Activation of signal transducer and activator of transcription 3 by oncogenic RET/PTC (rearranged in transformation/papillary thyroid carcinoma) tyrosine kinase: roles in specific gene regulation and cellular transformation

Targeting cyclin D1 as a therapeutic approach for papillary thyroid carcinoma

Cyclin D1 functions as a mitogenic sensor that specifically binds to CDK4/6, thereby integrating external mitogenic inputs and cell cycle progression. Cyclin D1 interacts with transcription factors and regulates various important cellular processes, including differentiation, proliferation, apoptosis, and DNA repair. Therefore, its dysregulation contributes to carcinogenesis. Cyclin D1 is highly expressed in papillary thyroid carcinoma (PTC). However, the particular cellular mechanisms through which abnormal cyclin D1 expression causes PTC are poorly understood. Unveiling the regulatory mechanisms of cyclin D1 and its function in PTC may help determine clinically effective strategies, and open up better opportunities for further research, leading to the development of novel PTC regimens that are clinically effective. This review explores the mechanisms underlying cyclin D1 overexpression in PTC. Furthermore, we discuss the role of cyclin D1 in PTC tumorigenesis via its interactions with other regulatory elements. Finally, recent progress in the development of therapeutic options targeting cyclin D1 in PTC is examined and summarized.

Adefovir Dipivoxil as a Therapeutic Candidate for Medullary Thyroid Carcinoma: Targeting RET and STAT3 Proto-Oncogenes

Aberrant gene expression is often linked to the progression of various cancers, making the targeting of oncogene transcriptional activation a potential strategy to control tumor growth and development. The RET proto-oncogene’s gain-of-function mutation is a major cause of medullary thyroid carcinoma (MTC), which is part of multiple endocrine neoplasia type 2 (MEN2) syndrome. In this study, we used a cell-based bioluminescence reporter system driven by the RET promoter to screen for small molecules that potentially suppress the RET gene transcription. We identified adefovir dipivoxil as a transcriptional inhibitor of the RET gene, which suppressed endogenous RET protein expression in MTC TT cells. Adefovir dipivoxil also interfered with STAT3 phosphorylation and showed high affinity to bind to STAT3. Additionally, it inhibited RET-dependent TT cell proliferation and increased apoptosis. These results demonstrate the potential of cell-based screening assays in identifying transcriptional inhibitors for other oncogenes.

Centrosome Amplification Is a Potential Molecular Target in Paediatric Acute Lymphoblastic Leukemia

Acute lymphoblastic leukemia (ALL) is the most common form of cancer in children, with most cases arising from fetal B cell precursor, termed B-ALL. Here, we use immunofluorescence analysis of B-ALL cells to identify centrosome amplification events that require the centrosome clustering pathway to successfully complete mitosis. Our data reveals that primary human B-ALL cells and immortal B-ALL cell lines from both human and mouse sources show defective bipolar spindle formation, abnormal mitotic progression, and cell death following treatment with centrosome clustering inhibitors (CCI). We demonstrate that CCI-refractory B-ALL cells exhibit markers for increased genomic instability, including DNA damage and micronuclei, as well as activation of the cyclic GMP-AMP synthase (cGAS)-nuclear factor kappa B (NF-κB) signalling pathway. Our analysis of cGAS knock-down B-ALL clones implicates cGAS in the sensitivity of B-ALL cells to CCI treatment. Due to its integral function and specificity to cancer cells, the centrosome clustering pathway presents a powerful molecular target for cancer treatment while mitigating the risk to healthy cells.

OLFM4-RET fusion is an oncogenic driver in small intestine adenocarcinoma

Small intestine adenocarcinoma is a rare intestinal malignancy with distinct clinical, pathological, and molecular characteristics. Recently, a fusion of the intestinal stem-cell marker olfactomedin 4 (OLFM4) and the proto-oncogene RET has been identified in a small intestine adenocarcinoma patient. Here we investigated the biological effects of OLFM4-RET fusion and whether it can initiate tumorigenesis in small intestine. OLFM4 expression was found to be frequently lost or reduced in human small intestine adenocarcinoma, and its downregulation correlated with high tumor grade and advanced tumor stage. Expression of OLFM4-RET fusion-induced cellular transformation in HEK293 cells and blocked RET-induced inhibition of colony growth in HuTu 80 small intestine adenocarcinoma cells. Further, expression of OLFM4-RET activated the RAS-RAF-MAPK and STAT3 cell signaling pathways in both HEK293 cells and HuTu 80 cells. OLFM4-RET expression in HEK293 cells upregulated multiple families of genes related to carcinogenesis, cancer progression, and metastasis. Targeted expression of OLFM4-RET in the small intestine led to the development of hyperplasia, adenoma, or adenocarcinoma in transgenic mice. Our study suggests that OLFM4-RET is an oncogenic driver of small intestine tumorigenesis. Therefore, the small intestine adenocarcinoma patients with OLFM4-RET fusion may benefit from treatment with RET kinase inhibitor.

RET Regulates Human Medullary Thyroid Cancer Cell Proliferation through CDK5 and STAT3 Activation

Medullary thyroid cancer (MTC) is a neuroendocrine tumor that arises from the parafollicular C-cells, which produces the hormone calcitonin. RET is a transmembrane receptor protein-tyrosine kinase, which is highly expressed in MTC. Our previous studies reported that cyclin-dependent kinase 5 (CDK5) plays a crucial role in cancer progression, including MTC. However, the role of CDK5 in GDNF-induced RET signaling in medullary thyroid cancer proliferation remains unknown. Here, we investigated RET activation and its biochemically interaction with CDK5 in GDNF-induced medullary thyroid cancer proliferation. Our results demonstrated that GDNF stimulated RET phosphorylation and thus subsequently resulted in CDK5 activation by its phosphorylation. Activated CDK5 further caused STAT3 activation by its specific phosphorylation at Ser727. Moreover, we also found that GDNF treatment enhanced ERK1/2 and EGR1 activity, which is involved in p35 activation. Interestingly, we identified for the first time that CDK5 physically interacted with RET protein in MTC. Overall, our results provide a new mechanism for medullary thyroid cancer cell proliferation, suggesting that targeting CDK5 may be a promising therapeutic candidate for human medullary thyroid cancer in the near future.

Astrocytic mobilization of glutathione peroxidase-1 contributes to the protective potential against cocaine kindling behaviors in mice via activation of JAK2/STAT3 signaling

Compelling evidence indicates that oxidative stress contributes to cocaine neurotoxicity. The present study was performed to elucidate the role of the glutathione peroxidase-1 (GPx-1) in cocaine-induced kindling (convulsive) behaviors in mice. Cocaine-induced convulsive behaviors significantly increased GPx-1, p-IkB, and p-JAK2/STAT3 expression, and oxidative burdens in the hippocampus of mice. There was no significant difference in cocaine-induced p-IkB expression between non-transgenic (non-TG) and GPx-1 overexpressing transgenic (GPx-1 TG) mice, but significant differences were observed in cocaine-induced p-JAK2/STAT3 expression and oxidative stress between non-TG and GPx-1 TG mice. Cocaine-induced glial fibrillary acidic protein (GFAP)-labeled astrocytic level was significantly higher in the hippocampus of GPx-1 TG mice. Triple-labeling immunocytochemistry indicated that GPx-1-, p-STAT3-, and GFAP-immunoreactivities were co-localized in the same cells. AG490, a JAK2/STAT3 inhibitor, but not pyrrolidone dithiocarbamate, an NFκB inhibitor, significantly counteracted GPx-1-mediated protective potentials (i.e., anticonvulsant-, antioxidant-, antiapoptotic-effects). Genetic overexpression of GPx-1 significantly attenuated proliferation of Iba-1-labeled microglia induced by cocaine in mice. However, AG490 or astrocytic inhibition (by GFAP antisense oligonucleotide and α-aminoadipate) significantly increased Iba-1-labeled microglial activity and M1 phenotype microglial mRNA levels, reflecting that proinflammatory potentials were mediated by AG490 or astrocytic inhibition. This microglial activation was less pronounced in GPx-1 TG than in non-TG mice. Furthermore, either AG490 or astrocytic inhibition significantly counteracted GPx-1-mediated protective potentials. Therefore, our results suggest that astrocytic modulation between GPx-1 and JAK2/STAT3 might be one of the underlying mechanisms for protecting against convulsive neurotoxicity induced by cocaine.

