Ligands for peroxisome proliferator-activated receptor gamma inhibit growth and induce apoptosis of human papillary thyroid carcinoma cells

A selective retinoid X receptor agonist bexarotene (LGD1069, targretin) inhibits angiogenesis and metastasis in solid tumours

The present study determined the influence of a retinoid X receptor agonist bexarotene on angiogenesis and metastasis in solid tumours. In the experimental lung metastasis xenograft models, treatment with bexarotene inhibited the development of the lung tumour nodule formation compared to control. In vivo angiogenesis assay utilising gelfoam sponges, bexarotene reduced angiogenesis in sponges containing vascular endothelial growth factor, epidermal growth factor and basic fibroblast growth factor to various extent. To determine the basis of these observations, human breast and non-small-cell lung cancer cells were subjected to migration and invasion assays in the presence of bexarotene. Our data showed that bexarotene decrease migration and invasiveness of tumour cells in a dose-dependent manner. Furthermore, bexarotene inhibited angiogenesis by directly inhibiting human umbilical vein endothelial cell growth and indirectly inhibiting tumour cell-mediated migration of human umbilical vein endothelial cells through Matrigel matrix. Analysis of tumour-conditioned medium indicated that bexarotene decreased the secretion of angiogenic factors and matrix metalloproteinases and increased the tissue inhibitor of matrix metalloproteinases. The ability of bexarotene to inhibit angiogenesis and metastasis was dependent on activation of its heterodimerisation partner peroxisome proliferator-activated receptor gamma. Collectively, our results suggest a role of bexarotene in treatment of angiogenesis and metastasis in solid tumours.

RAI(ShcC/N-Shc)-dependent recruitment of GAB 1 to RET oncoproteins potentiates PI 3-K signalling in thyroid tumors

RAI, also named ShcC/N-Shc, one of the members of the Shc proteins family, is a substrate of the RET receptor tyrosine kinase. Here, we show that RAI forms a protein complex with both RET/MEN 2 A and RET/PTC oncoproteins. By co-immunoprecipitation, we found that RAI associates with the Grb 2-associated binder 1 (GAB 1) adapter. This association is constitutive, but, in the presence of RET oncoproteins, both RAI and GAB 1 are tyrosine-phosphorylated, and the stoichiometry of this interaction remarkably increases. Consequently, the p 85 regulatory subunit of phosphatidylinositol-3 kinase (PI-3 K) is recruited to the complex, and its downstream effector Akt is activated. We show that human thyroid cancer cell lines derived from papillary or medullary thyroid carcinoma (PTC or MTC) carrying, respectively, RET/PTC and RET/MEN 2 A oncoproteins express RAI proteins. We also show that human PTC samples express higher levels of RAI, when compared to normal thyroid tissue. In thyroid cells expressing RET/PTC 1, ectopic expression of RAI protects cells from apoptosis; on the other hand, the silencing of endogenous RAI by small inhibitory duplex RNAs in a PTC cell line that expresses endogenous RET/PTC 1, increases the rate of spontaneous apoptosis. These data suggest that RAI is a critical substrate for RET oncoproteins in thyroid carcinomas.

Peroxisome proliferator-activated receptor (PPAR)gamma is highly expressed in normal human pituitary gland

OBJECTIVE

Expression of peroxisome proliferator-activated receptor (PPAR)gamma in normal pituitary seems to be restricted to ACTH-secreting cells. The aim of the study was to evaluate the expression of PPARgamma in normal human pituitary tissue and to study its localization in the pituitary secreting cells.

MATERIALS AND METHODS

Normal pituitary tissue samples were obtained form 11 patients with non-secreting adenoma who underwent surgical excision of the tumor. Expression of PPARgamma was evaluated by immunostaining and western blotting; localization of PPARgamma in each pituitary secreting cell lineage was evaluated by double immunofluorescence using confocal microscopy. Pituitary non-functioning adenomas served as Controls.

RESULTS

PPARgamma was highly expressed in all pituitary samples with a (mean +/- SD) 81 +/- 6.5% of stained cells; expression of PPARgamma was confirmed by western blotting. Non-functioning pituitary adenomas had 74 +/- 11% PPARgamma positive cells. Expression of PPARy was either in cytoplasm or nuclei. In addition, treatment of GH3 cells, with a PPARgamma ligand was associated with traslocation of the receptor from cytoplasm into the nucleus. Double immunostaining revealed that every pituitary secreting cell (GH, TSH, LH, FSH, PRL and ACTH) had PPARgamma expressed.

