Papillary thyroid cancer: high inter-(simple sequence repeat) genomic instability in a typically indolent cancer

Aberrant expression of posterior HOX genes in well differentiated histotypes of thyroid cancers

Molecular etiology of thyroid cancers has been widely studied, and several molecular alterations have been identified mainly associated with follicular and papillary histotypes. However, the molecular bases of the complex pathogenesis of thyroid carcinomas remain poorly understood. HOX genes regulate normal embryonic development, cell differentiation and other critical processes in eukaryotic cell life. Several studies have shown that HOX genes play a role in neoplastic transformation of several human tissues. In particular, the genes belonging to HOX paralogous group 13 seem to hold a relevant role in both tumor development and progression. We have identified a significant prognostic role of HOX D13 in pancreatic cancer and we have recently showed the strong and progressive over-expression of HOX C13 in melanoma metastases and deregulation of HOX B13 expression in bladder cancers. In this study we have investigated, by immunohistochemisty and quantitative Real Time PCR, the HOX paralogous group 13 genes/proteins expression in thyroid cancer evolution and progression, also evaluating its ability to discriminate between main histotypes. Our results showed an aberrant expression, both at gene and protein level, of all members belonging to paralogous group 13 (HOX A13, HOX B13, HOX C13 and HOX D13) in adenoma, papillary and follicular thyroid cancers samples. The data suggest a potential role of HOX paralogous group 13 genes in pathogenesis and differential diagnosis of thyroid cancers.

Genomic instability in invasive breast carcinoma measured by inter-Simple Sequence Repeat PCR

We have measured genomic instability in invasive breast carcinomas and assessed the relationship of genomic instability to known tumor prognostic factors. DNAs from tumors and adjacent normal tissue of 18 breast cancer patients were subjected to inter-Simple Sequence Repeat (inter-SSR) PCR for quantitation of tumor genomic instability. Associations between genomic instability level and known breast cancer prognostic factors were evaluated using the Pearson Product Moment Correlation, the Kruskal-Wallis test of independent samples and the Mann-Whitney non-parametric test. Genomic instability was detected by inter-SSR PCR in over 90% of the breast tumors. The mean instability index was 3.08% (0-7.59%), approximately the same mean value observed in studies of colorectal and thyroid carcinomas. Significantly higher levels of instability were associated with tumors exhibiting necrosis. Genomic instability as measured is detected in the majority of breast cancers at levels comparable to other tumor types. Hypoxia, such as that observed in necrotic regions of tumors, has been associated with elevated genomic damage. We hypothesize that the higher levels of genomic instability detected in necrotic tumors is a consequence of hypoxia-associated DNA damage.

Pituitary tumour transforming gene (PTTG) induces genetic instability in thyroid cells

Cancer reflects the progressive accumulation of genetic alterations and subsequent genetic instability of cells. Cytogenetic studies have demonstrated the importance of aneuploidy in differentiated thyroid cancer development. The pituitary tumour transforming gene (PTTG), also known as securin, is a mitotic checkpoint protein which inhibits sister chromatid separation during mitosis. PTTG is highly expressed in many cancers and overexpression of PTTG induces aneuploidy in vitro. Using fluorescent intersimple sequence repeat PCR (FISSR-PCR), we investigated the relationship between PTTG expression and the degree of genetic instability in normal and tumorous thyroid samples. The genomic instability index (GI index) was 6.7-72.7% higher in cancers than normal thyroid tissues. Follicular thyroid tumours exhibited greater genetic instability than papillary tumours (27.6% (n=9) versus 14.5% (n=10), P=0.03). We also demonstrated a strong relationship between PTTG expression and the degree of genetic instability in thyroid cancers (R2=0.80, P=0.007). To further investigate PTTG's role in genetic instability, we transfected FTC133 thyroid follicular cells and observed increased genetic instability in cells overexpressing PTTG compared with vector-only-transfected controls (n=3, GI Index VO=29.7+/-5.2 versus PTTG=63.7+/-6.4, P=0.013). Further, we observed a dose response in genetic instability and PTTG expression (GI Index low dose (0.5 microg DNA/ six-well plate) PTTG=15.3%+/-1.7 versus high dose (3 microg DNA) PTTG=50.8%+/-3.3, P=0.006). Overall, we describe the first use of FISSR-PCR in human cancers, and demonstrate that PTTG expression correlates with genetic instability in vivo, and induces genetic instability in vitro. We conclude that PTTG may be an important gene in the mutator phenotype development in thyroid cancer.

Molecular Prognosticators and Genomic Instability in Papillary Thyroid Cancer

OBJECTIVES/HYPOTHESIS

Tumor progression has been attributed to the accumulation of DNA damage concurrent with selection of advantageous mutations; this DNA damage may result from failure to maintain genomic integrity or from susceptibility to carcinogens. Glutathione S-transferases (GSTs), enzymes that metabolize many carcinogens, may play a role in preserving genome integrity. The objectives of this study are to assess the relationship of GST genotypes with prognosis, clinicopathologic parameters, and genomic instability in papillary thyroid cancer.

STUDY DESIGN

Prospective analysis.

METHODS

GSTM1 and GSTT1 genotypes of 35 matched normal and papillary thyroid cancer specimens were determined by polymerase chain reaction (PCR) using primers specific for the coding sequences of each gene. Genomic instability was measured by intersimple sequence repeat PCR for each tumor/normal pair and compared with the GAMES prognostic scoring system and clinicopathologic parameters including age, extrathyroidal extension, tumor grade, size, stage metastasis, sex, and smoking history.

