Coregulator-related diseases

Thyroid hormone resistance syndrome caused by heterozygous A317T mutation in thyroid hormone receptor β gene: Report of one Chinese pedigree and review of the literature

BACKGROUND

Thyroid hormone resistance syndrome (THRS) is a rare disorder with increased concentrations of free thyroxine (FT4) and triiodothyronine (FT3), but normal or slightly increased thyroid-stimulating hormone (TSH). The mutations in the thyroid hormone receptor β (THRβ) gene are thought to be the main pathogenesis.

OBJECTIVES

The aims of this study were to present 1 pedigree of Chinese THRS, summarize their clinical characteristics, and analyze the gene mutation.

METHODS

The clinical characteristics and thyroid function of the proband and his family members were collected. Gene mutations were analyzed by DNA sequencing.

RESULTS

The proband and his mother exhibited symptoms of hyperthyroidism, such as palpitations, heat intolerance, and perspiration. The mother also had atrial fibrillation. The rest of the kindred did not display clinical manifestations of hyper- or hypothyroidism. DNA sequencing revealed a heterozygous G>A missense mutation at position 949 in Exon 9 of THRβ both in the patient and his mother, which led to the transition from alanine to threonine at position 317 of THRβ protein (A317T), whereas the rest of the kindred did not share this mutation. The proband and his mother were diagnosed with pituitary resistance to thyroid hormone. Oral administration of methimazole was stopped and β-receptor blockers were administrated.

CONCLUSIONS

We present 1 pedigree of THRS with heterozygous A317T mutation in THRβ gene in the proband and his mother, which is the first reported mutation in Chinese and provides a comprehensive review of available literature.

Recovering protein-protein and domain-domain interactions from aggregation of IP-MS proteomics of coregulator complexes

Coregulator proteins (CoRegs) are part of multi-protein complexes that transiently assemble with transcription factors and chromatin modifiers to regulate gene expression. In this study we analyzed data from 3,290 immuno-precipitations (IP) followed by mass spectrometry (MS) applied to human cell lines aimed at identifying CoRegs complexes. Using the semi-quantitative spectral counts, we scored binary protein-protein and domain-domain associations with several equations. Unlike previous applications, our methods scored prey-prey protein-protein interactions regardless of the baits used. We also predicted domain-domain interactions underlying predicted protein-protein interactions. The quality of predicted protein-protein and domain-domain interactions was evaluated using known binary interactions from the literature, whereas one protein-protein interaction, between STRN and CTTNBP2NL, was validated experimentally; and one domain-domain interaction, between the HEAT domain of PPP2R1A and the Pkinase domain of STK25, was validated using molecular docking simulations. The scoring schemes presented here recovered known, and predicted many new, complexes, protein-protein, and domain-domain interactions. The networks that resulted from the predictions are provided as a web-based interactive application at http://maayanlab.net/HT-IP-MS-2-PPI-DDI/.

Abnormal urinary steroid profiles in four hypertensive obese children

BACKGROUND

There is a poorly understood association between obesity and hypertension. We demonstrated abnormalities of adrenal androgen and cortisol metabolites in four hypertensive obese children.

PATIENTS

Four males (aged 10 to 15 years) were evaluated for systolic blood pressures consistently above the 99.6th percentile. All were overweight with BMI ranging from 27-35. Clinical examinations, renal ultrasound and DMSA scans were normal. Plasma electrolytes, renin, aldosterone, cortisol, testosterone, ACTH and TSH were normal. 24-Hour urinary steroid profiles showed a generalised excess of adrenal androgen and cortisol metabolites in all cases. Relevant recognised disorders of adrenal androgen and cortisol metabolism were excluded.

CONCLUSION

There is no clinical condition explaining these abnormal urinary steroid profiles. These results support previous findings and provide new data on abnormal urinary adrenal androgen excretion in obese hypertensive patients. Further studies may determine the relationship between obesity, hypertension and the observed abnormalities of urinary steroid excretion.

Importance of steroid receptor coactivators in the modulation of steroid action on brain and behavior

Steroid receptors such as estrogen and androgen receptors are nuclear receptors involved in the transcriptional regulation of a large number of target genes. Steroid-dependent protein expression in the brain controls a large array of biological processes including spatial cognition, copulatory behavior and neuroprotection. The discovery of a competition, or squelching, between two different nuclear receptors introduced the notion that common cofactors may be involved in the modulation of transcriptional activity of nuclear receptors. These cofactors or coregulatory proteins are functionally divided into coactivators and corepressors and are involved in chromatin remodeling and stabilization of the general transcription machinery. Although a large amount of information has been collected about the in vitro function of these coregulatory proteins, relatively little is known regarding their physiological role in vivo, particularly in the brain. Our laboratory and others have demonstrated the importance of SRC-1 in the differentiation and activation of steroid-dependent sexual behaviors and the related neural genes. For example, we report that the inhibition of SRC-1 expression blocks the activating effects of exogenous testosterone on male sexual behaviors and increases the volume of the median preoptic area. Other coactivators are likely to be involved in the modulation in vivo of steroid receptor activity and it seems that the presence of a precise subset of coactivators could help define the phenotype of the cell by modulating a specific downstream pathway after steroid receptor activation. The very large number of coactivators and their association into preformed complexes potentially allows the determination of hundreds of different phenotypes. The study of the expression of the coactivator and their function in vivo is required to fully understand steroid action and specificity in the brain.