DISCUSSION

The present study demonstrated that PPARgamma is highly expressed in every normal pituitary secreting cell lineage. It can translocate into the nucleus by ligand binding; however, its role in pituitary hormone regulation remains to be elucidated.

Follicular thyroid tumors with the PAX8-PPARgamma1 rearrangement display characteristic genetic alterations

Follicular thyroid carcinomas (FTC) arise through oncogenic pathways distinct from those involved in the papillary histotype. Recently, a t(2;3)(q13;p25) rearrangement, which juxtaposes the thyroid transcription factor PAX8 to the peroxisome proliferator-activated receptor (PPAR) gamma1, was described in FTCs. In this report, we describe gene expression in 11 normal tissues, 4 adenomas, and 8 FTCs, with or without the PAX8-PPARgamma1 translocation, using custom 60-mer oligonucleotide microarrays. Results were confirmed by quantitative real-time polymerase chain reaction of 65 thyroid tissues and by immunohistochemistry. Statistical analysis revealed a pattern of 93 genes discriminating FTCs, with or without the translocation, that were morphologically undistinguishable. Although the expression of thyroid-specific genes was detectable, none appeared to be differentially regulated between tumors with or without the translocation. Differentially expressed genes included genes related to lipid/glucose/amino acid metabolism, tumorigenesis, and angiogenesis. Surprisingly, several PPARgamma target genes were up-regulated in PAX8-PPARgamma-positive FTCs such as angiopoietin-like 4 and aquaporin 7. Moreover many genes involved in PAX8-PPARgamma expression profile presented a putative PPARgamma-promoter site, compatible with a direct activity of the fusion product. These data identify several differentially expressed genes, such as FGD3, that may serve as potential targets of PPARgamma and as members of novel molecular pathways involved in the development of thyroid carcinomas.

Chemopreventive Effect of Peroxisome Proliferator–Activated Receptor γ on Gastric Carcinogenesis in Mice

Peroxisome proliferator-activated receptor gamma (PPARgamma) is known to be expressed in several cancers, and the treatment of these cancer cells with PPARgamma ligands often induces cell differentiation and apoptosis. Recently, the chemopreventive potential of PPARgamma ligands on colon carcinogenesis was reported, although the effect of PPARgamma on colon carcinogenesis and the mechanism of the effect remain controversial. In this study, we attempted to elucidate the role of PPARgamma in gastric carcinogenesis and explored the possible use of PPARgamma ligand as a chemopreventive agent for gastric cancer. N-methyl-N-nitrosourea (MNU, 240 ppm) was given in drinking water for 10 weeks to induce gastric cancer in PPARgamma wild-type (+/+) and heterozygous-deficient (+/-) mice, followed by treatment with PPARgamma ligand [troglitazone, 0.15% (w/w) in powder food] or the vehicle alone for 42 weeks. At the end of the experiment, PPARgamma (+/-) mice were more susceptible to MNU-induced gastric cancer than wild-type (+/+) mice (89.5%/55.5%), and troglitazone significantly reduced the incidence of gastric cancer in PPARgamma (+/+) mice (treatment 55.5%/vehicle 9%) but not in PPARgamma (+/-) mice. The present study showed that (a) PPARgamma suppresses gastric carcinogenesis, (b) the PPARgamma ligand troglitazone is a potential chemopreventive agent for gastric carcinogenesis, and (c) troglitazone's chemopreventive effect is dependent on PPARgamma.

Critical Role of Peroxisome Proliferator-Activated Receptor γ on Anoikis and Invasion of Squamous Cell Carcinoma

PURPOSE

Peroxisome proliferator-activated receptor gamma (PPARgamma) plays a important role in various physiological functions. We examined whether PPARgamma is expressed in primary squamous cell carcinoma and lymph node metastasis and whether PPARgamma is a potential target for tumor therapy.

