Switching from the tablet to the powder formulation of levothyroxine corrects severe hypothyroidism in a patient with lactose intolerance.

We describe a case of a 38-year-old woman who, after radioactive iodine therapy for Graves' disease, developed severe hypothyroidism despite receiving a high dose of levothyroxine (L-T4) tablet as replacement therapy. Her thyroid stimulating hormone (TSH) remained to be high despite the dose of L-T4 tablets to 400 µg/day after treatment for hypothyroidism, and the patient complained of general malaise and edema of the legs. Reduced intestinal absorption of L-T4 is the most common cause of failure to achieve the therapeutic target in hypothyroid patients receiving replacement therapy. She was admitted to our hospital for severe hypothyroidism due to resistance to treatment with L-T4 tablet. Our patient was found to have lactose intolerance (LI) by a detailed examination during hospitalization. Therefore, we assumed that LI was impairing intestinal absorption of L-T4 tablet in our patient, leading to severe hypothyroidism. The patient was switched to the powder formulation of L-T4 at the same daily dose, and serum levels of thyroid-stimulating hormone and thyroid hormones normalized. This is the case in which hypothyroidism due to reduced absorption of L-T4 tablet in a patient with LI was resolved by switching to L-T4 powder formulation.

Symptomatic hypocalcemia after treatment for hyperthyroidism in a woman with chromosome 22q11.2 deletion syndrome complicated by Graves' disease: longitudinal changes in the number of subsets of CD4 and CD8 lymphocytes after thyroidectomy.

Chromosome 22q11.2 deletion syndrome is a multisystem genetic disorder that presents with hypocalcemia due to congenital hypoparathyroidism; cardiovascular, renal, and facial anomalies; and skeletal defects. This syndrome is also associated with an increased risk of autoimmune disease. We report here on a 33-year-old Japanese woman with 22q11.2 deletion syndrome complicated by Graves' disease. The patient had facial abnormalities and a history of a surgical procedure for a submucous cleft palate at age 3 years. At age 33, the patient was diagnosed with Graves' disease because both hyperthyroidism and thyroid stimulating hormone receptor antibody were present. The patient's serum calcium level was within the normal range, but symptomatic hypocalcemia developed 1 month after treatment with methimazole was started for thyrotoxicosis. Methimazole was discontinued because it caused liver dysfunction, so the patient underwent total thyroidectomy to treat her Graves' disease. We examined longitudinal changes in the number of subsets of CD4 and CD8 lymphocytes, including regulatory T (T reg) cells and PD-1+CD4+ and PD-1+CD8+ T cells, after treatment by total thyroidectomy. A flowcytometry analysis demonstrated that circulating PD-1+CD4+ and PD-1+CD8+ T cells gradually decreased over time, as did circulating T reg cells and circulating CD19+ B cells. These findings suggest that PD-1-positive CD4+ and CD8+ T cells and T reg cells may have been associated with the autoimmunity in our patient with chromosome 22q11.2 deletion syndrome complicated by Graves' disease.

The SGLT2 Inhibitor Canagliflozin Prevents Carcinogenesis in a Mouse Model of Diabetes and Non-Alcoholic Steatohepatitis-Related Hepatocarcinogenesis: Association with SGLT2 Expression in Hepatocellular Carcinoma.

The aim of the present study is to investigate the effects of canagliflozin, a selective sodium-glucose co-transporter 2 (SGLT2) inhibitor, on non-alcoholic steatohepatitis (NASH) and NASH-related hepatocellular carcinoma (HCC) in a mouse model of diabetes and NASH-HCC. First, mice aged five weeks were divided into two groups (vehicle group and canagliflozin group) and were treated for three weeks. Then, mice aged five weeks were divided into three groups of nine animals each: the vehicle group, early canagliflozin group (treated from five to nine weeks), and continuous canagliflozin group (treated from five to 16 weeks). Canagliflozin was administered at a dose of 30 mg/kg in these experiments. In addition, the in vitro effects of canagliflozin were investigated using HepG2 cells, a human HCC cell line. At the age of eight or 16 weeks, the histological non-alcoholic fatty liver disease activity score was lower in the canagliflozin-treated mice than in vehicle-treated mice. There were significantly fewer hepatic tumors in the continuous canagliflozin group than in the vehicle group. Immunohistochemistry showed significantly fewer glutamine synthetase-positive nodules in the continuous canagliflozin group than in the vehicle group. Expression of α-fetoprotein mRNA, a marker of HCC, was downregulated in the continuous canagliflozin group when compared with the vehicle group. At 16 weeks, there was diffuse SGLT1 expression in the hepatic lobules and strong expression by hepatocytes in the vehicle group, while SGLT2 expression was stronger in liver tumors than in the lobules. In the in vitro study, canagliflozin (10 µM) suppressed the proliferation of HepG2 cells. Flow cytometry showed that canagliflozin reduced the percentage of HepG2 cells in the G2/M phase due to arrest in the G1 phase along with decreased expression of cyclin D and Cdk4 proteins, while it increased the percentage of cells in the G0/1 phase. Canagliflozin also induced apoptosis of HepG2 cells via activation of caspase 3. In this mouse model of diabetes and NASH/HCC, canagliflozin showed anti-steatotic and anti-inflammatory effects that attenuated the development of NASH and prevented the progression of NASH to HCC, partly due to the induction of cell cycle arrest and/or apoptosis as well as the reduction of tumor growth through the direct inhibition of SGLT2 in tumor cells.

