No abstract

MicroRNAs (miRNAs) are a class of small non-coding RNAs involved in a wide range of basic processes such as cell proliferation, development, apoptosis and stress response. It has recently been found that they are also abnormally expressed in many types of human cancer. We analyzed the genome-wide miRNA expression profile in human thyroid papillary carcinomas (PTCs) using a microarray (miRNACHIP microarray) containing hundreds of human precursor and mature miRNA oligonucleotide probes. Using this approach, we found an aberrant miRNA expression profile that clearly differentiates PTCs from normal thyroid tissues. In particular, a significant increase in miRNA (miR)-221, -222 and -181b was detected in PTCs in comparison with normal thyroid tissue. These results were further confirmed by northern blot and quantitative RT-PCR analyses. Moreover, RT-PCR revealed miR-221, -222 and -181b overexpression in fine needle aspiration biopsies corresponding to thyroid nodules, which were eventually diagnosed as papillary carcinomas after surgery. Finally, miR-221, -222 and -181b overexpression was also demonstrated in transformed rat thyroid cell lines and in mouse models of thyroid carcinogenesis. Functional studies, performed by blocking miR-221 function and by overexpressing miR-221 in human PTC-derived cell lines, suggest a critical role of miR-221 overexpression in thyroid carcinogenesis. In conclusion, these data, taken together, indicate an miRNA signature associated with PTCs, and suggest miRNA deregulation as an important event in thyroid cell transformation.

A system of epithelial cells is described in which it is possible to study the number and the nature of genes capable of conferring the malignant phenotype. Two fully differentiated, hormone-responsive cell lines from rat thyroid glands are presented which are susceptible to one-step or two-step transformation upon infection with several murine acute retroviruses. After infection, both cell lines became independent from their thyrotropic hormone requirement for growth. However, complete transformation was achieved with one of the cell lines (FRTL-5 Cl 2), whereas the other cell line (PC Cl 3) failed to grow in agar and to give rise to tumors in vivo. The latter cell line was susceptible to complete transformation upon cooperation of the v-ras-Ha and the human c-myc oncogenes.

Using DNA transfection analysis on NIH 3T3 cells, activated human oncogenes have been isolated from a variety of fresh solid tumours. Thyroid neoplasias show a wide range of lesions varying from slowly progressive well-differentiated tumours to anaplastic highly malignant neoplasms. Therefore they represent an attractive model to investigate the role of oncogene activation in different stages of the neoplastic state. Here we report the detection of transforming activity in DNAs extracted from five thyroid papillary carcinomas and two of their respective lymph-nodal metastases.

Elevated expression of the three high-mobility group I (HMGI) proteins (HMGI, HMGY, and HMGI-C) has previously been correlated with the presence of a highly malignant phenotype in epithelial and fibroblastic rat thyroid cells and in experimental thyroid, lung, mammary, and skin carcinomas. Northern (RNA) blot and run-on analyses demonstrated that the induction of HMGI genes in transformed thyroid cells occurs at the transcriptional level. An antisense methodology to block HMGI-C protein synthesis was then used to analyze the role of this protein in the process of thyroid cell transformation. Transfection of an antisense construct for the HMGI-C cDNA into normal thyroid cells, followed by infection with transforming myeloproliferative sarcoma virus or Kirsten murine sarcoma virus, generated cell lines that expressed significant levels of the retroviral transforming oncogenes v-mos or v-ras-Ki and removed the dependency on thyroid-stimulating hormones. However, in contrast with untransfected cells or cells transfected with the sense construct, those containing the antisense construct did not demonstrate the appearance of any malignant phenotypic markers (growth in soft agar and tumorigenicity in athymic mice). A great reduction of the HMGI-C protein levels and the absence of the HMGI(Y) proteins was observed in the HMGI-C antisense-transfected, virally infected cells. Therefore, the HMGI-C protein seems to play a key role in the transformation of these thyroid cells.