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Mingzhao Xing

Publications and source records attributed to Mingzhao Xing.

18 recordsLinked to original sources
PubMed2006

Association of aberrant methylation of tumor suppressor genes with tumor aggressiveness and BRAF mutation in papillary thyroid cancer.

The role of aberrant tumor suppressor gene methylation in the aggressiveness of papillary thyroid cancer (PTC) has not been documented. By showing promoter methylation-induced gene silencing in PTC-derived cell lines, we first demonstrated the functional consequence of methylation of several recently identified tumor suppressor genes, including those for tissue inhibitor of metalloproteinase-3 (TIMP3), SLC5A8, death-associated protein kinase (DAPK) and retinoic acid receptor beta2 (RARbeta2). We then investigated the role of methylation of these genes in the aggressiveness of PTC by examining the relationship of their aberrant methylation to clinicopathological characteristics and BRAF mutation in 231 primary PTC tumors. Methylation of TIMP3, SLC5A8 and DAPK was significantly associated with several aggressive features of PTC, including extrathyroidal invasion, lymph node metastasis, multifocality and advanced tumor stages. Methylation of these genes was also significantly associated with BRAF mutation in PTC, either individually or collectively in various combinations. Methylation of these genes, either individually or collectively, occurred more frequently in more aggressive classical and tall-cell PTC subtypes than in less aggressive follicular-variant PTC, with the latter known to infrequently harbor BRAF mutation. Several other tumor suppressor genes investigated were not methylated. These results suggest that aberrant methylation and hence silencing of TIMP3, SLC5A8, DAPK and RARbeta2, in association with BRAF mutation, may be an important step in PTC tumorigenesis and progression.

Apoptosis Regulatory Proteins↗
PubMed2006

Gene methylation in thyroid tumorigenesis.

Aberrant gene methylation plays an important role in human tumorigenesis, including thyroid tumorigenesis. Many tumor suppressor genes are aberrantly methylated in thyroid cancer, and some even in benign thyroid tumors, suggesting a role of this epigenetic event in early thyroid tumorigenesis. Methylation of some of these genes tends to occur in certain types of thyroid cancer and is related to specific signaling pathways. For example, methylation of PTEN and RASSF1A genes occurs mostly in follicular thyroid cancer, and its tumorigenic role may be related to the phosphatidylinositol 3-kinase/Akt signaling pathway, whereas methylation of genes for tissue inhibitor of metalloproteinase-3, SLC5A8, and death-associated protein kinase occurs in papillary thyroid cancer and is related to the BRAF/MAPK kinase/MAPK pathway. Methylation of thyroid-specific genes, such as those for sodium/iodide symporter and thyroid-stimulating hormone receptor, is also common in thyroid cancer. Although its tumorigenic role is not clear, methylation, and hence silencing, of these thyroid-specific genes is a cause for the failure of clinical radioiodine treatment of thyroid cancer. Unlike gene methylation, histone modifications have been relatively poorly investigated in thyroid tumors. Future studies need to emphasize the mechanistic aspects of these two types of epigenetic alterations to uncover new molecular mechanisms in thyroid tumorigenesis and to provide novel therapeutic targets for thyroid cancer.

Animals↗
PubMed2005

Detection of serum deoxyribonucleic acid methylation markers: a novel diagnostic tool for thyroid cancer.

