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)

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.

STK11 Prevents Invasion through Signal Transducer and Activator of Transcription 3/5 and FAK Repression in Cutaneous Melanoma

The STK11/LKB1 is a tumor suppressor involved in metabolism and cell motility. In BRAFV600E melanoma, STK11 is inactivated by extracellular signal‒regulated kinase and RSK, preventing it from binding and activating adenosine monophosphate-activated protein kinase and promoting melanoma cell proliferation. Although STK11 mutations occur in 5‒10% of cutaneous melanoma, few functional studies have been performed. By knocking out STK11 with CRISPR/Cas9 in two human BRAF-mutant melanoma cell lines, we found that STK11 loss reduced the sensitivity to a BRAF inhibitor. More strikingly, STK11 loss led to an increased invasive phenotype in both three-dimensional spheroids and in vivo zebrafish xenograft models. STK11 overexpression consistently reversed the invasive phenotype. Interestingly, STK11 knockout increased invasion also in an NRAS-mutant melanoma cell line. Furthermore, although STK11 was expressed in primary human melanoma tumors, its expression significantly decreased in melanoma metastases, especially in brain metastases. In the STK11-knockout cells, we observed increased activating phosphorylation of signal transducer and activator of transcription 3/5 and FAK. Using inhibitors of signal transducer and activator of transcription 3/5 and FAK, we reversed the invasive phenotype in both BRAF- and NRAS-mutated cells. Our findings confirm an increased invasive phenotype on STK11 inactivation in BRAF- and NRAS-mutant cutaneous melanoma that can be targeted by signal transducer and activator of transcription 3/5 and FAK inhibition.

LKB1/AMPK Pathway and Drug Response in Cancer: A Therapeutic Perspective

Inactivating mutations of the tumor suppressor gene Liver Kinase B1 (LKB1) are frequently detected in non-small-cell lung cancer (NSCLC) and cervical carcinoma. Moreover, LKB1 expression is epigenetically regulated in several tumor types. LKB1 has an established function in the control of cell metabolism and oxidative stress. Clinical and preclinical studies support a role of LKB1 as a central modifier of cellular response to different stress-inducing drugs, suggesting LKB1 pathway as a highly promising therapeutic target. Loss of LKB1-AMPK signaling confers sensitivity to energy depletion and to redox homeostasis impairment and has been associated with an improved outcome in advanced NSCLC patients treated with chemotherapy. In this review, we provide an overview of the interplay between LKB1 and its downstream targets in cancer and focus on potential therapeutic strategies whose outcome could depend from LKB1.

ETS1 regulates Twist1 transcription in a KrasG12D/Lkb1-/- metastatic lung tumor model of non-small cell lung cancer

Distinct members of the Ets family of transcription factors act as positive or negative regulators of genes involved in cellular proliferation, development, and tumorigenesis. In human lung cancer, increased ETS1 expression is associated with poor prognosis and metastasis. We tested whether ETS1 contributes to lung tumorigenesis by binding to Twist1, a gene involved in tumor cell motility and dissemination. We used a mouse lung cancer model with metastasis driven by conditionally activated Kras and concurrent tumor suppressor Lkb1 loss (Kras^G12D/ Lkb1^-/- model) and a similar model of lung cancer that does not metastasize, driven by conditionally activated Kras alone (Kras^G12D model). We show that Ets1 and Twist1 gene expression differs between Kras^G12D tumors (low Ets1 and Twist1 expression) and Kras^G12D/Lkb1^-/- tumors (high Ets1 and Twist1 expression). In human lung tumors, ETS1 and TWIST1 expression positively correlates and low combined ETS1 and TWIST1 levels are associated with improved survival compared to high levels. Using mouse cell lines derived from Kras^G12D and Kras^G12D/Lkb1^-/- mouse models and the human lung cancer (A549) cell line, we show that ETS1 regulates Twist1 expression. Chromatin immunoprecipitation assays confirm binding of ETS1 to the Twist1 promoter. Overexpression studies show that ETS1 transactivates Twist1 promoter activity in mouse and human cells. Silencing endogenous Ets1 by siRNA in mouse cell lines decreases Twist1 mRNA levels, decreases invasion, and increases cell growth. Ets1 and Twist1 are at the crossroad of several signaling pathways in cancer. Understanding their regulation may inform the development of therapies to impair lung tumor metastasis.

