Biomedical subjects

William R Hays

Publications and source records attributed to William R Hays.

4 recordsLinked to original sources

PubMed2005

Effects of rexinoids on thyrotrope function and the hypothalamic-pituitary-thyroid axis.

Retinoid X receptor (RXR)-selective retinoids (rexinoids) can cause central hypothyroidism in humans, and this effect has been confirmed in rodent models. In this report, we characterized the effect of rexinoids on the hypothalamic-pituitary-thyroid axis in mice and TSH regulation in a thyrotrope-derived cell line. The synthetic rexinoid (LG 268) suppressed TSH and T4 levels in mice. Hypothalamic TRH mRNA was unaffected, but steady-state pituitary TSHbeta mRNA levels were significantly lowered, suggesting a direct effect of rexinoids on thyrotropes. LG 268 suppressed TSH protein secretion and TSHbeta mRNA in TalphaT1 thyrotropes as early as 8 h after treatment, whereas the retinoic acid receptor-selective retinoid (TTNPB) had no effect. Type 2 iodothyronine deiodinase (D2) mRNA and activity were suppressed by LG 268 in TalphaT1 cells, whereas only D2 mRNA was suppressed in mouse pituitaries. LG 268 suppressed TSHbeta promoter activity by 42% and the -200 to -149 region accounted for a majority of the LG 268-mediated suppression of promoter activity. The RXRgamma isotype is expressed in thyrotropes. In vitro transfection and in vivo transgenic studies indicate that any RXR isotype can mediate TSH suppression by rexinoids, but the RXRgamma isotype is most efficient at mediating this response. RXRgamma-deficient mice lacked pituitary D2 mRNA suppression by LG 268, but D2 activity remained intact. In summary, RXR-selective retinoids (rexinoids) have multiple effects on the hypothalamic-pituitary-thyroid axis. Rexinoids directly suppress TSH secretion, TSHbeta mRNA levels and promoter activity, and D2 mRNA levels but have no direct effect on hypothalamic TRH levels. Rexinoids also stimulate type 1 iodothyronine deiodinase activity in the liver and pituitary.

Animals↗

PubMed2004

Retinoid X receptor gamma-deficient mice have increased skeletal muscle lipoprotein lipase activity and less weight gain when fed a high-fat diet.

Retinoids, derivatives of vitamin A, induce hypertriglyceridemia through decreased clearance of very low-density lipoprotein by a lipoprotein lipase (LPL)-dependent pathway. The retinoid X receptor (RXR) gamma isotype, which is highly expressed in skeletal muscle, may be important in mediating the effects of retinoids on skeletal muscle metabolism and triglyceride (TG) clearance. RXRgamma-deficient (-/-) mice had lower fasting plasma TG levels compared with wild-type littermates (33.1 +/- 2.0 vs. 51.7 +/- 6.3 mg/dl, respectively; P < 0.05). Skeletal muscle LPL activity was higher in RXRgamma mice (18.7 +/- 2.2 vs. 13.3 +/- 1.3 nmol free fatty acids/min.g; P = 0.03), but LPL activity was not different in adipose and cardiac tissue, suggesting a specific effect of RXRgamma in skeletal muscle. In addition, when exposed to a 14-wk high-fat diet, RXRgamma -/- mice had less weight gain, which was entirely due to lower fat mass (11.9 +/- 1.8 vs. 14.4 +/- 1.1 g; P = 0.01), and leptin levels were also lower in the RXRgamma -/- mice (17.6 +/- 5.0 vs. 30.9 +/- 6.4 ng/ml; P = 0.03). These data suggest that RXRgamma -/- mice are resistant to gain in fat mass in response to high-fat feeding. This occurs, at least in part, through up-regulation of LPL activity in skeletal muscle. An understanding of the mechanisms governing the role of RXR in TG disposal and metabolism may lead to the rational design of RXR-selective agonists and antagonists that may be useful in common disorders such as dyslipidemia and obesity.

