corticotropin-like-intermediate-lobe-peptide and Adenoma

Many peptides contribute to the heterogeneity of immunoreactive adrenocorticotropin (ACTH) in man. The use of a radioimmunoassay (RIA) specifically directed against the C-terminal end of ACTH allowed us to study precisely the following four peptides: ACTH itself, corticotropin-like intermediary lobe peptide (CLIP) or ACTH (18-39) and their phosphorylated forms on Ser31. We have set up a high-performance liquid chromatography system that separates these four molecules in a single run, to establish their relative distributions in tumors responsible for Cushing's disease or for the ectopic ACTH syndrome, and to evaluate the possible interference of phospho-Ser31 on various RIA or immunoradiometric assay (IRMA) recognition systems for ACTH. In this system, alkaline phosphatase treatment shifted the retention time of the phosphorylated peptides to that of their non-phosphorylated counterparts. In three tumors responsible for the ectopic ACTH syndrome, CLIP peptides were predominant in two and phosphorylated molecules represented between 22% and 50% of immunoreactive materials. In five pituitary tumors responsible for Cushing's disease, ACTH peptides were predominant and the phosphorylated molecules varied between 35% and 75% in four of them. In the same tumor the ratios of phosphorylated to non-phosphorylated CLIP or ACTH were identical. The presence of phospho-Ser31 did not affect the recognition ability of two mid-ACTH and two C-terminal ACTH RIAs, nor of the ACTH IRMA (Allegro, Nichols).

Topics: Adenoma; Adrenal Gland Neoplasms; Adrenocorticotropic Hormone; Chromatography, High Pressure Liquid; Corticotropin-Like Intermediate Lobe Peptide; Humans; Immunoradiometric Assay; Peptide Fragments; Pheochromocytoma; Phosphorylation; Pituitary Neoplasms; Radioimmunoassay

In order to evaluate which of human (h) corticotrophin-like intermediary lobe peptide (CLIP) or h beta-melanocyte stimulating hormone5-22 (h beta MSH5-22) was the better marker of alternate pro-opiomelanocortin (POMC) processing, both peptides were simultaneously sought in the same tissue extracts from a normal human pituitary, six corticotrophic adenomas, and four non-pituitary tumours responsible for an ectopic ACTH syndrome. Human CLIP was detected using a combination of gel exclusion chromatography and two different radioimmunoassays (RIAs): a mid-ACTH RIA which recognized ACTH but not CLIP, and a COOH-ACTH RIA which recognized both molecules. Human beta MSH5-22 had been measured previously. Neither hCLIP nor h beta MSH5-22 were detected in the normal or tumoural pituitaries. The four non-pituitary tumours, in contrast, contained both peptides; the hCLIP and h beta MSH5-22 ratios (CLIP/CLIP + ACTH and h beta MSH5-22/h beta MSH5-22 + h gamma LPH) ranged from 40 to 94% and from 24 to 46%, respectively. In a given tissue the hCLIP ratio was always higher than the h beta MSH5-22 ratio. hCLIP is therefore the better marker of alternate POMC processing.

Topics: ACTH Syndrome, Ectopic; Adenoma; Adrenocorticotropic Hormone; Biomarkers, Tumor; Bronchial Neoplasms; Carcinoid Tumor; Chromatography, Gel; Corticotropin-Like Intermediate Lobe Peptide; Humans; Melanocyte-Stimulating Hormones; Paraneoplastic Endocrine Syndromes; Peptide Fragments; Pituitary Neoplasms; Pro-Opiomelanocortin; Radioimmunoassay; Thymus Neoplasms