CONTEXT: Serum DNA methylation markers may potentially be useful in diagnosing thyroid cancer and monitoring its recurrence. OBJECTIVE: The objective of the study was to assess the utility of serum DNA methylation as a diagnostic test for patients with thyroid nodules and a monitoring test to detect thyroid cancer recurrence in previously treated patients. DESIGN, SETTING, AND SUBJECTS: Using real-time quantitative methylation-specific PCR, we analyzed the methylation status of five genes (CALCA, CDH1, TIMP3, DAPK, and RARbeta2) on 96 bisulfite-treated serum DNA samples isolated preoperatively from either solid thyroid nodule patients or patients in follow-up for history of treated thyroid cancer. MAIN OUTCOME MEASURE: Diagnostic sensitivity, specificity, and accuracy of serum DNA methylation marker for thyroid cancer were measured. RESULTS: For the patients with thyroid nodules, when a positive result was defined by a serum methylation level above the appropriately chosen cutoff value for any one of the five genes, the preoperative diagnostic sensitivity for thyroid cancer was 68% (26 of 38), the specificity was 95% (18 of 19), and the overall preoperative diagnostic accuracy was 77%, with positive and negative predictive values of 96 and 60%, respectively. In a subset of patients with cytologically indeterminate thyroid nodules, serum DNA methylation testing could correctly diagnose eight of 11 (73%) cancers and four of four (100%) benign tumors, with a diagnostic accuracy of 80%. We also analyzed these serum DNA methylation markers in 39 previously treated thyroid cancer patients. Among the 10 patients proved to have recurrent disease by conventional measures, seven (70%) were positive on methylation testing. Among the 29 patients who had no corroboration of residual or recurrent disease by conventional studies, six (21%) were positive for serum DNA methylation markers. CONCLUSIONS: We have demonstrated the potential usefulness of serum DNA methylation markers as a novel tool for differential diagnosis of solid thyroid nodules and thyroid cancer recurrence monitoring.

Biomarkers↗
PubMed2005

Tumor-specific changes in mtDNA content in human cancer.

Mitochondrial DNA (mtDNA) alterations are associated with various cancer types, suggesting that the mitochondrial genome may be a critical contributing factor in carcinogenesis. mtDNA alterations have been suggested as a potentially sensitive and specific biomarker for several cancer types. We examined mtDNA content in 25 pairs of normal and tumor breast tissue samples, 37 papillary thyroid carcinoma (PTC), 21 benign thyroid neoplasms and in 20 paired normal and PTC samples. Our results showed that mtDNA content was reduced in 80% of the breast tumors relative to their corresponding normal. mtDNA was increased in papillary thyroid carcinomas, however, when compared to the corresponding normal DNA taken from the same individual. Also, mtDNA content was increased in none-paired PTC samples compared to the normal controls. Our findings indicate that changes in mtDNA content during carcinogenesis may be regulated in a tumor specific manner. Additionally, changes in mtDNA levels did not correlate with tumor grade and metastasis, suggesting that these alterations may occur in the early stages of tumorigenesis. Our findings suggest that mtDNA content can be used as a molecular diagnostic tool to help identify genetic abnormalities in human tumors.

Breast Neoplasms↗
PubMed2005

BRAF mutation predicts a poorer clinical prognosis for papillary thyroid cancer.

CONTEXT: Use of BRAF mutation in papillary thyroid cancer (PTC) has the potential to improve risk stratification of this cancer. OBJECTIVE: The objective of the study was to investigate the prognostic value of BRAF mutation in patients with PTC. DESIGN, SETTING, AND SUBJECTS: In a multicenter study of 219 PTC patients, data on their clinicopathological characteristics and clinical courses between 1990 and 2004 were retrospectively collected, and their tumor BRAF mutation status was determined. Associations of BRAF mutation with initial tumor characteristics and subsequent recurrence were analyzed. MAIN OUTCOME MEASURE: Relationships between the BRAF mutation status and clinicopathological outcomes, including recurrence, were measured. RESULTS: We found a significant association between BRAF mutation and extrathyroidal invasion (P < 0.001), lymph node metastasis (P < 0.001), and advanced tumor stage III/IV (P = 0.007) at initial surgery. This association remained significant on multivariate analysis, adjusting for conventional clinicopathological predictors of recurrence excluding the histological PTC subtype, but was lost when the tumor subtype was included in the model. BRAF mutation was also significantly associated with tumor recurrence, 25 vs. 9% with and without mutation, respectively (P = 0.004), during a median of 15 (interquartile range, 3-29) months of follow-up. This association remained significant on multivariate analysis adjusting for conventional clinicopathological predictors of recurrence, even including the PTC subtype (odds ratio, 4.0; 95% confidence interval, 1.1-14.1; P = 0.03). BRAF mutation was even an independent predictor of recurrence in patients with stage I/II disease, 22 vs. 5% with and without BRAF mutation, respectively (P = 0.002). BRAF mutation was also more frequently associated with absence of tumor I-131 avidity and treatment failure of recurrent disease. CONCLUSIONS: In patients with PTC, BRAF mutation is associated with poorer clinicopathological outcomes and independently predicts recurrence. Therefore, BRAF mutation may be a useful molecular marker to assist in risk stratification for patients with PTC.

