Glutathione-responsive AP site captor Probe-NEt for anaplastic thyroid cancer: in vitro and in vivo experimental studies

Thyroid cancer (TC) is the most common endocrine cancer. Effective treatment options for papillary (PTC) and follicular (FTC) thyroid cancers afford positive patient prognoses. However, there are no effective, long-lasting treatments for anaplastic thyroid cancer (ATC), which has a median survival of five to six months. While the receptor tyrosine kinase inhibitor sorafenib can extend ATC patient survival to eleven months, tumor reoccurrence and drug resistance often develop. Therefore, there is a need for more effective targeted therapies for ATC. While the cell signaling landscape is well described in ATC, little is known about tumorigenic adaptations in ATC metabolism. Tumors exhibit an increased consumption of glucose compared to normal tissues to fuel tumor progression. Some cancers meet this high glucose requirement by storing and breaking down glycogen. While glycogen has been detected in bovine and canine thyroids, no report thus far has investigated glycogen in normal human thyroids or thyroid cancer. Therefore, our objective was to determine if normal thyroid and TC cells metabolize glycogen and to evaluate pharmacological inhibition of glycogen metabolism in ATC cells. We show for the first time that normal thyroid, PTC, FTC, and ATC cells express glycogen synthase and glycogen phosphorylase brain and liver (PYGB, PYGL) isoforms. We confirmed these observations in patient samples of normal thyroid and TC tissues via immunofluorescence. We revealed that the TC samples expressed high levels of PYGB compared to normal thyroid tissue. Electron microscopy revealed that normal thyroid cells organized glycogen in discrete glycosomes, while ATC cells exhibited smaller, dispersed glycogen packets. Importantly, we demonstrated that the glycogen synthase inhibitor guaiacol depleted glycogen content and reduced ATC cell viability. Conversely, the glycogen phosphorylase inhibitor CP-91,149 (CP) increased glycogen levels and induced apoptosis. Importantly, CP also reduced the number of stem cells in the ATC cell population. We further showed that CP synergized with sorafenib to more effectively inhibit ATC proliferation. CP enhanced glycolysis but inhibited oxidative phosphorylation as revealed using Seahorse. We confirmed an increase in glucose transporter expression using RT-qPCR and glucose import following CP treatment. This possibly represents a futile response to PYGB inhibition. We reasoned that glycogen was preferentially metabolized in ATC to fuel the pentose phosphate pathway to protect against reactive oxygen species (ROS). Indeed, we detected significantly higher levels of ROS in ATC cells treated with CP. We demonstrated that thyroid cells are able to metabolize glycogen and identified a potential biomarker for thyroid cancer (PYGB), which was targeted with CP-91,149. Our work establishes glycogen metabolism as a novel metabolic process in thyroid cells that is associated with TC dedifferentiation and provides insight to the effectiveness of inhibiting glycogen metabolism as a novel therapeutic strategy in ATC. Citation Format: Cole Davidson, Jennifer Tomczak, Eyal Amiel, Frances Carr. Glycogen phosphorylase and synthase inhibitors: Novel therapeutic approaches in anaplastic thyroid cancer [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2021 Oct 7-10. Philadelphia (PA): AACR; Mol Cancer Ther 2021;20(12 Suppl):Abstract nr P148.

Aim: Anaplastic thyroid cancer (ATC) is the most aggressive subtype of thyroid cancer, presenting high mortality. Currently, no curative treatments exist and new therapeutic strategies are required. Although nutraceuticals were reported to have anticancer properties, few studies exist on ATC. This study aimed to investigate the anticancer effects of nutraceuticals in ATC cell lines (T235, T238) in comparison with normal thyroid cells (PCCL3).Methods: The IC50 values of isothiocyanates (ITCs: sulforaphane, SFN; phenethyl isothiocyanate, PEITC) and polymethoxylated flavones (PMFs: nobiletin; orange peel extract, OPE) were determined. ITCs decreased ATC metabolic viability more efficiently than PMFs. The effects of PEITC and nobiletin on viability and cell cycle, alone or in combination with conventional drugs, were evaluated.Results: PEITC did not affect viability of normal thyroid and ATC cells, while nobiletin decreased viability in a dose-dependent manner in all cell lines, although cell cycle was not arrested. At 100 μM, nobiletin reduced ATC cell viability as efficiently as conventional drugs, such as cisplatin, while being less toxic to normal thyroid cells. When conjugated with 1 μM cisplatin, the combination decreased viability of T235 cells more efficiently than each compound alone.Conclusion: These results suggest nobiletin as a potential anticancer agent that warrants further investigation in ATC.