Upregulation of RSPO2-GPR48/LGR4 signaling in papillary thyroid carcinoma contributes to tumor progression

The signaling pathway involving the R-spondins and its cognate receptor, GPR48/LGR4, is crucial in development and carcinogenesis. However, the functional implications of the R-spondin-GPR48/LGR4 pathway in thyroid remain to be identified. The aim of this study was to investigate the role of R-spondin-GPR48/LGR4 signaling in papillary thyroid carcinomas. We retrospectively reviewed a total of 214 patients who underwent total thyroidectomy and cervical lymph node dissection for papillary thyroid carcinoma. The role of GPR48/LGR4 in proliferation and migration was examined in thyroid cancer cell lines. R-spondin 2, and GPR48/LGR4 were expressed at significantly higher levels in thyroid cancer than in normal controls. Elevated GPR48/LGR4 expression was significantly associated with tumor size (P=0.049), lymph node metastasis (P=0.004), recurrence (P=0.037), and the BRAFV600E mutation (P=0.003). Moreover, high GPR48/LGR4 expression was an independent risk factor for lymph node metastasis (P=0.027) and the BRAFV600E mutation (P=0.009). in vitro assays demonstrated that elevated expression of GPR48/LGR4 promoted proliferation and migration of thyroid cancer cells, whereas downregulation of GPR48/LGR4 decreased proliferation and migration by inhibition of the β-catenin pathway. Moreover, treatment of thyroid cancer cells with exogenous R-spondin 2 induced activation of the β-catenin pathway through GPR48/LGR4. The R-spondin 2-GPR48/LGR4 signaling axis also induced the phosphorylation of ERK, as well as phosphorylation of LRP6 and serine 9 of GSK3β. Our findings demonstrate that upregulation of the R-spondin 2-GPR48/LGR4 pathway contributes to tumor aggressiveness in papillary thyroid carcinoma by promoting ERK phosphorylation, suggesting that this pathway represents a novel therapeutic target for treatment of differentiated thyroid cancer.

Oncogenes, mitochondrial metabolism, and quality control in differentiated thyroid cancer

Thyroid cancer is one of the most common malignancies of endocrine organs, and its incidence rate has increased steadily over the past several decades. Most differentiated thyroid tumors derived from thyroid epithelial cells exhibit slow-growing cancers, and patients with these tumors can achieve a good prognosis with surgical removal and radioiodine treatment. However, a small proportion of patients present with advanced thyroid cancer and are unusually resistant to current drug treatment modalities. Thyroid tumorigenesis is a complex process that is regulated by the activation of oncogenes, inactivation of tumor suppressors, and alterations in programmed cell death. Mitochondria play an essential role during tumor formation, progression, and metastasis of thyroid cancer. Recent studies have successfully observed the mitochondrial etiology of thyroid carcinogenesis. This review focuses on the recent progress in understanding the molecular mechanisms of thyroid cancer relating to altered mitochondrial metabolism.

STAT3 targeting by polyphenols: Novel therapeutic strategy for melanoma

Melanoma or malignant melanocytes appear with the low incidence rate, but very high mortality rate worldwide. Epidemiological studies suggest that polyphenolic compounds contribute for prevention or treatment of several cancers particularly melanoma. Such findings motivate to dig out novel therapeutic strategies against melanoma, including research toward the development of new chemotherapeutic and biologic agents that can target the tumor cells by different mechanisms. Recently, it has been found that signal transducer and activator of transcription 3 (STAT3) is activated in many cancer cases surprisingly. Different evidences supply the aspect that STAT3 activation plays a vital role in the metastasis, including proliferation of cells, survival, invasion, migration, and angiogenesis. This significant feature plays a vital role in various cellular processes, such as cell proliferation and survival. Here, we reviewed the mechanisms of the STAT3 pathway regulation and their role in promoting melanoma. Also, we have evaluated the emerging data on polyphenols (PPs) specifically their contribution in melanoma therapies with an emphasis on their regulatory/inhibitory actions in relation to STAT3 pathway and current progress in the development of phytochemical therapeutic techniques. An understanding of targeting STAT3 by PPs brings an opportunity to melanoma therapy. © 2016 BioFactors, 43(3):347-370, 2017.

The management of thyroid nodules and cancer in the molecular era

The incidence of thyroid cancer is increasing worldwide. Current standards in the diagnosis and management of thyroid cancer are limited by the uncertainty of fine-needle aspiration samples that are indeterminate in nature. Molecular markers have the potential to improve the accuracy of thyroid fine-needle aspiration and to aid the physician in giving a more accurate diagnosis and prognosis. This paper summarizes the various molecular markers currently available.

Iodide- and glucose-handling gene expression regulated by sorafenib or cabozantinib in papillary thyroid cancer

CONTEXT

The aberrant silencing of iodide-handling genes accompanied by up-regulation of glucose metabolism presents a major challenge for radioiodine treatment of papillary thyroid cancer (PTC).

OBJECTIVE

This study aimed to evaluate the effect of tyrosine kinase inhibitors on iodide-handling and glucose-handling gene expression in BHP 2-7 cells harboring RET/PTC1 rearrangement.

MAIN OUTCOME MEASURES

In this in vitro study, the effects of sorafenib or cabozantinib on cell growth, cycles, and apoptosis were investigated by cell proliferation assay, cell cycle analysis, and Annexin V-FITC apoptosis assay, respectively. The effect of both agents on signal transduction pathways was evaluated using the Western blot. Quantitative real-time PCR, Western blot, immunofluorescence, and radioisotope uptake assays were used to assess iodide-handling and glucose-handling gene expression.

RESULTS

Both compounds inhibited cell proliferation in a time-dependent and dose-dependent manner and caused cell cycle arrest in the G0/G1 phase. Sorafenib blocked RET, AKT, and ERK1/2 phosphorylation, whereas cabozantinib blocked RET and AKT phosphorylation. The restoration of iodide-handling gene expression and inhibition of glucose transporter 1 and 3 expression could be induced by either drug. The robust expression of sodium/iodide symporter induced by either agent was confirmed, and (125)I uptake was correspondingly enhanced. (18)F-fluorodeoxyglucose accumulation was significantly decreased after treatment by either sorafenib or cabozantinib.

CONCLUSIONS

Sorafenib and cabozantinib had marked effects on cell proliferation, cell cycle arrest, and signal transduction pathways in PTC cells harboring RET/PTC1 rearrangement. Both agents could be potentially used to enhance the expression of iodide-handling genes and inhibit the expression of glucose transporter genes.

Down-regulation of microRNA-21 is involved in the propofol-induced neurotoxicity observed in human stem cell-derived neurons

BACKGROUND

Recent studies in various animal models have suggested that anesthetics such as propofol, when administered early in life, can lead to neurotoxicity. These studies have raised significant safety concerns regarding the use of anesthetics in the pediatric population and highlight the need for a better model to study anesthetic-induced neurotoxicity in humans. Human embryonic stem cells are capable of differentiating into any cell type and represent a promising model to study mechanisms governing anesthetic-induced neurotoxicity.

METHODS

Cell death in human embryonic stem cell-derived neurons was assessed using terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate in situ nick end labeling staining, and microRNA expression was assessed using quantitative reverse transcription polymerase chain reaction. miR-21 was overexpressed and knocked down using an miR-21 mimic and antagomir, respectively. Sprouty 2 was knocked down using a small interfering RNA, and the expression of the miR-21 targets of interest was assessed by Western blot.

