Primary HUVECs tested for contamination were purchased from PromoCell GmbH (Heidelberg, Germany) and cultured as previously described (Hannah et al., 2005 (link)). Human Embryonic Kidney-293 (HEK-293) cells were cultured in Minimal Essential Medium (MEM) Alpha Medium 1x (Invitrogen) supplemented with 10% fetal calf serum (Biosera, Ringmer, UK) and 50 μg/ml gentamycin (Invitrogen) at 37°C, 5% CO2 as previously described (Kiskin et al., 2010 (link)). Secreted VWF propolypeptide (VWFpp) was assayed by specific ELISA as previously described (Hewlett et al., 2011 (link)). Primary antibodies (Abs) along with the dilutions for immunofluorescence or western blotting are given in supplementary Table S1. All reagents were from Sigma-Aldrich unless otherwise stated. Fura-2/AM was from Invitrogen.