QUANTITATION OF BETA-1 TRIIODOTHYRONINE RECEPTOR MESSENGER-RNA IN HUMAN TISSUES BY COMPETITIVE REVERSE TRANSCRIPTION-POLYMERASE CHAIN-REACTION

Thyroid hormones act by binding to nuclear receptor proteins, the thyr oid hormone receptors (TR) alpha and beta. Data from cell culture and animal studies indicate that TR expression may be regulated to modulat e target organ responsiveness to thyroid hormone. To investigate wheth er such adaptive changes in TR expression occur in humans, we determin ed the mRNA levels of the hTR beta 1 in various thyroid states. Patien ts with overt hypo- or hyperthyroidism were enrolled in the study. Tot al RNA was isolated from peripheral blood mononuclear cells and hTR be ta 1 mRNA levels determined by quantitative competitive reverse transc ription PCR. For comparison, hTR beta 1 mRNA levels were determined in lymphocytes and normal thyroid tissue of euthyroid patients. Human TR beta 1 mRNA levels in lymphocytes were 1.8+/-0.4, 1.9+/-0.5, 1.1+/-0. 4 10(-18) mol/mu g RNA in hypo-, eu- and hyperthyroid patients, respec tively, corresponding to an estimated 0.5 - 2 molecules per cell, Alth ough the mean hTR beta 1 mRNA levels were 40% lower in hyperthyroid th an in euthyroid subjects. this difference did not reach statistical si gnificance. Similar levels of hTR beta 1 mRNA levels were detected in thyroid gland from euthyroid patients. In summary, we developed an ass ay for the quantitative determination of hTR beta 1 mRNA levels in sma ll human tissue samples, containing as little as 50 ng of total RNA. A bsolute hTR beta 1 mRNA levels are very low with an estimated one mole cule of mRNA being present in a mononuclear blood cell or thyrocyte. N o up-regulation of hTR beta 1 was seen in hypothyroid relative to euth yroid patients. However, there is a nonsignificant trend towards a dow n-regulation of hTR beta 1 mRNA levels in hyperthyroid patients.