PRSS21 and neoplasm: To confirm that testisin anchored on a tumor cell surface can process PrAg-PCIS to an activated form, HEK293T cells stably expressing full-length human testisin (HEK/GPI-testisin) or vector alone (HEK/vector) (Supplementary Figure S2) were exposed to PrAg-PCIS or PrAg-WT for various times up to 6 hours and assayed for the appearance of the 63-kDa activation product.