BRET measurement: Assay plates were equilibrated at room temperature for 15 min. A 3X solution of complete substrate plus inhibitor was prepared with NanoGlo substrate (1:166 dilution, Promega #N157D) and extracellular NanoLuc inhibitor (1:500 dilution, Promega #N235C) in Opti-MEM without phenol red. For one 96-well assay plate, this consists of 30 µL of NanoGlo substrate and 10 µL of extracellular NanoLuc inhibitor in 4,960 mL of Opti-MEM without phenol red. 3X complete substrate plus inhibitor (50 µL) was added to each well and the plates mixed on an orbital shaker for 15 seconds at 300 rpm. The plates were read on a GloMax Discover luminometer (Promega) containing a 450 nm BP filter (donor) and a 600 nm LP filter (acceptor) at a 0.3 s integration time. Raw BRET values were calculated as a ratio of acceptor (600 nm) to donor (450 nm) emissions.