TISSUE-SPECIFIC AND SUBUNIT-SPECIFIC REGULATION OF G-PROTEIN EXPRESSION BY HYPOTHYROIDISM AND HYPERTHYROIDISM

Thyroid hormone status has profound effects on signal transduction in various tissues throughout the body. Therefore, we quantified the sign al transducing G-proteins in the rat heart, cerebral cortex, vas defer ens and liver by immunoblotting and pertussis toxin labeling in respon se to chemically induced hypothyroidism (treatment with propylthiourac il) and hyperthyroidism (treatment with triiodothyronine). Levels of t he pertussis toxin (PTX) substrates G(ialpha) and G(oalpha) in the hea rt and vas deferens were inversely correlated with thyroid hormone lev els, i.e. G(ialpha) and G(oalpha) were decreased or unchanged in hyper thyroid rats and increased in hypothyroid rats compared to control ani mals. The cerebral cortex and liver expression of PTX substrates G(ial pha) and G(oalpha) was not affected by changes in thyroid hormone. Reg ulation of G(salpha) protein was more complex in that G(salpha) was el evated in the hearts from both hypothyroid and hyperthyroid rats compa red to control rats, while G(salpha) was unaffected in the other tissu es tested. Expression of G-protein beta-subunits was not affected by t hyroid status in the heart, liver, or cerebral cortex. Our results sug gest that tissue- and G-protein-specific factors are involved in the r egulation of G-protein subunits by thyroid hormone. Moreover, cardiac expression of G(salpha) is upregulated by increases or decreases in th e normal level of thyroid hormone.