ECTOPIC CORTICOTROPIN-RELEASING HORMONE PRODUCED BY A TRANSFECTED CELL-LINE CHRONICALLY ACTIVATES THE PITUITARY-ADRENAL AXIS IN TRANSKARYOTIC RATS

Hypothalamic CRH is the primary positive regulatory factor of the pitu itary-adrenal axis. The purpose of our study was to analyze the chroni c effects of CRH on the production and secretion of POMC peptides from both the anterior lobe (AL) and neurointermediate lobe (NIL) of the p ituitary by mimicking the syndrome of ectopic CRH secretion from neuro endocrine tumors. We first generated stably transfected W2 medullary t hyroid carcinoma cell lines with a rat CRH expression vector under the transcriptional control of a cytomegalovirus gene promoter. These cel l lines constitutively expressed the foreign gene, accurately processe d the encoded prepro-CRH, and secreted biologically active CRH with an estimated potency equivalent to that of synthetic CRH-(1-41)NH2. The cell line designated W2CRH-7 was implanted sc in the syngeneic rat str ain WAG/Rij and produced tumors that abundantly secreted CRH into the peripheral circulation. Four weeks postimplantation, W2CRH-7, but not wild-type W2, cells caused significant increases in the AL content of beta-endorphin-like immunoreactivity comparable to that caused by adre nalectomy (ADX). Plasma ACTH and serum beta-endorphin-like immunoreact ivity were increased to a greater extent by ADX than by W2CRH-7 cell i mplantation. The NIL of both male and female rats showed either no cha nge or a tendency to decreased beta-endorphin concentrations with no c hange in the acetylation or carboxy-shortening profiles judged by cati on exchange chromatography in response to the ectopic CRH treatment. R ats of both sexes maintained a profound activation of the pituitary ad renal axisi up to 16 weeks postimplantation, with normalized adrenal g land weights 5 times that of controls. The chronic secretion of CRH by W2CRH-7 cells resulted in a complete cessation of body growth in all rats up to the maximum time tested of 16 weeks. The lack of growth was partly ameliorated by concomitant ADX, suggesting an important role f or adrenal glucocorticoids in these effects. We conclude that 1) the t ransplantable W2CRH-7 cell line provides a highly effective and reprod ucible means of sustained CRH treatment that mimics the syndrome of ec topic CRH expression by neuroendocrine tumors; 2) AL corticotrophs res pond to chronic CRH by a sustained production and secretion of POMC pe ptides, leading to a marked adrenal cortical hyperplasia, with no evid ence of biologically significant desensitization; 3) chronic CRH tends to decrease the NIL content of beta-endorphin, with remarkably little effect on posttranslational processing; and 4) the syndrome of chroni c ectopic CRH in WAG/Rij rats includes a cessation of body growth at l east partly due to products of the adrenal glands.