Diacylglycerol kinase δ associates with receptor for activated C kinase 1, RACK1

The delta-isozyme (type II) of diacylglycerol kinase (DGK) is known to positively regulate growth factor receptor signaling. DGK delta, which is distributed to clathrin-coated vesicles, interacts with DGK delta itself, protein kinase C and AP2 alpha. To search for additional DGK delta-interacting proteins, we screened a yeast two-hybrid cDNA library from HepG2 cells using aa 896-1097 of DGK delta as a bait. We identified aa 184-317 (WD40 repeats 5-7) of receptor for activated C kinase 1 (RACK1), which interacts with various important signaling molecules, as a novel binding partner of DGK delta. Co-immunoprecipitation analysis, using COS-7 cells co-expressing RACK1 and DGK delta, revealed that RACK1 selectively interacted with DGK delta, but not with type I DGKs, in mammalian cells. The interaction was dynamically regulated by phorbol ester. Intriguingly, DGK delta appeared to recruit RACK1 to clathrin-coated vesicles and co-localized with RACK1. These results suggest that DGK delta serves as an adaptor protein to regulate the localization of the versatile scaffold protein, RACK1. (c) 2009 Elsevier B.V. All rights reserved.