Metallothionein 1G acts as an oncosupressor in papillary thyroid carcinoma

Abstract

The molecular pathogenesis of tumors arising from the thyroid follicular epithelial cells, including papillary (PTC) and follicular thyroid carcinoma (FTC), is only partially understood, and the role of tumor suppressor genes has not yet been assessed. The metallothionein (MT) gene family encodes a class of metal-binding proteins involved in several cellular processes, and their expression is often deregulated in human tumors. Recently, downregulation of MT gene expression in PTC has been reported, suggesting a possible oncosuppressor role of this gene family in the pathogenesis of thyroid tumors. To further explore this possibility, we performed expression and functional studies. Analysis of microarray data of thyroid tumors of different histologic types showed that several MT genes were downregulated with respect to normal tissue. The microarray data were corroborated by quantitative PCR experiments, showing downregulation of MTs in PTC and FTC, but to a greater extent in papillary carcinoma. The expression of MTs was also investigated at the protein level by immunohistochemistry; the results were consistent with the microarray data, showing general downregulation in tumor samples, which was more evident in PTC. The functional consequence of MT downregulation was addressed employing an experimental model made of the PTC-derived K1 cell line in which MT1G expression is repressed by promoter methylation. Restoration of MT1G expression by cDNA transfection affected growth rate and in vivo tumorigenicity of K1 cells, indicating an oncosuppressor role for MT1G in thyroid papillary tumorigenesis. Several tumor types, differing in biological and clinical behavior, originate from the thyroid epithelial follicular cells. They include well-differentiated, indolent papillary thyroid and follicular thyroid carcinomas (PTC and FTC), as well as extremely aggressive anaplastic carcinoma. 1 Studies performed in several laboratories, including ours, have demonstrated that distinct molecular events are associated with specific tumor types. 2 FTC is characterized by the PAX8/ PPARg rearrangement and activating mutations of RAS genes. 1 PTC is associated with rearrangements involving the RET and NTRK1 tyrosine kinase receptors, 2 and the V600E BRAF-activating mutation. [3][4][5] More recently, microarray studies have identified several genes that might be important in the molecular pathogenesis and the malignant progression of thyroid cancer and could be used as diagnostic or prognostic molecular markers. These candidate genes are involved in several different processes, such as cell adhesion, cell cycle progression, mitogenic control and tumorigenesis. [6][7][8][9][10] In spite of that, the molecular pathogenesis of thyroid cancer is still incomplete; in particular, a role of tumor suppressor genes has not yet been assessed. Metallothioneins (MTs) are low-molecular weight proteins of 6-7 kDa, with high content of cysteine (30%) and complete absence of aromatic amino acids and histidine 11 capable of binding heavy metals with hig...

TIMP3 regulates migration, invasion and in vivo tumorigenicity of thyroid tumor cells

“…Although a role for tumor-suppressor genes in thyroid carcinogenesis has not been assessed yet, functional studies have allowed some genes downregulated in PTCs to be classified as tumor suppressors, based on their ability to modulate transformed properties of thyroid tumor cell lines (Ferrario et al, 2008;Latini et al, 2008;Pallante et al, 2008;Vizioli et al, 2010;Zuo et al, 2010). With this study, we have demonstrated that TIMP3 exerts a negative regulatory role in thyroid tumor cells, thus corroborating its oncosuppressor role suggested by hypermetylation and gene expression studies.…”

“…To this end, we analyzed several microarray data of tumor and normal thyroid tissues. In cDNA microarray data produced in our laboratory (Ferrario et al, 2008), in comparison with TIMP3 gene expression level of normal thyroid, TIMP3 downregulation was evident in both the classical histotype and the tall cell variant (Po0.01; Figure 1a). Frequent downregulation of TIMP3 in comparison with normal samples was also observed when a number of independent data sets of microarray gene expression data of PTC samples, publicly available and all obtained using Affymetrix HG-U133 series platforms, were considered.…”

“…Putative oncosuppressor genes relevant for thyroid carcinomas have been suggested by methylation studies (Xing 2007(Xing , 2008. In the past few years, some genes identified as downregulated in the context of gene expression studies were classified as tumor suppressors by functional studies, as their re-expression modulated transformed properties of thyroid carcinoma cell lines (Ferrario et al, 2008;Latini et al, 2008;Pallante et al, 2008;Vizioli et al, 2010;Zuo et al, 2010).…”

Metallothionein 1G and Zinc Sensitize Human Colorectal Cancer Cells to Chemotherapy

“…The MT1G cDNA was cloned into the pcDNA3.1/mycHis(-)A expression vector, resulting in a MT1G-myc fusion protein as previously described (21). OXA and 5-FU were obtained in the pharmacy of the Alexander Fleming Institute (Buenos Aires, Argentina).…”

Oxidative Stress in Human Thyroid Gland Under Iodine Deficiency Nodular Goiter: From Harmlessness to Hazard Depending on Copper and Iodine Subcellular Distribution

“…Additionally, MTs can function as efficient scavengers of reactive oxygen species to preserve homeostasis of cells. The latest study have indicated a possible role of MTs as a tumor suppressor in papillary thyroid cancer [8] and their part in the distribution of metals, thereby optimizing the function of thyroid gland [4].…”