Inhibition of IL-33 signaling ameliorate hepatic fibrosis with decreasing MCP-1 in a mouse model of diabetes and non-alcoholic steatohepatitis; comparison for luseogliflozin, an SGLT2 inhibitor.

Non-alcoholic fatty liver disease (NAFLD) is increasing globally, and seeking therapeutic molecule targets is urgent. Several studies have demonstrated that IL-33 plays an important role in the progression of Non-alcoholic steatohepatitis (NASH) with fibrosis and the proliferation of hepatocellular carcinoma (HCC). However, whether the inhibition of IL-33 signaling prevents NAFLD from progressing to NASH and HCC has not been clarified. We investigated the effects of a novel antibody, IL-33RAb, and luseogliflozin, a SGLT2 inhibitor, when administered to a model mouse for NASH and HCC, and their effects were compared to investigate the mechanisms of how IL-33 is involved in the pathogenesis of NASH progression. Compared with the positive control of luseogliflozin, inhibition of IL-33 signaling ameliorated decreasing hepatic fibrosis via decreasingαSMA and MCP-1, and also partially suppressed the progression of the HCC cell line in in vitro experiments. These findings suggest that inhibition of IL-33 possibly prevents progression from NASH to HCC, and their effect may be a newly arrived therapeutic agent.

Diabetes with GLP-1R polymorphism (rs3765467) accompanied by myotonic dystrophy: A case of myotonic dystrophy with p.R131Q polymorphism at the glucagon-like peptide-1 receptor (rs3765467) resulting in marked effects of its agonist, dulaglutide.

A 47-year-old woman was diagnosed with myotonic dystrophy when admitted for traumatic subarachnoid hemorrhage. Her glycemic control was poor despite administration of pioglitazone, a PPARɤ agonist, and subcutaneous insulin infusion. However, adding a GLP-1 receptor (GLP-1R) agonist markedly improved blood glucose levels, resulting in eventual insulin withdrawal. Genetic testing revealed a heterozygous variant, p.R131Q, in the GLP1R (rs3765467), a common variant in Asia. This variant is known to be associated with increased endogenous insulin from beta cells in response to exogenous GLP-1 infusion. This is the first report and short review of a Japanese case of myotonic dystrophy accompanied by GLP-1R gene polymorphism.

Functional variants in a TTTG microsatellite on 15q26.1 cause familial nonautoimmune thyroid abnormalities.

Insufficient thyroid hormone production in newborns is referred to as congenital hypothyroidism. Multinodular goiter (MNG), characterized by an enlarged thyroid gland with multiple nodules, is usually seen in adults and is recognized as a separate disorder from congenital hypothyroidism. Here we performed a linkage analysis of a family with both nongoitrous congenital hypothyroidism and MNG and identified a signal at 15q26.1. Follow-up analyses with whole-genome sequencing and genetic screening in congenital hypothyroidism and MNG cohorts showed that changes in a noncoding TTTG microsatellite on 15q26.1 were frequently observed in congenital hypothyroidism (137 in 989) and MNG (3 in 33) compared with controls (3 in 38,722). Characterization of the noncoding variants with epigenomic data and in vitro experiments suggested that the microsatellite is located in a thyroid-specific transcriptional repressor, and its activity is disrupted by the variants. Collectively, we presented genetic evidence linking nongoitrous congenital hypothyroidism and MNG, providing unique insights into thyroid abnormalities.