Effective treatment options for well-differentiated papillary (PTC) and follicular (FTC) thyroid cancers afford positive patient prognoses. The absence of effective interventions for the stem-like, dedifferentiated anaplastic thyroid cancer (ATC) results in poor patient outcomes with a mortality rate higher than all other endocrine cancers combined (1). While receptor tyrosine kinase inhibitors such as sorafenib can extend ATC patient survival, drug resistance and tumor reoccurrence often develop (2). Therefore, there is a critical need for more effective targeted therapies for ATC. Although the cell signaling landscape of ATC tumors is well described, very little is known about tumorigenic adaptations in ATC cellular metabolism. Tumors exhibit an increased consumption of glucose compared to normal tissues to fuel tumor progression. Some cancers meet this high glucose requirement by storing and breaking down glycogen. In our studies here, we show for the first time that normal thyroid, PTC, FTC, and ATC cells express genes necessary for glycogen metabolism. We confirm these observations in patient samples in normal thyroid and thyroid cancer patient samples via immunofluorescence in tissue microarrays. Furthermore, we detect intracellular glycogen stores in cell lines representing normal thyroid, PTC, FTC, and ATC cells. Importantly, we demonstrate that glycogen phosphorylase inhibitors result in accumulation of intracellular glycogen and induce subsequent apoptosis in ATC cells. We further show that glycogen phosphorylase inhibitors synergize with kinase inhibitors such as sorafenib and buparlisib to decrease ATC cell viability. Our work establishes glycogen metabolism as a novel metabolic process in thyroid cells that is associated with thyroid cancer dedifferentiation and provides insight to the effectiveness of inhibiting glycogen metabolism as a therapeutic strategy in ATC.

Background Anaplastic thyroid carcinoma (ATC) is considered to be one of the most aggressive cancers. Our previous study proved that highly expressed lysine acetyltransferase 5 (KAT5) in ATC is associated with a poorer prognosis. Here, this study examined the effects of a KAT5 inhibitor (NU9056) in human ATC cells. Methods First, the Cancer Genome Atlas (TCGA) dataset was used to detect the relationship between KAT5 expression and outcomes of thyroid carcinoma patients. Then, both in vitro and in vivo experiments were conducted to investigate the effects of NU9056 on normal and ATC human thyroid cells. Finally, microRNA sequencing, qPCR, and dual-luciferase reporter assay were performed to explore potential mechanisms by identifying downstream microRNA related to NU9056. Results KAT5 dysregulation correlated with more advanced-stage and poorer outcomes of thyroid carcinoma patients. Endogenous KAT5 protein and mRNA levels were much higher in ATC cells than in normal thyroid cells. Suppression of KAT5 by NU9056 inhibited survival, growth, migration, invasion, and tube formation, and increased radiosensitivity and chemosensitivity in ATC cells but showed no impact on normal thyroid cells. Mechanistically, microRNA-202-5p (miR-202) was identified as the most significantly decreased miRNA after NU9056 treatment. Knockdown of miR-202 suppressed ATC cell progression, while forced expression of miR-202 partially blocked the inhibitory effect of NU9056 on ATC cells. Furthermore, c-Myc was validated as the transcription factor of miR-202, and NU9056 decreased the c-Myc protein level by shortening its half-life. Finally, we proved that NU9056 inhibited ATC proliferation in vivo. Conclusions Our results indicated that NU9056 targets KAT5, shortens c-Myc half-life, subsequently downregulates miR-202 expression, and results in the suppression of ATC cells. Overall, KAT5 could be a potential target for clinical treatment for ATC.

<h3>Abstract</h3> Anaplastic thyroid cancer (ATC) is one of the most lethal solid tumors, yet there are no effective, long-lasting treatments for ATC patients. Most tumors, including tumors of the endocrine system, exhibit an increased consumption of glucose to fuel cancer progression, and some cancers meet this high glucose requirement by metabolizing glycogen. Our goal was to determine if ATC cells metabolize glycogen and if this could be exploited for treatment. We detected glycogen synthase and glycogen phosphorylase (PYG) isoforms in normal thyroid and thyroid cancer cell lines and patient-derived biopsy samples. Inhibition of PYG using CP-91,149 induced apoptosis in ATC cells but not normal thyroid cells. CP-91,149 decreased NADPH levels and induced reactive oxygen species accumulation. CP-91,149 severely blunted ATC tumor growth <i>in vivo</i>. Our work establishes glycogen metabolism as a novel metabolic process in thyroid cells that presents a unique, oncogenic target that could offer an improved clinical outcome. <h3>Significance</h3> Glycogen metabolism plays an important role in combating reactive oxygen species and apoptosis in anaplastic thyroid cancer. Glycogen phosphorylase was inhibited with small molecule inhibitors that limited cell proliferation <i>in vitro</i> and blunted tumor growth in a nude mouse xenograft. This study demonstrates that glycogen metabolism is a viable target in one of the most lethal solid tumors.

