Functional retinoid and thyroid hormone receptors in human thyroid-carcinoma cell lines and tissues

Thyroid carcinomas no longer accessible to radio-iodide or TSH-suppressive T4 therapy, due to loss of thyroid-specific functions, might be sufficiently re-differentiated by retinoic acid (RA) to be treated by conventional methods again. To help evaluate the feasibility of RA re-differentiation therapy in thyroid carcinomas, we examined the functionality of RA receptors (RARs/RXRs), central RA signal mediators, in human thyroid-carcinoma cell lines as model systems. [3H]-RA binding assays with nuclear extracts from follicular thyroid-carcinoma cell lines FTC-133 and -238 revealed high-affinity binding sites for RA. Electrophoretic mobility shift and super-shift assays using a DR2 ("direct repeat" 2) RA response element demonstrated DNA-binding of RARalpha, RARgamma, RXRalpha and RXRbeta in nuclear extracts of FTC-133 and anaplastic HTh74 cells. Use of a DR5 RA response element revealed no difference in DNA binding. In supershift assays with a DR4 T3 response element, we found DNA-binding by TRalpha1, TRalpha2, and TRbeta. Northern-blot analysis showed low expression of RXRbeta mRNA in FTC-133 and of TRalpha1 mRNA in FTC-133 and FTC-238 cells. Using RT-PCR, we detected mRNA for RARalpha, RARbeta, RARgamma, RXRalpha, and RXRbeta in the 4 cell lines and in human thyroid-carcinoma samples. RARbeta mRNA was reduced in FTC-238 cells and RXRbeta mRNA was decreased in anaplastic C643 cells and 9 of 12 tumor samples. Differential RA regulation of RA-receptor-mRNA expression was observed in the various cell lines. Thus, RA and T3 nuclear receptors are present in thyroid-carcinoma cell lines or tissues, albeit with cell-line and tumor-dependent variations; in the cell lines, they were shown to be functional with respect to DNA and/or ligand binding.     

Identification of DNA binding sites for the V-erbA oncoprotein, the viral homolog to thyroid hormone receptor alpha

It is estimated that 20-25% of cancer patients suffer often unrecognized and untreated long-term depression, a condition that can make life miserable. Symptoms can include: lack of sleep; loss of interest in life; anxiety; irritation; loss of concentration; and, in severe cases, thoughts of suicide; leading to an overall poor quality of life. Given that the majority of patients diagnosed with clinical depression can be effectively treated with one form of treatment or another (psychological, pharmacological or a combination) it is now important that health care professionals routinely assess and offer treatment for depression in cancer patients. Therefore, this article reviews the literature on depression caused by cancer and highlights practical ways in which health care workers can measure and subsequently treat depression using pharmacological and psychological approaches.     

Expression of retinoid X receptors in human dermal fibroblasts

Retinoic acid (RA) is known to exert profound effects on growth and differentiation in human dermal fibroblasts. In the observations presented here, we examined the regulation of expression of members of the RXR multigene family in human dermal fibroblasts. We showed that the messenger RNAs for both RXR alpha and RXR beta are expressed in human fibroblasts, but that the messenger RNA for RXR gamma is not detectable in these cells. Electrophoretic mobility shift studies of binding to the beta 2RARE in human dermal fibroblasts demonstrated that a single complex binds to beta 2RARE in the absence of RA. Stimulating cells with all-trans RA induced a second complex. An antibody to the RXR beta protein supershifted both complexes, while an antibody to the RXR alpha S/B protein had no effect on the binding. These data demonstrate that RXR beta plays an important role in retinoid-regulated signal transduction pathways in human dermal fibroblasts and the regulation of expression of the RXR gene family is different from that of the RAR gene family.     

