CKA, a novel multidomain protein, regulates the JUN N-terminal kinase signal transduction pathway in Drosophila.

The Drosophila melanogaster JUN N-terminal kinase (DJNK) and DPP (decapentaplegic) signal transduction pathways coordinately regulate epithelial cell sheet movement during the process of dorsal closure in the embryo. By a genetic screen of mutations affecting dorsal closure in Drosophila, we have now identified a multidomain protein, connector of kinase to AP-1 (cka), that functions in the DJNK pathway and controls the localized expression of dpp in the leading-edge cells. We have also investigated how CKA acts. This unique molecule forms a complex with HEP (DJNKK), BSK (DJNK), DJUN, and DFOS. Complex formation activates BSK kinase, which in turn phosphorylates and activates DJUN and DFOS. These data suggest that CKA represents a novel molecule regulating AP-1 activity by organizing a molecular complex of kinases and transcription factors, thus coordinating the spatial-temporal expression of AP-1-regulated genes.