miRNA‑148a inhibits cell growth of papillary thyroid cancer through STAT3 and PI3K/AKT signaling pathways

The function of miRNA‑148a in lymphatic metastases of papillary thyroid cancer and its mechanism were tested. In this investigation, miRNA‑148a expression of lymphatic metastases of papillary thyroid cancer patients was inhibited, compared with normal group. We found that miRNA‑148a overexpression was effectively reduced cell cell proliferation and metastases, and induced apoptosis of papillary thyroid cancer in vitro. Overexpression of miRNA‑148a significantly induced Bax protein expression and caspase‑3/9 levels, and suppressed phosphorylation STAT3 (p‑STAT3), PI3K and p‑Akt protein expression of papillary thyroid cancer in vitro. Next, si‑STAT3, could inhibit p‑STAT3 protein expression, reducing cell-cell proliferation and metastases, and inducing apoptosis of papillary thyroid cancer following miRNA‑148a overexpression. Then, the PI3K inhibitor was able to inhibit PI3K and p‑Akt protein expression, reduced cell cell proliferation and metastases, and induced apoptosis of papillary thyroid cancer following miRNA‑148a overexpression. Taken together, our results suggest that miRNA‑148a inhibits lymphatic metastases of papillary thyroid cancer through STAT3 and PI3K/AKT signaling pathways.

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.

STK11 Mutation Identified in Thyroid Carcinoma

Peutz-Jeghers syndrome (PJS) is an autosomal-dominant disorder, in which germline mutation of serine threonine-protein kinase 11 (STK11) is identified in up to 90 % of the patients who meet clinical criteria for PJS. Hematoxylin and eosin (H&E) slides of the tumor were reviewed to confirm areas with at least 25 % of tumor cellularity. Then, the designated area was extracted for genomic DNA. Targeted next-generation sequencing analysis was performed using a 47-gene panel. Case 1 is a 71-year-old man with high grade follicular thyroid carcinoma with clear cell and oncocytic features. The carcinoma showed a missense mutation in TP53 (p.R342G, c.1024C > G) and a 16-nucleotide intronic deletion started next to the 3' of exon 6 (involving the canonical +1 and +2 bases of the splice donor site) in STK11 (p.?, c.862 + 1_862 + 16delGTGGGAGCCTCATCCC). Case 2 is a 76-year-old woman with tall cell variant papillary thyroid carcinoma. The carcinoma demonstrated a missense mutation in BRAF (p.V600E, c.1799T > A) and a missense mutation in STK11 (p.F354L, c.1062C > G). In summary, we present two elderly patients with thyroid carcinoma harboring STK11 mutation without clinical manifestation of PJS. The findings suggest that STK11 may play a role in thyroid carcinoma development.

Regulation of triple-negative breast cancer cell metastasis by the tumor-suppressor liver kinase B1

Liver kinase B1 (LKB1), also known as serine/threonine kinase 11 (STK11), has been identified as a tumor suppressor in many cancers including breast. Low LKB1 expression has been associated with poor prognosis of breast cancer patients, and we report here a significant association between loss of LKB1 expression and reduced patient survival specifically in the basal subtype of breast cancer. Owing to the aggressive nature of the basal subtype as evidenced by high incidences of metastasis, the purpose of this study was to determine if LKB1 expression could regulate the invasive and metastatic properties of this specific breast cancer subtype. Induction of LKB1 expression in basal-like breast cancer (BLBC)/triple-negative breast cancer cell lines, MDA-MB-231 and BT-549, inhibited invasiveness in vitro and lung metastatic burden in an orthotopic xenograft model. Further analysis of BLBC cells overexpressing LKB1 by unbiased whole transcriptomics (RNA-sequencing) revealed striking regulation of metastasis-associated pathways, including cell adhesion, extracellular matrix remodeling, and epithelial-to-mesenchymal transition (EMT). In addition, LKB1 overexpression inhibited EMT-associated genes (CDH2, Vimentin, Twist) and induced the epithelial cell marker CDH1, indicating reversal of the EMT phenotype in the MDA-MB-231 cells. We further demonstrated marked inhibition of matrix metalloproteinase 1 expression and activity via regulation of c-Jun through inhibition of p38 signaling in LKB1-expressing cells. Taken together, these data support future development of LKB1 inducing therapeutics for the suppression of invasion and metastasis of BLBC.