EXPERIMENTAL DESIGN AND RESULTS

A high-level expression of PPARgamma was observed in tumor cells of human primary squamous cell carcinoma, lymph node metastasis, and squamous cell carcinoma cell lines. Treatment with PPARgamma-specific antagonists, but not agonists, caused apoptotic cell death on squamous cell carcinoma cell lines in a concentration-dependent manner. Small interfering RNA for PPARgamma also inhibited cell adhesion and growth of squamous cell carcinomas. The phosphorylation of focal adhesion kinase (FAK) was decreased by treatment with PPARgamma antagonists, and resulted in decreases in phosphorylation of Erk and mitogen-activated protein kinase. Furthermore, PPARgamma antagonists decreased the adhesion of squamous cell carcinomas into fibronectin-coated plates, indicating the inhibition of interaction between squamous cell carcinomas and fibronectin. Expression of integrin alpha5, a counter adhesion molecule for fibronectin, was inhibited by the treatment with PPARgamma antagonists. These results indicate that the decrease in integrin alpha5 and following inhibition of cell adhesion may cause the inhibition of FAK signaling pathways. PPARgamma antagonists also strongly inhibited invasion of squamous cell carcinoma via down-regulation of CD151 expression.

CONCLUSIONS

The cell death caused by the PPARgamma antagonists was a result of direct interference with cell adhesion "anoikis" involving intracellular FAK signaling pathways. These results imply a potentially important and novel role for the inhibition of PPARgamma function via the use of specific antagonists in the treatment of squamous cell carcinoma and the prevention of tumor invasion and metastasis.

Expression profiling reveals a distinct transcription signature in follicular thyroid carcinomas with a PAX8-PPARγ fusion oncogene

The demonstration of the PAX8-PPAR(gamma) fusion oncogene in a subset of follicular thyroid tumors provides a new and promising starting point to dissect the molecular genetic events involved in the development of this tumor form. In the present study, we compared the gene expression profiles of follicular thyroid carcinomas (FTCs) bearing a PAX8-PPAR(gamma) fusion against FTCs that lack this fusion. Using unsupervised clustering and multidimensional scaling analyses, we show that FTCs possessing a PAX8-PPAR(gamma) fusion have a highly uniform and distinct gene expression signature that clearly distinguishes them from FTCs without the fusion. The PAX8-PPAR(gamma)(+) FTCs grouped in a defined cluster, where highly ranked genes were mostly associated with signal transduction, cell growth and translation control. Notably, a large number of ribosomal protein and translation-associated genes were concurrently underexpressed in the FTCs with the fusion. Taken together, our findings further support that follicular carcinomas with a PAX8-PPAR(gamma) rearrangement constitute a distinct biological entity. The current data represent one step to elucidate the molecular pathways in the development of FTCs with the specific PAX8-PPAR(gamma) fusion.

Underexpression of peroxisome proliferator-activated receptor (PPAR)gamma in PAX8/PPARgamma-negative thyroid tumours

The expression of peroxisome proliferator-activated receptor (PPAR)γ in thyroid neoplasias and in normal thyroid (NT) tissues has not been fully investigated. The objectives of the present work were: to study and compare the relative expression of PPARγ in normal, benign and malignant thyroid tissues and to correlate PPARγ immunostaining with clinical/pathological features of patients with thyroid cancer. We analysed the expression of PPARγ in several types of thyroid tissues by reverse transcription–polymerase chain reaction (RT–PCR), interphase fluorescent in situ hybridisation, real-time RT–PCR and immunohistochemistry. We have demonstrated that NT tissues express PPARγ both at mRNA and at protein level. PAX8-PPARγ fusion gene expression was found in 25% (six of 24) of follicular thyroid carcinomas (FTCs) and in 17% (six of 36) of follicular thyroid adenomas, but in none of the 10 normal tissues, 28 nodular hyperplasias, 38 papillary thyroid carcinomas (PTCs) and 11 poorly differentiated thyroid carcinomas (PDTCs). By real-time RT–PCR, we observed that tumours negative for the PAX8-PPARγ rearrangement expressed lower levels of PPARγ mRNA than the NT. Overexpression of PPARγ transcripts was detected in 80% (four of five) of translocation-positive tumours. Diffuse nuclear staining was significantly (P<0.05) less prevalent in FTCs (53%; 18 of 34), PTCs (49%; 19 of 39) and PDTCs (0%; zero of 13) than in normal tissue (77%; 36 of 47). Peroxisome proliferator-activated receptorγ-negative FTCs were more likely to be locally invasive, to persist after surgery, to metastasise and to have poorly differentiated areas. Papillary thyroid carcinomas with a predominantly follicular pattern were more often PPARγ negative than classic PTCs (80% vs 28%; P=0.01). Our results demonstrated that PPARγ is underexpressed in translocation-negative thyroid tumours of follicular origin and that a further reduction of PPARγ expression is associated with dedifferentiation at later stages of tumour development and progression.

