AMY-1 (associate of Myc-1) localization to the trans-Golgi network through interacting with BIG2, a guanine-nucleotide exchange factor for ADP-ribosylation factors

AMY-1 (associate of Myc-1) was originally identified as a c-Myc-binding protein that enhances the c-Myc transcription activity, and subsequently found to interact with A-kinase-anchoring proteins (AKAPs), including AKAP149, S-AKAP84 and AKAP95. We show here that, using anti-AMY-1 antibodies we raised, AMY-1 localizes to the trans-Golgi network (TGN) and the nucleus. To explore the possible function of AMY-1, we have undertaken a search for interacting partners by co-immunoprecipitation experiments using cells stably expressing FLAG-tagged AMY-1. Interestingly, we have found that AMY-1 interacts with BIG2 and BIG1, both of which are high molecular weight guanine-nucleotide exchange factors for ADP-ribosylation factors (ARFs) and mainly localize to the TGN. Furthermore, we have demonstrated that AMY-1 is associated with the TGN through interacting with BIG2 but not with BIG1 using an RNA interference approach, although AMY-1 can interact with both BIG1 and BIG2 in vitro. Taken together with the facts that BIG2 contains domains that bind to regulatory subunits of protein kinase A and that recruitment of ARF1 onto Golgi membranes is mediated, at least in part, by activation of protein kinase A, these results suggest that BIG2 alone or in concert with recruited AMY-1 coordinates ARF-mediated membrane trafficking and signaling pathways.