Routing and processing of lactase-phlorizin hydrolase in transfected Caco-2 cells

Human lactase-phlorizin hydrolase (LPH) is a digestive enzyme that is expressed in the small intestinal brush-border membrane, After terminal glycosylation in the Golgi apparatus, the 230-kDa pro-LPH is cleaved into the 160-kDa brush-border LPH beta and the 100-kDa profragment (LPH alpha). Since LPH beta is not transport-competent when it is expressed separately from LPH alpha in COS-1 cells, it was suggested that LPH alpha functions as an intramolecular chaperone, What happens to LPH alpha after cleavage is still unclear, To analyze and localize LPH alpha in polarized epithelial cells, wild type and tagged LPH were stably expressed in Caco-2 cells, In tagged LPH, a vesicular stomatitis virus epitope tag was inserted into the LPH alpha region, Wild type and tagged proteins were processed at similar rates, and both cleaved LPH beta forms were expressed at the apical cell surface, Pro-LPH was recognized by antibodies against LPH, a profragment epitope and the vesicular stomatitis virus tag, LPH alpha alone, however, could not be recovered by these antibodies, Our data suggest that LPH alpha is degraded immediately after cleavage.