Independent Down-Regulation of Insulin and Calcitonin Receptors on a Human Tumour Cell Line

Abstract

A human lung cancer cell line (BEN cells) with a calcitonin receptor and calcitonin-responsive adenylate cyclase also possesses an insulin receptor. This has been characterized and found to have properties similar to those of other mammalian cell insulin receptors. A receptor number of 58 000 per cell was calculated from curvilinear Scatchard plots, and dissociation of bound labelled insulin by dilution was facilitated by the addition of unlabelled insulin, consistent with negatively co-operative interactions among binding sites. Preincubation of cells with either calcitonin or insulin led to loss of hormone binding in washed cells. In the case of calcitonin this was associated with loss of adenylate cyclase response. For each hormone the state of down-regulation was characterized by a decrease in receptor number, and for calcitonin there was also a low in sensitivity of adenylate cyclase. Down-regulation to calcitonin was more rapid than that to insulin and in each case recovery had occurred by 16 h after removal of the hormone. Induction of down-regulation was specific, in that preincubation with one hormone did not influence the subsequent binding or response of the other. Such data are consistent with independent modulation of peptide receptors in the same cell.

Identification of key components in the irreversibility of salmon calcitonin binding to calcitonin receptors

“…These results are concordant with earlier observations, which demonstrated that 'irreversibility' of 125 I-sCT binding was independent of the system of assay, occurring in whole cells (Findlay et al 1981, Chao & Forte 1983, membranes (Fischer et al 1981, Nicholson et al 1988b) and solubilised receptor (Nicholson et al 1988a) preparations.…”

“…In virtually all the systems studied, the binding of 125 I-sCT to its receptor has been essentially irreversible. This is true of human or rat tissue membrane preparations (Fischer et al 1981, Nicholson et al 1988b, as well as clonal cell lines of rat or human origin (Findlay et al 1981, Chao & Forte 1983. Poor reversibility is also maintained in solubilised receptor preparations (Nicholson et al 1988a).…”

Downregulation of calcitonin receptor mRNA expression by calcitonin during human osteoclast-like cell differentiation.

“…Downregulation of CT receptors also been reported in mouse calvariae, human carcinoma cell lines, and rat kidney cells (34,(36)(37)(38), and internalization of CTR and necessity of new protein synthesis for new receptor formation has been reported in a human breast cancer cell line (36). However, the "escape phenomenon" cannot be explained solely on receptor internalization, because many other receptors such as the insulin receptor also are internalized (38), and forskolin, an adenylate cyclase activator, induced similar effects in osteoclasts, including the "escape phenomenon" and inhibition of bone resorption (39).…”

Abundant calcitonin receptors in isolated rat osteoclasts. Biochemical and autoradiographic characterization.

“…In other work, using immunocytochemical methods, we have shown that calcitonin treatment of rat osteoclasts is associated with an increase in cy- The present work provides a basis for studying its significance, besides offering a means of studying directly in osteoclasts some particular features of calcitonin action which might be related to its therapeutic use. These include the phenomena of calcitonin-induced receptor loss (43,44), "escape" (45), persistent activation of adenylate cyclase (12, 46), and homologous desensitization (12, 43).…”