Lack of adenylate and guanylate cyclases responsiveness to hormones in a spontaneous murine thyroid tumor

Abstract

Animals with tumors were obtained from Dr. ZAJDELA and belong to sublines (XVIInc/Z/E) in which some individuals (TT) developed after 15 months thyroid tumors weighing between 150 and 1200 mg. Hyperplasia affects thyrocytes which do not present a follicular structure. The purpose of our work was to assay the action of various effectors on the adenylate and guanylate cyclase system in vitro. The following results have been obtained: the cyclic-AMP content of tumor tissue is not raised either by TSH or PGE 2. Nevertheless, TSH enhances the phosphatidylinositol phosphate turnover (phospholipid effect) as in normal tissue. This latter observation points at the existence of functional TSH receptors in tumor cells. The study of adenylate cyclase activity of the tumor homogenate shows the presence of this enzyme and its responsiveness to NaF and GppNHp. Unexpectedly, the cyclase is also sensitive to the stimulation by TSH.A tentative interpretation of these facts is that no component of the cyclase is missing, but that they are physically separated. The homogeneization allows the various components to interact productively. A parallel study was devoted to cyclic-GMP. Carbamylcholine fails to increase the cyclic-GMP content of the tumor tissue, whereas it has the described phospholipid effect on phosphatidylinositol. Nevertheless, there is no deficiency in the guanylate cyclase activity, since nitroprusside enhances strongly the cyclic-GMP content of the tumor. To conclude, the murine thyroid tumor presents a genetic alteration that results in the uncoupling of effector binding and catalytic stimulation of adenylate and guanylate cyclase.