Regulation of sodium iodide symporter gene expression by Rac1/p38ß mitogen-activated protein kinase signaling pathway in MCF-7 breast cancer cells.

Activation of p38 MAPK is a key pathway for cell proliferation and differentiation in breast cancer and thyroid cells. The sodium/iodide symporter (NIS) concentrates iodide in the thyroid and lactating breast. All-trans-retinoic acid (tRA) markedly induces NIS activity in some breast cancer cell lines and promotes uptake of ß-emitting radioiodide (131)I sufficient for targeted cytotoxicity. To identify a signal transduction pathway that selectively stimulates NIS expression, we investigated regulation by the Rac1-p38 signaling pathway in MCF-7 breast cancer cells and compared it with regulation in FRTL-5 rat thyroid cells. Loss of function experiments with pharmacologic inhibitors and small interfering RNA, as well as RT-PCR analysis of p38 isoforms, demonstrated the requirement of Rac1, MAPK kinase 3B, and p38ß for the full expression of NIS in MCF-7 cells. In contrast, p38α was critical for NIS expression in FRTL-5 cells. Treatment with tRA or overexpression of Rac1 induced the phosphorylation of p38 isoforms, including p38ß. A dominant negative mutant of Rac1 abolished tRA-induced phosphorylation in MCF-7 cells. Overexpression of p38ß or Rac1 significantly enhanced (1.9- and 3.9-fold, respectively), the tRA-stimulated NIS expression in MCF-7 cells. This study demonstrates differential regulation of NIS by distinct p38 isoforms in breast cancer cells and thyroid cells. Targeting isoform-selective activation of p38 may enhance NIS induction, resulting in higher efficacy of (131)I concentration and treatment of breast cancer.

Thyroid hormone receptor isoform-specific modification by small ubiquitin-like modifier (SUMO) modulates thyroid hormone-dependent gene regulation.

Thyroid hormone receptor (TR) α and ß mediate thyroid hormone action at target tissues. TR isoforms have specific roles in development and in adult tissues. The mechanisms underlying TR isoform-specific action, however, are not well understood. We demonstrate that posttranslational modification of TR by conjugation of small SUMO to TRα and TRß plays an important role in triiodothyronine (T3) action and TR isoform specificity. TRα was sumoylated at lysines 283 and 389, and TRß at lysines 50, 146, and 443. Sumoylation of TRß was ligand-dependent, and sumoylation of TRα was ligand-independent. TRα-SUMO conjugation utilized the E3 ligase PIASxß and TRß-SUMO conjugation utilized predominantly PIAS1. SUMO1 and SUMO3 conjugation to TR was important for T3-dependent gene regulation, as demonstrated in transient transfection assay and studies of endogenous gene regulation. The functional role of SUMO1 and SUMO3 in T3 induction in transient expression assays was closely matched to the pattern of TR and cofactor recruitment to thyroid hormone response elements (TREs) as determined by ChIP assays. SUMO1 was required for the T3-induced recruitment of the co-activator CREB-binding protein (CBP) and release of nuclear receptor co-repressor (NCoR) on a TRE but had no significant effect on TR DNA binding. SUMO1 was required for T3-mediated recruitment of NCoR and release of CBP from the TSHß-negative TRE. SUMO3 was required for T3-stimulated TR binding to the TSHß-negative TRE and recruitment of NCoR. These findings demonstrate that conjugation of SUMO to TR has a TR-isoform preference and is important for T3-dependent gene induction and repression.

Retinoic acid induces expression of the thyroid hormone transporter, monocarboxylate transporter 8 (Mct8).

