoskeletal prote
ins with FPPPP motif target Ena/VASP/WASP proteins to sites of actin modula
tion. We identified palladin in a yeast two-hybrid search as an ezrin-assoc
iated protein. An interaction between palladin and ezrin was further verifi
ed by affinity precipitation and blot overlay assays. The interaction was m
ediated by the a-helical domain of ezrin and by Ig-domains 2-3 of palladin.
Ezrin is typically a component of the cortical cytoskeleton, but in smooth
muscle cells it is localized along microfilaments. These cells express pal
ladin abundantly and thus palladin may be involved in the microfilament loc
alization of ezrin. Palladin expression was up-regulated in differentiating
dendritic cells (DCs), coinciding with major cytoskeletal and morphologica
l alterations. In immature DCs, palladin localized in actin-containing podo
somes and in mature DCs along actin filaments. The regulated expression and
localization suggest a role for palladin in the assembly of DC cytoskeleto
n.