Functional expression of the CXCR4 chemokine receptor is induced by RET/PTC oncogenes and is a common event in human papillary thyroid carcinomas

To identify genes involved in the transformation of thyroid follicular cells, we explored, using DNA oligonucleotide microarrays, the transcriptional response of PC Cl3 rat thyroid epithelial cells to the ectopic expression of the RET/PTC oncogenes. We found that RET/PTC was able to induce the expression of CXCR4, the receptor for the chemokine CXCL12/SDF-1alpha/beta. We observed that CXCR4 expression correlated with the transforming ability of the oncoprotein and depended on the integrity of the RET/PTC-RAS/ERK signaling pathway. We found that CXCR4 was expressed in RET/PTC-positive human thyroid cancer cell lines, but not in normal thyroid cells. Furthermore, we found CXCR4 expression in human thyroid carcinomas, but not in normal thyroid samples by immunohistochemistry. Since CXCR4 has been recently implicated in tumor proliferation, motility and invasiveness, we asked whether treatment with SDF-1alpha was able to induce a biological response in thyroid cells. We observed that SDF-1alpha induced S-phase entry and survival of thyroid cells. Invasion through a reconstituted extracellular matrix was also supported by SDF-1alpha and inhibited by a blocking antibody to CXCR4. Taken together, these results suggest that human thyroid cancers bearing RET/PTC rearrangements may use the CXCR4/SDF-1alpha receptor-ligand pathway to proliferate, survive and migrate.

Retinoid X receptor-γ and peroxisome proliferator-activated receptor-γ expression predicts thyroid carcinoma cell response to retinoid and thiazolidinedione treatment

Poorly differentiated, metastatic thyroid cancer is difficult to treat. These tumors often do not concentrate radioactive iodine and may require chemotherapy, which is suboptimal and toxic. Nuclear hormone receptors peroxisome proliferator-activated receptor γ (PPARγ) and retinoid X receptor (RXR) are variably expressed in thyroid carcinoma cell lines. Expression of these receptors may predict thyroid cancer cell response to treatment with rexinoids and thiazolidinediones. We studied three thyroid carcinoma cell lines: BHP 5-16 (PPARγ−/RXRγ+), BHP 2-7 (PPARγ±/RXRγ−), and DRO-90 (RXRγ+/PPARγ+). BHP 5-16 (RXRγ+) cells treated with rexinoid had decreased proliferation to 69 ± 6% growth compared with vehicle. BHP 2-7 (PPARγ+) cells treated with thiazolidinedione had no decrease in cellular proliferation. DRO-90 (RXRγ+ and PPARγ+) cells had 36 ± 10%, 15 ± 3%, and 13 ± 4% growth when treated with rexinoid, thiazolidinedione, or a combination, respectively. We next investigated the role of apoptosis in the ligand-responsive BHP 5-16 and DRO-90 cells. BHP 5-16 cells underwent no significant apoptosis with rexinoid (1 μmol/L). DRO-90 cells, however, had 3.6 ± 1.3% apoptotic cells with vehicle, 13 ± 3.5% with rexinoid (1 μmol/L), 18 ± 4% with thiazolidinedione (1 μmol/L), and 28 ± 6% with combination treatment (1 μmol/L), suggesting that apoptosis plays a major role in this anaplastic cell line and that the effects of the two ligands are additive. We conclude that receptor expression is necessary for inhibition of thyroid carcinoma growth with ligand treatment but may not be sufficient for response. Additionally, expression of both RXRγ and PPARγ may be necessary for maximal growth inhibition by ligands and may be required for the increased apoptosis.