RESULTS

Propofol dose and exposure time dependently induced significant cell death (n = 3) in the neurons and down-regulated several microRNAs, including miR-21. Overexpression of miR-21 and knockdown of Sprouty 2 attenuated the increase in terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate in situ nick end labeling-positive cells following propofol exposure. In addition, miR-21 knockdown increased the number of terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate in situ nick end labeling-positive cells by 30% (n = 5). Finally, activated signal transducer and activator of transcription 3 and protein kinase B (Akt) were down-regulated, and Sprouty 2 was up-regulated following propofol exposure (n = 3).

CONCLUSIONS

These data suggest that (1) human embryonic stem cell-derived neurons represent a promising in vitro human model for studying anesthetic-induced neurotoxicity, (2) propofol induces cell death in human embryonic stem cell-derived neurons, and (3) the propofol-induced cell death may occur via a signal transducer and activator of transcription 3/miR-21/Sprouty 2-dependent mechanism.

KIF5B-RET fusion kinase promotes cell growth by multilevel activation of STAT3 in lung cancer

Background

Lung cancer in nonsmokers tends to be driven by a single somatic mutation or a gene fusion. KIF5B-RET fusion is an oncogene identified in non-small cell lung cancers. In this study, we verified the oncogenic activity of KIF5B-RET fusion and investigated how KIF5B-RET activates the specific signaling pathways for cellular transformation. We aimed to provide a basis for the further development of the therapy for KIF5B-RET positive lung cancer patients.

Methods

RT-PCR was used to screen for KIF5B-RET fusions in Chinese lung cancer patients. To verify the oncogenic activity of KIF5B-RET kinase in lung cancer cells, we manipulated its expression genetically followed by colony formation and tumor formation assays. The mechanism by which KIF5B-RET kinase induces proliferation was investigated by western blot, coimmunoprecipitation, and administration of RET, MAPK and STAT3 inhibitors.

Results

Our study identified a KIF5B-RET fusion in Chinese NSCLC patients and demonstrated that KIF5B-RET transfected cells showed a significantly increased proliferation rate and colony-forming ability. Furthermore, we found that KIF5B-RET fusion kinase induced multilevel activation of STAT3 at both Tyr⁷⁰⁵ and Ser⁷²⁷, and KIF5B-RET-STAT3 signaling related inhibitors repressed the proliferation and tumorigenicity of lung cancer cells significantly.

Conclusions

Our data suggest that KIF5B-RET promotes the cell growth and tumorigenicity of non-small cell lung cancers through multilevel activation of STAT3 signaling, providing possible strategies for the treatment of KIF5B-RET positive lung cancers.

The Role of STAT3 in Thyroid Cancer

Thyroid cancer is the most common endocrine malignancy and its global incidence rates are rapidly increasing. Although the mortality of thyroid cancer is relatively low, its rate of recurrence or persistence is relatively high, contributing to incurability and morbidity of the disease. Thyroid cancer is mainly treated by surgery and radioiodine remnant ablation, which is effective only for non-metastasized primary tumors. Therefore, better understanding of the molecular targets available in this tumor is necessary. Similarly to many other tumor types, oncogenic molecular alterations in thyroid epithelium include aberrant signal transduction of the mitogen-activated protein kinase, phosphatidylinositol 3-kinase/AKT (also known as protein kinase B), NF-кB, and WNT/β-catenin pathways. However, the role of the Janus kinase (JAK)/signal transducer and activator of transcription (STAT3) pathway, a well-known mediator of tumorigenesis in different tumor types, is relatively less understood in thyroid cancer. Intriguingly, recent studies have demonstrated that, in thyroid cancer, the JAK/STAT3 pathway may function in the context of tumor suppression rather than promoting tumorigenesis. In this review, we provide an update of STAT3 function in thyroid cancer and discuss some of the evidences that support this hypothesis.

Role of STAT3 in cancer metastasis and translational advances

Signal transducer and activator of transcription 3 (STAT3) is a latent cytoplasmic transcription factor, originally discovered as a transducer of signal from cell surface receptors to the nucleus. It is activated by tyrosine phosphorylation at position 705 leading to its dimerization, nuclear translocation, DNA binding, and activation of gene transcription. Under normal physiological conditions, STAT3 activation is tightly regulated. However, compelling evidence suggests that STAT3 is constitutively activated in many cancers and plays a pivotal role in tumor growth and metastasis. It regulates cellular proliferation, invasion, migration, and angiogenesis that are critical for cancer metastasis. In this paper, we first describe the mechanism of STAT3 regulation followed by how STAT3 is involved in cancer metastasis, then we summarize the various small molecule inhibitors that inhibit STAT3 signaling.

Comparison of SILAC and mTRAQ quantification for phosphoproteomics on a quadrupole orbitrap mass spectrometer

Advances in mass spectrometric methodology and instrumentation have promoted a continuous increase in analytical performance in the field of phosphoproteomics. Here, we employed the recently introduced quadrupole Orbitrap (Q Exactive) mass spectrometer for quantitative signaling analysis to a depth of more than 15 000 phosphorylation sites. In parallel to the commonly used SILAC approach, we evaluated the nonisobaric chemical labeling reagent mTRAQ as an alternative quantification technique. Both enabled high phosphoproteome coverage in H3122 lung cancer cells. Replicate quantifications by mTRAQ identified almost as many significant phosphorylation changes upon treatment with ALK kinase inhibitor crizotinib as found by SILAC quantification. Overall, mTRAQ was slightly less precise than SILAC as evident from a somewhat higher variance of replicate phosphosite ratios. Direct comparison of SILAC- and mTRAQ-quantified phosphosites revealed that the majority of changes were detected by either quantification techniques, but also highlighted the aspect of false negative identifications in quantitative proteomics applications. Further inspection of crizotinib-regulated phosphorylation changes unveiled interference with multiple antioncogenic mechanisms downstream of ALK fusion kinase in H3122 cells. In conclusion, our results demonstrate a strong analytical performance of the Q Exactive in global phosphoproteomics, and establish mTRAQ quantification as a useful alternative to metabolic isotope labeling.

GDNF family ligand dependent STAT3 activation is mediated by specific alternatively spliced isoforms of GFRα2 and RET

Neurturin (NRTN), a member of the GDNF family of ligands (GFL), is currently investigated in a series of clinical trials for Parkinson's disease. NRTN signals through its cognate receptor GFRα2 and co-receptor RET to induce neurite outgrowth, but the underlying mechanism remains to be better understood. STAT3 was previously shown to be activated by oncogenic RET, independent of ligand and GFRα. In this study, we demonstrated that NRTN induced serine(727) but not tyrosine(705) phosphorylation of STAT3 in primary cortical neuron and neuronal cell lines. Remarkably, STAT3 phosphorylation was found to be mediated specifically by GFRα2c and RET9 isoforms. Furthermore, serine but not tyrosine dominant negative mutant of STAT3 impaired NRTN induced neurite outgrowth, indicative of the role of STAT3 as a downstream mediator of NRTN function. Similar to NGF, the NRTN induced P-Ser-STAT3 was localized to the mitochondria but not to the nucleus. Mitochondrial STAT3 was further found to be intimately involved in NRTN induced neurite outgrowth. Collectively, these findings demonstrated the hitherto unrecognized and novel role of specific GFRα2 and RET isoforms in mediating NRTN activation of STAT3 and the transcription independent mechanism whereby the mitochondria localized P-Ser-STAT3 mediated NRTN induced neurite outgrowth.

