Expression of preprosomatostatin in heterologous cells: biosynthesis, posttranslational processing, and secretion of mature somatostatin.

Somatostatin is a 14 amino acid peptide hormone that is synthesized as part of a larger precursor, preprosomatostatin, which comprises about 120 amino acids. The overall organization of the precursor is conserved in many species in that it consists of a signal peptide followed by a proregion of 90-100 amino acids and the mature hormone is located at the carboxyl terminus of the molecule. To understand the role of the propeptide in generating the mature hormone, we have used gene-transfer experiments to introduce angler fish preprosomatostatin into mammalian cells. Here we report the results of transfection of COS-7 cells with an SV40 expression vector containing preprosomatostatin cDNA cloned into the VP-1 late gene. Analysis of the parameters of somatostatin gene expression showed that COS cells synthesized prosomatostatin, which was detected intracellularly; the prosomatostatin, was proteolytically processed to mature somatostatin; and the mature hormone was secreted by the COS cells into the tissue culture medium. Our results suggest that COS cells, which do not normally secrete polypeptide hormones, contain the necessary proteolytic processing enzymes to convert preprosomatostatin to the mature hormone and the cellular apparatus necessary for its secretion.