Mitochondrial Energy Metabolism and Thyroid Cancers

Primary thyroid cancers including papillary, follicular, poorly differentiated, and anaplastic carcinomas show substantial differences in biological and clinical behaviors. Even in the same pathological type, there is wide variability in the clinical course of disease progression. The molecular carcinogenesis of thyroid cancer has advanced tremendously in the last decade. However, specific inhibition of oncogenic pathways did not provide a significant survival benefit in advanced progressive thyroid cancer that is resistant to radioactive iodine therapy. Accumulating evidence clearly shows that cellular energy metabolism, which is controlled by oncogenes and other tumor-related factors, is a critical factor determining the clinical phenotypes of cancer. However, the role and nature of energy metabolism in thyroid cancer remain unclear. In this article, we discuss the role of cellular energy metabolism, particularly mitochondrial energy metabolism, in thyroid cancer. Determining the molecular nature of metabolic remodeling in thyroid cancer may provide new biomarkers and therapeutic targets that may be useful in the management of refractory thyroid cancers.

Synergistic effects of eukaryotic co-expression plasmid-based STAT3-specific siRNA and LKB1 on ovarian cancer in vitro and in vivo

The signal transducer and activator of transcription 3 (STAT3) are ideal targets for ovarian cancer. Previous studies showed that downregulation of STAT3 using specific short hairpin RNAs (shRNA) can significantly reduce ovarian tumor growth. However, RNA interference does not fully ablate target gene expression due to idiosyncrasies associated with shRNAs and their targets. To enhance the therapeutic efficacy of STAT3-specific shRNA, we employed a combinatorial expression of STAT3-specific shRNA and liver kinase B1 (LKB1), a tumor suppressor. Thus, the LKB1 coding sequences and STAT3-specific shRNAs were constructed in a eukaryotic co-expression plasmid pCDNA3.1, and then transfected into ovarian cancer cells to evaluate the synergistic effects of this combination on anticancer activity and explore the relevant molecular mechanisms. Co-expression of STAT3‑specific siRNA and LKB1 (pSi-STAT3-LKB1) synergistically inhibited ovarian cancer cell growth, invasion and migration, induced cell apoptosis and arrested the cell cycle in vitro when compared with monotherapy. The results showed that the co-expression of plasmid pSi-STAT3-LKB1 inserted subcutaneously into ovarian tumor xenograft resulted in more significant inhibition of tumor growth. Further study showed that the synergistic anti-ovarian cancer effects of the co-expression of STAT3-specific siRNA and LKB1 may be associated with the upregulation of p-p53, p21 and downregulation of survivin, BCL-2 and cyclin D1. Results of the present study suggested that combined therapy with eukaryotic co-expression of the plasmid‑carrying STAT3-specific siRNA and LKB1 is a novel and efficient treatment strategy for human ovarian cancer.