Feline hyperthyroidism is a common, spontaneous disease in older cats that is similar clinically and histopathologically to human toxic multinodular goiter (TNG). In this study, the functional response of feline normal thyroid (NT) and hyperthyroid (HT) cells grown in monolayer culture to thyrotropin (TSH) was determined. Basal levels of DNA synthesis were similar in NT and HT cells. TSH stimulated concentration-dependent DNA synthesis in NT and HT cells, with maximal stimulation seen at 1 and 10 mU/mL TSH in NT and HT cells, respectively. HT cells had higher basal levels of thyroglobulin (Tg) expression. TSH stimulated Tg expression in NT and HT cells in a concentration-dependent fashion, with maximal activity at 0.5 and 5 mU/mL TSH, respectively. These results demonstrate that NT and HT cells in monolayer culture exhibit growth and functional responses to TSH. HT cells have higher basal Tg expression than NT cells and require higher TSH concentrations to stimulate DNA synthesis and Tg expression, two measures of thyroid cell activation. These data support the idea that feline hyperthyroidism is caused by cell abnormalities, resulting in dysregulated growth and hormone synthesis, and emphasize its importance as an animal model for TNG.

Because some papillary thyroid cancers continue to grow when thyroid-stimulating hormone (TSH) levels are suppressed, we questioned whether desensitization (i.e., a decreased cAMP response to repeat stimulation with TSH) occurs in normal and neoplastic thyroid tissue. If desensitization does occur, is it similar or different in these human thyroid cells? Normal and papillary thyroid cancer cells from the same patient were cultured as we have previously described. Normal and neoplastic thyroid tissues responded to TSH (0.01-10.0 mU/ml) by increasing cAMP production and growth in a dose-dependent manner. In normal cells there was an 11-fold mean increase in cAMP production at 4 hours, and all thyroid cultures responded. In neoplastic cells cAMP production increased from 1.5-fold to 3.0-fold with a mean 2.0-fold increase at 4 hours. In normal thyroid cells the cAMP response to a second TSH stimulus (desensitization) decreased up to 75% (range 25-75%), and desensitization occurred in all normal thyroid cell cultures. In neoplastic thyroid cells, however, the cAMP response to a second TSH stimulus decreased up to 17% (range 0-17%); and desensitization occurred in only two of the five neoplastic thyroid cell cultures. Thus when normal thyroid and neoplastic cells from the same patients were studied, greater desensitization occurred in the normal cells (75% vs. 17%). These studies document that there is greater desensitization in normal tissue than in neoplastic thyroid tissue, which may account for the increased growth of thyroid neoplasms in the presence of ever-changing low levels of TSH.

Papillary thyroid cancer (PTC) is the most prevalent of all endocrine cancers. In recent studies, the presence of receptors for pituitary-type growth hormone-releasing hormone (pGHRH-R) has been demonstrated in various human cancers, including human prostate, brain, and other cancer lines. Thyroid malignancies, however, have not yet been investigated in this regard. In this study, we found that pGHRH-R and its functional splice variant, SV1, are present in normal thyroid and PTC cells. We also treated seven normal and PTC tumor thyroid cells in vitro with a GHRH antagonist, MIA-602, to compare its anti-proliferation and anti-invasion potential against vehicle-treated cells. We found that treatment with GHRH antagonist increases the expression of SV1 and pGHRH-R in tumor cells compared to tumor cells exposed to vehicle only, a response which may alter the sensitivity of signaling kinases within the cells. GHRH antagonist treatment of tumor cells also reduced activity of the tumor invasion marker, matrix metalloproteinase (MMP)-2, compared to tumor cells exposed to vehicle only. The expression of pGHRH-R and SV1, as well as MMP-2 activity, in normal thyroid cells remained unaffected by GHRH antagonist treatment. Similarly, cell proliferation rates for tumor or normal thyroid cells were not affected by GHRH antagonist treatment. Our findings have important implications for the therapeutic use of GHRH antagonist in cases of aggressive PTC refractory to conventional treatment modalities, and in which protein expression and MMP-2 activity in normal thyroid tissue is left unaltered.

