ACBD3 modulates KDEL receptor interaction with PKA for its trafficking via tubulovesicular carrier

Abstract

Background KDEL receptor helps establish cellular equilibrium in the early secretory pathway by recycling leaked ER-chaperones to the ER during secretion of newly synthesized proteins. Studies have also shown that KDEL receptor may function as a signaling protein that orchestrates membrane flux through the secretory pathway. We have recently shown that KDEL receptor is also a cell surface receptor, which undergoes highly complex itinerary between trans-Golgi network and the plasma membranes via clathrin-mediated transport carriers. Ironically, however, it is still largely unknown how KDEL receptor is distributed to the Golgi at steady state, since its initial discovery in late 1980s. Results We used a proximity-based in vivo tagging strategy to further dissect mechanisms of KDEL receptor trafficking. Our new results reveal that ACBD3 may be a key protein that regulates KDEL receptor trafficking via modulation of Arf1-dependent tubule formation. We demonstrate that ACBD3 directly interact with KDEL receptor and form a functionally distinct protein complex in ArfGAPs-independent manner. Depletion of ACBD3 results in re-localization of KDEL receptor to the ER by inducing accelerated retrograde trafficking of KDEL receptor. Importantly, this is caused by specifically altering KDEL receptor interaction with Protein Kinase A and Arf1/ArfGAP1, eventually leading to increased Arf1-GTP-dependent tubular carrier formation at the Golgi. Conclusions These results suggest that ACBD3 may function as a negative regulator of PKA activity on KDEL receptor, thereby restricting its retrograde trafficking in the absence of KDEL ligand binding. Since ACBD3 was originally identified as PAP7, a PBR/PKA-interacting protein at the Golgi/mitochondria, we propose that Golgi-localization of KDEL receptor is likely to be controlled by its interaction with ACBD3/PKA complex at steady state, providing a novel insight for establishment of cellular homeostasis in the early secretory pathway.

KDEL Receptor Trafficking to the Plasma Membrane is Regulated by ACBD3 and Rab4-GTP

“…Upon examination using live cell confocal imaging, we found greatly increased frequency in KDELR1-positive tubulovesicular carrier formation in ACBD3 KD cells, compared to the control cells (Figure 3E) (6). Unexpectedly, Golgi-derived KDELR1-positive tubular carriers showed relatively poor overlap with either mCherry-Rab14 or Rab11 (Fig- ure 3E), indicating that increased targeting of KDELR1 to the PM in ACBD3-depleted cells may not result from elevated rate of Rab14-and Rab11-mediated KDELR recycling to the PM.…”

“…In our earlier study, we reported that ACBD3 plays a key role in suppressing PKA activity on KDELR, thereby facilitating Golgi localization of KDELR under steady state condition (6). To study whether ACBD3 may be involved in the receptor export from the Golgi to the PM, we tested surface expression of KDELR1-mCherry in ACBD3 knockout HT1080 cells using surface biotinylation protocol (11).…”

“…At steady state, KDELR mostly localizes to the Golgi by a scaffold protein, acyl-CoA binding containing protein 3 (ACBD3) and maintains dynamic homeostasis in the early secretory pathway (6,7). Previous studies have reported that a small fraction of KDELR resides on the cell surface as well and circulates between the plasma membrane and the Golgi via a complex trafficking itinerary (8)(9)(10)(11).…”

“…The Golgi-to-ER retrograde transport of KDEL-containing ER proteins requires protein kinase A (PKA) phosphorylation of the C-terminus of KDELR, which in turn allows the recruitment of ArfGAP1/COPI proteins to the Golgi membranes and ensures the retrieval of KDELR ligands (19,20). Our previous study had shown that ACBD3, a putative PKA anchoring protein (AKAP), regulates KDELR-PKA interaction and ER traffic-induced retrograde transport of KDELR via ADP-ribosylation factor 1 (Arf1)-dependent tubulovesicular carriers (6). The Src tyrosine kinase has been shown to regulate KDELR retrograde transport to the ER (21).…”

KDEL Receptors: Pathophysiological Functions, Therapeutic Options, and Biotechnological Opportunities

“…This signaling cascade participates in the retrograde Golgi to ER trafficking and is important to balance transport fluxes between these organelles ( Figure 2 ). Prohibitin (PHB) and acyl-CoA binding domain-containing 3 (ACBD3) scaffold proteins belong to the KDELR-PKA signalosome and take part in the retro-translocation of the KDELR [ 31 , 32 ]. To accomplish this task, KDELR-activated PKA phosphorylates numerous proteins involved in membrane trafficking, although many other PKA targets play a role in cell growth, motility, energy metabolism, and transcription [ 30 ].…”