Schematic representation of a working model depicting machinery associated with actomyosin-dependent expulsion of VWF from endothelial cells. (1) Upon stimulation, WPBs are trafficked to the cell surface where fusion with the plasma membrane occurs. (2) Septin rings are recruited to fused WPBs (independently of actin), where they likely transfer myosins (eg, NMII or Myo1C) or their activators. This process is PAK2 dependent. (3) Actin rings are formed by rearrangement of cortical actin or de novo nucleation. Possible candidates from our screen include FHOD1 and Arp3. Actin ring formation itself could displace the septin ring. (4) The actin ring contracts/compresses with the aid of NMII and cofilin 1. Myo1c may play a role in tethering actin to the WPB membrane. Proteins in red and green were identified through proximity proteomics and loss of function screening approaches. Proteins in black were identified through previous research. (Bottom panel) Disrupting the formation of the septin ring during WPB exocytosis results in prolonged actin ring dynamics as well as an inhibition of VWF secretion and string formation. SEPT2 depletion reduces the phosphorylation status of MLC2. This results in actin rings contracting more slowly or failing to contract before being disassembled. Interfering with actin ring formation or function results in less efficient VWF secretion.