Calcitonin-responsive adenylate cyclase in a calcitonin-producing human cancer cell line

A calcitonin-responsive adenylate cyclase has been found in a cell line of a poorly differentiated bronchial carcinoma (BEN cells). The cells have previously been shown to secrete an immunoreactive form of calcitonin in culture. Salmon calcitonin (SCT), porcine calcitonin (PCT) and human calcitonin (CT-M) all stimulated adenylate cyclase activity in particulate preparations. CT-M sulphoxide had little effect. The concentrations of the calcitonins required for half the maximum activation of adenylate cyclase were 6-8, 18 and 90 nm respectively. SCT (30pm) and CT-M (60 pm) increased the intracellular concentration of cyclic AMP from 11-2+/-0-2 (s.e.) to 18-2+/-0-2 and 16-7+/-0-2 respectively over a 2-5-min period. SCT (labelled with 125I) bound to particulate preparations of Ben cells, and competition for binding occurred with unlabelled SCT and CT-M. The concentration of SCT required for half the maximum inhibition of [125I]SCT binding was 11 nm. CT-M sulphoxide inhibited only at high concentration (3 micron). The characteristics of the adenylate cyclase response to SCT did not change over the period between cell adhesion (after subculture) and confluence. However, pre-incubation of cells for 4 h with SCT (150 nm) abolished the subsequent adenylate cyclase response of particulate preparations to further hormone. The practical difficulties encountered in purifying and quantifying the large-mol.-wt. form of CT-M secreted by BEN cells has precluded direct investigation of the potential relationship between hormone secretion and the occurrence of the calcitonin receptor. This relationship is discussed in terms of its possible biological significance.

Lung tumours and ACTH production

ACTH levels measured by N- and C-terminal immunoassays and cytochemical bioassay, were measured in fourteen lung tumours not associated with the ectopic ACTH syndrome and in macroscopically normal lung tissue taken from the same patients at thoracotomy. Significant concentrations of immunocative (greater than 3 ng/g wet weight) and bioactive (greater than 0.2 ng/g wet weight) ACTH were found in all the carcinoid and oat cell tumours (n=9), a combined tumour (poorly differentiated adenocarcinoma with large cell carcinoid elements), and a poorly differentiated squamous cell tumour. All the carcinoid tumours contained more C- than N-terminal ACTH immunoactivity. The squamous cell tumours (n=2), anaplastic tumours (n=2) and adenocarcinoma contained insignificant ACTH levels. There was a good correlation between the ACTH levels and the presence of secretory granules in the tumours examined ultrastructually. All the macroscopically normal samples of lung tissue contained immuno and bioactive ACTH-like material, the levels of which correlated well with ACTH levels in the tumour tissue. It is suggested that all lung tumours of carcinoid or oat cell type synthesize ACTH-like materials although clinical evidence of the ectopic ACTH syndrome may be absent. The presence of ACTH-like materials in non-tumorous lung tissue in patients with lung cancer may indicate a low level of ACTH production throughout the lung or sequestration of ACTH containing granules secreted by the tumour.

Hormone receptors and cyclic nucleotide metabolism in cancer cells

The possibility of a relationship between cyclic AMP formation and metabolic processes in tumours has been investigated. Changes in basal activity and hormone-responsiveness of adenylate cyclase were demonstrated in plasma membranes and intact cells from pre-cancerous liver of rats fed a diet containing the carcinogen 3'-methyl-4-dimethylaminoazobenzene. Basal adenylate cyclase activity in hyperplastic parathyroid gland membranes was 200% higher than that in parathyroid adenoma membranes, corresponding with their relative rates of parathyroid hormone secretion in vitro. Membrane adenylate cyclase activity in hypernephromas was consistently 100--300% higher than in adjacent human renal cortex. Furthermore the adenylate cyclase activity of the tumour membranes was not influenced by a wide range of hormones which were effective stimulants in 'normal' renal cortex membranes. Conversion of 25-hydroxycholecalciferol to 1,25-dihydrocholecalciferol could not be demonstrated in either hypernephroma or adjacent renal cortical tissue. However, three of the four hypernephromas tested secreted a bone-resorbing factor. Cyclic AMP formation was increased by salmon, human and porcine calcitonins in both plasma membranes and intact cells from a poorly differentiated epidermoid cell carcinoma which was itself secreting calcitonin in culture. This phenomenon might be related to a feedback regulation of calcitonin production in this cell line. The observations are consistent with the concept of a relationship between cyclic AMP formation and certain metabolic functions (e.g. hormone production) in tumour cells.

Immunoreactive calcitonin production by human lung carcinoma cells in culture

Monolayer cultures have been established from a poorly differentiated carcinoma of the lung. Homogeneous cell growth and morphology have been maintained for over 18 months through more than 80 subculture passages, and the cells have been found to produce both immunoreactive calcitonin and an immunoreactive carcinoembryonic antigen-like material.