FURIN and colon carcinoma: We used Vero cells, an easily transfectable cell line frequently used in the field, A549 cells, a human adenocarcinoma alveolar basal epithelial cell line, to better understand S in a more relevant cell model, cath L-mouse embryonic fibroblast (MEF), a previously generated cath L knockout cell line used to understand the contribution of cath L to S processing, WT MEFs, as a control to the cath L-line, and LoVo cells, a human colon carcinoma line that does not express functional furin to allow for analysis of the role of furin.