Dissociation between transformed and differentiated phenotype in rat thyroid epithelial cells after transformation with a temperature-sensitive mutant of the Kirsten murine sarcoma virus

FAK phosphorylation by ERK primes ras-induced tyrosine dephosphorylation of FAK mediated by PIN1 and PTP-PEST

Activated Ras has been found in many types of cancer. However, the mechanism underlying Ras-promoted tumor metastasis remains unclear. We demonstrate here that activated Ras induces tyrosine dephosphorylation and inhibition of FAK mediated by the Ras downstream Fgd1-Cdc42-PAK1-MEK-ERK signaling cascade. ERK phosphorylates FAK S910 and recruits PIN1 and PTP-PEST, which colocalize with FAK at the lamellipodia of migrating cells. PIN1 binding and prolyl isomerization of FAK cause PTP-PEST to interact with and dephosphorylate FAK Y397. Inhibition of FAK mediated by this signal relay promotes Ras-induced cell migration, invasion, and metastasis. These findings uncover the importance of sequential modification of FAK-by serine phosphorylation, isomerization, and tyrosine dephosphorylation--in the regulation of FAK activity and, thereby, in Ras-related tumor metastasis.

Role of the isoprenoid pathway in ras transforming activity, cytoskeleton organization, cell proliferation and apoptosis

The isoprenoid pathway, by its end-products lipids, has an important role in the control of ras transforming activity, cytoskeleton organization, cell proliferation and apoptosis. In particular, prenylation, a post-translational addition of farnesol and geranylgeraniol, is an important event for the biological activity of many proteins that play critical roles in signal transduction and cytoskeletal regulation, as well as in cell proliferation and apoptosis. We have been interested in studying the: (a) regulation of the isoprenoid pathway in the processing of cellular transformation induced by the K-ras oncogene, (b) role of the isoprenoid pathway in the control of cell proliferation and apoptosis, (c) role of the isoprenoid pathway in the control of cytoskeleton organization and (d) control of Rab expression by the isoprenoid pathway.

Impaired response to hepatocyte growth factor in FRTL-5 rat thyroid cells expressing a functional hepatocyte growth factor receptor

The FRTL-5 rat thyroid cell line is widely used for studies of thyrocyte function and growth. The objective of the present study was to investigate the effects of hepatocyte growth factor (HGF) on FRTL-5 cells. HGF has previously been known to be a potent regulator of thyrocyte growth and differentiation. Met, the receptor for HGF was expressed in FRTL-5 cells, as well as in primary cultures of porcine thyrocytes included in the study as control. On HGF stimulation Met was tyrosine phosphorylated in both porcine and FRTL-5 cells, indicating an activation of the receptor. Addition of HGF induced changes of cell shape, scattering and proliferation of the porcine thyrocytes, but not in the FRTL-5 cells; yet, a functional coupling of Met to the p85 subunit of the phosphatidylinositol-3'-kinase (PI3'-K) in coprecipitation experiments, formation of focal adhesions detected in immunofluorescence staining with an antivinculin antibody, and induction of c-fos mRNA in Northern blot analysis was observed in FRTL-5 cells, showing a transduction of the HGF/Met signal. In summary, despite the expression of apparently functional Met, the FRTL-5 cells are unable to properly respond to HGF.

Heregulin-dependent autocrine loop regulates growth of K-ras but not erbB-2 transformed rat thyroid epithelial cells

The EGF-like family of proteins, such as epidermal growth factor (EGF), transforming growth factor alpha (TGFalpha), amphiregulin (AR), betacellulin (BTC), cripto-1 (CR-1), and heregulin (HRG), plays an important role in the pathogenesis of several human carcinomas as autocrine growth factors. Differentiation and proliferation of rat thyroid cells in culture (FRTL-5 cells) are regulated by thyrotropin (TSH); withdrawal of TSH from culture medium produces growth arrest, whereas its addition to quiescent cells stimulates cell entry into S phase. Instead, transformed thyroid cell lines as FRTL-5H2 cell line, overexpressing erbB-2, Kimol cells, transformed by the wild-type K-ras and A6 clone, transformed by a temperature sensitive K-ras mutant, can grow without addition of TSH to the culture medium. In order to identify whether EGF-like growth factors and corresponding receptors (erbB-2, erbB-3, and erbB-4) could be involved in the autonomous growth of these transformed rat thyroid epithelial cells, Northern blot for mRNA analysis and Western blot for protein expression were performed. In contrast to normal control FRTL-5 cells, both K-ras and erbB-2-transformed cells expressed elevated levels of erbB-2 receptor. Moreover, both K-ras transformed cells, Kimol and A6 cells, but no FRTL-5H2 cells, were found able to express also high levels of erbB-4 receptor and HRG/NDF ligand. Treatment of K-ras transformed thyroid cells with neutralizing antibody against HRG/NDF reduced by 50% cell proliferation. These data indicate that unlike the erbB-2 overexpressing FRTL-5 cells, in K-ras rat thyroid epithelial cells, the growth factor heregulin signals through the heterodimer erbB-2/erbB-4 receptors in an autocrine fashion.

