Interaction partners of Dlk/ZIP kinase: co-expression of Dlk/ZIP kinase and Par-4 results in cytoplasmic retention and apoptosis

Dlk/ZIP kinase is a newly discovered serine/threonine kinase which, due to its homology to DAP kinase, was named DAP like kinase, Dlk, This kinase is tightly associated with nuclear structures, it undergoes extensive autophos phorylation and phosphorylates myosin light chain and core histones H3, H2A and H4 in vitro. Moreover, it possesses a leucine zipper which mediates in teraction with transcription factor ATF-4, therefore it was called ZIP kina se, We employed the yeast two-hybrid system to identify interaction partner s of Dlk that might serve as regulators or targets. Besides ATF-4 and other s we found Par-4, a modulator of transcription factor WT1 and mediator of a poptosis. Complex formation between Dlk and Par-4 was confirmed by GST pull -down experiments and kinase reactions ill vitro and coexpression experimen ts in vivo. The interaction domain within Dlk was mapped to an arginine-ric h region between residues 338-417, rather than to the leucine zipper. Strik ingly, coexpression of Dlk and Par-4 lead to relocation of Dlk from the nuc leus to the cytoplasm, particularly to actin filaments. These interactions provoked a dramatic reorganization of the cytoskeleton and morphological sy mptoms of apoptosis, thus suggesting a functional relationship between Dlk and Par-4 in the control of apoptosis.