Down-Regulation of prostate-specific antigen expression by ligands for peroxisome proliferator-activated receptor gamma in human prostate cancer

The peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear receptor superfamily. Recent studies found that ligand-activated PPARgamma regulated differentiation and clonal growth of several types of cancer cells, including prostate cancer, suggesting that PPARgamma could be a tumor suppressor. Troglitazone was a widely used antidiabetic drug that activates PPARgamma. Recently, we reported that this agent had antiprostate cancer effects in vitro and in vivo. In this study, we administered troglitazone for over 1.5 years to an individual with occult recurrent prostate cancer. Using the prostate-specific antigen (PSA) levels as a surrogate marker of the disease, the oral administration of troglitazone (600-800 mg/day) reduced the increase velocity of PSA levels, suggesting clinical efficacy of troglitazone in prostate cancer. PSA promoter/ enhancer reporter assays showed that the PPARgamma ligands troglitazone (10(-5) M), pioglitazone (10(-5) M), or 15-deoxy-delta12,14-prostaglandin J2 (10(-5) M) down-regulated androgen-stimulated reporter gene activity in LNCaP cells, a prostate cancer cell line. The PSA promoter contains androgen receptor response elements (AREs). Reporter gene studies showed that troglitazone inhibited androgen activation of the AREs in the PSA regulatory region. Consistent with inhibition of gene expression, 2 days of incubation of LNCaP with troglitazone dramatically suppressed PSA protein expression without suppressing AR expression, suggesting that troglitazone inhibited ARE activation by a mechanism other than down-regulation of expression of the AR. Taken together, ligands of PPARgamma may be a useful therapeutic approach for the treatment of prostate cancer and may be acting, in part, by inhibiting transactivation of androgen-responsive genes.     

Growth inhibition through activation of peroxisome proliferator-activated receptor gamma in human oesophageal squamous cell carcinoma

Peroxisome proliferator-activated receptor gamma (PPARgamma) heterodimerises with retinoid X receptor alpha (RXRalpha) and is thought to be a novel therapeutic target for human malignancies. We evaluated the ability of troglitazone (TRO) alone or in combination with 9-cis retinoic acid (9CRA), ligands of PPARgamma and RXRalpha, respectively, to inhibit the growth of oesophageal squamous cell carcinoma (OSCC). All 10 tested OSCC cell lines of a KYSE series expressed PPARgamma and RXRalpha at both the mRNA and protein levels. In four tested cell lines, TRO inhibited growth, and a synergistic effect was observed with simultaneous 9CRA application. In KYSE 270 cells, a luciferase reporter assay showed that the simultaneous application of TRO and 9CRA to the cells increased the relative luciferase activity approximately 20-fold compared with the controls without TRO or 9CRA application. In this cell line, flow cytometry demonstrated that combined treatment with TRO and 9CRA greatly increased the sub-G1 phase, and Hoechst 33342/propidium iodide (PI) staining showed that apoptotic cell death was mainly induced through ligand treatment. In addition, implanted tumours in nude mice showed significant inhibition of tumour growth when treated with TRO. These results suggest that the PPARgamma/RXRalpha heterodimer may be a new therapeutic target for OSCC.     

Differential expression of peroxisome proliferator-activated receptor in histologically different human gastric cancer tissues

Gastric cancer cell lines express peroxisome proliferator-activated receptor gamma (PPARgamma), and treatment with PPARgamma ligands suppresses growth of subgroup of these cell lines. However, expression and subcellular distribution of PPARgamma in human gastric cancer tissues is still unknown. Therefore, expression and subcellular localization of PPARgamma were examined among different histological types of gastric cancer tissues. Immunohistochemical staining for PPARgamma was performed using biopsy specimens of human gastric cancer of various histological types, gastric adenomas, and intestinal metaplasia. All samples of intestinal metaplasia and most samples of gastric tumors, except for signet ring cell carcinoma, expressed PPARgamma in the epithelial cells. Most samples of signet ring cell cancer lacked PPARgamma expression. All samples of intestinal metaplasia expressed PPARgamma only in the cytosol. For adenoma, 90% was positive for PPARgamma in cytosol, and 40% was positive in nuclei, for well-differentiated adenocarcinoma, 80% was positive in cytosol, and 20% was positive in nuclei. For moderately differentiated adenocarcinomas, 70% was positive for cytosol, and 80% was positive for nuclei; for poorly differentiated adenocarcinoma, 30% was positive in cytosol, and 70% was positive in nuclei. The frequency of samples with positive cytosolic staining decreased as the differentiation stage turned from intestinal metaplasia to adenoma, well-, moderately-, and poorly-differentiated cancers. Simultaneously, there was a tendency toward an increased frequency of samples with positive nuclear PPARgamma staining as the differentiation stage transformed from intestinal metaplasia to poorly-differentiated cancer. There was a striking difference in subcellular localization according to the differentiation levels of gastric dysplastic cells. The findings also supported an intestinal metaplasia-adenoma-well-differentiated gastric cancer sequence, and signet ring cell cancer was suggested to be of a different lineage from other types of gastric cancers.     

