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 thyro id carcinomas in parallel to the dedifferentiation of the tumors. No d ata are currently available on the regulation of E-cadherin in messeng er RNA (mRNA) expression by physiological stimulators of thyroid proli feration and differentiation. The present study investigated the contr ol of E-cadherin steady state mRNA levels and protein expression in pr imary cultures of dog and human thyrocytes under the influence of phys iological regulators of thyroid differentiation and dedifferentiation using Northern blot analysis and immunohistochemistry. Following dedif ferentiation by epidermal growth factor and fetal calf serum in primar y cultures of dog and human thyrocytes, E-cadherin steady state mRNA e xpression was low but easily detectable. Stimulation of the cells by T SH (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-ca dherin 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-depend ent stimulation of E-cadherin mRNA levels and a parallel increase in p rotein 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 EG F did not markedly alter E-cadherin mRNA expression, whereas removal o f insulin from the medium slightly decreased E-cadherin mRNA and prote in levels. There is, therefore, a qualitative parallelism between the effect of the various factors on E-cadherin protein and mRNA levels. T hese results suggest that the cell-cell adhesion protein E-cadherin is under the control of the TSH-cAMP-dependent pathway and may play an i mportant physiological role on the action of this pathway in prolifera tion and differentiation.