Cyclin D1 and Cyclin E expression in malignant thyroid cells and in human thyroid carcinomas

Evidence of the involvement of cyclin gene alterations in human cancer is growing. In this study, we sought to determine the pattern of expression of cyclin D1 and cyclin E in normal and malignant thyroid cells. Quiescent rat thyroid cells in culture, induced to synthesize DNA by thyrotropin (TSH), expressed cyclin D1 gene after 6 hr and cyclin E gene with a peak at 18 hr from the stimulus; K-ras-transformed rat thyroid cells, which grew without addition of hormones necessary for normal cell proliferation, expressed elevated levels of cyclin D1 and cyclin E, compared with normal differentiated thyroid cells. Human benign and malignant thyroid tumors and their relative normal tissues were then analyzed. Neither major genetic alterations nor amplifications for cyclin D1 and cyclin E genes were found by Southern blot analysis in genomic DNAs extracted from all types of thyroid tumors. Moreover, statistical analyses of densitometric values from Northern blots did not show increased levels of cyclin D1 and E mRNAs in the tumor samples, compared with normal thyroid. Immunohistochemical analyses of formalin-fixed paraffin-embedded sections of tissues with specific antibodies revealed a prevalent cytoplasmic cyclin E staining in the thyroid tissues analyzed. Cyclin D1, instead, was present in the cytoplasm of normal thyroids and adenomas, but in 31% of thyroid papillary carcinomas analysed, it was overexpressed, with a localization in the nucleus. Our in vivo observations suggest that unlike cyclin E, elevated nuclear cyclin D1 expression defines a subset of thyroid papillary carcinomas, and might be a contributory factor to thyroid tumorigenesis.

Determination of functional domains of the human transcription factor PAX8 responsible for its nuclear localization and transactivating potential

The conserved structure of the transcription factors of the Pax gene family may reflect functional conservation. We have demonstrated that the human Pax8 transcription factor is organized in several functional domains and contains two regions responsible for its nuclear localization, in addition to an activating region at the carboxy terminus of the protein and an inhibitory region encoded by the exon 9 present only in a splice variant PAX8a. Regions of PAX8 determining the nuclear localization of the PAX8A/lacZ fusions contain short amino acid sequences similar to several described nuclear localization sites (NLS). These NLS were identified in the paired domain and between the octapeptide and the residual homeodomain, respectively. The activating domain is encoded by the exons 10 and 11 and its function is modulated by the adjacent domains encoded by the exons 9 and 12. The domain encoded by exon 9 significantly inhibits the function of the activating domain. Pax8 is expressed in thyroid cells and its product binds promoters of the thyroglobulin and thyroperoxidase genes through its paired domain. Thyroid cell growth and differentiation depend on thyrotropin which, by stimulating cAMP synthesis, activates the cAMP-dependent protein kinase A (PKA). We have investigated a link between thyrotropin stimulation and gene activation by Pax8. Stimulation of cAMP synthesis augments Pax8-specific transcription in thyroid cells, indicating that PKA is involved in Pax8 activation. Cotransfection of GAL4/PAX8 fusions and the catalytic subunit of PKA in A126, a PKA-deficient derivative of the PC12 pheochromocytoma cell line, synergistically activates the GAL4-specific reporter, suggesting the activating domain of PAX8 is dependent upon the catalytic subunit of the PKA. We propose that this dependence is due to a hypothetical adaptor which forms a target for PKA and interacts with the activating domain of PAX8. We show that PAX8 isolated from the thyroid cell line FTRL5 is a phosphoprotein in which phosphorylation is not dependant on cAMP pathway activation. Our results suggest that Pax8 is part of the cAMP signaling pathway and mediates thyrotropin-dependent gene activation in thyroid cells. Investigation of the PAX8 expression in a panel of Wilms' tumors shows a striking correlation between the expression of PAX8 and another transcription factor, WT1, indicating that these two genes may interact in vivo.