The tumor suppressor LKB1 antagonizes WNT signaling pathway through modulating GSK3β activity in cell growth of esophageal carcinoma

The tumor suppressor LKB1 gene encodes a serine-threonine kinase that regulates cell proliferation and polarity. Inactivation of LKB1 by mutations in LKB1 or loss of its expression is highly correlated with lung, ovarian, and pancreatic cancers, and WNT/β-catenin pathway is also known to be involved in many human malignancies. However, the relationship between LKB1 and WNT signaling pathway in esophageal carcinoma remains unknown. The expression of LKB1 in 62 cases of esophageal cancer patients was determined by quantitative real-time PCR. It was found that LKB1 mRNA level was significantly lower than the adjacent normal epithelium and that the LKB1 downregulation was correlating with TNM stages. Moreover, the expression of WNT target genes such as Cyclin D1, C-MYC, MMP2, and FZD2 was significantly upregulated in esophageal cancer tissues. LKB1 overexpression in TE10 cells inhibited TOPFlash luciferase reporter activity and WNT target gene expression even in the presence of WNT3A. Conversely, LKB1 knockdown enhanced WNT signaling activity in esophageal cancer cells. It was also found that LKB1 antagonized WNT signaling pathway through interaction with GSK3β to downregulate β-catenin expression level. Functional investigation revealed that LKB1 suppressed the promotion effects of WNT3A on the cell growth of TE10 cells. The LKB1 functions in regulating cell growth and WNT target genes expression were impaired by GSK3β inhibition, suggesting that LKB1 antagonized WNT-induced cell proliferation through enhancement of GSK3β activity. Together, the interaction between LKB1 and GSK3β upregulates GSK3β activity to suppress WNT-induced cell proliferation in esophageal carcinoma cells. Loss of LKB1 expression may result in the deregulation of WNT/β-catenin pathway to promote malignant progression of esophageal cancer.

Downregulation of LKB1 suppresses Stat3 activity to promote the proliferation of esophageal carcinoma cells

The tumor suppressor liver kinase B1 (LKB1) encodes a serine/threonine kinase. The defect in LKB1 is the primary cause of Peutz-Jeghers syndrome (PJS). Inactivation of LKB1 by mutations or loss of LKB1 expression is associated with ovarian, lung and pancreatic cancer; however, the correlation between LKB1 and esophageal carcinoma remains unknown. Thus, quantitative PCR was performed to determine the clinical significance of LKB1 expression in 60 cases of esophageal cancer and its adjacent normal epithelium. LKB1 expression was observed to significantly downregulate the accompanying cancer progression, which was verified at the protein level by western blot analysis. Furthermore, the phosphorylated signal transducer and activator of transcription 3 (Stat3) level is reversibly associated with LKB1 expression. To determine the function of LKB1 in esophageal cancer, LKB1 expression is induced in TE1 esophageal cancer cells. The results show that LKB1 overexpression suppresses the proliferation of TE1 cells, downregulates the expression of cyclin D1 and Myc and represses Stat3 phosphorylation. Suppression of cell proliferation and cyclin D1 expression by LKB1 is fully inhibited by constitutively active Stat3C coexpression, suggesting that LKB1 inhibits esophageal cancer cell proliferation through suppression of Stat3 transaction. In conclusion, downregulation of LKB1 expression suppresses Stat3 activity that may promote tumor growth during esophageal cancer progression.

Decreased expression of LKB1 correlates with poor prognosis in hepatocellular carcinoma patients undergoing hepatectomy

AIM

To study any correlation of LKB1 expression with prognosis in hepatocellular carcinoma (HCC) cases.

METHODS

A total of 70 HCC patients and 20 primary intrahepatic stone patients in the first affiliated hospital of Wenzhou Medical College were enrolled in this study. LKB1 expression was detected by immunohistochemistry. Patients were followed-up and prognostic factors were evaluated.

RESULT

LKB1 expression was decreased in the HCC samples. Loss of LKB1 expression in HCC was significantly related to histologic grade (P=0.010), vascular invasion (P=0.025) and TMN stage (P=0.011). Patients showing negative LKB1 expression had a significantly shorter disease-free and overall survival than those with positive expression (P = 0.001, P=0.000, respectively). Multivariate Cox regression analysis indicated that LKB1 expression level was an independent factor of survival (P = 0.033).

CONCLUSION

HCC patients with decreased expression LKB1 have a poor prognosis. The loss of LKB1 expression is correlated with a lower survival rate.

