INTERACTION OF HUMAN BETA-1 THYROID-HORMONE RECEPTOR AND ITS MUTANTS WITH DNA AND RETINOID-X RECEPTOR-BETA T(3) RESPONSE ELEMENT DEPENDENT DOMINANT-NEGATIVE POTENCY

Mutations in the human beta thyroid hormone receptor (h-TRbeta) gene a re associated with the syndrome of generalized resistance to thyroid h ormone. We investigated the interaction of three h-TRbeta1 mutants rep resenting different types of functional impairment (kindreds ED, OK, a nd PV) with different response elements for 3,3',5-triiodothyronine(T3 )and with retinoid X receptor beta (RXPbeta). The mutant receptors sho wed an increased tendency to form homodimers on a palindromic T3-respo nse element (TREpal), a direct repeat (DR + 4), and an inverted palind rome (TRElap). On TRElap, wild type TR binding was decreased by T3, wh ile the mutant receptors showed a variably decreased degree of dissoci ation from TRElap in response to T3. The extent of dissociation was pr oportional to their T3 binding affinities. RXRbeta induced the formati on of h-TRbeta1:RXRbeta heterodimers equally well for mutants and the wild type h-TRbeta1 on these T3 response elements. However, the T3-dep endent increase in heterodimerization with RXRbeta was absent or reduc ed for the mutant TRs. Transient transfection studies indicated that t he dominant negative potency was several-fold more pronounced on the T RElap as compared to TREpal or DR + 4. In CV-1 and HeLa cells, transfe ction of RXRbeta could not reverse the dominant negative action. These results demonstrate that the binding of mutant h-TRs to DNA, as well as their dominant negative potency, are TRE dependent. In addition, co mpetition for DNA binding, rather than for limiting amounts of RXRbeta , is likely to mediate the dominant negative action.