Anaplastic thyroid cancer (ATC) is one of the most lethal solid tumors, yet there are no effective, long-lasting treatments for ATC patients. Most tumors, including tumors of the endocrine system, exhibit an increased consumption of glucose to fuel cancer progression, and some cancers meet this high glucose requirement by metabolizing glycogen. Our goal was to determine whether ATC cells metabolize glycogen and if this could be exploited for treatment. We detected glycogen synthase and glycogen phosphorylase (PYG) isoforms in normal thyroid and thyroid cancer cell lines and patient-derived biopsy samples. Inhibition of PYG using CP-91,149 induced apoptosis in ATC cells but not normal thyroid cells. CP-91,149 decreased NADPH levels and induced reactive oxygen species accumulation. CP-91,149 severely blunted ATC tumor growth in vivo. Our work establishes glycogen metabolism as a novel metabolic process in thyroid cells, which presents a unique, oncogenic target that could offer an improved clinical outcome.

BackgroundSpatial chromatin structure is intricately linked with somatic aberrations, and somatic mutations of various cancer-related genes, termed co-mutations (CoMuts), occur in certain patterns during cancer initiation and progression. The functional mechanisms underlying these genetic events remain largely unclear in thyroid cancer (TC). With discrepant differentiation, papillary thyroid cancer (PTC) and anaplastic thyroid cancer (ATC) differ greatly in characteristics and prognosis. We aimed to reveal the spatial gene alterations and regulations between the two TC subtypes.MethodsWe systematically investigated and compared the spatial co-mutations between ATC (8305C), PTC (BCPAP and TPC-1), and normal thyroid cells (Nthy-ori-3–1). We constructed a framework integrating whole-genome sequencing (WGS), high-throughput chromosome conformation capture (Hi-C), and transcriptome sequencing, to systematically detect the associations between the somatic co-mutations of cancer-related genes, structural variations (SVs), copy number variations (CNVs), and high-order chromatin conformation.ResultsSpatial co-mutation hotspots were enriched around topologically associating domains (TADs) in TC. A common set of 227 boundaries were identified in both ATC and PTC, with significant overlaps between them. The spatial proximities of the co-mutated gene pairs in the two TC types were significantly greater than in the gene-level and overall backgrounds, and ATC cells had higher TAD contact frequency with CoMuts > 10 compared with PTC cells. Compared with normal thyroid cells, in ATC the number of the created novel three-dimensional chromatin structural domains increased by 10%, and the number of shifted TADs decreased by 7%. We found five TAD blocks with CoMut genes/events specific to ATC with certain mutations in genes including MAST-NSUN4, AM129B/TRUB2, COL5A1/PPP1R26, PPP1R26/GPSM1/CCDC183, and PRAC2/DLX4. For the majority of ATC and PTC cells, the HOXA10 and HIF2α signals close to the transcription start sites of CoMut genes within TADs were significantly stronger than those at the background. CNV breakpoints significantly overlapped with TAD boundaries in both TC subtypes. ATCs had more CNV losses overlapping with TAD boundaries, and noncoding SVs involved in intrachromosomal SVs, amplified inversions, and tandem duplication differed between ATC and PTC. TADs with short range were more abundant in ATC than PTC. More switches of A/B compartment types existed in ATC cells compared with PTC. Gene expression was significantly synchronized, and orchestrated by complex epigenetics and regulatory elements.ConclusionChromatin interactions and gene alterations and regulations are largely heterogeneous in TC. CNVs and complex SVs may function in the TC genome by interplaying with TADs, and are largely different between ATC and PTC. Complexity of TC genomes, which are highly organized by 3D genome-wide interactions mediating mutational and structural variations and gene activation, may have been largely underappreciated. Our comprehensive analysis may provide key evidence and targets for more customized diagnosis and treatment of TC.