Retinoic acid (RA) and thyroid hormone are critical for differentiation and organogenesis in the embryo. Mct8 (monocarboxylate transporter 8), expressed predominantly in the brain and placenta, mediates thyroid hormone uptake from the circulation and is required for normal neural development. RA induces differentiation of F9 mouse teratocarcinoma cells toward neurons as well as extraembryonal endoderm. We hypothesized that Mct8 is functionally expressed in F9 cells and induced by RA. All-trans-RA (tRA) and other RA receptor (RAR) agonists dramatically (>300-fold) induced Mct8. tRA treatment significantly increased uptake of triiodothyronine and thyroxine (4.1- and 4.3-fold, respectively), which was abolished by a selective Mct8 inhibitor, bromosulfophthalein. Sequence inspection of the Mct8 promoter region and 5'-rapid amplification of cDNA ends PCR analysis in F9 cells identified 11 transcription start sites and a proximal Sp1 site but no TATA box. tRA significantly enhanced Mct8 promoter activity through a consensus RA-responsive element located 6.6 kilobases upstream of the coding region. A chromatin immunoprecipitation assay demonstrated binding of RAR and retinoid X receptor to the RA response element. The promotion of thyroid hormone uptake through the transcriptional up-regulation of Mct8 by RAR is likely to be important for extraembryonic endoderm development and neural differentiation. This finding demonstrates cross-talk between RA signaling and thyroid hormone signaling in early development at the level of the thyroid hormone transporter.

Empagliflozin increases plasma levels of campesterol, a marker of cholesterol absorption, in patients with type 2 diabetes: Association with a slight increase in high-density lipoprotein cholesterol.

BACKGROUND AND AIMS: Sodium/glucose cotransporter 2 (SGLT2) inhibitors decrease plasma triglyceride levels and slightly increase low-density lipoprotein (LDL-c) and high-density lipoprotein cholesterol (HDL-c). However, the mechanisms underlying such changes in the blood lipid profile remain to be determined. We investigated how empagliflozin affects plasma markers of cholesterol absorption and synthesis, and evaluated the relationship between changes in these markers and blood lipids in patients with type 2 diabetes. METHODS AND RESULTS: In a randomized, active-controlled, open-label trial, 51 patients were randomly allocated in 2:1 ratio to receive empagliflozin 10 mg/day (n = 32) or standard therapy (n = 19) for 12 weeks. We measured plasma levels of lathosterol as a marker of cholesterol synthesis, and campesterol and sitosterol as markers of cholesterol absorption, at baseline and 12 weeks after treatment. In the empagliflozin group, serum HDL-c, but not LDL-c, significantly increased between baseline and 12 weeks (54.4 ±â€¯16.3 vs. 58.8 ±â€¯19.6 mg/dl; p = 0.0006), whereas in the standard therapy group, HDL-c and LDL-c remained unchanged. In the empagliflozin group, plasma campesterol also increased significantly (4.14 ±â€¯1.88 vs. 4.90 ±â€¯2.26 µg/ml, p = 0.0008), whereas no change in plasma campesterol or sitosterol was found in the control group. Although plasma lathosterol showed no change in the whole empagliflozin group, it decreased significantly in patients who were not taking statins. In statin non-users, plasma lathosterol decreased significantly after treatment with empagliflozin (2.71 ±â€¯0.99 vs. 1.91 ±â€¯0.99 µg/ml, p < 0.05). In the empagliflozin group, changes in plasma campesterol correlated positively with changes in HDL-c. CONCLUSION: Empagliflozin increases serum campesterol, a marker of cholesterol absorption, in patients with type 2 diabetes. This increase may be associated with SGLT2 inhibitor-induced increases in HDL cholesterol.

A Japanese Family with DICER1 Syndrome Found in Childhood-Onset Multinodular Goitre.

INTRODUCTION: Germline DICER1 mutations have recently been identified in familial multinodular goitre (MNG). The natural history of thyroid nodules in DICER1 carriers in children is unclear. The purpose of this study was to describe the clinical and genetic findings of childhood-onset MNG with DICER1 carrier in a patient who underwent total thyroidectomy. CASE PRESENTATION: The 6-year-old proband had a thyroid nodule, and the number and size of nodules increased over 3 years. A total thyroidectomy was chosen because of the rapid rise in thyroglobulin levels, discomfort when swallowing, and the mother's history of poorly differentiated thyroid cancer (PDTC). Histopathology revealed adenomatous goitre without malignant cells. Her mother, maternal aunt, and maternal grandmother also had thyroid nodules removed during adolescence. Also, her mother had PDTC with lung metastases, and her maternal aunt had an ovarian germ cell tumour. DICER1 mutation analysis identified a heterozygous novel nonsense mutation (c.4509C>G, p.Y1503X) for the patient, her mother, her maternal grandmother, and her asymptomatic elder brother. Y1503X was identified in all resected thyroid tissues, while heterozygous D1709G, D1810V, and E1813K mutations were identified in individual nodules. DISCUSSION/CONCLUSION: A thyroid nodule was detected in chemotherapy- or radiotherapy-naïve patient with DICER1 carrier aged 6 years, and MNG developed over 3 years. This pedigree highlights the natural history of nodular disease in DICER1 carriers and identifies a possible association between DICER1 and more aggressive malignancies.

