A GBF1-Dependent Mechanism for Environmentally Responsive Regulation of ER-Golgi Transport

Abstract

SummaryHow can anterograde membrane trafficking be modulated by physiological cues? A screen of Golgi-associated proteins revealed that the ARF-GEF GBF1 can selectively modulate the ER-Golgi trafficking of prohaemostatic von Willebrand factor (VWF) and extracellular matrix (ECM) proteins in human endothelial cells and in mouse fibroblasts. The relationship between levels of GBF1 and the trafficking of VWF into forming secretory granules confirmed GBF1 is a limiting factor in this process. Further, GBF1 activation by AMPK couples its control of anterograde trafficking to physiological cues; levels of glucose control GBF1 activation in turn modulating VWF trafficking into secretory granules. GBF1 modulates both ER and TGN exit, the latter dramatically affecting the size of the VWF storage organelles, thereby influencing the hemostatic capacity of the endothelium. The role of AMPK as a central integrating element of cellular pathways with intra- and extra-cellular cues can now be extended to modulation of the anterograde secretory pathway.

Sec22b determines Weibel-Palade body length by controlling anterograde ER-Golgi transport

“…Despite their length reduction, WPBs in Sec22b depleted cells normally recruited exocytotic components such as Rab27A and Slp4-a (Fig. S5), contrary to the enlarged WPBs in GBF1 ablated cells which failed to acquire post-Golgi cargo and Rab27A and which were secretion incompetent 62 . Although their short WPBs were still agonist responsive, Sec22b-depleted ECs secreted reduced levels of VWF through the regulated and basal secretory pathway ( Fig.…”

“…A recent study has identified GBF1 as a dynamic regulator of anterograde VWF trafficking and WPB morphology that, dependent on external/environmental cues, controls the flux of proteins (including VWF) from ER to Golgi 62 . Similar to what we observed after Sec22b 14 silencing, depletion of GBF1 led to accumulation of VWF in the ER and a reduction in the overall state of VWF proteolytic processing.…”

Modulation of endothelial organelle size as an antithrombotic strategy

“…A quantitative high-throughput microscopy-based workflow, dubbed highthroughput morphometry (HTM), allows rapid quantification of the size of tens to hundreds of thousands of WPBs within thousands of endothelial cells (Ferraro et al, 2014). HTM has been applied for analytical purposes and in phenotypic screens (Ferraro et al, 2014;Ferraro et al, 2016;Ketteler et al, 2017;Lopes-da-Silva et al, 2019;Stevenson et al, 2014). In the present report, HTM was deployed to identify compounds that can induce a reduction of WPB size in Human Umbilical Vein Endothelial Cells (HUVECs).…”

“…Short WPBs also form when VWF biosynthesis by endothelial cells is reduced, or following statin treatment, via Golgi fragmentation-independent and -dependent mechanisms, respectively (Ferraro et al, 2014;Ferraro et al, 2016). The metabolic status of endothelial cells also regulates WPB size through an AMPK-mediated signalling pathway (Lopes-da-Silva et al, 2019). Importantly, in vitro experiments have revealed that reducing WPB size results in the shortening of the VWF strings they generate and in much-reduced recruitment of platelets and soluble circulating VWF to the endothelial surface (Ferraro et al, 2014;Ferraro et al, 2016).…”

“…Importantly, in vitro experiments have revealed that reducing WPB size results in the shortening of the VWF strings they generate and in much-reduced recruitment of platelets and soluble circulating VWF to the endothelial surface (Ferraro et al, 2014;Ferraro et al, 2016). Conversely, endothelial cells respond to raised glucose levels (mimicking hyperglycemia) by producing longer WPBs, suggesting a link between long VWF strings and thrombotic manifestations in diabetes (Lopes-da-Silva et al, 2019), which is often associated with high levels of plasma VWF and microangiopathy (Westein et al, 2017). WPB size is, therefore, plastic and responds to physiological cues and pharmacological treatments.…”