somatostatin-28 and Thyroid-Neoplasms

Thirty-three cases of histologically proven calcitonin-positive medullary thyroid carcinoma were studied immunocytochemically for the occurrence of prosomatostatin-related peptides. Positive cells, identified with a panel of antisera raised against four different regions of the prosomatostatin molecule, were found in 100% of the tumors. Most but not all somatostatin-positive cells were also immunoreactive for calcitonin. Notably, seven patients harboring somatostatin-rich tumors revealed a more favorable clinical course. The results (1) indicate that somatostatin production is a universal concomitant of thyroid medullary carcinoma, (2) suggest that these cells are likely to produce a somatostatin precursor molecule similar to mammalian prosomatostatin, and (3) imply that somatostatin-reactive cells may have as yet unknown roles in these tumors, possibly in the realm of paracrine and autocrine regulation of cell growth.

Topics: Adolescent; Adult; Calcitonin; Carcinoma; Female; Gene Expression; Humans; Immunohistochemistry; Male; Middle Aged; Protein Precursors; Somatostatin; Thyroid Neoplasms

We have established a system, the CA77 rat medullary thyroid carcinoma cell line, for studying the products of somatostatin (SS) gene expression. Based on the amino acid sequence of proSS, we developed a RIA for the amino terminus of proSS (proSS-NTP) and demonstrated in acidic cell extracts two major proSS-NTP-containing species of 8000 and 4000 daltons. Studies were then performed on species secreted into culture medium. Serial dilutions of culture medium showed tracer displacement curves parallel to serial dilutions of synthetic proSS-NTP standard. Analysis by gel filtration chromatography of 24-h culture medium showed the major proSS-NTP-containing species to have an estimated mol wt of 8000 daltons. No 4000-dalton species was observed. The acute effects of calcium and glucagon, known secretagogues of SS, on secretion of immunoreactive (i) proSS-NTP were investigated in 3-h experiments. Basal (0.5 mM calcium) secretory rates (mean +/- SE) of iproSS-NTP and iSS were 1.29 +/- 0.36 and 7.38 +/- 1.51 ng/mg acid-extractable protein, respectively. High calcium (3 mM) stimulated iproSS-NTP and iSS secretion 302 +/- 100% and 363 +/- 105%, respectively. High calcium plus 10(-6) M glucagon also stimulated secretion of iproSS-NTP and iSS in a coordinate fashion. Analyses by gel filtration chromatography of 3-h culture medium revealed that high calcium markedly increased the 8000-dalton proSS-NTP-containing species. No 4000-dalton species was observed. The absence of 4000-dalton proSS-NTP species in 24-h culture medium, the lack of degradation of 4000-dalton proSS-NTP (recovered from CA77 cell extracts) added to tissue culture medium, and the selective secretion of the 8000-dalton proSS-NTP species under both basal and stimulated conditions coordinate with the secretion of SS indicate that the 4000-dalton proSS-NTP-containing species is not secreted.

Topics: Animals; Calcium; Carcinoma; Cell Line; Chromatography, Gel; Glucagon; Molecular Weight; Peptide Fragments; Protein Precursors; Radioimmunoassay; Rats; Somatostatin; Thyroid Neoplasms

We identified a system, the TT human medullary thyroid carcinoma cell line which contained 74.5 +/- 26.0 ng (mean +/- SD) immunoreactive SRIH/mg protein, for studying the products of SRIH gene expression. The close homology between man and rat for the entire proSRIH and complete homology for a portion of the amino terminus (proSRIH-NTP) permitted the application of a RIA directed toward the amino terminus of rat proSRIH. Immunohistochemical studies of the human TT cell line showed that SRIH and proSRIH-NTP immunoreactivities were present in the same cells. RIA of gel filtration fractions showed that the major cellular proSRIH-NTP-containing species lack SRIH and had an apparent mol wt of 8000. A 10,000-dalton SRIH-containing species coeluting with proSRIH-NTP immunoreactivity, putative proSRIH, also was found. Similar species were found in culture medium. The major cellular and secreted form of SRIH immunoreactivity had a mol wt of 1600 (SRIH). High pressure liquid chromatography revealed that both cellular and secreted 8000-dalton proSRIH-NTP-containing material consisted of a major and several minor species. None of the species contained SRIH. The precise structure of these proSRIH-NTP-containing species and their physiological roles are not known. The fact that proSRIH-NTP-containing species are secreted suggests that they may be functional. Since the processing of proSRIH and consequently the final products appear to be tissue specific, alterations in the relative presence of different forms might reflect specific pathological processes.

Topics: Carcinoma; Cell Line; Chromatography, Gel; Chromatography, High Pressure Liquid; Histocytochemistry; Humans; Immunoenzyme Techniques; Peptides; Protein Precursors; Radioimmunoassay; Somatostatin; Thyroid Neoplasms

Rat prosomatostatin was isolated from a somatostatin-producing cell line and was partially microsequenced. This indicated the amino terminal structure of cellular prosomatostatin and implied a 92-amino acid sequence for the somatostatin precursor. Based on the structure for cellular prosomatostatin, a peptide was synthesized and used to develop a radioimmunoassay directed toward the amino terminal portion of prosomatostatin. This assay has revealed two peptides containing the amino-terminal portion of prosomatostatin in a somatostatin-secreting CA-77 rat medullary thyroid carcinoma cell line. These two peptides - MW 4000 and 8000 daltons - lack somatostatin immunoreactivity. Thus, processing of prosomatostatin occurs both at the amino and carboxyl regions. These results open the way for elucidation of the structure, function and metabolism of non-somatostatin peptides derived from the amino terminus of prosomatostatin.

Topics: Amino Acid Sequence; Animals; Cell Line; Chromatography, High Pressure Liquid; Molecular Weight; Peptide Fragments; Protein Precursors; Radioimmunoassay; Rats; Somatostatin; Thyroid Neoplasms