Adult↗
PubMed2005

High prevalence and possible de novo formation of BRAF mutation in metastasized papillary thyroid cancer in lymph nodes.

CONTEXT: The role of the T1799A BRAF mutation in lymph node metastasis of papillary thyroid cancer (PTC) is not clear. OBJECTIVE: Our objective was to explore the relationship between BRAF mutation and lymph node metastasis of PTC by examining the mutation in both the primary tumors and their paired lymph node metastases. DESIGN: We isolated genomic DNA from primary thyroid tumors and paired lymph node metastases and performed direct sequencing of exon 15 of the BRAF gene mutation that carries the T1799A mutation. RESULTS: In a series of 33 cases, 21 harbored the T1799A mutation in the primary tumors, and 17 (81%) of them harbored the same mutation also in the paired lymph node metastases. Twelve cases did not harbor the T1799A mutation in the primary tumors, among which nine cases also did not harbor BRAF mutation in the lymph node-metastasized tumors, whereas the other three did harbor the T1799A mutation in lymph node-metastasized tumor tissues. A novel tandem TG1799-1800AA mutation within one allele was found in a lymph node-metastasized tumor but not in the primary tumor. This mutation results in the change of codon 600 (GTG) of the gene to GAA with the consequent amino acid change (V600E) in the B-type Raf (BRAF) protein, same as that caused by the T1799A mutation alone. CONCLUSION: The high prevalence of BRAF mutation in lymph node-metastasized PTC tissues from BRAF mutation-positive primary tumors and the possible de novo formation of BRAF mutation in lymph node-metastasized PTC were consistent with a role of BRAF mutation in facilitating the metastasis and progression of PTC in lymph nodes.

Adenine↗
PubMed2005

Somatic mutation and gain of copy number of PIK3CA in human breast cancer.

INTRODUCTION: Phosphatidylinositol 3-kinases (PI3Ks) are a group of lipid kinases that regulate signaling pathways involved in cell proliferation, adhesion, survival, and motility. Even though PIK3CA amplification and somatic mutation have been reported previously in various kinds of human cancers, the genetic change in PIK3CA in human breast cancer has not been clearly identified. METHODS: Fifteen breast cancer cell lines and 92 primary breast tumors (33 with matched normal tissue) were used to check somatic mutation and gene copy number of PIK3CA. For the somatic mutation study, we specifically checked exons 1, 9, and 20, which have been reported to be hot spots in colon cancer. For the analysis of the gene copy number, we used quantitative real-time PCR and fluorescence in situ hybridization. We also treated several breast cancer cells with the PIK3CA inhibitor LY294002 and compared the apoptosis status in cells with and without PIK3CA mutation. RESULTS: We identified a 20.6% (19 of 92) and 33.3% (5 of 15) PIK3CA somatic mutation frequency in primary breast tumors and cell lines, respectively. We also found that 8.7% (8 of 92) of the tumors harbored a gain of PIK3CA gene copy number. Only four cases in this study contained both an increase in the gene copy number and a somatic mutation. In addition, mutation of PIK3CA correlated with the status of Akt phosphorylation in some breast cancer cells and inhibition of PIK3CA-induced increased apoptosis in breast cancer cells with PIK3CA mutation. CONCLUSION: Somatic mutation rather than a gain of gene copy number of PIK3CA is the frequent genetic alteration that contributes to human breast cancer progression. The frequent and clustered mutations within PIK3CA make it an attractive molecular marker for early detection and a promising therapeutic target in breast cancer.