Thyroid cancer is the most frequent endocrine malignancy, with an incidence constantly increasing. Despite well-differentiated thyroid tumors are generally cured by conventional therapy, a fraction of them relapses and progresses towards undifferentiated forms, characterized by a poor prognosis. Target therapies introduced in clinical testing are often unsuccessful; therefore, novel therapeutic strategies are needed. To identify critical nodal points for therapeutic intervention, our laboratory faced the “non-oncogene addiction” (NOA) paradigm, which asserts that the tumorigenic state relies on the activity of genes that are essential to support the phenotype of cancer cells but not required to the same degree for normal cell viability. By screening a siRNA library on normal and tumor thyroid cell lines, we identified 15 genes whose silencing interfered with the growth of tumor but not normal thyroid cells. The overall aim of this project was to validate NOA genes to identify thyroid tumor cell vulnerabilities and to explore their role in the regulation of thyroid tumor cell biology. Among the 15 hit genes, we selected MASTL, Cyclin D1 and COPZ1 for validation studies. We confirmed the growth inhibitory effect of their silencing in tumor but not normal thyroid cells and observed that these effects were common to a panel of thyroid tumor cell lines, irrespective of the histotype or genetic lesion. Functional studies on MASTL demonstrated that its depletion in thyroid tumor cells inhibited cell growth, led to mitotic catastrophe and induced DNA damage and cell death. COPZ1 depletion induced abortive autophagy, endoplasmic reticulum stress and apoptotic cell death in thyroid tumor cells, as well as tumor growth inhibition in vivo. Together, our studies identified MASTL and COPZ1 as vulnerability genes for thyroid tumor cells and provided the rationale for future studies aimed to explore their targeting for potential therapeutic intervention.

We examined basal and bTSH-stimulated human thyroglobulin (hTg) secretion by autologous normal and abnormal (benign and malignant) human thyroid cell monolayers. Basal and bTSH-stimulated hTg secretion was highly variable and ranged from 50-700 ng/ml/10(5) cells over a 6 day period. All normal and benign 'non-functioning' adenoma cells demonstrated a dose and time related stimulation of hTg secretion in response to bTSH. Comparison of hTG secretion by autologous normal and abnormal cells showed that in six of eight pairs, the normal thyroid cells had a greater output of hTg than the benign adenoma cells in contrast to our previous studies using non-autologous cells. Malignant thyroid cell hTg production was less predictable than that obtained with normal and benign thyroid cells varying from absent to normal responses to bTSH. Characterization studies of the secreted hTg showed no difference between normal, benign and malignant thyroid cell hTg with reference to molecular weight. However, hTg secreted in vitro was non-iodinated and had a marked reduction (up to 200-fold) in immunoreactivity assessed by both polyclonal and monoclonal antibodies to hTg when compared to hTg standard prepared from intact thyroid tissue (which had 4.58 micrograms iodine/mg). This reduction in hTg immunoreactivity was greatest for hTg secreted by malignant thyroid cells. These data demonstrate the wide variability in the hTg secretory capacity of human thyroid cell monolayers and indicate, when compared to autologous normal cells, that abnormal human thyroid epithelial cells may be relatively deficient in their ability to secrete hTg in vitro. There were also qualitative differences in the immunoreactivity, and iodine content, of in-vitro secreted hTg. These observations suggest that there may be much greater heterogeneity in hTg secreted in vitro than previously realized, perhaps secondary to differences in iodine content and/or degree of glycosylation. Human thyroglobulin (hTg) is the major secretory protein of the thyroid cell (Van Herle et al., 1979). Intracellular hTg is the site of thyroid hormone iodination yet its extrathyroidal role, if any, remains unclear. While hTg is usually present in the peripheral circulation of normal individuals, in species of differing molecular weight (Feldt-Rasmussen et al., 1978), there have been few studies of in-vitro production of hTg by isolated human thyroid cells. Our interest in hTg is in its role as an antigen in thyroid autoimmune disease (De Bernardo et al., 1983; 1986).(ABSTRACT TRUNCATED AT 400 WORDS)

In the past decade, it became apparent that immune mediated cell death in a number of autoimmune endocrine diseases was due to the induction of apoptosis in target organ cells. This was conclusively demonstrated for thyroid follicular cells in Hashimoto’s (destructive autoimmune) thyroiditis, but the mechanisms underlying this cell death were not clear. Several hypotheses were put forth involving the role of deathsignalling molecules expressed on thyroid cells. While many of these hypotheses did not hold up under close scrutiny, this stimulated work on the molecular mechanisms of thyroid destruction. Several apoptosis signalling pathways, initiated by molecules such as Fas ligand (FASL) and tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), have been shown to be active in thyroid cells and may be involved in destructive thyroiditis. In this review we will attempt to sort out the inconsistencies in published data on the mechanisms of death-receptor mediated thyroid destruction. We will also review recently proposed models of these mechanisms, and outline directions for research that we feel might lead to discoveries of benefit to the clinician in the treatment and prevention of destructive autoimmune thyroiditis.

