Endothelial cells selectively release cargo stored in Weibel-Palade bodies (WPBs) to regulate vascular function, but the underlying mechanisms are poorly understood. Here we show that histamine evokes the release of the proinflammatory ligand, P-selectin, while diverting WPBs carrying non-inflammatory cargo away from the plasma membrane to the microtubule organizing center. This differential trafficking is dependent on Rab46 (CRACR2A), a newly identified Ca²⁺-sensing GTPase, which localizes to a subset of P-selectin–negative WPBs. After acute stimulation of the H₁ receptor, GTP-bound Rab46 evokes dynein-dependent retrograde transport of a subset of WPBs along microtubules. Upon continued histamine stimulation, Rab46 senses localized elevations of intracellular calcium and evokes dispersal of microtubule organizing center–clustered WPBs. These data demonstrate for the first time that a Rab GTPase, Rab46, integrates G protein and Ca²⁺ signals to couple on-demand histamine signals to selective WPB trafficking.

The coronavirus disease 2019 (COVID-19) pandemic, caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has resulted in more than 692 million cases worldwide and nearly 7 million deaths (August 2023). Severe COVID-19 is characterised in part by vascular thrombosis and a cytokine storm due to increased plasma concentrations of pro-thrombotic proteins such as von Willebrand factor and cytokines secreted from endothelial and T-cells. EFCAB4B is a gene that encodes for two proteins (CRACR2A and Rab46) that play important roles in endothelial and T-cell secretion. In this study, using patient data recorded in the UK Biobank, we demonstrate the importance of variants in the EFCAB4B genetic sequence with COVID-19 fatality. Using logistic regression analysis, we determined that three single-nucleotide polymorphisms (SNPs) in the gene cause missense variations in CRACR2A and Rab46, which are associated with COVID-19 fatality (rs9788233: p = 0.004, odds ratio = 1.511; rs17836273: p = 0.012, odds ratio = 1.433; rs36030417: p = 0.013, odds ratio = 1.393). All three SNPs cause changes in amino acid residues that are highly conserved across species, indicating their importance in protein structure and function. Two SNPs, rs17836273 (A98T) and rs36030417 (H212Q), cause amino acid substitutions in important functional domains: the EF-hand and coiled-coil domain, respectively. Molecular modelling shows minimal impact by the substitution of threonine at position 98 on the structure of the EF-hand. Since Rab46 is a GTPase that regulates both endothelial cell secretion and T-cell signalling, these missense variants may play a role in the molecular mechanisms underlying the thrombotic and inflammatory characteristics observed in patients with severe COVID-19 outcomes.