Apoptosis↗
PubMed2005

Uncommon mutation, but common amplifications, of the PIK3CA gene in thyroid tumors.

CONTEXT: As in many other human cancers, overactivation of the phosphotidylinositol 3-kinase (PI3K)/Akt signaling pathway occurs frequently in thyroid cancer, but the mechanism is not completely clear. OBJECTIVE: Because activating mutations and genomic amplification of the PIK3CA gene, which encodes the p110a catalytic subunit of PI3K, are common in many cancers, we sought to investigate this phenomenon in thyroid tumors. DESIGN: To search for PIK3CA mutations, we isolated genomic DNA from primary thyroid tumors of various types and performed direct sequencing of the exons of PIK3CA gene that carry the most common mutations in other cancers. We used real-time quantitative PCR to investigate genomic amplification of the PIK3CA gene. RESULTS: We found no PIK3CA gene mutations in 37 benign thyroid adenomas, 52 papillary thyroid cancers, 25 follicular thyroid cancers, 13 anaplastic thyroid cancers, 13 medullary thyroid cancers, and seven thyroid tumor cell lines. We found a C3075T single-nucleotide polymorphism in exon 20 of this gene in two cases. With a copy number of 4 or more defined as amplification, we found PIK3CA gene amplification in four of 34 (12%) benign thyroid adenomas, three of 59 (5%) papillary thyroid cancer, five of 21 (24%) follicular thyroid cancer, none of 14 (0%) medullary thyroid cancer, and five of seven (71%) thyroid tumor cell lines. The PIK3CA gene amplification and consequent Akt activation were confirmed by fluorescence in situ hybridization and Western blotting studies using cell lines, respectively. CONCLUSION: These data suggest that mutation of the PIK3CA gene is not common, but its amplification is relatively common and may be a novel mechanism in activating the PI3K/Akt pathway in some thyroid tumors.

Class I Phosphatidylinositol 3-Kinases↗
PubMed2005

DeltaNp63alpha up-regulates the Hsp70 gene in human cancer.

HSP70, a stress response protein, is known to be a determinant of cell death and cell transformation. We show that different isoforms of p63 have different transcriptional activities on hsp70 genes. DeltaNp63alpha, an abundantly expressed isoform of p63, activates (in vitro and in vivo), whereas TAp63gamma down-regulates the expression of hsp70. We further show that the transactivation domain at the NH(2) terminus of p63 represses, whereas the COOH terminus activates hsp70 transcription. In addition, DeltaNp63alpha regulates transcription of the hsp70 gene through its interaction with the CCAAT binding factor and NF-Y transcription factors which are known to form a complex with the CCAAT box located in the hsp70 promoter. Moreover, DeltaNp63alpha expression correlates with HSP70 expression in all head and neck cancer cell lines. Finally, we show colocalization of DeltaNp63alpha and HSP70 in the epithelium and coexpression of both proteins in 41 primary head and neck cancers. Our study provides strong evidence for the physiologic association between DeltaNp63alpha and hsp70 in human cancer, thus further supporting the oncogenic potential of DeltaNp63alpha.

Animals↗
PubMed2005

The T1799A BRAF mutation is not a germline mutation in familial nonmedullary thyroid cancer.

OBJECTIVE: Familial nonmedullary thyroid cancer (FNMTC) is relatively common but its predisposing genetic alteration is unclear. As the somatic T1799A BRAF mutation is highly prevalent in papillary thyroid cancer, the aim was to test whether this mutation was a susceptibility mutation for FNMTC. SUBJECTS AND METHODS: The T1799A BRAF mutation as a possible germline mutation was examined in 40 subjects from 23 families with a history of FNMTC. Direct DNA sequencing was performed on white blood cell DNA samples to analyse the mutation status. RESULTS: No T1799A BRAF mutation was found in this group of subjects as germline mutation. CONCLUSION: The T1799A BRAF mutation is not a germline mutation or susceptibility genetic event for FNMTC.

