Arf GTPase-Activating proteins SMAP1 and AGFG2 regulate the size of Weibel-Palade bodies and exocytosis of von Willebrand factor

Abstract

Arf GTPase-Activating proteins (ArfGAPs) mediate the hydrolysis of GTP bound to ADP-ribosylation factors, which are important for intracellular transport. ArfGAPs have been shown to be critical for cargo sorting in the Golgi-to-ER and post-Golgi traffic. However, their roles in the sorting of secretory proteins remains unclear. Weibel-Palade bodies (WPBs) are cigar-shaped secretory granules in endothelial cells that contain von Willebrand factor (vWF) as their main cargo. WPBs are formed at the trans-Golgi Network, and this process is thought to be coupled with the sorting of vWF. WPB biogenesis was reported to be regulated by ADP-ribosylation factors and their regulators, but the role of ArfGAPs has been unknown. In this study, we performed siRNA screening of ArfGAPs to investigate the biogenesis of WPBs. We found two ArfGAPs, SMAP1 and AGFG2, to be involved in WPB size and vWF exocytosis, respectively. SMAP1 depletion resulted in small-sized WPBs, and the lysosomal inhibitor leupeptin recovered the size of WPBs. These results indicate that SMAP1 functions in preventing the degradation of cigar-shaped WPBs. However, AGFG2 downregulation resulted in the inhibition of vWF secretion upon Phorbol 12-myristate 13-acetate (PMA)-stimulation, suggesting that AGFG2 plays a role in vWF exocytosis. Our study revealed unexpected processes regulated by ArfGAPs for vWF transport.

Dispatch and delivery at the ER–Golgi interface: how endothelial cells tune their hemostatic response

“…Further evidence for the involvement of Arf GTPases in control of organelle size comes from Arf GTPase activating proteins (Arf GAPs). Depletion of Small Arf GAP 1 (SMAP1) also leads to shortening of WPBs [33], but if this depends on loss of GAP activity for Arf GTPases or its ability to act as an Arf effector that recruits clathrin remains unclear.…”