ABSTRACT
Genetic code redundancy would yield, on the average, the assignment of three codons for each of the natural amino acids. The fact that this number is observed only for incorporating Ile and to stop RNA translation still waits for an overall explanation. Through a Structural Bioinformatics approach, the wealth of information stored in the Protein Data Bank has been used here to look for unambiguous clues to decipher the rationale of standard genetic code (SGC) in assigning from one to six different codons for amino acid translation. Leu and Arg, both protected from translational errors by six codons, offer the clearest clue by appearing as the most abundant amino acids in protein-protein and protein-nucleic acid interfaces. Other SGC hidden messages have been sought by analyzing, in a protein structure framework, the roles of over- and under-protected amino acids.
Subject(s)
Computational Biology , Genetic Code/genetics , Codon/genetics , Databases, Protein , Humans , Models, Molecular , Nucleic Acid Conformation , Protein Conformation , Proteins/chemistry , Proteins/geneticsABSTRACT
Peroxisome proliferator-activated receptor gamma (PPAR gamma) is a nuclear receptor involved in such cellular processes as adipogenesis, inflammation, atherosclerosis, cell cycle control, apoptosis, and carcinogenesis. PPAR gamma gene mutations have been found in 4 of 55 sporadic colon cancers, and a chimeric PAX8-PPAR gamma 1 gene frequently generates a chromosomal translocation in thyroid follicular carcinomas, implicating PPAR gamma in tumor suppression. We investigated whether PPAR gamma is involved in the growth regulation of normal and tumor thyroid cells. We found no mutations in PPAR gamma exons 3 and 5 in human thyroid carcinoma cell lines and tissues. Moreover, 1 cell line (NPA) of 6 analyzed did not express PPAR gamma. Treatment of NPA with PPAR gamma agonists did not induce any inhibitory effect. Conversely, PPAR gamma agonists and PPAR gamma overexpression led to a drastic reduction of the cell growth rate in PPAR gamma-expressing thyroid carcinoma cells. Restoration of PPAR gamma expression in NPA cells induced cell growth inhibition; PPAR gamma agonists induced further inhibition. Growth inhibition induced by PPAR gamma agonists or by PPAR gamma gene overexpression in thyroid carcinoma cells was associated with increased p27 protein levels and apoptotic cell death. Should these data be confirmed, PPAR gamma could be a novel target for innovative therapy of thyroid carcinoma, particularly anaplastic carcinomas, which represent one of the most aggressive tumors in mankind and are unresponsive to conventional therapy.
Subject(s)
Cell Division , Receptors, Cytoplasmic and Nuclear/physiology , Thiazolidinediones , Thyroid Neoplasms/pathology , Transcription Factors/physiology , Apoptosis , Cell Cycle Proteins/metabolism , Cell Division/drug effects , Cyclin-Dependent Kinase Inhibitor p27 , Cyclin-Dependent Kinases , DNA Mutational Analysis , Gene Expression , Humans , Mutation , Receptors, Cytoplasmic and Nuclear/agonists , Receptors, Cytoplasmic and Nuclear/genetics , Reverse Transcriptase Polymerase Chain Reaction , Sequence Analysis, DNA , Thiazoles/pharmacology , Thyroid Gland/pathology , Thyroid Neoplasms/genetics , Transcription Factors/agonists , Transcription Factors/genetics , Transfection , Tumor Cells, Cultured , Tumor Suppressor Proteins/metabolismABSTRACT
A novel human thyroid papillary carcinoma cell line (FB-2) has been established and characterized. FB-2 cells harbor the RET/PTC1 chimeric oncogene in which the RET kinase domain is fused to the H4 gene. FB-2 cells neither formed colonies in semisolid media nor induced tumors after heterotransplant into severe combined immunodeficient mice. However, HMGI(Y), HMGI-C and c-myc genes, which are associated to thyroid cell transformation, were abundantly expressed in FB-2 cells but not in normal thyroid cells. FB-2 cells only partially retained the differentiated thyroid phenotype. In fact, the PAX-8 gene, which codes for a transcriptional factor required for thyroid cell differentiation, was expressed, while thyroglobulin, TSH-receptor and thyroperoxidase genes were not. Moreover, FB-2 cells produced high levels of interleukin (IL)-6 and IL-8.