RESULTS

GSTM1 and GSTT1 null genotypes were found in the normal tissues of 46% and 45%, respectively. No gene losses were detected in the tumor specimens. A significant association between the GSTM1 null genotype and increased risk of recurrence and death was observed. Elevated GII correlated with smoking and tumor stage but not with GST genotype.

CONCLUSION

The association of GSTM1 null genotype with intermediate and high risk GAMES categories suggests that GSTM1 provides some protection against disease progression. However, this protection does not confer resistance to disease onset. GST genotyping may be a useful adjunct prognosticator with GAMES.

Gene expression profiling of differentiated thyroid neoplasms: diagnostic and clinical implications

PURPOSE

The purpose of this research was to identify novel genes that can be targeted as diagnostic and clinical markers of differentiated thyroid tumors.

EXPERIMENTAL DESIGN

Gene expression analysis using microarray platform was performed on 6 pathologically normal thyroid samples and 12 primary follicular and papillary thyroid neoplasms. Microarrays containing probes for 5,760 human full-length cDNAs were used for hybridization with total RNA from normal and tumor thyroid samples labeled with Cy3-dUTP and Cy5-dUTP, respectively. Scanned array images were recorded, and data analysis was performed. Selected sets of differentially expressed genes were analyzed using quantitative real-time reverse transcription-PCR for verification.

RESULTS

We identified 155 genes that differentiate histologically normal thyroid tissues from benign and malignant thyroid neoplasms. Of these 75 genes were differentiated between follicular neoplasms (adenoma and carcinoma) and the follicular variant of papillary carcinoma. Purely follicular neoplasms (adenomas and carcinomas) shared many genetic profiles, and only 43 genes were distinctly different between these tumors. Hierarchical cluster analysis also differentiated conventional papillary carcinoma from its follicular variant and follicular tumors. The differentially expressed genes were composed of members of cell differentiation, adhesion, immune response, and proliferation associated pathways. Quantitative real-time reverse transcription-PCR analysis of selected genes corroborated the microarray expression results.

CONCLUSIONS

Our study show the following: (1) differences in gene expression between tumor and nontumor bearing normal thyroid tissue can be identified, (2) a set of genes differentiate follicular neoplasm from follicular variant of papillary carcinoma, (3) follicular adenoma and carcinoma share many of the differentiated genes, and (4) gene expression differences identify conventional papillary carcinoma from the follicular variant.

Genome wide instability scanning in chewing-tobacco associated oral cancer using inter simple sequence repeat PCR

Genomic instability plays a major role in cancer, facilitating tumour progression and tumour heterogeneity. Inter simple sequence repeat PCR (ISSR-PCR) is a sensitive tool for detection of whole genome scanning. In fifteen oral cancer patients, using tumor tissue and adjacent normal tissue DNA, we investigated genomic instability regions using ISSR-PCR assay. The genomic fragments were cloned, sequenced and identified. Two-anchored dinucleotide repeat primers, (CA)(8)A/GG and (CA)(8)A/GC/T, were used in the study. About 40-50 fragments were observed on polyacrylamide gel electrophoresis, with 25 distinct fragments of less than 2 kb. The electrophoretic pattern highlighted several distinct fragments in tumor adjacent normal tissues. The distinct fragments of 258, 325, 430, 440, 600 and 900 bp sizes using (CA)(8)A/GG primer, and 300, 475, 675 and 800 bp using (CA)(8)A/GC/T primers, in the normal tissues showed partial (>50%) or complete loss in multiple tumor tissues. These fragments were eluted from the gel, cloned in pMos Blue vector and subjected to nucleotide sequencing. Insilico analysis defined the specific genomic sequences, given as follows: RP11-399D2 () on chromosome (chr)4; RP1-39J2 (), NKp44RG () and RP11-518I13 () on chr6; NC-T-2 () on chr7; RP11-586K2 () and RP11-495O10 () on chr8; RP11-101K10 () on chr9; R-794A8 () on chr14; and RP11-679B19 () on chr16. The sequences of our clones have been submitted to NCBI gene bank, accession numbers to , and . The Genomic Instability Index was calculated and ranged from 6% to 28.5% (median 12%) in the oral cancer samples, excluding one case where genomic instability was not observed. Thus, our results indicate presence of widespread genomic alterations in chewing-tobacco associated oral cancers.

Selectively advantageous mutations and hitchhikers in neoplasms: p16 lesions are selected in Barrett's esophagus

Neoplastic progression is an evolutionary process characterized by genomic instability and waves of clonal expansions carrying genetic and epigenetic lesions to fixation (100% of the cell population). However, an evolutionarily neutral lesion may also reach fixation if it spreads as a hitchhiker on a selective sweep. We sought to distinguish advantageous lesions from hitchhikers in the premalignant condition Barrett's esophagus. Patients (211) had biopsies taken at 2-cm intervals in their Barrett's segments. Purified epithelial cells were assayed for loss of heterozygosity and microsatellite shifts on chromosomes 9 and 17, sequence mutations in CDKN2A/MTS1/INK4a (p16) and TP53 (p53), and methylation of the p16 promoter. We measured the expanse of a lesion in a Barrett's segment as the proportion of proliferating cells that carried a lesion in that locus. We then selected the lesion having expanses >90% in the greatest number of patients as our first putative advantageous lesion. We filtered out hitchhikers by removing all expanses of other lesions that did not occur independent of the advantageous lesion. The entire process was repeated on the remaining expanses to identify additional advantageous lesions. p16 loss of heterozygosity, promoter methylation, and sequence mutations have strong, independent, advantageous effects on Barrett's cells early in progression. Second lesions in p16 and p53 are associated with later selective sweeps. Virtually all of the other lesion expansions, including microsatellite shifts, could be explained as hitchhikers on p16 lesion clonal expansions. These techniques can be applied to any neoplasm.