AZD1480 blocks growth and tumorigenesis of RET- activated thyroid cancer cell lines

Persistent RET activation is a frequent event in papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC). In these cancers, RET activates the ERK/MAPK, the PI3K/AKT/mTOR and the JAK/STAT3 pathways. Here, we tested the efficacy of a JAK1/2- inhibitor, AZD1480, in the in vitro and in vivo growth of thyroid cancer cell lines expressing oncogenic RET. Thyroid cancer cell lines harboring RET/PTC1 (TPC-1), RET M918T (MZ-CRC1) and RET C634W (TT) alterations, as well as TPC-1 xenografts, were treated with JAK inhibitor, AZD1480. This inhibitor led to growth inhibition and/or apoptosis of the thyroid cancer cell lines in vitro, as well as to tumor regression of TPC-1 xenografts, where it efficiently blocked STAT3 activation in tumor and stromal cells. This inhibition was associated with decreased proliferation, decreased blood vessel density, coupled with increased necrosis. However, AZD1480 repressed the growth of STAT3- deficient TPC-1 cells in vitro and in vivo, demonstrating that its effects in this cell line were independent of STAT3 in the tumor cells. In all cell lines, the JAK inhibitor reduced phospho-Y1062 RET levels, and mTOR effector phospho-S6, while JAK1/2 downregulation by siRNA did not affect cell growth nor RET and S6 activation. In conclusion, AZD1480 effectively blocks proliferation and tumor growth of activated RET- thyroid cancer cell lines, likely through direct RET inhibition in cancer cells as well as by modulation of the microenvironment (e.g. via JAK/phospho-STAT3 inhibition in endothelial cells). Thus, AZD1480 should be considered as a therapeutic agent for the treatment of RET- activated thyroid cancers.

STAT3 negatively regulates thyroid tumorigenesis

Although tyrosine-phosphorylated or activated STAT3 (pY-STAT3) is a well-described mediator of tumorigenesis, its role in thyroid cancer has not been investigated. We observed that 63 of 110 (57%) human primary papillary thyroid carcinoma (PTC) cases expressed nuclear pY-STAT3 in tumor cells, preferentially in association with the tumor stroma. An inverse relationship between pY-STAT3 expression with tumor size and the presence of distant metastases was observed. Using human thyroid cancer-derived cell lines [harboring rearranged during transfection (RET)/PTC, v-RAF murine sarcoma viral oncogene homolog B (BRAF), or rat sarcoma virus oncogene (RAS) alterations], we determined that IL-6/gp130/JAK signaling is responsible for STAT3 activation. STAT3 knockdown by shRNA in representative thyroid cancer cell lines that express high levels of pY-STAT3 had no effect on in vitro growth. However, xenografted short hairpin STAT3 cells generated larger tumors than control cells. Similarly, STAT3 deficiency in a murine model of BRAFV600E-induced PTC led to thyroid tumors that were more proliferative and larger than those tumors expressing STAT3wt. Genome expression analysis revealed that STAT3 knockdown resulted in the down-regulation of multiple transcripts, including the tumor suppressor insulin-like growth factor binding protein 7. Furthermore, STAT3 knockdown led to an increase in glucose consumption, lactate production, and expression of Hypoxia-inducible factor 1 (HIF1α) target genes, suggesting that STAT3 is a negative regulator of aerobic glycolysis. Our studies show that, in the context of thyroid cancer, STAT3 is paradoxically a negative regulator of tumor growth. These findings suggest that targeting STAT3 in these cancers could enhance tumor size and highlight the complexities of the role of STAT3 in tumorigenesis.

Rapamycin inhibits both motility through down-regulation of p-STAT3 (S727) by disrupting the mTORC2 assembly and peritoneal dissemination in sarcomatoid cholangiocarcinoma

Cholangiocarcinoma (CC) is a malignant epithelium neoplasm that originates from the bile epithelium and for which there are few therapeutic strategies. The mTOR pathway involved in many cellular processes was reported to be up-regulated in various cancers. We investigated the activation of the AKT/mTOR pathway in CC cell lines with different degrees of dedifferentiation and found that rapamycin could suppress the motility and the peritoneal dissemination of sarcomatoid SCK cells. Inhibition of the mTOR pathway with rapamycin decreased significantly the number of tumor nodules and prolonged the survival rates of nude mice inoculated with sarcomatoid CC cells. Prolonged treatments with rapamycin were found to disrupt the mTORC2 assembly and to reduce the phosphorylation of STAT3 at Ser 727. Rapamycin decreased both mRNA and protein levels of MMP2 and Twist1, which are regulated by STAT3 and associated with cancer metastasis. The overexpression of STAT3 S727A lacking the phosphorylation site resulted in significantly less sensitivity to rapamycin than the overexpression of STAT3 WT. Taken together, our results suggest that rapamycin could suppress the motility of sarcomatoid CC by down-regulating p-STAT3 (S727) through the impairment of mTORC2 assembly.

Thyroid-specific ablation of the Carney complex gene, PRKAR1A, results in hyperthyroidism and follicular thyroid cancer

Thyroid cancer is the most common endocrine malignancy in the population, and the incidence of this cancer is increasing at a rapid rate. Although genetic analysis of papillary thyroid cancer (PTC) has identified mutations in a large percentage of patients, the genetic basis of follicular thyroid cancer (FTC) is less certain. Thyroid cancer, including both PTC and FTC, has been observed in patients with the inherited tumor predisposition Carney complex, caused by mutations in PRKAR1A. In order to investigate the role of loss of PRKAR1A in thyroid cancer, we generated a tissue-specific knockout of Prkar1a in the thyroid. We report that the resulting mice are hyperthyroid and developed follicular thyroid neoplasms by 1 year of age, including FTC in over 40% of animals. These thyroid tumors showed a signature of pathway activation different from that observed in other models of thyroid cancer. In vitro cultures of the tumor cells indicated that Prkar1a-null thyrocytes exhibited growth factor independence and suggested possible new therapeutic targets. Overall, this work represents the first report of a genetic mutation known to cause human FTC that exhibits a similar phenotype when modeled in the mouse. In addition to our knowledge of the mechanisms of human follicular thyroid tumorigenesis, this model is highly reproducible and may provide a viable mechanism for the further clinical development of therapies aimed at FTC.

RET fusion genes are associated with chronic myelomonocytic leukemia and enhance monocytic differentiation

Myeloproliferative neoplasms are frequently associated with aberrant constitutive tyrosine kinase (TK) activity resulting from chimaeric fusion genes or point mutations such as BCR-ABL1 or JAK2 V617F. We report here the cloning and functional characterization of two novel fusion genes BCR-RET and FGFR1OP-RET in chronic myelomonocytic leukemia (CMML) cases generated by two balanced translocations t(10;22)(q11;q11) and t(6;10)(q27;q11), respectively. The two RET fusion genes leading to the aberrant activation of RET, are able to transform hematopoietic cells and skew the hematopoietic differentiation program towards the monocytic/macrophage lineage. The RET fusion genes seem to constitutively mimic the same signaling pathway as RAS mutations frequently involved in CMML. One patient was treated with Sorafenib, a specific inhibitor of the RET TK function, and demonstrated cytological and clinical remissions.

Intracellular signal transduction and modification of the tumor microenvironment induced by RET/PTCs in papillary thyroid carcinoma

RET gene rearrangements (RET/PTCs) represent together with BRAF point mutations the two major groups of mutations involved in papillary thyroid carcinoma (PTC) initiation and progression. In this review, we will examine the mechanisms involved in RET/PTC-induced thyroid cell transformation. In detail, we will summarize the data on the molecular mechanisms involved in RET/PTC formation and in its function as a dominant oncogene, on the activated signal transduction pathways and on the induced gene expression modifications. Moreover, we will report on the effects of RET/PTCs on the tumor microenvironment. Finally, a short review of the literature on RET/PTC prognostic significance will be presented.