Restored expression of transforming growth factor beta type II receptor in k-ras-transformed thyroid cells, TGF beta-resistant, reverts their malignant phenotype

Transforming growth factor beta 1 (TGF beta 1) inhibits the growth of normal rat epithelial thyroid cells (FRTL-5 strain) by counteracting thyrotropin (TSH)-stimulated DNA synthesis and by slowing the cells in the G1 phase of the cell cycle. Here, we have studied two clones of FRTL-5 thyroid cell line transformed by the wild type (wt) v-k-ras oncogene (K.M.A1, K.M.A2) and one clone (A6) transformed by a temperature-sensitive (ts) v-k-ras mutant. Anchorage-dependent as well as anchorage-independent growth of these k-ras-transformed cells was not inhibited by TGF beta 1. TGF beta 1 resistance appeared to be dependent by a functional p21 k-ras, because A6 cell growth was partially inhibited at the nonpermissive temperature (39 degrees C). To determine the basis for TGF beta 1 resistance in k-ras-transformed thyroid cells, we looked for possible defects in the expression of type I (T beta R-I/ALK5) and type II TGF beta receptors (T beta R-II). Lower levels of type II receptors were present in all of the k-ras-transformed clones, as revealed by both Northern blot and cross-linking experiments. A partial reversion of the malignant phenotype of the wt k-ras-transformed clone was obtained in two clones isolated after transfection of the malignant thyroid cells (K.M.A1) with a T beta R-II expression vector. These two clones also showed restored levels of exogenous T beta R-II mRNA and protein, and both clones showed a partially reacquired sensitivity to TGF beta 1. Similarly, the reversion of the malignant phenotype of the A6 clone grown at the nonpermissive temperature was accompanied by a restored expression of the T beta R-II receptors. These data indicate that active k-ras oncogene can induce TGF beta 1 resistance in rat thyroid cells and suggest that one of the possible mechanisms of escape from TGF beta 1 growth control in k-ras-induced thyroid carcinogenesis involves a reduced expression of T beta R-II receptors.

Regulation of 3-hydroxy-3-methylglutaryl coenzyme A reductase gene expression in FRTL-5 cells. II. Down-regulation by v-K-ras oncogene

3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase activity and mRNA levels were significantly reduced in FRTL-5 cells transformed with the Kirsten-Moloney sarcoma virus (KiMol); these cells have lost thyrotropin dependence and express high levels of p21ras. FRTL-5 cells, transformed with a temperature-sensitive mutant of the v-K-ras oncogene (Ats cells: 33 degrees C, permissive; 39 degrees C, nonpermissive), showed significant reduction of HMG-CoA reductase expression when exposed to 33 degrees C. In KiMol cells, as well as in Ats cells at 33 degrees C, the transcription driven by cAMP-responsive element was probed by measuring chloramphenicol acetyl transferase (CAT) levels after transfection with a chimeric plasmid containing the reporter gene linked to the rat reductase promoter. Basal CAT activity in KiMol cells transfected with wild-type promoter was lower than in FRTL-5 cells but was increased by forskolin to the levels attained in thyrotropin-stimulated FRTL-5 cells. Forskolin failed to increase CAT activity in KiMol cells transfected with the plasmid harboring a reductase promoter in which the cAMP-responsive element octamer was mutated to a nonpalindromic sequence. The effect of v-K-ras could be mimicked in FRTL-5 cells by tetradecanoyl phorbol acetate and reverted in KiMol and Ats cells, expressing active Ras protein, by increasing intracellular cAMP and/or by protein kinase C inhibition. The data are consistent with the contention that v-K-ras, through protein kinase C and depletion of intracellular cAMP, is inhibitory for the protein kinase A pathway. This is the first demonstration that active v-K-ras down-regulates HMG-CoA reductase expression.

