Accumulation of nonamidated preprogastrin and preprocholecystokinin products in porcine pituitary corticotrophs. Evidence of post-translational control of cell differentiation.

Using gel and ion-exchange chromatography monitored by radioimmunoassays specific for sequences essential in the processing of preprogastrin and preprocholecystokinin, the products were characterized in extracts of porcine pituitary lobes before and after incubation with trypsin, carboxypeptidase B, and arylsulfatase. The intermediate and neural lobes contained only fully activated (i.e. alpha-amidated) preprogastrin products (component I, gastrin-34, and gastrin-17). In contrast, the anterior lobe contained, in addition to traces of alpha-amidated gastrin (2 pmol/g), hundredfold higher amounts of a nonamidated progastrin (189 pmol/g; Mr approximately 7000) and two nonamidated procholecystokinin fragments (75 pmol/g; Mr approximately 7000 and 5000). These results show that hormone genes, in spite of translation of their mRNA, are not necessarily expressed in functional peptides in cells outside the principal production regions. Hence, the study indicates that differentiation of endocrine cells may be controlled at the post-translational level.