Comparison of ACTH and ACTH precursor peptides secreted by human pituitary and lung tumour cells in vitro

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Abstract
The molecular forms of ACTH secreted by established human small cell lung cancer (SCLC) cells and primary cultures derived from a bronchial carcinoid tumour, a pituitary adenoma and hyperplastic pituitary tissue have been characterized by Sephadex G-75 chromatography and quantified with two novel immunoradiometric assays for ACTH and ACTH precursor peptides. Pro-opiomelanocortin (POMC; Mr 31 000) and pro-ACTH (Mr 22 000) were secreted by all cell types. No smaller peptides were identified in the culture media from SCLC and bronchial carcinoid cells, implying a deficiency in the enzymes and/or intracellular organelles required for extensive POMC processing. A more heterogeneous profile of ACTH-containing peptides was produced by cells of pituitary origin, indicating more extensive proteolytic processing of POMC. However, the major peptide secreted by cells from a large aggressive pituitary adenoma was unprocessed POMC (Mr 31 000). These results suggest that both lung and pituitary cells in vitro retain their in-vivo pattern of POMC processing and provide valuable models in which to study the regulation of ACTH synthesis and secretion. Journal of Endocrinology (1990) 125, 147–152