Elevated levels and mitogenic activity of lysophosphatidylinositol in k-ras-transformed epithelial cells

In cell lines stably (KiKi) or reversibly (Ts) transformed by the k-ras oncogene originated from a differentiated rat thyroid line (FRTL5 cells), k-ras-induced transformation has been associated with an increased phospholipase A2 activity. Here we provide evidence that this enzymic activity is phosphoinositide specific and leads to the formation of lysophosphatidylinositol. The levels of this lysolipid increased by 2-3-fold in ras-transformed cells (KiKi cells and Ts cells at the permissive temperature of 33 degrees C) as compared to differentiated cells (FRTL5) or to Ts cells maintained at 39 degrees C, i.e. at the temperature where ras-p21, the product of the ras oncogene, is inactive. Since another lysoderivative, lysophosphatidic acid, has been shown to be a mitogen, we have tested whether lysophosphatidylinositol could have a similar activity on thyroid cells. Lysophosphatidylinositol (10-100 microM) induced a 5-10-fold increase in [3H]thymidine incorporation in both FRTL5 and KiKi cells, whereas lysophosphatidic acid was active only in differentiated cells. Lysophosphatidylinositol (approximately 25 microM) and lysophosphatidic acid (50-100 microM) acted synergistically with insulin in increasing [3H]thymidine incorporation. Moreover, lysophosphatidylinositol at concentrations three-fold higher than those found to be mitogenic, inhibited the activity of the GTPase-activating protein. We conclude that lysophosphatidylinositol is a mitogen that might play a role in the modulation of k-ras transformed cell proliferation.

In vitro differentiation of the human osteosarcoma cell lines, HOS and KHOS

The osteogenic potential of the two human osteosarcoma cell lines HOS and KHOS; a cell line produced by the transformation of the HOS cells by the Kirsten murine sarcoma virus, was studied in vitro. HOS cells cultured more than 2 weeks formed nodules composed of two morphologically distinct layers, an epithelial-like surface cell layer and a collagen-rich inner cell layer. Alkaline phosphatase (ALPase) activity occurred in the plasma membrane of the surface cell layer, and calcified substances developing along collagen fibers were detected in the collagen-rich inner cell layer. The calcified substances were further examined by analytical electron microscopy and were shown to be hydroxyapatite crystals. In contrast, there was neither ALPase nor the deposition of a calcified substance in the KHOS cells.

Malignant transformation of rat thyroid cells transfected with the human TSH receptor cDNA

Growth and function of well differentiated FRTL-5 thyroid cells depend on thyrotropin as its main regulatory hormone. We demonstrate here that stable transfection of FRTL-5 cells with the human thyrotropin receptor cDNA results in cellular transformation of these cells with altered cell shape and loss of contact inhibition. The transformed cells replicate in soft agar and form invasive tumors when cell suspensions are implanted onto nude mice. They have lost their thyrotropin dependent growth and their ability to concentrate iodide and synthesize thyroglobulin. But they still express the rat thyrotropin receptor mRNA and accumulate cAMP in response to thyrotropin stimulation. However, although the full length human thyrotropin receptor cDNA is integrated into their genome, transformed cells do not express the human thyrotropin receptor mRNA.

De novo HLA class II and enhanced HLA class I molecule expression in SV40 transfected human thyroid epithelial cells

Human thyroid follicular cells normally synthesize and express HLA Class I molecules but in glands affected by autoimmune or neoplastic diseases they express Class II molecules. We have investigated the effect of SV40 virus transformation on the expression of MHC molecules in human thyrocytes. Primary cultures of human thyroid from two different glands were transfected with the plasmid pX-8, containing the 'early' region of SV40 virus, and two continuous lines of thyrocytes were obtained. The cell lines maintained features of parental thyroid epithelial cells showing the characteristic cytokeratin filament network, microvillar protrusion and tight junctions. In addition, the SV40-transfected cells responded to graded doses of TSH with increased c-AMP production. Thyrocytes from both cell lines hyperexpressed Class I molecules and a significant proportion of them also acquired constitutive Class II expression, as determined by indirect immunofluorescence (IFL), flow cytometry and Northern blotting hybridization using a DR beta probe. These cells were found to be normally up-regulated by interferon (IFN)-gamma. Indirect IFL and flow cytometry analysis were used to detect and quantify the expression of HLA-DR, DP and DQ subregions. A co-ordinated expression (DR greater than DP much greater than DQ), reminiscent of the inappropriate HLA expression found in thyroid autoimmune disease in vivo and of the in vitro regulation in normal thyrocytes, was observed. Clones derived from these cell lines differed in their level of constitutive Class II expression and in their sensitivity to Class II induction by IFN-gamma. In conclusion, these thyroid cell lines could provide a useful tool for further investigation of HLA gene regulation in thyroid cells and for elucidating on the mechanism involved in the inappropriate HLA expression described in autoimmune and neoplastic diseases of the thyroid.