A CASE OF FAMILIAL NONAUTOIMMUNE HYPERTHYROIDISM DURING PREGNANCY.

OBJECTIVE: Familial nonautoimmune hyperthyroidism (FNAH) is a rare disease. To date there are few, if any, reports of pregnancies in women with FNAH. Our objective here is to present such a case. METHODS: Free thyroxine (free T4), free triiodothyronine (free T3), thyroid-stimulating hormone (TSH), and antibodies related to the thyroid were measured. Fetal thyroid function indicators including thyroid volume and ossification were checked using ultrasound. Thyroid-stimulating hormone receptor (TSHR) gene analyses were performed. RESULTS: The patient was a 30-year-old woman with no past medical history. She was introduced to our hospital in the fifth gestational week for pregnancy care because her family history revealed that her mother had nonautoimmune hyperthyroidism with a TSHR-activating germ-line mutation (Asn406Ser). The serum free T4 was 1.88 ng/dL (normal, 0.62 to 1.19 ng/dL), free T3 was 3.27 pg/mL (normal, 2.55 to 3.88 pg/mL), TSH was 0.02 µIU/mL (normal, 0.007 to 3.619 µIU/mL), and TSHR was negative which were considered to be consistent with mild primary hyperthyroidism. Serum free T4, free T3, and TSH concentrations were monitored every 4 to 6 weeks with a peak free T4 of 2.23 ng/dL noted at gestational week 9. The patient had no signs related to hyperthyroidism throughout pregnancy. The patient delivered a 3,518 g girl at 40 weeks of gestation. Genetic analysis of her TSHR gene showed heterozygous Asn406Ser mutation. The offspring did not show any signs of prenatal hyperthyroidism, and thyroid function at day 6 after delivery revealed a free T4 of 2.41 ng/dL (normal, 1.83 to 2.91 ng/dL) and a TSH of 3.55 µIU/mL (normal, 0.51 to 4.57 µIU/mL). CONCLUSION: Women with FNAH and mild thyrotoxicosis prior to pregnancy may have continuous hyperthyroidism with additional change due to the series of human chorionic gonadotropin secretion during pregnancy.

Genetic alteration of ARMC5 in a patient diagnosed with meningioma and primary macronodular adrenal hyperplasia: a case report.

A monoallelic germline alteration of ARMC5 causes primary bilateral macronodular adrenal hyperplasia (PBMAH) with Cushing's syndrome via its subsequent somatic alteration on the other allele as the second hit. PBMAH is sometimes complicated with meningioma. Dependency of such a multi-organ disease on the second hit mechanism was reported before, but this finding has not been confirmed yet. We describe a case of a 65-year-old female with PBMAH, carrying a heterozygous germline alteration of ARMC5, p.R267*, complicated with meningioma associated with somatic loss of heterozygosity (LOH) of the unaffected allele. Pathogenic alterations of ARMC5 may also contribute to the development of meningioma by the two-hit mechanism.

A case of hypoparathyroidism, deafness, and renal dysplasia (HDR) syndrome with a novel frameshift variant in GATA3, p.W10Cfs40, lacks kidney malformation.

Autosomal dominant hypoparathyroidism, deafness, and renal dysplasia (HDR) syndrome are typically diagnosed by manifestations of the three features with a positive family history. Our case carried a de novo variant in causative gene, GATA3, but presenting no renal dysplasia or family history. The phenotypic heterogeneity raises a caution for diagnosis.

Denosumab improves clinical manifestations of hypophosphatemic osteomalacia by adefovir-induced Fanconi syndrome: a case report.

