PREDOMINANT BASOLATERAL PROTEOLYTIC PROCESSING OF PROSOMATOSTATIN INTO SOMATOSTATIN-28 IN POLARIZED LLC-PK1 CELLS

Polarized epithelial cells secrete specific proteins through their api cal or basolateral membrane. In the present study, we have expressed t he human prosomatostatin cDNA in the pig kidney epithelial cell line ( LLC-PK1) and monitored the processing and release of the somatostatin- related peptides. Analysis by high-performance liquid chromatography a nd radioimmunoassay of the somatostatin-related peptides synthesized b y the transfected cells showed that the LLC-PK1 cells released prosoma tostatin and somatostatin-28 (S-28) in the culture medium. Furthermore , when the cells were polarized, we observed release of prosomatostati n from both membrane domains (apical and basolateral), while liberatio n of S-28 was mostly from the basolateral side. This observation sugge sts that, in these cells, the proprotein convertase(s) responsible for prosomatostatin processing is(are) associated with the basolateral se cretory pathway.