Absence of thyroid hormone receptor beta-retinoid X receptor interactions in auditory function and in the pituitary-thyroid axis

THYROID hormone receptor beta-deficient (TRbeta-/-) mice have defective auditory-evoked brain stem responses (ABR). Since in vitro, TRbeta binds to DNA as homodimers or as heterodimers with retinoid X receptors (RXRs), we investigated whether the TRbeta-/- phenotype may reflect loss of RXR-TRbeta heterodimer or TRbeta homodimer function. Normal ABR thresholds were recorded in RXRbeta-/-, RXRgamma-/-, RXRalpha-/+ and RXR compound mutant mice. When RXR mutations were introduced onto TRbeta-/+ or TRbeta-/- backgrounds, thresholds were dictated solely by TRbeta and not RXR genotype. TRbeta-/-mice also over-produce thyroid hormones and thyroid stimulating hormone; however, levels of these hormones were unaltered by RXR mutations. This suggests that, contrary to in vitro models, RXRs may be dispensable and that TRbeta may function in vivo by an RXR-independent mechanism in the auditory system and pituitary-thyroid axis.     

TOR: a new orphan receptor expressed in the thymus that can modulate retinoid and thyroid hormone signals

Vitamin A and other fat-soluble hormones and vitamins have important roles as modulators of essential biological processes such as homeostasis, development, differentiation, and oncogenesis and also as regulators of the immune system. The active form of vitamin A, retinoic acid, as well as vitamin D3 and thyroid hormones exert their actions by binding to specific nuclear receptors that represent one subfamily of the steroid/thyroid hormone receptor superfamily. To identify new members of the retinoid/thyroid hormone receptor subfamily that could play a role in the immune system, a screening of a T cell cDNA library was performed using a retinoid X receptor probe. A clone was isolated encoding a novel nuclear receptor expressed mainly in the thymus and T cell lines. This new receptor, TOR (thymus orphan receptor), is most closely related in both its DNA-binding domain and ligand-binding domain, 90% and 53%, respectively, to ROR alpha/RZR alpha and clusters with these two receptors and RZR beta in a phylogenetic tree, when both the DNA-binding domain and the ligand-binding domain sequences of nuclear receptors are compared. Thus, TOR is part of a subgroup of receptors, one of which has recently been reported to be activated by melatonin. TOR binds specifically to a direct repeat of the half-site sequence 5'-AGGTCA-3' with a four- or five-nucleotide spacer, DNA sequences that also serve as binding sites for thyroid hormone (TR), and retinoic acid receptors (RAR). In transient transfection experiments TOR does not activate a reporter gene carrying these sequences in the absence or the presence of any known nuclear receptor ligands. TOR, however, is able to repress TR and RAR activity on DR-4-TREs or DR-5-RAREs, respectively. Therefore, our data suggest that TOR, similar to COUP-TF, can negatively regulate retinoic acid and thyroid hormone signals. However, the response elements recognized by TOR and COUP-TF differ as do the expression patterns of these receptors. Thus, one important role of TOR could be to modulate retinoid and thyroid hormone signals in the thymus.     

The phantom ligand effect: allosteric control of transcription by the retinoid X receptor

OBJECTIVE: This two-part study investigated the cognitive processing of food- and threat-related information in a non-eating-disordered population, particularly exploring the mechanisms that might explain the process of cognitive avoidance among women with bulimic attitudes. METHOD: In the first study, 30 female students solved anagrams of neutral, food, and threat words. In the second study, 50 male and female students solved anagrams of words reflecting physical threat, self-directed ego threat, and ego threat directed from others. RESULTS: In this task, there was no association between slower processing of threats and eating characteristics, but there were associations with Eating Disorders Inventory (EDI) scales that reflect "ego development." DISCUSSION: The most reliable evidence of cognitive avoidance was among those participants who show the ego development characteristics that have been identified as important in the development and etiology of eating psychopathology. The implications for models of eating psychopathology and their treatment are discussed.     