The insulin resistance Grb14 adaptor protein promotes thyroid cancer ret signaling and progression

The growth factor receptor-bound protein (Grb) 14 is an adapter molecule of the Grb7/10/14 family with characteristic BPS domains serving to avidly bind tyrosine kinases. Grb14 inhibits insulin receptor (IR) catalytic activity through interaction with the BPS domain and impedes peptide substrate binding. Members of this Grb family have also been shown to interact with other kinases through their SH2 domain. Here we examined the functional role of Grb14 in thyroid cancer using loss- and gain-of-function approaches. Stable knockdown of Grb14 in thyroid cancer cells facilitated insulin receptor signaling. In contrast, RET phosphorylation was diminished in concert with reduced activation of Akt and STAT3. Loss of Grb14 also resulted in diminished cell proliferation and invasion both in vitro and in mouse flank xenografts. In complementary studies, forced expression of Grb14 interrupted insulin receptor signaling but facilitated RET activation, STAT3, and Akt phosphorylation. Consistent with these findings Grb14 over-expression enhanced cell invasion and resulted in striking metastases in an orthotopic thyroid cancer mouse xenograft model. Primary human thyroid cancer microarrays revealed a positive correlation between Grb14 expression and invasive behavior. Our findings uncover a new role for Grb14 in finely tuning receptor signaling and modulating thyroid cancer progression.

Sunitinib inhibits MEK/ERK and SAPK/JNK pathways and increases sodium/iodide symporter expression in papillary thyroid cancer

BACKGROUND

Sunitinib malate (Sutent, Pfizer, Inc.; SU11248) is a selective, multitargeted inhibitor of receptor tyrosine kinases and has been shown to inhibit receptors for VEGF, PDGF, KIT, FLT3, and RET. The objective of this study was to determine the effects of sunitinib on signal transduction pathways and on gene expression of iodide-metabolizing proteins in papillary cancer cells with the RET/PTC1 rearrangement.

METHODS

We investigated the effects of sunitinib on cell growth, signal transduction pathways, and thyroid-specific gene expression in papillary thyroid cancer (PTC) cell lines that had the RET/PTC1 rearrangement.

RESULTS

Sunitinib inhibited proliferation of RET/PTC1 subclones in a time- and dose-related manner. The mean 50% lethal concentration in the RET/PTC1 subclones was 1.81 microM. Incubation of RET/PTC1 cells with 1 microM sunitinib inhibited their migration potential and transformed their morphology. Sunitinib inhibited RET autophosphorylation at Y1062 and the activation of signal transducer and activator of transcription 3 by blocking Y705 phosphorylation. Sunitinib caused cell cycle arrest in the G0/G1 phase and dephosphorylation of retinoblastoma protein, but did not induce apoptosis. Western blot analysis of the p38, MEK/ERK, and SAPK/JNK mitogen-activated protein kinase signal transduction pathways showed that sunitinib blocked ERK 1/2 and JNK phosphorylation in the cytoplasm. Sunitinib treatment of RET/PTC1 cell lines, in combination, with forskolin induced expression of the sodium (Na)/iodide (I) symporter (NIS) and the transcription factors that bind the NIS upstream enhancer. Mechanistically, the inhibition of both MEK/ERK and SAPK/JNK cytoplasmic pathways individually and in combination caused an increase in NIS gene expression.

CONCLUSION

Sunitinib appears to target the cytosolic MEK/ERK and SAPK/JNK pathways in the RET/PTC1 cell lines, suggesting that blocking these pathways is at least part of the mechanism by which sunitinib inhibits cell proliferation and causes stimulation of NIS gene expression in RET/PTC1 cells.

Role of STAT3 in in vitro transformation triggered by TRK oncogenes

TRK oncoproteins are chimeric versions of the NTRK1/NGF receptor and display constitutive tyrosine kinase activity leading to transformation of NIH3T3 cells and neuronal differentiation of PC12 cells. Signal Transducer and Activator of Transcription (STAT) 3 is activated in response to cytokines and growth factors and it has been recently identified as a novel signal transducer for TrkA, mediating the functions of NGF in nervous system. In this paper we have investigated STAT3 involvement in signalling induced by TRK oncogenes. We showed that TRK oncogenes trigger STAT3 phosphorylation both on Y705 and S727 residues and STAT3 transcriptional activity. MAPK pathway was involved in the induction of STAT3 phosphorylation. Interestingly, we have shown reduced STAT3 protein level in NIH3T3 transformed foci expressing TRK oncogenes. Overall, we have unveiled a dual role for STAT3 in TRK oncogenes-induced NIH3T3 transformation: i) decreased STAT3 protein levels, driven by TRK oncoproteins activity, are associated to morphological transformation; ii) residual STAT3 transcriptional activity is required for cell growth.

Inhibition of the JAK-STAT3 pathway by andrographolide enhances chemosensitivity of cancer cells to doxorubicin

Andrographolide (Andro), a diterpenoid lactone isolated from a traditional herbal medicine Andrographis paniculata, is known to possess potent anti-inflammatory and anticancer properties. In this study, we sought to examine the effect of Andro on signal transducer and activator of transcription 3 (STAT3) pathway and evaluate whether suppression of STAT3 activity by Andro could sensitize cancer cells to a chemotherapeutic drug doxorubicin. First, we demonstrated that Andro is able to significantly suppress both constitutively activated and IL-6-induced STAT3 phosphorylation and subsequent nuclear translocation in cancer cells. Such inhibition is found to be achieved through suppression of Janus-activated kinase (JAK)1/2 and interaction between STAT3 and gp130. For understanding the biological significance of the inhibitory effect of Andro on STAT3, we next investigated the effect of Andro on doxorubicin-induced apoptosis in human cancer cells. In our study the constitutive activation level of STAT3 was found to be correlated to the resistance of cancer cells to doxorubicin-induced apoptosis. Both the short-term MTT assay and the long-term colony formation assay showed that Andro dramatically promoted doxorubicin-induced cell death in cancer cells, indicating that Andro enhances the sensitivity of cancer cells to doxorubicin mainly via STAT3 suppression. These observations thus reveal a novel anticancer function of Andro and suggest a potential therapeutic strategy of using Andro in combination with chemotherapeutic agents for treatment of cancer.

Linear combinations of docking affinities explain quantitative differences in RTK signaling

Receptor tyrosine kinases (RTKs) process extracellular cues by activating a broad array of signaling proteins. Paradoxically, they often use the same proteins to elicit diverse and even opposing phenotypic responses. Binary, ‘on–off' wiring diagrams are therefore inadequate to explain their differences. Here, we show that when six diverse RTKs are placed in the same cellular background, they activate many of the same proteins, but to different quantitative degrees. Additionally, we find that the relative phosphorylation levels of upstream signaling proteins can be accurately predicted using linear models that rely on combinations of receptor-docking affinities and that the docking sites for phosphoinositide 3-kinase (PI3K) and Shc1 provide much of the predictive information. In contrast, we find that the phosphorylation levels of downstream proteins cannot be predicted using linear models. Taken together, these results show that information processing by RTKs can be segmented into discrete upstream and downstream steps, suggesting that the challenging task of constructing mathematical models of RTK signaling can be parsed into separate and more manageable layers.

ret/PTC-1 expression alters the immunoprofile of thyroid follicular cells

Background

Hashimoto Thyroiditis (H.T.) is a destructive autoimmune thyroid condition whose precise molecular pathogenesis remains unclear. ret/PTC-1 is a chimeric transcript which has been described in autoimmune thyroid disease (AITD) and thyroid neoplasia. The purpose of this study was to observe the immunogenic effect exposure to H.T. and control lymphocyte supernatant would have on normal (Nthy-ori) and ret/PTC-1 (TPC-1) expressing thyroid cell line models.

Results

A 2 × 2 matrix comprising Nthy-ori and TPC-1 cell lines and H.T. and control lymphocyte supernatant was designed and utilised as follows; activated lymphocytic supernatant from a H.T. and normal control were co-cultured with a cell line derived from normal thyroid (Nthy-ori) and also a cell line derived from a papillary thyroid carcinoma that endogenously expresses ret/PTC-1 (TPC-1). The co-cultures were harvested at 0, 6 and 18 hour time points. Gene expression analysis was performed on RNA extracted from thyrocytes using TaqMan^® Immune profiling Low-Density Arrays (Applied Biosystems, CA, USA) comprising gene expression markers for 93 immune related targets plus 3 endogenous controls.