Adolescent↗
PubMed2004

Early occurrence of RASSF1A hypermethylation and its mutual exclusion with BRAF mutation in thyroid tumorigenesis.

Follicular epithelial cell-derived thyroid tumors are common neoplasms comprised mainly of benign thyroid adenomas, follicular thyroid cancers, and papillary thyroid cancers (PTCs). Hypermethylation of the tumor suppressor gene RASSF1A and activating mutation of BRAF gene have been reported recently in thyroid cancers. To additionally investigate the roles of these two epigenetic/genetic alterations in thyroid tumor progression, we examined their occurrences and relationship in both benign and malignant thyroid neoplasms. With real-time quantitative methylation-specific PCR, we found that 4 of 9 (44%) benign adenomas, 9 of 12 (75%) follicular thyroid cancers tumors, and 6 of 30 (20%) of PTC tumors harbored promoter methylation in > or = 25% of RASSF1A alleles. Additional quantitative analysis revealed RASSF1A methylation only in BRAF mutation-negative PTCs. A similar inverse correlation of RASSF1A methylation with BRAF mutation was seen in thyroid tumor cell lines. Our results, therefore, suggest that epigenetic inactivation of RASSF1A through aberrant methylation is an early step in thyroid tumorigenesis. Like the previously reported mutually exclusive relationship between BRAF mutation and other Ras pathway components such as RET/PTC rearrangement, a mutually exclusive relationship also exists between BRAF mutation and RASSF1A methylation in thyroid tumorigenesis.

Cell Line, Tumor↗
PubMed2004

Detection of BRAF mutation on fine needle aspiration biopsy specimens: a new diagnostic tool for papillary thyroid cancer.

Numerous biomolecular markers have been studied to improve the accuracy of fine needle aspiration biopsy (FNAB) in the diagnostic and prognostic evaluation of thyroid tumors, but none of them has yet become clinically useful. The recently discovered BRAF mutation, which occurs specifically in papillary thyroid cancers (PTC) with a high prevalence and is associated with poor clinicopathological outcomes, has the potential to be a useful diagnostic and prognostic marker for PTC. In the present study, we investigated whether detection of BRAF mutation on FNAB specimens was technically possible and could be used as an adjunct diagnostic tool with routine FNAB. Evaluation of a new colorimetric mutation detection method demonstrated 100% sensitivity and 100% specificity in comparison with conventional DNA sequencing as the "gold standard" in a large pool of DNA samples from various primary thyroid tumor specimens and cell lines. We found this novel technique even more sensitive in detecting BRAF mutation on FNAB specimens than conventional sequencing. In a series of 48 patients undergoing thyroidectomy, mostly for thyroid cancer or for suspicion of cancer, we performed preoperative FNAB and, using the colorimetric mutation detection method, identified BRAF mutation on the cytological specimens. Prospective analysis showed that 50% of the nodules that proved to be PTC on surgical histopathology were correctly diagnosed by BRAF mutation analysis on FNAB specimens; there were no false positive findings. Thus, we have demonstrated the usefulness of BRAF mutation detection on FNAB specimens that can help diagnose and identify those PTC patients who may need more aggressive surgical treatment and vigilant clinical monitoring.

Biomarkers, Tumor↗
PubMed2003

Hypermethylation of the Pendred syndrome gene SLC26A4 is an early event in thyroid tumorigenesis.

Expression of the recently cloned Pendred syndrome gene SLC26A4 or PDS has been found to be decreased or even absent in various thyroid tumors. To explore the underlying mechanism, we conducted DNA sequencing and methylation-specific PCR studies in 64 primary thyroid tumors and 6 thyroid cell lines. We found aberrant hypermethylation of the SLC26A4 gene in 44% of histologically benign adenomas, 46% of follicular thyroid cancers, 71% of papillary thyroid cancers, 71% of anaplastic thyroid cancers, and 100% of cell lines. A reciprocal relationship between methylation and expression of the gene was confirmed in cell lines and thyroid tissues. We have thus demonstrated epigenetic changes as a new mechanism in altering the SLC26A4 gene function, in addition to genetic mutation in Pendred syndrome. SLC26A4 gene methylation in benign adenomas and the relatively well-differentiated WRO cell line suggest that this alteration is an early event in thyroid tumorigenesis.