RWJ-241947 (MCC-555), A Unique Peroxisome Proliferator-Activated Receptor-γ Ligand with Antitumor Activity against Human Prostate Cancer in Vitro and in Beige/Nude/ X-Linked Immunodeficient Mice and Enhancement of Apoptosis in Myeloma Cells Induced by Arsenic Trioxide

PURPOSE

RWJ-241947 (MCC-555) is a novel peroxisome proliferator-activated receptor-gamma ligand of the thiazolidinedione class that was recently developed as an antidiabetic drug with unique properties. Some thiazolidinediones have anticancer activity against solid and hematological malignancies; the anticancer potency of RWJ-241947 has not been examined. We, therefore, investigated these effects in vitro and in vivo either alone or in combination with other compounds.

EXPERIMENTAL DESIGN

Tumor growth was examined by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, soft agar colony assay in vitro, and xenografts in nude mice. Its effects on cell cycle, differentiation, and apoptosis were examined.

RESULTS

In vitro studies using various solid and hematological tumor cell lines showed that RWJ-241947 had antiproliferative activity against prostate cancer cells, with the strongest effect against the androgen-independent PC-3 prostate cancer cells. It increased expression of cyclin-dependent kinase inhibitor p21(WAF1), deceased cyclin E, and induced apoptosis in PC-3 cells. It increased E-cadherin and lowered protein expression of prostate-specific antigen without down-regulating the androgen receptor in androgen-dependent LNCaP prostate cancer cells. Reporter gene assays showed that this peroxisome proliferator-activated receptor-gamma ligand inhibited androgen activation of the androgen receptor response elements of the prostate-specific antigen gene. Remarkably, in vivo treatment of male beige/nude/X-linked immunodeficient (BNX) mice with RWJ-241947 profoundly suppressed growth of PC-3 prostate cancer xenografts with prominent apoptosis, as well as fibrosis, including inflammatory and giant cell reaction in the remaining tumor tissue. Notably, the experimented mice had a significantly decreased cholesterol. In addition, we studied the combination of arsenic trioxide (As2O3), which is used in the treatment of multiple myeloma, and RWJ-241947; these two reagents together prominently inhibited proliferation and caused apoptosis of multiple myeloma cells.

CONCLUSIONS

RWJ-241947 has surprisingly potent antiproliferative effects against prostate cancer cells in vivo, and it enhances the antitumor activity of As2O3 against myeloma cells. Small, well-defined clinical studies using RWJ-241947 are in order for these cancers.

Induction of differentiation and peroxisome proliferator-activated receptor gamma expression in colon cancer cell lines by troglitazone

PURPOSE

We investigated the relationship between the effects of troglitazone (TGZ) on cellular growth, differentiation and apoptosis induction, and the induction of peroxisome proliferator-activated receptor (PPAR) gamma in three human colon cancer cell lines, HCT-15, DLD-1and LoVo.

METHODS

Viable cell number was evaluated by the Alamar blue assay and apoptotic cell death by TUNEL methods. Expression of PPARgamma mRNA and protein was examined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blot, respectively. The differentiation markers of colonic mucosa, villin and MUC2 mRNAs, were analyzed by real-time RT-PCR.

RESULTS

HCT-15 and DLD-1 cells proliferated rapidly while LoVo cells grew slowly. TGZ dose-dependently inhibited the proliferation of all the cell lines, and also induced apoptotic cell death. High expression of PPARgamma mRNA and protein was demonstrated in DLD-1 and LoVo cells before TGZ treatment. After the treatment, PPARgamma mRNA and protein levels were increased in HCT-15 and LoVo cells. Villin and MUC2 mRNAs were increased by TGZ treatment in HCT-15 cells while villin mRNA was repressed in LoVo cells. Changes in expression of PPARgamma, villin or MUC2 mRNAs were not observed in DLD-1 cells.

CONCLUSIONS

These results suggest that PPARgamma levels are not correlated with the rates of cell proliferation. Differentiation induction by TGZ was only observed in the cell lines with enhanced PPARgamma expression.

15d-PGJ2 inhibits cell growth and induces apoptosis of MCG-803 human gastric cancer cell line

AIM: To investigate the influence of peroxisome proliferator-activated receptor γ (PPARγ) ligand, 15-deoxy-△12, 14-prostaglandin J₂ (15dPGJ₂) on the proliferation and apoptosis of MCG-803 human gastric cancer cell lines.