Different functions for the thyroid hormone receptors TRalpha and TRbeta in the control of thyroid hormone production and post-natal development

Par-4 is a widely expressed protein that sensitizes both prostatic and non-prostatic cells to apoptosis. Constitutive- or regulated- overexpression of Par-4 caused a reduction in the levels of the anti-apoptotic protein Bcl-2. Replenishment of Bcl-2 levels abrogated susceptibility to Par-4-dependent apoptosis, suggesting that Par-4-mediated apoptosis requires downmodulation of Bcl-2 levels. The inverse correlation between Par-4 and Bcl-2 expression was recapitulated in human prostate tumors. Par-4 but not Bcl-2 was detected in the secretory epithelium of benign prostatic tumors and in primary and metastatic prostate cancers that are apt to undergo apoptosis. Moreover, xenografts of human, androgen-dependent CWR22 tumors showed Par-4 but not Bcl-2 expression. By contrast, androgen-independent CWR22R tumors derived from the CWR22 xenografts showed mutually exclusive expression patterns of Par-4 and Bcl-2. These findings suggest a mechanism by which Par-4 may sensitize prostate tumor cells to apoptosis.     

Structure and function of the thyroid hormone receptor

Cloning of the thyroid hormone receptor and its identification as a cellular counterpart of the viral oncogene v-erbA was a major breakthrough in the study of thyroid hormone action. However, contrary to our initial expectations, many astonishing findings which have accumulated since the receptor cloning, especially the presence of two receptor types, made the elucidation of the thyroid hormone action extremely complicated. In this paper, we mainly did a phylogenic comparison of the amino acid sequence between alpha- and beta-type receptor from Xenopus laevis to humans, hoping to obtain some clue to clarify the functional differences between these receptors. There are several consistent amino acid differences between alpha- and beta-receptor through species in the DNA binding domain, one of which is non-conservative and is located in the portion supposed to be critical to the protein-protein interaction. We believe that clarification of the physiological significance of the presence of two receptor types will facilitate the study of thyroid hormone action.     

Mitogenic effect of retinoid X receptor agonists in rat liver

Thirty-nine acrylates and methacrylates that had been used in dental resin materials were evaluated by a cytotoxicity test, and the relationships between their structures and cytotoxicity were studied to predict cytotoxic levels of dental resin materials in order to develop new low-toxic resin materials. All the acrylates evaluated were more toxic than corresponding methacrylates. In both the acrylates and methacrylates, a hydroxyl group seemed to enhance cytotoxicity. Dimethacrylates with 14 or fewer oxyethylene chains showed similar cytotoxicity while dimethacrylates with 23 oxyethylene chains showed lower cytotoxicity. The cytotoxicity ranking of monomers widely used in dental resin materials was bisphenol A bis 2-hydroxypropyl methacrylate (bisGMA) > urethane dimethacrylate (UDMA) > triethyleneglycol dimethacrylate (3G) > 2-hydroxyethyl methacrylate (HEMA) > methyl methacrylate (MMA). In acrylates, methacrylates, and ethylmethacrylates with either substituents, the lipophilicity of substituents affected their cytotoxicity, and an inverse correlation between IC50 and logP was observed. These results will be useful in developing new resin materials with low toxic monomer compositions.     

Transcriptional repression: lessons from thyroid hormone action and promyelocytic leukaemia

We report seemingly unique craniofacial malformations and deglutition dysfunction in a sib pair. The boy had right maxillomandibular alveolar synechae, ankylosis of right temporomandibular joint, hypoplasia of the zygomatico-maxillary region, nasal deviation to the left, choanal stenosis, and exophthalmos due to shallow orbita. His ears were apparently low-set with prominent lobules. He had severe gastroesophageal reflux and increasing respiratory problems and died at age 11 months. Psychomotor development was normal. His 10-year-old sister had similar craniofacial malformations and a cleft soft palate. She also had a severe deglutition dysfunction and developed a thoracolumbar kyphoscoliosis. Psychomotor development was normal. The parents were healthy and non-consanguineous. The malformations in the sibs do not fit any reported craniofacial malformation syndrome and may represent a previously unrecognized monogenic disorder. This may be an autosomal recessive or dominant trait with gonadal mosaicism in one of the parents.