Stimulation of the normal thyroid cell line model with activated T cell supernatant from the H.T. donor yielded global up-regulation of immune targets when compared with control supernatant stimulation. In particular, a cohort of targets (granzyme B, CD3, CD25, CD152, CD45) associated with cytotoxic cell death; T cell receptor (TCR) and T cell signaling were up-regulated in the normal cell line model. When the ret/PTC-1 expressing thyroid cell line was co-cultured with H.T. lymphocyte supernatant, in comparison to control supernatant stimulation, down-regulation of the same subset of immune targets was seen.

Conclusion

Co-culturing H.T. lymphocyte supernatant with a normal thyroid cell line model leads to over-expression of a subset of targets which could contribute to the pathogenesis of H.T. via cytotoxic cell death and TCR signalling. Stimulation of the ret/PTC-1 positive cell line with the same stimulus led to a down-regulated shift in the gene expression pattern of the cohort of immune targets. We hypothesize that ret/PTC-1 activation may dampen immunogenic responses in the thyroid, which could possibly facilitate papillary thyroid carcinoma development.

Modulatory role of phospholipase D in the activation of signal transducer and activator of transcription (STAT)-3 by thyroid oncogenic kinase RET/PTC

Background

RET/PTC (rearranged in transformation/papillary thyroid carcinomas) gene rearrangements are the most frequent genetic alterations identified in papillary thyroid carcinoma. Although it has been established that RET/PTC kinase plays a crucial role in intracellular signaling pathways that regulate cellular transformation, growth, and proliferation in thyroid epithelial cells, the upstream signaling that leads to the activation of RET/PTC is largely unknown. Based on the observation of high levels of PLD expression in human papillary thyroid cancer tissues, we investigated whether PLD plays a role in the regulating the RET/PTC-induced STAT3 activation.

Methods

Cancer tissue samples were obtained from papillary thyroid cancer patients (n = 6). The expression level of PLD was examined using immunohistochemistry and western blotting. Direct interaction between RET/PTC and PLD was analyzed by co-immunoprecipitation assay. PLD activity was assessed by measuring the formation of [³H]phosphatidylbutanol, the product of PLD-mediated transphosphatidylation, in the presence of n-butanol. The transcriptional activity of STAT3 was assessed by m67 luciferase reporter assay.

Results

In human papillary thyroid cancer, the expression levels of PLD2 protein were higher than those in the corresponding paired normal tissues. PLD and RET/PTC could be co-immunoprecipitated from cells where each protein was over-expressed. In addition, the activation of PLD by pervanadate triggered phosphorylation of tyrosine 705 residue on STAT-3, and its phosphorylation was dramatically higher in TPC-1 cells (from papillary carcinoma) that have an endogenous RET/PTC1 than in ARO cells (from anaplastic carcinoma) without alteration of total STAT-3 expression. Moreover, the RET/PTC-mediated transcriptional activation of STAT-3 was synergistically increased by over-expression of PLD, whereas the PLD activity as a lipid hydrolyzing enzyme was not affected by RET/PTC.

Conclusion

These findings led us to suggest that the PLD synergistically functions to activate the STAT3 signaling by interacting directly with the thyroid oncogenic kinase RET/PTC.

Tumor Suppressor LKB1 Inhibits Activation of Signal Transducer and Activator of Transcription 3 (STAT3) by Thyroid Oncogenic Tyrosine Kinase Rearranged in Transformation (RET)/Papillary Thyroid Carcinoma (PTC)

The tumor suppressor LKB1 (STK11) is a cytoplasmic/nuclear serine/threonine kinase, defects in which cause Peutz-Jeghers syndrome (PJS) in humans and animals. Recent studies showed that loss of function of LKB1 is associated with sporadic forms of lung, pancreatic, and ovarian cancer. In cancer cells, LKB1 is inactivated by two mechanisms: mutations in its central kinase domain or complete loss of LKB1 expression. Inactivation of LKB1 is associated with progression of PJS and transformation of benign polyps into malignant tumors. This study examines the effect of LKB1 on regulation of STAT3 and expression of transcriptional targets of STAT3. The results show that LKB1 inhibits rearranged in transformation (RET)/papillary thyroid carcinoma (PTC)-dependent activation of signal transducer and activator of transcription 3 (STAT3), which is mediated by phosphorylation of STAT3 tyrosine 705 by RET/PTC. Suppression of STAT3 transactivation by LKB1 requires the kinase domain but not the kinase activity of LKB1. The centrally located kinase domain of LKB1 is an approximately 260-amino-acid region that binds to the linker domain of STAT3. Chromatin immunoprecipitation studies indicate that expression of LKB1 reduces the binding of STAT3 to its target promoters and suppresses STAT3-mediated expression of Cyclin D1, VEGF, and Bcl-xL. Knockdown of LKB1 by specific small interfering RNA led to an increase in STAT3 transactivation activity and promoted cell proliferation in the presence of RET/PTC. Thus, this study suggests that LKB1 suppresses tumor growth by inhibiting RET/PTC-dependent activation of oncogenic STAT3.

RET(MEN 2B) is active in the endoplasmic reticulum before reaching the cell surface

MEN 2B (multiple endocrine neoplasia type 2B) is an autosomal dominant cancer syndrome caused by an oncogenic form of the receptor tyrosine kinase REarranged during transfection (RET). The MEN 2B syndrome is associated with an abnormal autophosphorylation of the mutated receptor even without ligand-stimulation. Here, we characterize the activation of a RET(MEN 2B) variant carrying the point mutation Met918Thr, and show that the 150 kDa precursor of RET(MEN 2B) becomes phosphorylated already during synthesis in the endoplasmic reticulum (ER). At least three different tyrosine residues (Tyr905, Tyr1062, Tyr1096) of the RET(MEN 2B) precursor are phosphorylated before the oncogenic receptor reaches the cell surface. We also demonstrate that the precursor of RET(MEN 2B) interacts with both growth factor receptor-bound protein and Src homology 2 domain-containing already in the ER, and that this interaction is dependent on the kinase activity of RET. With the aid of two RET mutants (RET(MEN 2B/S32L) and RET(MEN 2B/F393L)), which accumulate in the ER, we show that the oncogenic precursor of the receptor has the capacity to activate AKT, extracellular signal-regulated kinase and signal transducer and activator of transcription 3 from the ER. Taken together, our data demonstrate that the oncogenic precursor of RET(MEN 2B) is phosphorylated, interacts with adapter proteins and induces downstream signalling from the ER.

Ras/ERK1/2-mediated STAT3 Ser727 phosphorylation by familial medullary thyroid carcinoma-associated RET mutants induces full activation of STAT3 and is required for c-fos promoter activation, cell mitogenicity, and transformation

The precise role of STAT3 Ser(727) phosphorylation in RET-mediated cell transformation and oncogenesis is not well understood. In this study, we have shown that familial medullary thyroid carcinoma (FMTC) mutants RET(Y791F) and RET(S891A) induced, in addition to Tyr(705) phosphorylation, constitutive STAT3 Ser(727) phosphorylation. Using inhibitors and dominant negative constructs, we have demonstrated that RET(Y791F) and RET(S891A) induce STAT3 Ser(727) phosphorylation via a canonical Ras/ERK1/2 pathway and that integration of the Ras/ERK1/2/ELK-1 and STAT3 pathways was required for up-regulation of the c-fos promoter by FMTC-RET. Moreover, inhibition of ERK1/2 had a more severe effect on cell proliferation and cell phenotype in HEK293 cells expressing RET(S891A) compared with control and RET(WT)-transfected cells. The transforming activity of RET(Y791F) and RET(S891A) in NIH-3T3 cells was also inhibited by U0126, indicating a role of the ERK1/2 pathway in RET-mediated transformation. To investigate the biological significance of Ras/ERK1/2-induced STAT3 Ser(727) phosphorylation for cell proliferation and transformation, N-Ras-transformed NIH-3T3 cells were employed. These cells displayed elevated levels of activated ERK1/2 and Ser(727)-phosphorylated STAT3, which were inhibited by treatment with U0126. Importantly, overexpression of STAT3, in which the Ser(727) was mutated into Ala (STAT3(S727A)), rescued the transformed phenotype of N-Ras-transformed cells. Immunohistochemistry in tumor samples from FMTC patients showed strong nuclear staining of phosphorylated ERK1/2 and Ser(727) STAT3. These data show that FMTC-RET mutants activate a Ras/ERK1/2/STAT3 Ser(727) pathway, which plays an important role in cell mitogenicity and transformation.