LKB1 controls human bronchial epithelial morphogenesis through p114RhoGEF-dependent RhoA activation

LKB1 is a Ser/Thr kinase that plays an important role in controlling both energy metabolism and cell polarity in metazoan organisms. LKB1 is also a tumor suppressor, and homozygous, inactivating mutations are found in a wide range of human cancers. In lung cancer, inactivating mutations are found in 10 to 50% of cases, but the consequences of functional loss in this context are poorly understood. We report here that LKB1 is required for the maturation of apical junctions in the human bronchial epithelial cell line 16HBE14o- (16HBE). This activity is dependent on an interaction with the Rho guanine nucleotide exchange factor p114RhoGEF but is independent of LKB1 kinase activity. Together, LKB1 and p114RhoGEF control RhoA activity in these cells to promote apical junction assembly.

Tumor-derived mutations in the gene associated with retinoid interferon-induced mortality (GRIM-19) disrupt its anti-signal transducer and activator of transcription 3 (STAT3) activity and promote oncogenesis

The signal transducer and activator of transcription 3 (STAT3) protein is critical for multiple cytokine and growth factor-induced biological responses in vivo. Its transcriptional activity is controlled by a transient phosphorylation of a critical tyrosine. Constitutive activation of STAT3 imparts resistance to apoptosis, promotes cell proliferation, and induces de novo micro-angiogenesis, three of the six cardinal hallmarks of a typical cancer cell. Earlier we reported the isolation of GRIM-19 as a growth suppressor using a genome-wide expression knockdown strategy. GRIM-19 binds to STAT3 and suppresses its transcriptional activity. To understand the pathological relevance of GRIM-19, we screened a set of primary head and neck tumors and identified three somatic mutations in GRIM-19. Wild-type GRIM-19 suppressed cellular transformation by a constitutively active form of STAT3, whereas tumor-derived mutants L71P, L91P and A95T significantly lost their ability to associate with STAT3, block gene expression, and suppress cellular transformation and tumor growth in vivo. Additionally, these mutants lost their capacity to prevent metastasis. These mutations define a mechanism by which STAT3 activity is deregulated in certain human head and neck tumors.

Low dose irradiation of thyroid cells reveals a unique transcriptomic and epigenetic signature in RET/PTC-positive cells

The high doses of radiation received in the wake of the Chernobyl incident and the atomic bombing of Hiroshima and Nagasaki have been linked to the increased appearance of thyroid cancer in the children living in the vicinity of the site. However, the data gathered on the effect of low doses of radiation on the thyroid remain limited. We have examined the genome wide transcriptional response of a culture of TPC-1 human cell line of papillary thyroid carcinoma origin with a RET/PTC1 translocation to various doses (0.0625, 0.5, and 4Gy) of X-rays and compared it to response of thyroids with a RET/PTC3 translocation and against wild-type mouse thyroids irradiated with the same doses using Affymetrix microarrays. We have found considerable overlap at a high dose of 4Gy in both RET/PTC-positive systems but no common genes at 62.5mGy. In addition, the response of RET/PTC-positive system at all doses was distinct from the response of wild-type thyroids with both systems signaling down different pathways. Analysis of the response of microRNAs in TPC-1 cells revealed a radiation-responsive signature of microRNAs in addition to dose-responsive microRNAs. Our results point to the fact that a low dose of X-rays seems to have a significant proliferative effect on normal thyroids. This observation should be studied further as opposed to its effect on RET/PTC-positive thyroids which was subtle, anti-proliferative and system-dependent.

The association of adrenocortical carcinoma and thyroid cancer in a child with Peutz-Jeghers syndrome

Peutz-Jeghers syndrome (PJS) is a rare, dominantly inherited disorder characterized by gastrointestinal hamartomatous polyps, mucocutaneous hyperpigmentation, and an increased risk of cancer. We present a 16-month-old child diagnosed with PJS, who had distinguishing features compared with the previously reported cases with respect to her clinical presentation, associated malignancies, and genetic analysis. To our knowledge, this is the first report of adrenocortical carcinoma in association with PJS, as well as the first instance of associated thyroid cancer in a child with PJS. We briefly review the relevant literature and highlight the recent progress achieved in the investigation of the syndrome.

