REGULATION OF THE CELL-CELL ADHESION PROTEIN, E-CADHERIN, IN DOG AND HUMAN THYROCYTES IN-VITRO

E-cadherin, a cell-cell adhesion protein specifically expressed at the basolateral membrane of thyrocytes, is variably dysregulated in thyroid carcinomas in parallel to the dedifferentiation of the tumors. No data are currently available on the regulation of E-cadherin in messenger RNA (mRNA) expression by physiological stimulators of thyroid proliferation and differentiation. The present study investigated the control of E-cadherin steady state mRNA levels and protein expression in primary cultures of dog and human thyrocytes under the influence of physiological regulators of thyroid differentiation and dedifferentiation using Northern blot analysis and immunohistochemistry. Following dedifferentiation by epidermal growth factor and fetal calf serum in primary cultures of dog and human thyrocytes, E-cadherin steady state mRNA expression was low but easily detectable. Stimulation of the cells by TSH (1 mU/ml) or forskolin (10 mu M) induced an increase in E-cadherin mRNA levels with a maximal effect after 20 h. An up-regulation of E-cadherin protein levels are also observed by immunostaining with anti-E-cadherin antibodies. A concentration-response relation determined for TSH stimulation (10 mu U/ml to 10 mU/ml) led to a concentration-dependent stimulation of E-cadherin mRNA levels and a parallel increase in protein expression with a minimal effective concentration of 10-30 mu U/ml. These effects depend on protein synthesis as they are completely blocked by the presence of 10 mu g/ml cycloheximide. Treatment with EGF did not markedly alter E-cadherin mRNA expression, whereas removal of insulin from the medium slightly decreased E-cadherin mRNA and protein levels. There is, therefore, a qualitative parallelism between the effect of the various factors on E-cadherin protein and mRNA levels. These results suggest that the cell-cell adhesion protein E-cadherin is under the control of the TSH-cAMP-dependent pathway and may play an important physiological role on the action of this pathway in proliferation and differentiation.