Enhancement of BRCA1 gene expression by the peroxisome proliferator-activated receptor gamma in the MCF-7 breast cancer cell line

BRCA1 has been linked to the genetic susceptibility of a majority of familial breast and ovarian cancers. Several lines of evidence indicate that BRCA1 is a tumor suppressor and its expression is downregulated in sporadic breast and ovarian cancer cases. Therefore, the identification of genes involved in the regulation of BRCA1 gene expression might lead to new insights into the pathogenesis and treatment of these tumors. Peroxisome proliferator-activated receptor gamma (PPARgamma) is a member of the nuclear receptor superfamily that has well-established roles in the regulation of adipocyte development and glucose homeostasis. More recently, it has been shown that ligands of PPARgamma have a potent antitumorigenic activity in breast cancer cells. In the present study we have found that two distinct ligands of PPARgamma; 15-deoxy-delta-(12,14)-prostaglandin J2 (15dPG-J2) and rosiglitazone, increase the levels of BRCA1 protein in human MCF-7 breast cancer cells. Immunofluorescence microscopy analysis showed that, after treatment with 15dPG-J2, the BRCA1 protein is mainly localized in the nucleus. Functional analysis by transient transfection of different 5'-flanking region fragments, as well as gel mobility shift assays and mutagenic analysis, suggests that the effects of 15dPG-J2 and rosiglitazone are mediated through a functional DR1 located between the nucleotides -241 and -229, which is a canonical PPARgamma type response element. Our data suggest that PPARgamma is a crucial gene regulating BRCA1 gene expression and might therefore be important for the BRCA1 regulatory pathway involved in the pathogenesis of sporadic breast and ovarian cancer.     

过氧化物酶体增殖激活性受体γ(PPARγ)在肝癌组织中的差异性表达

目的检测过氧化物酶体增殖激活性受体γ(PPARγ)在肝癌组织中有无差异性表达且有无突变.方法用半定量RT-PCR,Western blot,FISH,PCR-SSCP等方法进行鉴定.结果用半定量RT-PCR检测,有8/14为癌中高表达;Western blot方法检测,9/15为癌中高表达.免疫组化显示PPARγ在所有的癌旁组织中定位于细胞浆中;而在5个癌组织中定位于细胞核中;突变热点PPARγ外显子3和5在34对肝癌标本中没有突变.结论过氧化物酶体增殖激活性受体γ在肝癌组织中有差异性表达并且在肝癌标本中没有突变.提示PPARγ可能与肝癌的发展有一定的相关性.     

beta-Carotene induces apoptosis and up-regulates peroxisome proliferator-activated receptor gamma expression and reactive oxygen species production in MCF-7 cancer cells

Although the pharmacological role of beta-carotene in the prevention and treatment of many cancer cells has received increasing attention, the molecular mechanisms underlying such chemopreventive activity are not clear. Since peroxisome proliferator-activated receptor gamma (PPAR-gamma) has been implicated in regulating breast cancer cell differentiation and apoptosis, the effects of beta-carotene on the PPAR-gamma-mediated pathway and its association with reactive oxygen species production in MCF-7 cells were investigated in the present study. The results demonstrated that beta-carotene significantly increased PPAR-gamma mRNA and protein levels in time-dependent manner. In addition, beta-carotene increased the cyclin-dependent kinase inhibitor p21(WAF1/CIP1) expression and decreased the prostanoid synthesis rate-limiting enzyme cyclooxygenase-2 expression. 2-chloro-5-nitro-N-phenylbenzamide (GW9662), an irreversible PPAR-gamma antagonist, partly attenuated the cell death caused by beta-carotene. Further, reactive oxygen species (ROS) production was induced by beta-carotene, resulting in mitochondrial dysfunction and cytochrome C release. Reduced glutathione (GSH) treatment decreases the intracellular ROS and prevents cytochrome C release and cell apoptosis induced by beta-carotene. In total, these observations suggest that the synergistic effect of PPAR-gamma expression and ROS production may account for beta-carotene-mediated anticancer activities.