Transformation by the k-ras oncogene correlates with increases in phospholipase A2 activity, glycerophosphoinositol production and phosphoinositide synthesis in thyroid cells

Two cell lines transformed by the k-ras oncogene (KiKi and KiMol cells) and a temperature sensitive clone (Ts), all originated from a normal rat thyroid line (FRTL5 cells), have been employed to analyse the intracellular mechanisms affected by the ras p21. In k-ras transformed cells two phosphoinositide derivatives, glycerophosphoinositol and inositol monophosphate, were markedly increased, whereas inositol bisphosphate and trisphosphate maintained the same level as in normal cells. Cytosolic Ca2+ was also unaffected. This indicates that in epithelial cells the phospholipase C activity is not altered upon ras transformation. The formation of glycerophosphoinositol involved the activation of a phosphoinositide specific phospholipase A2. The higher phospholipase A2 activity in ras transformed cells could be further demonstrated by the increase in total arachidonic acid release. In the Ts clone the increase in glycerophosphoinositol and inositol monophosphate was evident only at the permissive temperature (33 degrees C), whereas it disappeared at 39 degrees C. At 33 degrees C the cells were also characterized by an enriched membrane pool of phosphoinositides. All these changes occurred in parallel with morphological transformation. We propose that cell transformation by the k-ras oncogene affects different steps of the membrane lipid metabolism, among which the most prominent one is the activation of a phosphoinositide specific phospholipase A2. These effects could originate mitogenic metabolites. Moreover, they correlate well with the induction of the malignant phenotype.

Thyrotropin receptor gene expression in oncogene-transfected rat thyroid cells: correlation between transformation, loss of thyrotropin-dependent growth, and loss of thyrotropin receptor gene expression

Rat FRTL-5 and PC-Cl-3 thyroid cells are continuously cultured, clonal lines which require thyrotropin to grow and function. Both can be efficiently transformed when infected with RNA or DNA viruses carrying oncogenes or when directly transfected with activated oncogenes. Transformation, assayed by the appearance of cell growth in agar and by tumorigenicity in syngeneic rats or nude mice, is associated with the loss of thyrotropin-dependent cell division and thyrotropin-regulated functions such as thyroglobulin synthesis. In 16 clones of FRTL-5 or PC-Cl-3 cells transformed with different oncogenes, we show that loss of thyrotropin-dependent growth and function correlates with the loss of thyrotropin receptor gene expression, measured with a rat thyrotropin receptor cDNA probe.

Thyroid nuclear factor 1 (TTF-1) contains a homeodomain and displays a novel DNA binding specificity

The cDNA for TTF-1, a thyroid nuclear factor that binds to the promoter of thyroid specific genes, has been cloned. The protein encoded by the cDNA shows binding properties indistinguishable from those of TTF-1 present in nuclear extracts of differentiated rat thyroid cells. The DNA binding domain of TTF-1 is a novel mammalian homeodomain that shows considerable sequence homology to the Drosophila NK-2 homeodomain. TTF-1 mRNA and corresponding binding activity are detected in thyroid and lung. The chromosomal localization of the TTF-1 gene has been determined in humans and mice and corresponds to chromosomes 14 and 12, respectively, demonstrating that the TTF-1 gene is not located within previously described clusters of homeobox-containing genes.

