The biogenesis and cell-specific expression of cholecystokinin peptides

Cholecystokinin (CCK) is a complex and widespread peptide messenger system. Consequently, it is essential to understand the CCK expression cascade from the gene to the bioactive CCK peptides. This chapter, therefore, describes the structure of the CCK gene, regulatory elements of the promoter, transcription factors, mRNA structure, and the primary translational product, preproCCK. Furthermore, the chapter details the cell-specific posttranslational processing of proCCK to bioactive receptor-bound peptides released from cells as different as enteroendocrine cells, extraintestinal endocrine cells, central and peripheral neurons, cardiac myocytes, male germ cells, immune cells, and tumor cells. Thus, the chapter throws into relief the paradox of a hormonal peptide originally named after a single function but later shown to be expressed in multiple molecular forms in an array of different cell types. Accordingly, CCK peptides are involved in a plethora of mechanisms, of which several may be more important for health than that of the original focus, which is the postprandial emptying of the gallbladder. In support, it is important to remember that the successful species, the rat, does not have a gallbladder but synthesizes abundant CCK in the gut and elsewhere.