Quantitative analysis of DNA binding affinity and dimerization properties of wild-type and mutant thyroid hormone receptor beta1

Secretory expression of thyroid hormone receptor using transgenic silkworms and its DNA binding activity

Silkworms are economically important insects that have the ability to produce large amounts of silk. They have mass breeding methods and silk glands, which are specialized tissues that secrete silk fibroin and sericin. Thus, the production of recombinant proteins in a transgenic silkworm system is a promising approach. We developed a silkworm, Bombyx mori, as a host expression insect for recombinant proteins and successfully produced different proteins including antibodies, glycoproteins, and membrane receptors. The thyroid hormone receptor (TR) is a regulatory factor for many physiological phenomena. It is a lipophilic protein that has DNA-binding and ligand-binding domains. Based on our previous experiences, it was inferred that the recombinant TR easily formed aggregates and precipitates which is potentially due to an unstructured hinge domain. We applied the silkworm expression system to produce mice TRβ1 that was fused with glutathione S-transferase. Using 160 larvae, the yield of the recombinant GST-TRβ was approximately 4 mg, and the purified GST-TRβ completely retained its physiological activity. Our results indicated that the recombinant TRβ was secreted extracellularly using the silk fibroin signal peptide sequence. Moreover, we found that the expression system of silkworms was applicable to nuclear proteins.

Efficacy and safety of pulsed intravenous methylprednisolone in early active thyroid eye disease

Introduction: The mainstay of therapy for active inflammatory phase of thyroid eye disease (TED) is immunosuppression. Patients in our centre with early active TED are treated with pulsed intravenous methylprednisolone (IVMP). Two different protocols are offered in our centre: High dose (1g/day for 3 days, monthly for 6 months), or EUGOGO protocol (500 mg weekly for six weeks, followed by 250 mg weekly for the next 6 weeks). Methods: A prospective cohort study of patients undergoing the two IVMP protocols was performed from January 2009 to May 2015. Main outcome measures were improvement of Clinical Activity Score (CAS) and International Thyroid Eye Disease (ITEDS) - VISA Inflammatory Index. Results: We had a total of 63 patients. Mean age was 43.1 ± 13.1years, females comprised 49.2% (n = 31), and 31 (49.2%) had a positive smoking history. Following IVMP, 65.0% (n = 41) had good response, 31.7% (n = 20) partial, and 3.3% (n = 2) poor. There were significant differences (p < 0.001) in CAS and ITEDS scores between pre-IVMP and post-IVMP visits, for both protocols. A higher proportion of patients receiving the modified EUGOGO protocol (58.3%) had persistent activity and required additional immunosuppression compared to those who underwent the high dose protocol (33.3%). Mild side effects were experienced by 5 (7.9%) and 3 (4.8%) patients at 3 and 6 months, respectively. There were no severe side effects, cardiovascular events or liver failure. Conclusion: With adequate screening and follow-up, six repeated cycles of high dose pulsed IVMP is an effective treatment for TED and can significantly reduce the morbidity associated with this debilitating condition. None of the 51 patients from the high dose protocol met with any serious side effects.

Rearrangements in Thyroid Hormone Receptor Charge Clusters That StabilizeBound 3,5′,5-Triiodo-L-thyronine and Inhibit HomodimerFormation

In this study, we investigated how thyroid hormone (3,5',5-triiodo-l-thyronine, T3) inhibits binding of thyroid hormone receptor (TR) homodimers, but not TR-retinoid X receptor heterodimers, to thyroid hormone response elements. Specifically we asked why a small subset of TRbeta mutations that arise in resistance to thyroid hormone syndrome inhibit both T3 binding and formation of TRbeta homodimers on thyroid hormone response elements. We reasoned that these mutations may affect structural elements involved in the coupling of T3 binding to inhibition of TR DNA binding activity. Analysis of TR x-ray structures revealed that each of these resistance to thyroid hormone syndrome mutations affects a cluster of charged amino acids with potential for ionic bond formation between oppositely charged partners. Two clusters (1 and 2) are adjacent to the dimer surface at the junction of helices 10 and 11. Targeted mutagenesis of residues in Cluster 1 (Arg338, Lys342, Asp351, and Asp355) and Cluster 2 (Arg429, Arg383, and Glu311) confirmed that the clusters are required for stable T3 binding and for optimal TR homodimer formation on DNA but also revealed that different arrangements of charged residues are needed for these effects. We propose that the charge clusters are homodimer-specific extensions of the dimer surface and further that T3 binding promotes specific rearrangements of these surfaces that simultaneously block homodimer formation on DNA and stabilize the bound hormone. Our data yield insight into the way that T3 regulates TR DNA binding activity and also highlight hitherto unsuspected T3-dependent conformational changes in the receptor ligand binding domain.