PROHORMONE CONVERTASE-1 IS NECESSARY FOR THE FORMATION OF CHOLECYSTOKININ-8 IN RIN5F AND STC-1 CELLS

Several immortalized cell lines serve as models for procholecystokinin (pro-CCK) processing, Rin5F cells, derived from a rat insulinoma, and STC-1 cells, derived from a murine intestinal tumor, process pro-CCK mainly to amidated CCK 8, Both also make significant quantities of ami dated CCK 22, a slightly larger form found in the gut, Many modificati ons are necessary during pro-CCK processing including cleavages perfor med by endoproteases, the identities of which are unknown, A candidate endoprotease is prohormone convertase 1 (PC1) also known as PC3, a Ca 2+-dependent serine endoprotease of the subtilisin family, Constitutiv e expression of antisense PC1 message in stably transfected Rin5F cell s resulted in a significant reduction of the cellular content of CCK 8 as measured by radioimmunoassay, Several affected cell lines displaye d about 80% reduction in CCK content in early passages after transfect ion. Expression of antisense PC1 message in these cell lines resulted in a selective depletion of CCK 8 and a comparative sparing of CCK 22. The induction of antisense PC1 message within a single subclone of Ri n5F cells using the Lac Switch system also resulted in a significant i nhibition of CCK content, Expression of antisense PC1 message in a sta bly transfected STC-1 cell line also resulted in a decrease in CCK con tent and in PC1 protein expression, and the specific depletion of CCK 8 with comparative sparing of CCK 22, These observations support the h ypothesis that PC1 is necessary for pro-CCK processing in Rin5F and ST C-1 cells and suggests a role for PC1 endoprotease in the biosynthesis of CCK 8 in vivo.