Carrier Proteins↗
PubMed2003

Methylation of the thyroid-stimulating hormone receptor gene in epithelial thyroid tumors: a marker of malignancy and a cause of gene silencing.

Thyroid-stimulating hormone receptor (TSHR) expression is frequently silenced in epithelial thyroid cancers associated with decreased or absent TSH-promoted iodine uptake. To study the underlying molecular mechanism of decreased TSHR expression, we examined the methylation status of the TSHR gene promoter by sequencing bisulfite-treated DNA from thyroid tumors. After identification of methylated sites by sequencing bisulfite-treated DNA, we used methylation-specific polymerase chain reaction and found frequent CpG methylation in papillary thyroid cancer (23 of 39 patients; 59%) and follicular thyroid cancers (7 of 15 patients; 47%). In contrast, we saw no methylation in normal thyroid tissues and benign adenomas (0 of 8 patients; 0%). In human thyroid tumor cell lines, we observed that TSHR was normally expressed at the protein and mRNA level in cells where the TSHR gene was unmethylated, whereas it was silenced in cell lines where the TSHR promoter was hypermethylated. Treatment of the latter cells with a demethylating agent partially restored TSHR expression. We thus demonstrate aberrant methylation of human TSHR as a likely molecular pathway responsible for the silencing of this gene in thyroid cancers. We propose that methylation of TSHR may provide a novel diagnostic marker of malignancy and a basis for potential use of demethylating agents in conjunction with TSH-promoted radioiodine therapy for epithelial thyroid cancers.

Adenoma↗
PubMed2003

BRAF mutation in papillary thyroid carcinoma.

The BRAF gene has been found to be activated by mutation in human cancers, predominantly in malignant melanoma. We tested 476 primary tumors, including 214 lung, 126 head and neck, 54 thyroid, 27 bladder, 38 cervical, and 17 prostate cancers, for the BRAF T1796A mutation by polymerase chain reaction (PCR)-restriction enzyme analysis of BRAF exon 15. In 24 (69%) of the 35 papillary thyroid carcinomas examined, we found a missense thymine (T)-->adenine (A) transversion at nucleotide 1796 in the BRAF gene (T1796A). The T1796A mutation was detected in four lung cancers and in six head and neck cancers but not in bladder, cervical, or prostate cancers. Our data suggest that activating BRAF mutations may be an important event in the development of papillary thyroid cancer.

Adenine↗
PubMed2003

Mitochondrial DNA alterations in thyroid cancer.

BACKGROUND: Alterations in mitochondrial DNA have been identified in a number of solid tumor types, including gastric, head and neck, breast, colorectal, lung, and bladder carcinomas. Recently, a homopolymeric C stretch (D310) located within the noncoding D-loop of the mitochondrial genome was identified and described as a mutational hotspot. The objective of the present study was to examine a series of thyroid cancers for genetic alterations in this region. METHODS: Seventy-two (72) thyroid cancers were examined for alterations in D310 using PCR-based methods. The primary tumors tested included 35 papillary carcinomas, 18 medullary carcinomas, 9 anaplastic carcinomas, 9 follicular carcinomas, and 1 insular carcinoma. RESULTS: Alterations in D310 were observed in 2/35 papillary carcinomas (5.7%), 1/18 medullary carcinomas (5.6%), 1/9 anaplastic carcinomas (11.1%), and 1/9 follicular carcinomas (11.1%). Overall, the rate of alterations was 5/72 (6.9%). CONCLUSIONS: Mutations in the D310 region of the D-loop of mitochondrial DNA are found in thyroid tumors of varying histologic types and grades. This mutation rate is lower than the reported rate of alteration in tumors of epithelial origin, and shows no relationship to histologic grade.

Adenocarcinoma↗