Costimulation of adenylyl cyclase and phospholipase C by a mutant alpha(1B)-adrenergic receptor transgene promotes malignant transformation of thyroid follicular cells

Proliferation of thyroid follicular cells is controlled by three intracellular cascades [cAMP, inositol 1,4,5-triphosphate (IP3)/Ca2+/diacylglycerol (DAG), and tyrosine kinases] that are activated by distinct extracellular signals and receptors. We had previously generated a transgenic mouse model in which the cAMP cascade was permanently stimulated in thyroid cells by an adenosine A(2a) receptor (Tg-A(2a)R model). In the present work, we have generated a transgenic model characterized by the chronic stimulation of both adenylyl cyclase and phospholipase C in thyroid follicular cells. The bovine thyroglobulin gene promoter was used to direct the expression of a constitutively active mutant of the alpha(1B) adrenergic receptor, which is known to couple to both cascades in transfected cell lines. The expression of the trans gene resulted, as expected, in the activation of phospholipase C and adenylyl cyclase, as demonstrated by the direct measurement of IP3 and cAMP in thyroid tissue. The phenotype resulting from this dual stimulation included growth stimulation, hyperfunction, cell degeneracy attributed to the overproduction of free radicals, and the development of malignant nodules invading the capsule, muscles, and blood vessels. Differentiated metastases were found occasionally in old animals. The development of malignant lesions was more frequent and of earlier onset than in our previous Tg-A(2a)R model, in which only the cAMP cascade was stimulated. These observations demonstrate that the cAMP and IP3/Ca2+/DAG cascades can cooperate in vice toward the development of thyroid follicular cell malignancies.