Thyroid nuclear factor 1 (TTF-1) contains a homeodomain and displays a novel DNA binding specificity

The cDNA for TTF-1, a thyroid nuclear factor that binds to the promoter of thyroid specific genes, has been cloned. The protein encoded by the cDNA shows binding properties indistinguishable from those of TTF-1 present in nuclear extracts of differentiated rat thyroid cells. The DNA binding domain of TTF-1 is a novel mammalian homeodomain that shows considerable sequence homology to the Drosophila NK-2 homeodomain. TTF-1 mRNA and corresponding binding activity are detected in thyroid and lung. The chromosomal localization of the TTF-1 gene has been determined in humans and mice and corresponds to chromosomes 14 and 12, respectively, demonstrating that the TTF-1 gene is not located within previously described clusters of homeobox-containing genes.

Thyrotropin stimulates transcription from the ferritin heavy chain promoter

Thyrotropin (TSH) is the primary hormone regulating the activity of the thyroid gland. We have recently shown that TSH stimulates H-ferritin mRNA levels in rat thyroid. Ferritin plays a key role in determining the intracellular fate of iron. The induction of ferritin synthesis by iron in liver is regulated both at transcriptional and translational levels. Here we present evidence that the mechanisms by which TSH regulates the mRNA levels are mediated by a diffusible product acting in trans on its own promoter. In fact, the H-ferritin promoter mediates increased CAT activity in response to hormone induction. Our results identify transcription as an important regulatory step of TSH action. They suggest that TSH induces expression of the ferritin gene, and that continuous protein synthesis is required to maintain basal ferritin gene expression in the absence of hormone.

Protein binding domains of the rat thyroglobulin promoter

We have previously shown that DNA elements controlling tissue specific expression of the rat thyroglobulin gene extend 170 bp upstream of the cap site and have identified a thyroid specific nuclear factor which binds the promoter in the -60 region (site C). Here we report that the distal portion of the promoter, extending from -160 to -120, contains two contiguous DNA elements (sites A and B) which interact with the same thyroid-specific factor binding to proximal site C. A second nuclear factor, ubiquitously distributed, binds to the distal site A. Transient cotransfection-competition studies show that all the three binding sites A, B and C titrate a trans-acting factor(s) which is necessary for the transcription of the thyroglobulin gene.

The block of thyroglobulin synthesis, which occurs upon transformation of rat thyroid epithelial cells, is at the transcriptional level and it is associated with methylation of the 5' flanking region of the gene

Transformation of rat thyroid epithelial cells by Kirsten murine sarcoma virus results in the block of certain thyroid differentiated functions, such as synthesis and secretion of thyroglobulin. Our studies, performed by a run-on assay, demonstrate that this block occurs at the transcriptional level. We also demonstrate the de novo methylation of two methylation-sensitive sites, located within the 5' end regulatory sequences of the thyroglobulin gene, in transformed cells, in the absence of any rearrangement of the gene. These two methylation-sensitive sites were methylated also in a rat thyroid cell line transformed by another retrovirus and in two normal cell lines which do not express the thyroglobulin gene.

Adenylate cyclase activity of v-ras-k transformed rat epithelial thyroid cells

The regulation of adenylate cyclase has been analyzed in normal rat thyroid cells as well as in the same cells transformed by the v-ras-k oncogene. In both cell types the adenylate cyclase complex consists of the two GTP-binding proteins, Gi and Gs, as demonstrated by the specific ADP-ribosylation induced by pertussis and cholera toxin, respectively. The response of adenylate cyclase of the transformed cells to forskolin, pertussis toxin and cholera toxin is attenuated with respect to the control cell line. The thyrotropic hormone (TSH), that acts on normal thyroid cells in culture as a growth factor by stimulating the adenylate cyclase activity, is not able to induce DNA synthesis nor does it stimulate adenylate cyclase in v-ras-k transformed cells.

SGHTL-34, a thyrotrophin-responsive immortalised human thyroid cell line generated by transfection

Normal human thyrocytes were immortalised by electroporation-mediated transfection with the plasmid pSV3neo. One resultant cell line (SGHTL-34) contains approximately 10 copies of simian virus 40 (SV40) early region incorporated into the genome and has been in continuous monolayer culture for 9 months. SGHTL-34 cells grow rapidly (doubling time 30 h) and contain cytokeratin filaments. They demonstrate a morphological change in response to thyrotrophin (TSH) and possess a TSH- and forskolin-sensitive adenylate cyclase, the thresholds for stimulation being 10 microU/ml bovine TSH- and forskolin-sensitive development of this novel human thyrocyte cell line may allow further study of the regulation of human thyroid growth and differentiation.