BACKGROUND: Adefovir dipivoxil is a nucleotide analogue that is approved for treatment of chronic hepatitis B. Adefovir dipivoxil is associated with proximal tubular dysfunction, resulting in Fanconi syndrome, which can cause secondary hypophosphatemic osteomalacia. We describe a case of a patient with hypophosphatemic osteomalacia secondary to Fanconi syndrome induced by adefovir dipivoxil concomitantly with osteoporosis in whom clinical symptoms were improved by adding denosumab (a human monoclonal antibody targeting the receptor activator of nuclear factor-κB ligand) to preceding administration of vitamin D3. CASE PRESENTATION: A 60-year-old Japanese man had been receiving low-dose adefovir dipivoxil (10 mg/day) to treat chronic hepatitis B for approximately 5 years. He presented to an orthopedic surgeon with severe pain of the right hip and no trauma history, and fracture of the neck of the right femur was identified. In addition, 99mTc-hydroxymethylene diphosphate scintigraphy revealed significantly abnormal uptake in the bilateral ribs, hips, and knees, and he was therefore referred to our university hospital for evaluation of multiple pathological fractures. We diagnosed hypophosphatemic osteomalacia due to Fanconi syndrome induced by adefovir dipivoxil therapy. Although we reduced the patient's adefovir dipivoxil dose and added calcitriol (active vitamin D3), he did not respond and continued to complain of bone pain. Several bone resorption markers and bone-specific alkaline phosphatase were also persistently elevated. Therefore, we added denosumab to vitamin D3 supplementation for treatment of excessive bone resorption. Two months after initiation of denosumab, his hip and knee pain was relieved, along with a decrease in serum alkaline phosphatase and some bone resorption markers. CONCLUSIONS: Although denosumab is not generally an appropriate treatment for acquired Fanconi syndrome, it may be useful for patients who have hypophosphatemic osteomalacia due to adefovir dipivoxil-induced Fanconi syndrome associated with excessive bone resorption. However, clinicians should keep in mind that if denosumab is administered to patients with hypophosphatemic osteomalacia accompanied by excessive bone resorption, adequate vitamin D and/or phosphate supplementation should be done before administration of denosumab.

Congenital Primary Hypothyroidism with the Homozygous Nonsense Mutation P.K1374* in the Thyroglobulin Gene and a Normal-sized Thyroid Gland on Levothyroxine Replacement.

Thyroglobulin (TG) gene mutations cause thyroid dyshormonogenesis, which is typically associated with a congenital goiter. We herein report the case of a 64-year-old man with congenital primary hypothyroidism who had a normal-sized thyroid gland on levothyroxine replacement. He had short stature (-3.1 standard deviations) and mild intellectual impairment. Thyroid autoantibodies were all negative, and the serum TG levels were undetectable. Eventually, he was found to have the novel homozygous nonsense mutation p.K1374* in the TG gene. The possibility of TG mutation should be considered for patients with congenital primary hypothyroidism and a very low serum TG level, regardless of the thyroid size.

Retinoic acid stimulation of the sodium/iodide symporter in MCF-7 breast cancer cells is mediated by the insulin growth factor-I/phosphatidylinositol 3-kinase and p38 mitogen-activated protein kinase signaling pathways.

CONTEXT: All-trans retinoic acid (tRA) induces differentiation in MCF-7 breast cancer cells, stimulates sodium/iodide symporter (NIS) gene expression, and inhibits cell proliferation. Radioiodine administration after systemic tRA treatment has been proposed as an approach to image and treat some differentiated breast cancer. OBJECTIVE: The objective of this work was to study the relative role of genomic and nongenomic pathways in tRA stimulation of NIS expression in MCF-7 cells. DESIGN: We inspected the human NIS gene locus for retinoic acid-responsive elements and tested them for function. The effects of signal transduction pathway inhibitors were also tested in tRA-treated MCF-7 cells and TSH-stimulated FRTL-5 rat thyroid cells, followed by iodide uptake assay, quantitative RT-PCR of NIS, and cell cycle phase analysis. RESULTS: Multiple retinoic acid response elements around the NIS locus were identified by sequence inspection, but none of them was a functional tRA-induced element in MCF-7 cells. Inhibitors of the IGF-I receptor, Janus kinase, and phosphatidylinositol 3-kinase (PI3K), significantly reduced NIS mRNA expression and iodide uptake in tRA-stimulated MCF-7 cells but not FRTL-5 cells. An inhibitor of p38 MAPK significantly reduced iodide uptake in both tRA-stimulated MCF-7 cells and TSH-stimulated FRTL-5 cells. IGF-I and PI3K inhibitors did not significantly reduce the basal NIS mRNA expression in MCF-7 cells. Despite the chronic inhibitory effects on cell proliferation, tRA did not reduce the S-phase distribution of MCF-7 cells during the period of NIS induction. CONCLUSION: The IGF-I receptor/PI3K pathway mediates tRA-stimulated NIS expression in MCF-7 but not FRTL-5 thyroid cells.