TUMOR CELL SYNTHESIS AND SECRETION OF PEPTIDE HORMONES

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The objective of this research project is to elucidate in tumor cells of endocrine and nonendocrine origin and in their normal precursor cells the molecular events by which the synthesis, storage, and secretion of polypeptide hormones are regulated. It is concerned with the transcription, processing, and structure of the mRNAs encoding the peptides and the translation, posttranslational processing, secretion, and structure of the peptide products themselves. It is directed primarily at ACTH and the other proopiomelanocortin (POMC) peptides. Because nonpituitary tumor secretion of POMC peptides is often associated with that of calcitonin (CT), arginine vasopressin (AVP), and gastrin-releasing peptide (GRP) and because corticotropin-releasing hormone (CRH) may be involved in regulating ectopic as well as eutopic POMC peptide secretion and may be ectopically secreted itself, tumor secretion of these polypeptide hormones will also be investigated. Studies on the regulation of POMC peptide secretion in the dog with Cushing's disease, a common animal model of a rare human condition, will be completed. The structure of the POMC mRNA from DMS 79 human small cell lung carcinoma cell will be elucidated by sequence determination and/or S1 nuclease or RNase mapping of its unusual 5' extension. The fundamental question whether tumors secrete these hormones ectopically or merely inappropriately will be answered by measuring immunoreactive POMC peptides and Hybridizable POMC mRNA in normal rat and human tissues, and the cells responsible for their synthesis will be identified by immunocytochemical and in situ mRNA hybridization studies on tissue sections. Adult Syrian golden hamsters to which a systemic carcinogen, diethylnitrosamine (DEN), is administered will be studied to determine if the neuroendocrine cells comprising neuroepithelial bodies (NEBs) in bronchial epithelium, when stimulated to hyperplasia and eventually neoplasia by DEN, merely produce inappropriate quantities of their normal product, CT, or begin to produce ectopically POMC peptides, AVP or GRP, three of the most common peptides produced by lung cancers. The results will provide strong evidence for or against derepression of hormonal genes not expressed by the normal cell or origin. Regulation of POMC secretion in normal rat adrenal medullary cells and PC12 rat adrenal pheochromocytoma cells will be examined in a dispersed cell perifusion column system. Both agonists and antagonists and their intracellular signal transduction pathways will be explored. The perfusion system will also be used to test the hypothesis that the relative resistance to glucocorticoid negative feedback in POMC-secreting human pituitary microadenomas causing Cushing's disease is simply a function of cell number. The results of these studies will provide new insights into the phenomenon of peptide hormone synthesis and secretion by tumor cells.