Cell lines are crucial to elucidate mechanisms of tumorigenesis and serve as tools for cancer treatment screenings. Therefore, careful validation of whether these models have conserved properties of in vivo tumors is highly important. Thyrocyte-derived tumors are very interesting for cancer biology studies because from one cell type, at least five histologically characterized different benign and malignant tumor types can arise. To investigate whether thyroid tumorderived cell lines are representative in vitro models, characteristics of eight of those cell lines were investigated with microarrays, differentiation markers, and karyotyping. Our results indicate that these cell lines derived from differentiated and undifferentiated tumor types have evolved in vitro into similar phenotypes with gene expression profiles the closest to in vivo undifferentiated tumors. Accordingly, the absence of expression of most thyrocyte-specific genes, the nonresponsiveness to thyrotropin, as well as their large number of chromosomal abnormalities, suggest that these cell lines have acquired characteristics of fully dedifferentiated cells. They represent the outcome of an adaptation and evolution in vitro, which questions the reliability of these cell lines as models for differentiated tumors. However, they may represent useful models for undifferentiated cancers, and by their comparison with differentiated cells, can help to define the genes involved in the differentiation/dedifferentiation process. The use of any cell line as a model for a cancer therefore requires prior careful and thorough validation for the investigated property. [Cancer Res 2007;67(17):8113-20]

Papillary thyroid cancers (PTCs) incidence dramatically increased in the vicinity of Chernobyl. The cancer-initiating role of radiation elsewhere is debated. Therefore, we searched for a signature distinguishing radio-induced from sporadic cancers. Using microarrays, we compared the expression profiles of PTCs from the Chernobyl Tissue Bank (CTB, n ¼ 12) and from French patients with no history of exposure to ionising radiations (n ¼ 14). We also compared the transcriptional responses of human lymphocytes to the presumed aetiological agents initiating these tumours, g-radiation and H 2 O 2 . On a global scale, the transcriptomes of CTB and French tumours are indistinguishable, and the transcriptional responses to g-radiation and H 2 O 2 are similar. On a finer scale, a 118 genes signature discriminated the g-radiation and H 2 O 2 responses. This signature could be used to classify the tumours as CTB or French with an error of 15 -27%. Similar results were obtained with an independent signature of 13 genes involved in homologous recombination. Although sporadic and radio-induced PTCs represent the same disease, they are distinguishable with molecular signatures reflecting specific responses to g-radiation and H 2 O 2 . These signatures in PTCs could reflect the susceptibility profiles of the patients, suggesting the feasibility of a radiation susceptibility test.

The cAMP signaling pathway regulates growth of many cell types, including somatotrophs, thyrocytes, melanocytes, ovarian follicular granulosa cells, adrenocortical cells, and keratinocytes. Mutations of partners from the cAMP signaling cascade are involved in tumor formation. Thyroid-stimulating hormone (TSH) receptor and Gs␣ activating mutations have been detected in thyroid autonomous adenomas, Gs␣ mutations in growth hormone-secreting pituitary adenomas, and PKAR1A mutations in Carney complex, a multiple neoplasia syndrome. To gain more insight into the role of cAMP signaling in tumor formation, human primary cultures of thyrocytes were treated for different times (1.5, 3, 16, 24, and 48 h) with TSH to characterize modulations in gene expression using cDNA microarrays. This kinetic study showed a clear difference in expression, early (1.5 and 3 h) and late (16 -48 h) after the onset of TSH stimulation. This result suggests a progressive sequential process leading to a change of cell program. The gene expression profile of the long-term stimulated cultures resembled the autonomous adenomas, but not papillary carcinomas. The molecular phenotype of the adenomas thus confirms the role of long-term stimulation of the TSH-cAMP cascade in the pathology. TSH induced a striking up-regulation of different negative feedback modulators of the cAMP cascade, presumably insuring the oneshot effect of the stimulus. Some were down-or nonregulated in adenomas, suggesting a loss of negative feedback control in the tumors. These results suggest that in tumorigenesis, activation of proliferation pathways may be complemented by suppression of multiple corresponding negative feedbacks, i.e., specific tumor suppressors.cyclic AMP ͉ microarrays ͉ papillary tumors ͉ thyrotropin T ight regulation of the second messenger cAMP is of crucial importance for cells because it regulates function, differentiation, and proliferation (1). In cells in which cAMP stimulates growth, activating mutations in partners of this pathway induce uncontrolled growth. In most benign thyroid autonomous adenomas, activating mutations have been found in the thyroidstimulating hormone (TSH) receptor (TSHR) (2) and, to a lesser extent, in the Gs␣ protein, an activator of the cAMP-producing adenylyl cyclase (1, 3). These mutations result in a TSHindependent growth and lead to hyperfunction (1). In addition, activating mutations of the Gs␣ protein have been detected in growth hormone-secreting pituitary adenomas (4) and inactivating mutations in the type I-␣ regulatory subunit inhibiting protein kinase A (PKAR1A) in Carney complex, a multiple neoplasia syndrome (5).Our knowledge of the genes regulated by the cAMP-protein kinase A cascade and its uncontrolled activation is still sketchy (6). To gain more insight into the cAMP-activated signal transduction cascade in tumors, human primary cultures of thyrocytes treated for different times with the TSH growth and differentiation stimulus were used as a model. Thyrocytes in primary culture are expected to be better mod...

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