METHODS: Cell proliferation was measured by ³H-TdR assay. Apoptosis was determined by ELISA and TUNEL staining. Protein and mRNA level of bcl-2 family and COXs were measured by Western blotting and Northern blotting respectively. PGE₂ production was examined by RIA.

RESULTS: 15dPGJ₂ inhibited cell growth and induced apoptosis of MCG-803 cells. The COX-2 and bcl-2/bax ratios were decreased following 15dPGJ₂ treatment. The PGE₂ production in supernatants was also decreased. These changes were in a dose-dependent manner.

CONCLUSION: 15dPGJ₂ may be a useful therapeutic agent for the treatment of gastric cancer.

Peroxisome proliferator-activated receptor gamma is frequently downregulated in a diversity of sporadic nonmedullary thyroid carcinomas

Peroxisome proliferator-activated receptor gamma (PPARgamma) has previously been implicated in the pathogenesis of follicular thyroid carcinoma (FTC), where a translocation with PAX8 has been reported in some 50% of tumors in three small series. The resultant fusion protein inhibits normal PPARgamma function by a dominant-negative mechanism. In a series of 19 FTCs, we identified this translocation in only two tumors (10.5%). However, microarray analysis and semiquantitative RT-PCR demonstrated greatly reduced PPARgamma expression in 13 of 17 (76%) nontranslocation tumors. Immunohistochemical analysis of 142 thyroid tumors showed a statistically significant reduction in PPARgamma immunoreactive protein, not only in FTCs but also in papillary thyroid carcinomas and Hurthle cell carcinomas. This suggests that while the overall frequency of the PAX8-PPARgamma translocation in FTCs may be lower than previously thought, functional downregulation of PPARgamma is a key event in multiple types of thyroid neoplasia and is a possible target for therapeutic intervention.

PPAR-gamma receptor ligands: novel therapy for pituitary adenomas

Pituitary tumors cause considerable morbidity due to local invasion, hypopituitarism, or hormone hypersecretion. In many cases, no suitable drug therapies are available, and surgical excision is currently the only effective treatment. We show here abundant expression of nuclear hormone receptor PPAR-gamma in all of 39 human pituitary tumors. PPAR-gamma activating thiazolidinediones (TZDs) rosiglitazone and troglitazone induced G(0)-G(1) cell-cycle arrest and apoptosis in human, rat somatolactotroph, and murine gonadotroph pituitary tumor cells, and suppressed in vitro hormone secretion. In vivo development and growth of murine somatolactotroph and gonadotroph tumors, generated by subcutaneous injection of prolactin-secreting (PRL-secreting) and growth hormone-secreting (GH-secreting) GH3 cells, luteinizing hormone-secreting (LH-secreting) LbetaT2 cells, and alpha-T3 cells, was markedly suppressed in rosiglitazone-treated mice, and serum GH, PRL, and LH levels were attenuated in all treated animals (P < 0.009). These results demonstrate that PPAR-gamma is an important molecular target in pituitary adenoma cells and PPAR-gamma ligands inhibit tumor cell growth and GH, PRL, and LH secretion in vitro and in vivo. TZDs are proposed as novel oral medications for managing pituitary tumors.

Genetic and biological subgroups of low-stage follicular thyroid cancer

Investigations of cancer-specific gene rearrangements have increased our understanding of human neoplasia and led to the use of the rearrangements in pathological diagnosis of blood cell and connective tissue malignancies. Here, we have investigated 3p25 rearrangements of the peroxisome proliferator-activated receptor gamma (PPAR gamma) gene in follicular epithelial tumors of the human thyroid gland. Eleven of 42 (26%) low-stage follicular carcinomas, 0 of 40 follicular adenomas, 1 of 30 Hurthle cell carcinomas, 1 of 90 papillary carcinomas, and 0 of 10 nodular goiters had 3p25 rearrangements by interphase fluorescence in situ hybridization. All 11 follicular carcinomas with 3p25 rearrangement exhibited strong, diffuse nuclear immunoreactivity for PPAR gamma, consistent with expression of PPAR gamma fusion protein. Twelve of 42 (29%) low-stage follicular carcinomas had 3p25 aneusomy without PPAR gamma rearrangement (P = 0.01), suggesting that PPAR gamma rearrangement and aneuploidy are independent early events in follicular cancer. Eleven of 12 follicular carcinomas with 3p25 aneusomy exhibited no PPAR gamma immunoreactivity, supporting the existence of two independent pathways. Follicular carcinoma patients with PPAR gamma rearrangement more frequently had vascular invasion (P = 0.01), areas of solid/nested tumor histology (P < 0.001), and previous non-thyroid cancers (P < 0.01) compared with follicular carcinoma patients without PPAR gamma rearrangement. Our experiments identify genetic subgroups of low-stage follicular thyroid cancer and provide evidence that follicular carcinomas with PPAR gamma rearrangement are a distinct biological entity. The findings support a model in which separate genetic alterations initiate distinct pathways of oncogenesis in thyroid carcinoma subtypes.

