metallothionein and Adenocarcinoma--Papillary

We previously obtained gene expression profiles of 8 matched papillary thyroid carcinoma (PTC) and normal tissues using DNA microarrays. To identify novel tumor suppressor genes involved in thyroid carcinogenesis, we here analyze genes showing lower expression in PTC tumors than in normal thyroid tissues. A search for loss of heterozygosity (LOH) in 49 regions that harbor consistently down-regulated genes revealed LOH in only 4 regions and in just a very small number of tumors. To determine whether the underexpression might be due to promoter methylation, we used combined bisulfite restriction analysis and bisulfite sequencing to study 7 underexpressed genes. Loss of expression of MT1G and CRABP1 is accompanied by hypermethylation in the 5' regions of these genes, but methylation was not seen in other genes tested. Combined treatment with the DNA methyltransferase inhibitor 5-aza-2'-deoxycytidine (5-Aza-dC) and the histone deacetylase inhibitor trichostatin A (TSA) resulted in demethylation and re-expression of the MT1G gene in the cell line K2. Treatment with 5-Aza-dC alone restored CRABP1 expression in a colorectal cancer cell line, SW48. In conclusion, LOH is a remarkably rare mechanism of loss of gene function in PTC. In contrast, hypermethylation of promoter CpG islands seems to occur at higher frequency. MT1G and CRABP1 are novel genes that are likely involved in the pathogenesis of sporadic PTC.

Topics: Adenocarcinoma, Papillary; Adult; Aged; Azacitidine; Base Sequence; CpG Islands; DNA Methylation; Enzyme Inhibitors; Female; Gene Expression Regulation, Neoplastic; Gene Silencing; Genes, Tumor Suppressor; Humans; Hydroxamic Acids; Loss of Heterozygosity; Male; Metallothionein; Microsatellite Repeats; Middle Aged; Molecular Sequence Data; O(6)-Methylguanine-DNA Methyltransferase; Polymerase Chain Reaction; Promoter Regions, Genetic; Receptors, Retinoic Acid; Thyroid Neoplasms; Tumor Cells, Cultured

Transgenic mice were developed by injecting a mouse metallothionein promoter-human growth hormone (Mt-hGH) gene fragment into the pronucleus of C57Bl x DBA/2J-f2 or C57Bl x CBA-f2 one cell embryos. Six founder animals with the C57Bl x DBA genetic background grew 1.3-2.2 times larger than littermate controls and had higher levels of hGH in plasma (4.6-279 mU/l). Three of the four female transgenic founders developed malignant papillar adenocarcinomas of mammary origin at 27-43 weeks of age. One male transgenic founder was successfully mated and two of three female transgenic offsprings developed mammary tumors. To examine if the tumor induction was dependent on the strain of mice used the experiments were repeated using animals with different genetic background. Fourteen female hGH transgenic mice from five founder animals were generated using C57Bl x CBA-f2 mice. Thirteen of the animals had elevated levels of hGH in plasma (7-1960 mU/l) and grew larger than control animals. Nine of the animals developed mammary adenocarcinomas. Four of the hGH expressing animals did not demonstrate macroscopic tumor formation but have not yet been analyzed histologically. The present study suggests that markedly elevated endogenous levels of GH cause mammary carcinoma in hGH transgenic mice. The present animal model might prove useful for studying molecular mechanisms involved in the development of hormonally induced mammary tumors.

Topics: Adenocarcinoma, Papillary; Animals; Body Weight; Female; Growth Hormone; Humans; Male; Mammary Neoplasms, Experimental; Metallothionein; Mice; Mice, Inbred C57BL; Mice, Inbred CBA; Mice, Inbred DBA; Mice, Transgenic; Promoter Regions, Genetic; Recombinant Fusion Proteins

High levels of metallothionein (MT) are present in the developing mammalian liver; however, a remarkable decrease is observed during postnatal life after weaning. This developmental profile is similar to that of certain oncofetal gene products such as alpha-fetoprotein, which is used as a tumor marker. This study deals with the reexpression of MT genes in thyroid tumors. With an immunohistochemical method, the presence of MT was investigated in tissue sections of normal and neoplastic human thyroid glands. Tissue sections of 34 thyroid tumors and 10 normal human thyroid glands were studied by means of the peroxidase-antiperoxidase method. MT was localized in 31 of the thyroid gland tumors. MT was also present in two of the normal thyroid glands. These findings indicate that although high levels of MT are mainly found in the fetal liver, it may also be expressed actively in certain human thyroid neoplastic tissues, and occasionally in normal thyroid tissue.

Topics: Adenocarcinoma; Adenocarcinoma, Papillary; Adenoma; Adolescent; Adult; Aged; Aged, 80 and over; Cell Nucleus; Cytoplasm; Female; Humans; Immunohistochemistry; Male; Metallothionein; Middle Aged; Thyroid Neoplasms