title: Sequences required for the transition from monomeric to homodimeric forms of thyroid hormone receptor alpha and v-erbA.
abstract: Thyroid hormone receptor alpha (TRalpha) and the oncoprotein v-erbA (a mutated form of TRalpha incapable of binding T3) bind as heterodimers with retinoid X receptor (RXR) to DNA sequences with different orientations of AGGTCA half sites. v-erbA can also form homodimers, whereas, TRalpha1 homodimerizes poorly. Therefore, in order to obtain a better understanding for the distinct homodimerization properties between TRalpha1 and v-erbA, we created chimeras between these two receptors and tested their abilities to homodimerize on direct and everted repeats (DRs, ERs). We found that the enhanced homodimerization properties of v-erbA compared to TRalpha1 map to isoleucine at position 339 in conjunction with serine at position 351 and alanine at position 358. Our data indicate that the methyl group in isoleucine at position 339 plays an important role in v-erbA homodimerization, particularly on ER 6. Functional studies with I339V+S351P+A358T, a v-erbA mutant unable to homodimerize but still able to heterodimerize with RXR on ERs and DRs, indicate that v-erbA-RXR heterodimers mediate the dominant negative activity of v-erbA on DRs. However, the repressor activity of this mutant is weaker than that of the wild type v-erbA on ERs, suggesting that v-erbA homodimers rather than v-erbA-RXR heterodimers mediate the potent dominant negative activity of v-erbA on ERs.
authors.affiliation: G.V. Montgomery Veterans Administration Medical Center, R&E Building (151), 1500 E. Woodrow Wilson Blvd., Jackson, MS 39216, USA.
authors.forename: Inna
authors.initials: I
authors.lastname: Zubkova
authors.forename: Jose S
authors.initials: JS
authors.lastname: Subauste
mesh_terms: D000595:Amino Acid Sequence / Q000502:physiology; D000818:Animals; D019281:Dimerization; D051379:Mice; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D018774:Oncogene Proteins v-erbA / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017354:Point Mutation; D017433:Protein Structure, Secondary; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000235:genetics; D047488:Retinoid X Receptors; D016415:Sequence Alignment; D037021:Thyroid Hormone Receptors alpha / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D014157:Transcription Factors / Q000378:metabolism; D014162:Transfection
chemical_list: D018774:Oncogene Proteins v-erbA; D018168:Receptors, Retinoic Acid; D011993:Recombinant Fusion Proteins; D047488:Retinoid X Receptors; D037021:Thyroid Hormone Receptors alpha; D014157:Transcription Factors