Peroxisome proliferator-activated receptor gamma activation induces cell cycle arrest via the p53-independent pathway in human anaplastic thyroid cancer cells

Anaplastic thyroid carcinoma is one of the most aggressive human malignancies. Outcomes of intensive multimodal therapy have been far from satisfactory. Furthermore, p53 gene dysfunction, often found in this type of cancer, is known to impair the efficacy of the therapeutic agents. Specific ligands for peroxisome proliferator activated receptor gamma (PPAR-gamma) induce growth suppression in some tumor cells. In this study, we investigated the role of PPAR-gamma in anaplastic thyroid cancer cell lines (OCUT-1, ACT-1). PPAR-gamma was expressed and functional in both cell lines. Activation of PPAR-gamma with its specific ligands, troglitazone and 15-deoxy-delta 12,14-prostaglandin J2, inhibited cell growth in a dose-dependent manner through inducing G1 cell cycle arrest. P53 protein expression differed in OCUT-1 and in ACT-1, though the levels stayed constant irrespective of ligand exposure in both cell lines. In contrast, p21 and p27 proteins were induced in a dose-dependent manner in both situations. This study showed that PPAR-gamma ligands were able to induce growth suppression in anaplastic thyroid cancer cells via a p53-independent, but p21- and p27-dependent cytostatic pathway. These tumor-suppressive effects of PPAR-gamma may provide a novel approach to the treatment of anaplastic thyroid cancer.

PPARgamma ligands inhibit primary tumor growth and metastasis by inhibiting angiogenesis

Several drugs approved for a variety of indications have been shown to exhibit antiangiogenic effects. Our study focuses on the PPARgamma ligand rosiglitazone, a compound widely used in the treatment of type 2 diabetes. We demonstrate, for the first time to our knowledge, that PPARgamma is highly expressed in tumor endothelium and is activated by rosiglitazone in cultured endothelial cells. Furthermore, we show that rosiglitazone suppresses primary tumor growth and metastasis by both direct and indirect antiangiogenic effects. Rosiglitazone inhibits bovine capillary endothelial cell but not tumor cell proliferation at low doses in vitro and decreases VEGF production by tumor cells. In our in vivo studies, rosiglitazone suppresses angiogenesis in the chick chorioallantoic membrane, in the avascular cornea, and in a variety of primary tumors. These results suggest that PPARgamma ligands may be useful in treating angiogenic diseases such as cancer by inhibiting angiogenesis.

PPARgamma ligands inhibit primary tumor growth and metastasis by inhibiting angiogenesis

Several drugs approved for a variety of indications have been shown to exhibit antiangiogenic effects. Our study focuses on the PPARgamma ligand rosiglitazone, a compound widely used in the treatment of type 2 diabetes. We demonstrate, for the first time to our knowledge, that PPARgamma is highly expressed in tumor endothelium and is activated by rosiglitazone in cultured endothelial cells. Furthermore, we show that rosiglitazone suppresses primary tumor growth and metastasis by both direct and indirect antiangiogenic effects. Rosiglitazone inhibits bovine capillary endothelial cell but not tumor cell proliferation at low doses in vitro and decreases VEGF production by tumor cells. In our in vivo studies, rosiglitazone suppresses angiogenesis in the chick chorioallantoic membrane, in the avascular cornea, and in a variety of primary tumors. These results suggest that PPARgamma ligands may be useful in treating angiogenic diseases such as cancer by inhibiting angiogenesis.