An in vitro model of thyroid neoplasia: permanently transfected FRTL-5 cells with thyroglobulin promoter-cholera toxin A1 subunit minigene.

Abstract

Activating mutations of protein Gs alpha that stimulates adenylyl cyclase are present in a subset of thyroid adenomas. Cholera toxin A1 subunit (CT) mimics these mutations via adenosine diphosphate-ribosylation of Gs alpha. To test the role of activated Gs alpha in thyroid neoplasia we developed an in vitro model. With molecular genetic techniques a transgene (TG-CT) in which the thyroglobulin gene (TG) promoter directs expression of CT was made. This transgene was transfected into rat thyroid follicular cells (FRTL-5). Integration of TG-CT transgene and its expression were examined. Polymerase chain reaction of DNA from transfected FRTL-5 cells identified the TG-CT transgene in six cell lines. The TG-CT transfected clones exhibited up to a 65-fold (1.29 +/- 0.37 pmols cyclic adenosine monophosphate (cAMP)/micrograms DNA) increase in cAMP over nontransfected FRTL-5 cells (0.02 +/- 0.001 pmols cAMP/micrograms DNA). Insulin, a known stimulator of the TG promoter, further induced CT gene expression and led to a 209-fold (10.43 +/- 0.10 pmols cAMP/micrograms DNA) increase in cAMP over nontransfected cells (0.05 +/- 0.00 pmols cAMP/microgram DNA). By mimicking a known mutation associated with thyroid neoplasms, these permanently transfected FRTL-5 cell lines will serve as a model to examine the long-term potential neoplastic effects of activated Gs alpha on thyroid follicular cells.