Animals↗

PubMed2004

Retinoic acid and retinoid X receptors are differentially expressed in thyroid cancer and thyroid carcinoma cell lines and predict response to treatment with retinoids.

Therapy for patients with advanced thyroid carcinoma is limited. Clinical and in vitro studies suggest that some patients with advanced thyroid cancer may respond to therapy with retinoic acid. mRNA expression of the six retinoic acid (RAR) and retinoid X receptor (RXR) isoforms (RARalpha, -beta, -gamma and RXRalpha, -beta, -gamma) was measured in four human thyroid cell lines, and protein expression was subsequently measured in 10 thyroid cancer cell lines. Two isoforms, RARbeta and RXRgamma, were differentially expressed in the four cell lines. Comparison of 10 thyroid tumors and matched normal thyroid tissue confirmed differential tumor expression of RARbeta and RXRgamma and lack of the RXRgamma isoform in normal thyroid tissue. Cell lines expressing both RARbeta and RXRgamma demonstrated significant growth suppression when treated with retinoids, whereas cell lines lacking these isoforms were unaffected. Expression of RARbeta, the isoform associated with suppression of tumor growth in other cancer types, was not affected by treatment with retinoids in the thyroid cancer cell lines. LG346 increased apoptosis and decreased cells in the S-phase in an anaplastic carcinoma cell line, suggesting that this retinoid causes growth suppression of these cells by multiple mechanisms. In summary, we identified the RARbeta and RXRgamma isoform to be differentially expressed in thyroid cancer cell lines and tumor tissue. These isoforms seem to predict response to retinoid therapy in thyroid cancer cell lines.

Antineoplastic Agents↗

PubMed2004

Retinoid X receptor-gamma and peroxisome proliferator-activated receptor-gamma expression predicts thyroid carcinoma cell response to retinoid and thiazolidinedione treatment.

Poorly differentiated, metastatic thyroid cancer is difficult to treat. These tumors often do not concentrate radioactive iodine and may require chemotherapy, which is suboptimal and toxic. Nuclear hormone receptors peroxisome proliferator-activated receptor gamma (PPARgamma) and retinoid X receptor (RXR) are variably expressed in thyroid carcinoma cell lines. Expression of these receptors may predict thyroid cancer cell response to treatment with rexinoids and thiazolidinediones. We studied three thyroid carcinoma cell lines: BHP 5-16 (PPARgamma-/RXRgamma+), BHP 2-7 (PPARgamma+/-/RXRgamma-), and DRO-90 (RXRgamma+/PPARgamma+). BHP 5-16 (RXRgamma+) cells treated with rexinoid had decreased proliferation to 69 +/- 6% growth compared with vehicle. BHP 2-7 (PPARgamma+) cells treated with thiazolidinedione had no decrease in cellular proliferation. DRO-90 (RXRgamma+ and PPARgamma+) cells had 36 +/- 10%, 15 +/- 3%, and 13 +/- 4% growth when treated with rexinoid, thiazolidinedione, or a combination, respectively. We next investigated the role of apoptosis in the ligand-responsive BHP 5-16 and DRO-90 cells. BHP 5-16 cells underwent no significant apoptosis with rexinoid (1 micromol/L). DRO-90 cells, however, had 3.6 +/- 1.3% apoptotic cells with vehicle, 13 +/- 3.5% with rexinoid (1 micromol/L), 18 +/- 4% with thiazolidinedione (1 micromol/L), and 28 +/- 6% with combination treatment (1 micromol/L), suggesting that apoptosis plays a major role in this anaplastic cell line and that the effects of the two ligands are additive. We conclude that receptor expression is necessary for inhibition of thyroid carcinoma growth with ligand treatment but may not be sufficient for response. Additionally, expression of both RXRgamma and PPARgamma may be necessary for maximal growth inhibition by ligands and may be required for the increased apoptosis.

Apoptosis↗