Subject(s)
Carcinoma, Papillary/genetics , Neoplasms, Experimental/genetics , Nuclear Proteins , Oncogene Proteins, Fusion/genetics , Thyroid Neoplasms/genetics , Adult , Animals , Carcinoma, Papillary/metabolism , Carcinoma, Papillary/pathology , Cell Differentiation , Cell Division/drug effects , Cell Movement , DNA-Binding Proteins/biosynthesis , Female , HMGA1a Protein/biosynthesis , HMGA1a Protein/genetics , HMGA2 Protein/biosynthesis , HMGA2 Protein/genetics , Humans , Interleukin-6/biosynthesis , Interleukin-6/pharmacology , Interleukin-8/biosynthesis , Karyotyping , Mice , Mice, SCID , Neoplasm Transplantation , Neoplasms, Experimental/metabolism , Neoplasms, Experimental/pathology , Oncogene Proteins, Fusion/metabolism , PAX8 Transcription Factor , Paired Box Transcription Factors , Phenotype , Protein-Tyrosine Kinases , Proto-Oncogene Proteins c-myc/biosynthesis , Proto-Oncogene Proteins c-myc/genetics , RNA, Messenger/biosynthesis , Thyroid Gland/cytology , Thyroid Gland/metabolism , Thyroid Neoplasms/metabolism , Thyroid Neoplasms/pathology , Trans-Activators/biosynthesis , Tumor Cells, CulturedABSTRACT
The tall-cell variant (TCV) of papillary thyroid carcinoma (PTC), characterized by tall cells bearing an oxyphilic cytoplasm, is more clinically aggressive than conventional PTC. RET tyrosine kinase rearrangements, which represent the most frequent genetic alteration in PTC, lead to the recombination of RET with heterologous genes to generate chimeric RET/PTC oncogenes. RET/PTC1 and RET/PTC3 are the most prevalent variants. We have found RET rearrangements in 35.8% of TCV (14 of 39 cases). Whereas the prevalences of RET/PTC1 and RET/PTC3 were almost equal in classic and follicular PTC, all of the TCV-positive cases expressed the RET/PTC3 rearrangement. These findings prompted us to compare RET/PTC3 and RET/PTC1 in an in vitro thyroid model system. We have expressed the two oncogenes in PC Cl 3 rat thyroid epithelial cells and found that RET/PTC3 is endowed with a strikingly more potent mitogenic effect than RET/PTC1. Mechanistically, this difference correlated with an increased signaling activity of RET/PTC3. In conclusion, we postulate that the correlation between the RET/PTC rearrangement type and the aggressiveness of human PTC is related to the efficiency with which the oncogene subtype delivers mitogenic signals to thyroid cells.
Subject(s)
Carcinoma, Papillary/genetics , Carcinoma, Papillary/pathology , Growth Substances/physiology , Oncogenes/physiology , Phosphoprotein Phosphatases/genetics , Saccharomyces cerevisiae Proteins , Thyroid Neoplasms/genetics , Thyroid Neoplasms/pathology , Adolescent , Adult , Aged , Animals , Cell Line , Child , Female , Gene Frequency , Humans , Male , Middle Aged , Oncogene Proteins, Fusion/physiology , Phosphoprotein Phosphatases/physiology , Protein Phosphatase 2 , Protein Phosphatase 2C , Protein-Tyrosine Kinases , Rats , Rats, Inbred F344ABSTRACT
Poorly differentiated carcinoma of the thyroid gland (PDC) represents an heterogeneous group of epithelial neoplasms with morphologic features and clinical characteristics intermediate between well differentiated and anaplastic (undifferentiated) carcinomas. Unlike well differentiated tumors, PDCs are associated with significant morbidity and mortality. The general prevalence of RET/PTC rearrangement in thyroid PDC and its impact on patient outcome are unknown. To address these issues and to identify prognostically relevant clinicopathologic parameters, we have investigated a series of 62 PDCs. RET/PTC rearrangement, analyzed by RT-PCR and immunohistochemistry using antibodies specific for the tyrosine kinase and juxtamembrane portions of the RET protein, was identified in 8/62 (12.9%) PDCs. RET/PTC was more common in cases with histologic evidence indicating coexistence with or possible evolution from a well differentiated papillary carcinoma (5 of 25 tumors, 20%) but did not correlate with other clinicopathologic parameters. The relatively low prevalence of RET activation in PDCs argues against a major role for RET/PTC in the progression from well to poorly differentiated thyroid tumor phenotypes. Survival analysis demonstrates that poor survival in PDC is associated with old age, male sex, invasion of extrathyroidal soft tissues, coexistence in the same tumor of oncocytic features with insular growth pattern, and distant metastases but not RET activation.
