Expression of porcine pro-opiomelanocortin cDNA in heterologous monkey kidney cells. Biosynthesis and secretion of the prohormone without processing.

Pro-opiomelanocortin is the common precursor to several pituitary hormones. These include alpha-melanotropic hormone, adrenocorticotropic hormone, beta-lipotropic hormone, and beta-endorphin. The porcine pro-opiomelanocortin cDNA was inserted downstream from the early promoter of a SV40-derived expression vector and transfected into the monkey kidney COS-1 cells. Transient expression of the pro-opiomelanocortin cDNA was observed between 48 and 70 h after transfection. Analysis of pro-opiomelanocortin-related material in COS-1 cell extracts and culture medium revealed that these cells synthesize and secrete constitutively pro-opiomelanocortin without further processing into its mature hormones. Our results suggest that COS-1 cells do not contain the necessary enzymatic machinery to process complex precursors such as pro-opiomelanocortin.