Neurotrophic factor receptor RET: structure, cell biology, and inherited diseases

RET (REarranged during Transfection) is a transmembrane receptor tyrosine kinase that is activated by a complex consisting of a soluble glial cell line-derived neurotrophic factor (GDNF) family ligand (GFL) and a glycosyl phosphatidylinositol-anchored co-receptor, GDNF family receptors alpha (GFRalpha). RET signalling is crucial for the development of the enteric nervous system. RET also regulates the development of sympathetic, parasympathetic, motor, and sensory neurons, and is necessary for the postnatal maintenance of dopaminergic neurons. The effect of GFLs on sensory, motor, and dopaminergic neurons has raised clinical interest towards these ligands. Outside the nervous system, RET is crucial for development of the kidney and plays a key role in spermatogenesis. Inactivating mutations in RET cause the Hirschsprung's disease characterized by megacolon aganglionosis. In contrast, activating mutations give rise to different types of cancer, multiple endocrine neoplasia type 2A and type 2B, familial medullary thyroid carcinoma, and papillary thyroid carcinoma. The multiple disease phenotypes correlate with differences in the molecular and cell biological functions of different oncogenic RET proteins. In this review we summarize how the different domains of the RET protein contribute to its normal function and how mutations in these domains affect the function of the receptor.

An orally administered multitarget tyrosine kinase inhibitor, SU11248, is a novel potent inhibitor of thyroid oncogenic RET/papillary thyroid cancer kinases

CONTEXT

The oncogenic RET/PTC tyrosine kinase causes papillary thyroid cancer (PTC). The use of inhibitors specific for RET/PTC may be useful for targeted therapy of PTC.

OBJECTIVE

The objective of the study was to evaluate the efficacies of the recently developed kinase inhibitors SU11248, SU5416, and SU6668 in inhibition of RET/PTC.

DESIGN

SU11248, SU5416, and SU6668 were synthesized, and their inhibitory potencies were evaluated using an in vitro RET/PTC kinase assay. The inhibitory effects of the compounds on RET/PTC were evaluated by quantifying the autophosphorylation of RET/PTC, signal transducer and activator of transcription (STAT)-3 activation, and the morphological reversal of RET/PTC-transformed cells.

RESULTS

An in vitro kinase assay revealed that SU5416, SU6668, and SU11248 inhibited phosphorylation of the synthetic tyrosine kinase substrate peptide E4Y by RET/PTC3 in a dose-dependent manner with IC(50) of approximately 944 nm for SU5416, 562 nm for SU6668, and 224 nm for SU11248. Thus, SU11248 effectively inhibits the kinase activity of RET/PTC3. RET/PTC-mediated Y705 phosphorylation of STAT3 was inhibited by addition of SU11248, and the inhibitory effects of SU11248 on the tyrosine phosphorylation and transcriptional activation of STAT3 were very closely correlated with decreased autophosphorylation of RET/PTC. SU11248 caused a complete morphological reversion of transformed NIH-RET/PTC3 cells and inhibited the growth of TPC-1 cells that have an endogenous RET/PTC1.

CONCLUSION

SU11248 is a highly effective tyrosine kinase inhibitor of the RET/PTC oncogenic kinase.

Conditional activation of RET/PTC3 and BRAFV600E in thyroid cells is associated with gene expression profiles that predict a preferential role of BRAF in extracellular matrix remodeling

Papillary thyroid cancers (PTC) are associated with nonoverlapping mutations of genes coding for mitogen-activated protein kinase signaling effectors (i.e., the TK receptors RET or NTRK and the signaling proteins RAS and BRAF). We examined the pattern of gene expression after activation of these oncoproteins in thyroid PCCL3 cells, with the goal of identifying pathways or gene subsets that may account for the phenotypic differences observed in human cancers. We hybridized cDNA from cells treated with or without doxycycline to induce expression of BRAF(V600E), RET/PTC3, or RET/PTC3 with small interfering RNA-mediated knockdown of BRAF, respectively, to slides arrayed with a rat 70-mer oligonucleotide library consisting of 27,342 oligos. Among the RET/PTC3-induced genes, 2,552 did not require BRAF as they were similarly regulated by RET/PTC3 with or without BRAF knockdown and not by expression of BRAF(V600E). Immune response and IFN-related genes were highly represented in this group. About 24% of RET/PTC3-regulated genes were BRAF dependent, as they were similarly modified by RET/PTC3 and BRAF(V600E) but not in cells expressing RET/PTC3 with knockdown of BRAF. A gene cluster coding for components of the mitochondrial electron transport chain pathway was down-regulated in this group, potentially altering regulation of cell viability. Metalloproteinases were also preferentially induced by BRAF, particularly matrix metalloproteinase 3 (MMP3), MMP9, and MMP13. Accordingly, conditional expression of BRAF was associated with markedly increased invasion into Matrigel compared with cells expressing RET/PTC3. The preferential induction of MMPs by BRAF could explain in part the more invasive behavior of thyroid cancers with BRAF mutations.

Influence of the BRAF V600E mutation on expression of vascular endothelial growth factor in papillary thyroid cancer

CONTEXT

The BRAF mutation may influence the expression patterns of molecular markers that are related to the development and progression of thyroid cancer.

OBJECTIVE

The objective of the study was to investigate the effects of the BRAF V600E mutation on expression of galectin-3, cyclooxygenase-2, cyclin D1, p53, and vascular endothelial growth factor (VEGF) in papillary thyroid cancer (PTC).

DESIGN, SETTING, AND SUBJECTS

One hundred sixty-three PTC and 28 nodular hyperplasia patients were selected retrospectively. The presence of the BRAF V600E mutation and the level of expression of the molecular markers were determined.

RESULTS

Of 161 PTC patients, 102 patients (63.4%) were BRAF V600E(+), and these cases had significantly larger tumor sizes (P = 0.01), compared with V600E(-) cases (n = 59, 36.6%). Although PTC tissues had higher expression levels of the selected molecular markers than nodular hyperplasia tissues, expression levels of several molecular markers in BRAF V600E(+) PTC were not significantly different from those of BRAF V600E(-) PTC. But VEGF was significantly up-regulated in BRAF V600E(+) PTC, compared with BRAF V600E(-) PTC. VEGF expression levels were strongly positively correlated to tumor size (P < 0.001), extrathyroidal invasion (P = 0.02), and tumor stage (P = 0.04). Multivariate analysis clearly showed that VEGF expression was up-regulated in BRAF V600E(+) PTC (odds ratio 2.5, confidence interval 1.1-5.6; P = 0.03).

CONCLUSIONS

BRAF V600E(+) PTC tended to have larger tumor volumes and higher expression of VEGF. The level of VEGF expression was closely correlated with tumor size, extrathyroidal invasion, and stage. The relatively high levels of VEGF expression may be related to poorer clinical outcomes and recurrences in BRAF V600E(+) PTC.