Objectives: 18F-fluorodeoxyglucose (FDG), an analogue of glucose, provides valuable functional information based on the increased glucose uptake and glycolysis in malignant tumor cells. Although both glucose transporter-1 (GLUT-1) and hexokinase2 (HK2) activity have been considered to associate with FDG uptake, the molecular mechanisms that determine FDG uptake are still largely unknown. Adenine nucleotide translocase 2 (ANT2) in the mitochondria inner membrane was reported to relate with tumor malignancy. We investigated the correlation between FDG uptake and Glut-1, HK2, and ANT2 expression in thyroid cancers throughout various spectrums of differentiation status. Methods: N-thy-ori (normal human thyroid cells), WRO (follicular cancer), BHP10-3 and TPC-1 (papillary cancer), and FRO (anaplastic cancer) were used for this research. GLUT-1, HK2, and ANT2 expressions were measured by western blot. ANT2 siRNAs and pcDNA3.1-ANT2 vectors were used to modify ANT2 expression. FDG uptakes were measured in thyroid cells and human embryonic kidney cells (293FT) with HK2 or ANT2 transfection. For patient tissue analysis, 95 thyroid tissue-array cores were evaluated, and which are classified 36 as normal, 44 as poorly differentiated (PD), and 15 as anaplastic thyroid cancer (ATC). ANT2 expression was measured by immunostaining, scored from 1 to 5. Results: FDG uptake in thyroid cancer cells was increased in anaplastic and poorly differentiated cells (P&amp;lt;0.001). GLUT-1 expression was higher in both TPC-1 and FRO than other cells. Whereas, HK2 was expressed only in cancer cells. ANT2 was expressed only in FRO cells and the highest FDG accumulation was also observed in FRO. ANT2 siRNA showed decreased FDG uptake (0.55-fold) and ANT2 overexpression increased FDG uptake (1.7-fold). In 293FT cells, HK2 and ANT2 transfection increased FDG uptake (P&amp;lt;0.01). PD tissues (mean = 41.7, SD = 19.7) and ATC (mean = 48.0, SD = 25.6) tissues from patients showed higher ANT2 expression than normal (P&amp;lt;0.05). Conclusion: We showed that ANT2 was expressed only in anaplastic thyroid cancer cells, and this was related to FDG uptake. Higher level of ANT2 expression was observed in dedifferentiated cancer, and this indicates that ANT2 can be used as a marker of malignancy in thyroid cancer. Citation Format: Chul-Hee Lee, Hyewon Youn, Seock-Jin Chung, Ha Kim, Cho Rong Park, Mi Jeong Kim, Young Joo Park, Sun Wook Cho, Keon Wook Kang, June-Key Chung. Adenine nucleotide translocase2 mediates 18F-FDG uptake in dedifferentiated thyroid cancer [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 3733. doi:10.1158/1538-7445.AM2017-3733

The expression of cellular oncogenes was examined in human thyroid tissue. Four thyroid adenomas and three thyroid carcinomas expressed c-myc oncogene mRNA transcripts, which were not expressed in normal thyroid tissues. Agarose gel electrophoresis of poly(A) RNA extracts of adenoma tissues followed by hybridization with v-myc DNA yielded two distinct c-myc mRNA species [2.1 and 4.0 kilobases (kb)]. Thyroid cancer tissue poly(A) RNA revealed a predominant larger c-myc mRNA species (approximately 6 kb) and a smaller 2.1-kb species. After enzymatic dispersion of thyroid adenoma cells, cytoplasmic dot blot hybridization of immobilized thyroid adenoma RNA extracts with the v-myc cDNA probe showed stimulation of c-myc mRNA expression by TSH in a dose- and time-dependent manner. After 72-h pretreatment with serum-free medium, the quiescent adenoma cells yielded a negligible hybridization signal which was stimulated by TSH (10 mU/ml) after 6 h of treatment. Although normal cultured thyroid cells did not contain detectable c-myc mRNA, TSH also stimulated the myc protooncogene expression in a time-dependent manner in normal thyroid cells. These results demonstrate the expression of c-myc mRNA in human thyroid tumors and the in vitro induction of c-myc mRNA in both normal and adenoma thyroid cell cultures by TSH.