Tumor Suppressor Serine/Threonine Kinase LKB1 Expression, Not Kinase Activity, Increased in the Vascular Smooth Muscle Cells and Neointima in the Rat Carotid Artery Injury Model

BACKGROUND AND OBJECTIVES

Vascular smooth muscle cell (VSMC) proliferation is responsible for the restenosis of previously inserted coronary stents. Angiotensin II (Ang II) is known to regulate VSMC proliferation. LKB1, a serine/threonine kinase, interacts with the p53 pathway and acts as a tumor suppressor.

MATERIALS AND METHODS

We assessed the association of Ang II and the expression of LKB1 in primary cultured murine VSMCs and neointima of the Sprague Dawley rat carotid artery injury model. We created carotid balloon injuries and harvested the injured carotid arteries 14 days after the procedure.

RESULTS

Ang II increased LKB1 expression in a time-dependent manner and peaked at an Ang II concentration of 10(-7) mole/L in VSMCs. In the animal experiment, neointima was markedly increased after balloon injury compared to the control group. Immunohistochemical studies showed that LKB1 expression increased according to neointima thickness. Ang II augmented LKB1 expression after the injury. Western blot analysis of LKB1 with carotid artery lysate revealed the same pattern as LKB1 immunohistochemistry. Increased LKB1 expression started at 5 days after the balloon injury, and peaked at 14 days after the injury. Although LKB1 expression was increased after the injury, LKB1 kinase activity was not increased. Ang II or balloon-injury increased the expression of LKB1 although the LKB1 activity was reduced.

CONCLUSION

Ang II increased LKB1 expression in VSMCs and neointima. These findings were not kinase dependant.

A germline mutation (A339V) in thyroid transcription factor-1 (TITF-1/NKX2.1) in patients with multinodular goiter and papillary thyroid carcinoma

BACKGROUND

The genetic factors that determine the risk of papillary thyroid carcinoma (PTC) among patients with multinodular goiter (MNG) remain undefined. Because thyroid transcription factor-1 (TTF-1) is important to thyroid development, we evaluated whether the gene that encodes it, TITF-1/NKX2.1, is a genetic determinant of MNG/PTC predisposition.

METHODS

Twenty unrelated PTC patients with a history of MNG (MNG/PTC), 284 PTC patients without a history of MNG (PTC), and 349 healthy control subjects were screened for germline mutation(s) in TITF-1/NKX2.1 by sequencing of amplified DNA from blood. The effects of the mutation on the growth and differentiation of thyroid cells were demonstrated by ectopic expression of wild-type (WT) and mutant proteins in PCCL3 normal rat thyroid cells, followed by tests of cell proliferation, activation of cell growth pathways, and transcription of TTF-1 target genes. All statistical tests were two-sided.

RESULTS

A missense mutation (1016C>T) was identified in TITF-1/NKX2.1 that led to a mutant TTF-1 protein (A339V) in four of the 20 MNG/PTC patients (20%). These patients developed substantially more advanced tumors than MNG/PTC or PTC patients without the mutation (P = .022, Fisher exact test). Notably, this germline mutation was dominantly inherited in two families, with some members bearing the mutation affected with MNG, associated with either PTC or colon cancer. The mutation encoding the A339V substitution was not found among the 349 healthy control subjects nor among the 284 PTC patients who had no history of MNG. Overexpression of A339V TTF-1 in PCCL3 cells, as compared with overexpression of WT TTF-1, was associated with increased cell proliferation including thyrotropin-independent growth (average A339V proliferation rate = 134.27%, WT rate = 104.43%, difference = 34.3%, 95% confidence interval = 12.0% to 47.7%, P = .010), enhanced STAT3 activation, and impaired transcription of the thyroid-specific genes Tg, TSH-R, and Pax-8.

CONCLUSION

This is the first germline mutation identified in MNG/PTC patients. It could contribute to predisposition for MNG and/or PTC and to the pathogenesis of PTC.