Lee MO, Han SY, Jiang S, Park JH, Kim SJDifferential effects of retinoic acid on growth and apoptosis in human colon cancer cell lines associated with the induction of retinoic acid receptor beta. Biochem Pharmacol 59: 485-496
Retinoids are well known as potential chemopreventive and chemotherapeutic agents against a variety of human cancers. Here, we report that retinoic acid (RA) induced differential growth inhibition in human colon cancer cell lines: while DLD-1, HT-29, and WiDr were relatively resistant, HCT-15 and Colo201 were relatively sensitive. All-trans-retinoic acid caused morphological and biochemical changes such as membrane shrinkage, chromatin condensation, and DNA cleavage, which are typical features of cells undergoing apoptosis in sensitive cell lines. Although retinoic acid receptor (RAR)alpha, beta, gamma and retinoid X receptor alpha were expressed in all cell lines examined, a significant induction of RARbeta by all-trans-RA was observed only in sensitive cell lines, suggesting important roles of RARbeta in RA sensitivity. When a vector containing the RARbeta gene was introduced into a relatively resistant cell line, DLD-1, the cells acquired RA sensitivity. Further, we found that the RARbeta transfectants of DLD-1 expressed an enhanced level of c-Myc and Bax proteins, which may result in the increased susceptibility of the cells to all-trans-RA-induced apoptosis. In summary, our data demonstrated that RA induced growth inhibition and apoptosis in human colon cancer cells and that the induction of RAR3 may mediate the retinoid action.
"In HT-29 cells ATRA-induced growth inhibition is mediated by RARα , whereas, in Caco-2 cells it is mediated by RARβ . However, other studies have reported that ATRA has no effect on growth inhibition in HT-29 cells . In certain contexts, ATRA also has the ability to mediate apoptosis . "
[Show abstract][Hide abstract] ABSTRACT: Cysteinyl leukotrienes (CysLTs) are potent pro-inflammatory mediators that are increased in samples from patients with inflammatory bowel diseases (IBDs). Individuals with IBDs have enhanced susceptibility to colon carcinogenesis. In colorectal cancer, the balance between the pro-mitogenic cysteinyl leukotriene 1 receptor (CysLT1R) and the differentiation-promoting cysteinyl leukotriene 2 receptor (CysLT2R) is lost. Further, our previous data indicate that patients with high CysLT1R and low CysLT2R expression have a poor prognosis. In this study, we examined whether the balance between CysLT1R and CysLT2R could be restored by treatment with the cancer chemopreventive agent all-trans retinoic acid (ATRA).
To determine the effect of ATRA on CysLT2R promoter activation, mRNA level, and protein level, we performed luciferase gene reporter assays, real-time polymerase chain reactions, and Western blots in colon cancer cell lines under various conditions.
ATRA treatment induces CysLT2R mRNA and protein expression without affecting CysLT1R levels. Experiments using siRNA and mutant cell lines indicate that the up-regulation is retinoic acid receptor (RAR) dependent. Interestingly, ATRA also up-regulates mRNA expression of leukotriene C4 synthase, the enzyme responsible for the production of the ligand for CysLT2R. Importantly, ATRA-induced differentiation of colorectal cancer cells as shown by increased expression of MUC-2 and production of alkaline phosphatase, both of which could be reduced by a CysLT2R-specific inhibitor.
This study identifies a novel mechanism of action for ATRA in colorectal cancer cell differentiation and demonstrates that retinoids can have anti-tumorigenic effects through their action on the cysteinyl leukotriene pathway.
BMC Cancer 07/2013; 13(1):336. DOI:10.1186/1471-2407-13-336 · 3.36 Impact Factor
"Instead, we observed a profound dysregulation of the retinoid pathway in this CRC. Downregulation of mRNA expression of RARβ often observed in cancer cells has been considered as a cellular mechanism to prevent retinoid-induced growth arrest [61,62]. On the other hand, while elevated levels of RAR mRNA expression has also been described in breast, liver and esophageal tumors [53,63,64], mechanism and significance are unknown. "
[Show abstract][Hide abstract] ABSTRACT: Epidemiological studies on risk factors for colorectal cancer (CRC) have mainly focused on diet, and being overweight is now recognized to contribute significantly to CRC risk. Overweight and obesity are defined as an excess of adipose tissue mass and are associated with disorders in lipid metabolism. Peroxisome proliferator-activated receptors (PPARs) and retinoid-activated receptors (RARs and RXRs) are important modulators of lipid metabolism and cellular homeostasis. Alterations in expression and activity of these ligand-activated transcription factors might be involved in obesity-associated diseases, which include CRC. Cyclooxygenase-2 (COX-2) also plays a critical role in lipid metabolism and alterations in COX-2 expression have already been associated with unfavourable clinical outcomes in epithelial tumors. The objective of this study is to examine the hypothesis questioning the relationship between alterations in the expression of nuclear receptors and COX-2 and the weight status among male subjects with CRC.
The mRNA expression of the different nuclear receptor subtypes and of COX-2 was measured in 20 resected samples of CRC and paired non-tumor tissues. The association between expression patterns and weight status defined as a body mass index (BMI) was statistically analyzed.
No changes were observed in PPAR gamma mRNA expression while the expression of PPAR delta, retinoid-activated receptors and COX-2 were significantly increased in cancer tissues compared to normal colon mucosa (P <or= 0.001). The weight status appeared to be an independent factor, although we detected an increased level of COX-2 expression in the normal mucosa from overweight patients (BMI >or= 25) compared to subjects with healthy BMI (P = 0.002).
Our findings show that alterations in the pattern of nuclear receptor expression observed in CRC do not appear to be correlated with patient weight status. However, the analysis of COX-2 expression in normal colon mucosa from subjects with a high BMI suggests that COX-2 deregulation might be driven by excess weight during the colon carcinogenesis process.
"This is in agreement with previous reports, which have shown that RAR-β expression is generally low or absent in pancreatic cancer cells (Kaiser et al, 1997). Although induction of RAR-β has been reported to be an indicator of retinoid response (Seewaldt et al, 1995; Lee et al, 2000; Sun et al, 2000), we could detect no induction of either RAR subtype upon retinoid treatment. This may seem surprising, but is likely to be due to methylation of the RAR-beta gene (Ueki et al, 2000). "
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