The p150-Spir protein provides a link between c-Jun N-terminal kinase function and actin reorganization

The Jun N-terminal kinase (INK) Is a downstream effector of pac and Cdc42 G TPases involved in actin reorganization [1-3]. A role of the Drosophila JNK homologue, Basket (DJNK/Bsk), in the regulation of cell shape changes and actin reorganization arises from its function in the process of dorsal clos ure [4-6]. One potential mechanism for induction of cytoskeletal changes by JNK is via transcriptional activation of the decapentaplegic gene (dpp, a member of the TGF beta superfamily) [6]. A direct link between JNK signalli ng and actin organization has not yet been found, however. We have identifi ed a novel DJNK-interacting protein, p150-Spir, that belongs to the Wiscott -Aldrich syndrome protein (WASP) homology domain 2 (WH2) family of proteins involved in actin reorganization [7,8]. It is a multidomain protein with a cluster of four WH2 domains, a modified FYVE zinc-finger motif [9], and a DEJL motif, a docking site for JNK [10], at its carboxy-terminal end, in mo use fibroblasts, p150-Spir colocalized with F-actin and Its overexpression induced clustering of filamentous actin around the nucleus. When coexpresse d with p150-Spir in NIH 3T3 cells, JNK translocated to and colocalizes with p150-Spir at discrete spots around the nucleus. Carboxy-terminal sequences of p150-Spir were phosphorylated by JNK both in vitro and in vivo. We conc lude that p150-spir is a downstream target of JNK function and provides a d irect link between JNK and actin organization.