Changes in cellular gene expression in rat thyroid epithelial cells transformed by the Kirsten murine sarcoma virus

We have exploited a recently characterized system of rat thyroid epithelial cells transformed by the wild-type (wt) and a temperature-sensitive (ts) mutant strain of the Kirsten murine sarcoma virus (Ki-MSV) in order to study the effects of the K-ras oncogene on the gene expression of differentiated thyroid epithelial cells. By using cDNAs isolated from normal thyroid glands as probes, we were able to identify three sets of cellular sequences whose expression is influenced by the v-K-ras oncogene. The first set of genes is irreversibly repressed by transformation with both the wt and the ts viruses. The second set of genes is repressed in the ts-Ki-MSV-transformed cells but not in the same cells grown at the nonpermissive temperature. A third set of genes is present at higher levels at the nonpermissive temperature than at the permissive temperature. This system has allowed us to isolate and characterize a number of cDNA clones belonging to each of these three sets of genes. These specific cDNAs are suitable probes to study phenotypical changes during transformation of epithelial cells.

Activated H-ras transforms rat intestinal epithelial cells with expression of alpha-TGF

We describe malignant transformation of cultured rat intestinal epithelial cells (IEC-18) by transfection with the activated human H-ras gene cloned from the EJ bladder carcinoma. Transformed cells showed a marked morphological change, expressed high levels of the transfected H-ras gene, were able to grow in agar and expressed antigenic markers identical with parental IEC-18 cells. When injected into syngeneic rats these cells formed rapidly growing tumors expressing the same intestinal-specific antigenic markers as the injected cells. Parallel to the high expression of H-ras mRNA in the transformants we document overexpression of rat alpha-TGF mRNA.

Increased level of thyroglobulin mRNA in a human familial goiter

Thyroglobulin (Tg) and its specific mRNA were analyzed in the thyroid gland of two cases of familial goiter. A three-fold increase in the level of stable protein and functional Tg mRNA was found in the goiter of one of the two patients in whom a desiodase defect was demonstrated. Normal concentrations of both Tg and its mRNA were found in the other goiter in which no enzymatic defect could be shown. Our results suggest that the increase of Tg mRNA levels found in the goiter with a desiodase defect was due to a chronic stimulation of the gland by TSH.

Sarcoma viruses carrying ras oncogenes induce differentiation-associated properties in a neuronal cell line

The growth-promoting and/or differentiation-blocking activities of Kirsten (Ki-MSV) or Harvey murine sarcoma virus (Ha-MSV) on various types of cells in vitro are well documented. Here we report an unexpected effect of these viruses on a rat phaeochromocytoma cell line, PC12. PC12 cells, which multiply indefinitely in growth medium, are known to respond to nerve growth factor (NGF) by cessation of cell division and expression of several properties resembling those of differentiated sympathetic neurones. We have found that Ki- and Ha-MSV mimic some, if not all, of the activities of NGF in PC12 cells, and there is evidence that the viral oncogenes, v-Ki-ras and v-Ha-ras, are responsible for this phenomenon. This system may be of value for studying the mechanism of action of the v-ras genes as well as the regulatory mechanism of growth and differentiation in neuronal cells.

Differential expression of thyroglobulin gene in normal and transformed thyroid cells

We have measured the synthesis of thyroglobulin in two differentiated cell lines, FRTL-5 and FRTL-424, and two transformed thyroid cell lines, FRA and 1-5G. The untransformed cells actively synthesized and exported thyroglobulin in the medium: however, the FRTL-5 cell line synthesized seven times less thyroglobulin than the FRTL-424 cell line, even though both cell types contained equal amounts of functional thyroglobulin mRNA. In contrast the transformed cells expressed extremely low levels of thyroglobulin mRNA, even though there was no detectable change in gene structure or copy number as determined by Southern blot analysis. On the basis of these data we conclude that (a) the different levels of thyroglobulin synthesis in the two untransformed cell lines are due to stable post-transcriptional alterations in the biosynthesis of thyroglobulin and (b) the transformation of thyroid cells results in a substantial reduction in thyroglobulin gene expression.