Modification of androgen receptor function by IGF-1 signaling implications in the mechanism of refractory prostate carcinoma

The androgen-androgen receptor (AR) system plays important roles in a variety of biological processes, including prostate cancer (PC) development and progression. Insulin and Insulin-like growth factor-1 (IGF-1) signaling negatively regulate a member of the forkhead box-containing protein O subfamily (FoxO), Foxo-1, and associated biological functions. IGF-1 can potentiate androgen signaling through AR activation. Foxo-1, phosphorylated and inactivated by phosphatidylinositol-3-kinase (PI3K)/Akt kinase induced by IGF-1 or insulin, suppresses ligand-mediated AR transactivation. Foxo-1 reduces expression of androgen-induced AR target genes and suppresses in vitro growth of PC cells. These inhibitory effects of Foxo-1 are attenuated by IGF-1, but enhanced when it was rendered Akt-non-phosphorylatable. Foxo-1 directly interacts with the C-terminus of AR in a ligand-dependent manner, and disrupts ligand-induced AR subnuclear compartmentalization. Foxo-1 is recruited by liganded AR to the chromatin of the AR target gene promoter, while IGF-1 or insulin abolishes the Foxo-1 occupancy on the promoter. Liganded AR stimulates IGF-1 receptor expression, suggesting the presence of local positive feedback between IGF-1 and AR signaling in PC cells, presumably resulting in higher IGF-1 signaling tension and further enhancing the functions of the receptor itself. Thus, Foxo-1 is a novel corepressor for AR and IGF-1/insulin signaling may confer stimulatory effects on AR by attenuating Foxo-1 inhibition. Positive feedback between the growth factor and androgen in the local cellular environment may play important roles in AR transactivation regulation in several clinical situations including refractory PC.

Androgen induction of the androgen receptor coactivator four and a half LIM domain protein-2: evidence for a role for serum response factor in prostate cancer

Androgen receptor (AR) activity is critical for prostate cancer progression. Overexpression of several AR-associated coactivators has been shown to be essential for AR activation during disease progression. The stimuli and signaling pathways leading to overexpression of these coregulators, however, remain largely elusive. Here, we investigated whether androgen signaling, which demarcates critical transitions during prostate cancer disease progression, can affect coregulator expression. We found that expression of four and a half LIM domain protein-2 (FHL2), a key AR coactivator that is overexpressed in prostate cancer and associates with a poor prognosis, is induced strongly by androgens. Androgen induction of this coactivator established a feed-forward mechanism that robustly activated the AR. Stimulation of FHL2 after androgen exposure was time- and dose-dependent and relied on the presence of a functional AR. Androgen induction of FHL2 depended on active transcription of the FHL2 gene, mediated by action of serum response factor (SRF) on its proximal promoter. Loss of SRF, a transcription factor that preferentially regulates the expression of genes involved in mitogenic response and cytoskeletal organization, hampered prostate cancer cell proliferation. These results suggest a novel indirect mechanism of androgen action on FHL2 expression and provide evidence that SRF is an important determinant of AR action in prostate cancer cells.

Testicular zinc finger protein recruits histone deacetylase 2 and suppresses the transactivation function and intranuclear foci formation of agonist-bound androgen receptor competitively with TIF2

We previously reported that testicular zinc finger protein (TZF) is a corepressor for androgen receptor (AR). The present study demonstrated that a central portion (amino acids 512-663) of TZF, TZF(512-663), is responsible for both binding to AR and repressing the transactivation. TZF recruited endogenous histone deacetylase 2 (HDAC2) and formed a complex with agonist-bound AR. Imaging analyses showed that TZF and TZF(512-663) were recruited by AR and simultaneously impaired distinct AR foci formation. Quantification of the foci number using a three-dimensional imaging method revealed that the number of intranuclear AR foci was related to its transactivation activity. Moreover, increased levels of TZF dissociated a coactivator, TIF2, from the AR foci and vice versa. These results indicate that the ligand-dependent transactivation function of AR is quantitatively related to its intranuclear foci formation, and suggest that corepressors, such as TZF, act on these intranuclear events competitively with coactivators.

Steroid receptor coactivator-1-deficient mice exhibit altered hypothalamic-pituitary-adrenal axis function

Steroidogenic factor-1 (SF-1), has emerged as a critical nuclear receptor regulating development and differentiation at several levels of the hypothalamic-pituitary-steroidogenic axis. Although many coregulatory factors have been shown to physically and functionally interact with SF-1, the relative importance of these interactions in SF-1 target tissues has not been thoroughly established. In this study we assessed roles of steroid receptor coactivator-1 (SRC-1) in hypothalamic-pituitary-adrenal (HPA) axis function using SRC-1-deficient (SRC-1-/-) mice in the absence or presence of SF-1 haploinsufficiency. Surprisingly, SRC-1 deficiency did not alter baseline HPA axis function or the acute rise in corticosterone after ACTH administration and failed to exacerbate adrenocortical dysfunction in SF-1+/- mice. However, after exposure to paradigms of acute and chronic stress, SRC-1-/- mice exhibited an elevation in serum corticosterone despite normal (nonsuppressed) ACTH, suggesting an increase in adrenal sensitivity as well as a concomitant defect in glucocorticoid-mediated feedback inhibition of the HPA axis. An examination of potential compensatory mechanism(s) revealed an increase in adrenal weight, selective elevation of melanocortin 2 receptor mRNA, and a coincident increase in SRC-2 and SRC-3 expression in SRC-1-/- adrenals. A reduction in blood glucose was observed in SRC-1-/- mice after chronic stress, consistent with a generalized state of glucocorticoid resistance. Dexamethasone suppression tests confirmed a weakened ability of glucocorticoids to 1) elevate serum glucose levels and induce hepatic phosphoenolpyruvate carboxykinase transcription and 2) suppress pituitary proopiomelanocortin transcript levels in SRC-1-/- animals. Collectively, these data are consistent with an indispensable role for SRC-1 in mediating actions of glucocorticoids in pituitary and liver.