Regulation of Protein Kinase B Tyrosine Phosphorylation by Thyroid-Specific Oncogenic RET/PTC Kinases

Papillary thyroid carcinoma (PTC) is a heterogenous disorder characterized by unique gene rearrangements and gene mutations that activate signaling pathways responsible for cellular transformation, survival, and antiapoptosis. Activation of protein kinase B (PKB) and its downstream signaling pathways appears to be an important event in thyroid tumorigenesis. In this study, we found that the thyroid-specific oncogenic RET/PTC tyrosine kinase is able to phosphorylate PKB in vitro and in vivo. RET/PTC-transfected cells showed tyrosine phosphorylation of endogenous and exogenous PKB, which was independent of phosphorylation of T308 and S473 regulated by the upstream kinases phosphoinositide-dependent kinase-1 and -2, respectively. The PKB Y315 residue, which is known to be phosphorylated by Src tyrosine kinase, was also a major site of phosphorylation by RET/PTC. RET/PTC-mediated tyrosine phosphorylation results in the activation of PKB kinase activity. The activation of PKB by RET/PTC blocked the activity of the forkhead transcription factor, FKHRL1, but a Y315F mutant of PKB failed to inhibit FKHRL1 activity. In summary, these observations suggest that RET/PTC is able to phosphorylate the Y315 residue of PKB, an event that results in maximal activation of PKB for RET/PTC-induced thyroid tumorigenesis.

Somatic and germline mutation in GRIM-19, a dual function gene involved in mitochondrial metabolism and cell death, is linked to mitochondrion-rich (Hurthle cell) tumours of the thyroid

Oxyphil or Hurthle cell tumours of the thyroid are characterised by their consistent excessive number of mitochondria. A recently discovered gene, GRIM-19 has been found to fulfil two roles within the cell: as a member of the interferon-beta and retinoic acid-induced pathway of cell death, and as part of the mitochondrial Complex I assembly. In addition, a gene predisposing to thyroid tumours with cell oxyphilia (TCO) has been mapped to chromosome 19p13.2 in one family. A cluster of genes involved in mitochondrial metabolism occurs in this region; one of these is GRIM-19. We have searched for GRIM-19 mutations in a series of 52 thyroid tumours. Somatic missense mutations in GRIM-19 were detected in three of 20 sporadic Hurthle cell carcinomas. A germline mutation was detected in a Hurthle cell papillary carcinoma arising in a thyroid with multiple Hurthle cell nodules. No mutations were detected in any of the 20 non-Hurthle cell carcinomas tested, nor in any of 96 blood donor samples. In one of the sporadic Hurthle cell papillary carcinomas positive for GRIM-19 mutation, we have also detected a ret/PTC-1 rearrangement. No GRIM-19 mutations were detected in any of the six cases of known familial Hurthle cell tumour tested, so that our results do not support the identification of GRIM-19 as the TCO gene. The GRIM-19 mutations we have detected are the first nuclear gene mutations specific to Hurthle cell tumours to be reported to date; we propose that such mutations can be involved in the genesis of sporadic or familial Hurthle cell tumours through the dual function of GRIM-19 in mitochondrial metabolism and cell death.

Regulation of Signal Transducer and Activator of Transcription 1 (STAT1) and STAT1-Dependent Genes by RET/PTC (Rearranged in Transformation/Papillary Thyroid Carcinoma) Oncogenic Tyrosine Kinases

Chimeric RET/PTC (rearranged in transformation/papillary thyroid carcinoma) oncoproteins are constitutively active tyrosine kinases found in thyroid papillary carcinoma and nonneoplastic Hashimoto’s thyroiditis. Although several proteins have been identified to be substrates of RET/PTC kinases, the pathogenic roles played by RET/PTC in malignant and benign thyroid diseases and the molecular mechanisms that are involved are not fully understood. We found that RET/PTC expression phosphorylates the Y701 residue of STAT1, a type II interferon (IFN)-responsive protein. RET/PTC-mediated signal transducer and activator of transcription 1 (STAT1) phosphorylation requires RET/PTC kinase activity to be intact but other tyrosine kinases, such as Janus kinases or c-Src, are not involved. RET/PTC-induced STAT1 transcriptional activation was not inhibited by suppressor of cytokine signaling-1 or -3, or protein inhibitors of activated STAT3 [(protein inhibitor of activated STAT (PIAS3)], but PIAS1 strongly repressed the RET/PTC-induced transcriptional activity of STAT1. RET/PTC-induced STAT1 activation caused IFN regulatory factor-1 expression. We found that STAT1 and IFN regulatory factor-1 cooperated to significantly increase transcription from type IV IFN-γresponsive promoters of class II transactivator genes. Significantly, cells stably expressing RET/PTC expressed class II transactivator and showed enhanced de novo membrane expression of major histocompatibility complex (MHC) class II proteins. Furthermore, RET/PTC1-bearing papillary thyroid carcinoma cells strongly expressed MHC class II (human leukocyte-associated antigen-DRα) genes, whereas the surrounding normal tissues did not. Thus, RET/PTC is able to phosphorylate and activate STAT1. This may lead to enhanced MHC class II expression, which may explain why the tissues surrounding RET/PTC-positive cancers are infiltrated with lymphocytes. Such immune response-promoting activity of RET/PTC may also relate to the development of Hashimoto’s thyroiditis.

Disruption of STAT3 signaling leads to tumor cell invasion through alterations of homotypic cell-cell adhesion complexes

STAT3 is frequently overexpressed and constitutively activated by tyrosine phosphorylation during malignant transformation. Despite the clear importance of STAT3 in cell proliferation and survival in diverse human cancers, its possible contribution to tumor cell adhesion, motility and invasion remains hypothetical. We therefore compared the transforming properties of STAT3wt, its constitutively activated dimeric form STAT3C, and the dominant negative mutant STAT3-Y705F in human colorectal HCT8/S11 cancer cells. Both STAT3wt and STAT3C exert a permissive action to the proinvasive activity of the scatter factor HGF in HCT8/S11 cells. In contrast, the monomeric and cytoplasmic mutant Y705F induces a constitutive invasive phenotype through Wnt/Rho-independent and EGFR/PI3-kinase-dependent pathways. Accordingly, Y705F decreases cell-cell homotypic adhesions, and increases cell motility and scattering, as well as lamellipodia-type cellular extensions. STAT3-Y705F-transfected HCT8/S11 cells display an increased tyrosine phosphorylation of the cell-cell adhesion regulator beta-catenin and its dissociation from the invasion suppressor E-cadherin at cell-cell contacts. Our data imply that both invasion promoter and repressor genes are controlled by the canonical STAT3 transcription pathways. Disruption of this cascade by Y705F reveals the proinvasive potential of altered forms of STAT3 as a persistent signaling adaptor in cytokine/transforming growth factor receptor scaffolds and oncogenic pathways.

Stimulation of hTAFII68 (NTD)-mediated transactivation by v-Src

The three genes hTAF(II)68, EWS, and TLS (called the TET family) encode related RNA binding proteins containing an RNA recognition motif and three glycine-, arginine-, and proline-rich regions in the C-terminus and a degenerated repeat containing the consensus sequence Ser-Tyr-Gly-Gln-Ser in the N-terminus. In many human cancers, the N-terminal portion of hTAF(II)68, EWS, or TLS is fused to the DNA binding domain of one of several transcription factors including Fli-1, ERG, ETV1, E1AF, WT1, ATF-1, CHOP, or TEC. We have recognized the presence of several potential tyrosine phosphorylation sites within the amino-terminal domain of hTAF(II)68 and have investigated the potential effects of cytoplasmic signaling on hTAF(II)68 function. Herein, we find that hTAF(II)68 is phosphorylated on tyrosine residue(s) by ectopic expression of v-Src protein tyrosine kinase in vitro and in vivo. The hTAF(II)68 protein can associated with the SH3 domains of several cell signaling proteins, including v-Src protein tyrosine kinase. We also document that full-length v-Src can stimulate hTAF(II)68-mediated transcriptional activation, whereas deletion mutants of v-Src are unable to exert this effect. In addition, cellular Src activity appears important for hTAF(II)68 function since hTAF(II)68-mediated transactivation is reduced in a dose-dependent fashion by ectopic overexpression of a dominant-negative mutant of Src. Taken together, our results suggest that the biological activities of hTAF(II)68 are linked to the cytoplasmic Src signal transduction pathway.