The Role of PPAR Ligands in Controlling Growth-Related Gene Expression and their Interaction with Lipoperoxidation Products

The role of NF-κB and PPARγ in experimentally induced colorectal cancer and chemoprevention by cyclooxygenase-2 inhibitors

Initiation of malignancy is dependent upon the basic ratio of cell proliferation and apoptosis. Many molecular proteins and pathways are responsible for the imbalance of proliferation and apoptosis ratio. For example, Akt is a key biomolecule which regulates the cell survival signals via various downstream pathways. One of those pathways is nuclear factor-κB activation which also regulates many downstream pathways that are essential for cell survival. Along with these anti-apoptotic pathways, cells do have a parallel mechanism to prevent malignancy with the help of the ligand-induced nuclear receptors, e.g., peroxisome proliferator-activated receptor gamma (PPARγ). PPARγ has been found to be expressed in many cancer cell types and reported to be a pro-apoptotic transcription factor. The study aimed to observe the ability of two cyclooxygenase-dependent non-steroidal anti-inflammatory drugs (NSAIDs) in the prevention of experimentally induced early neoplasm of colon via NF-κB and PPARγ pathways. Early stages of colorectal cancer were produced in rats with 1,2-dimethylhydrazine dihydrochloride. Western blotting and immunohistochemistry were performed along with morphological and histological analysis. According to the expression levels of NF-κB and PPARγ in the cell nuclei, it is observed that NSAIDs may prevent colorectal cancer in the early stages by a concomitant down-regulation of NF-κB and up-regulation of PPARγ. COX-independent mechanism of anti-carcinogenesis was observed by COX-dependent NSAIDs in colorectal cancer.

Nutrigenomics therapy of hepatisis C virus induced-hepatosteatosis

Nutrigenomics is a relatively new branch of nutrition science, which aim is to study the impact of the foods we eat on the function of our genes. Hepatosteatosis is strongly associated with hepatitis C virus infection, which is known to increase the risk of the disease progression and reduce the likelihood of responding to anti- virus treatment. It is well documented that hepatitis C virus can directly alter host cell lipid metabolism through nuclear transcription factors. To date, only a limited number of studies have been on the effect of human foods on the nuclear transcription factors of hepatitis C virus -induced hepatosteatosis.

Three nutrients, selected among 46 different nutrients: β-carotene, vitamin D₂, and linoleic acid were found in a cell culture system to inhibit hepatitis C virus RNA replication. In addition, polyunsaturated fatty acids (PUFAs) especially arachidonic acid (AA), docosahexaenoic acid (DHA), and eicosapentaenoic acid (EPA) have been demonstrated to inhibit hepatitis C virus RNA replication. These PUFAs, in particular the highly unsaturated n-3 fatty acids change the gene expression of PPARa and SREBP, suppress the expression of mRNAs encoding key metabolic enzymes and hereby suppress hepatic lipogenesis and triglyceride synthesis, as well as secretion and accumulation in tissues. A recent prospective clinical trial of 1,084 chronic hepatitis C patients compared to 2,326 healthy subjects suggests that chronic hepatitis C patients may benefit from strict dietary instructions.

Increasing evidence suggest that some crucial nuclear transcription factors related to hepatitis C virus -associated hepatosteatosis and hepatitis C virus RNA itself can be controlled by specific anti- hepatitis C virus nutrition. It seems important that these findings are taken into account and specific nutritional supplements developed to be used in combination with interferon as adjunctive therapy with the aim to improve both the early as well as the sustained virological response.

PPARgamma ligands inhibit telomerase activity and hTERT expression through modulation of the Myc/Mad/Max network in colon cancer cells

In human cells the length of telomeres depends on telomerase activity. This activity and the expression of the catalytic subunit of human telomerase reverse transcriptase (hTERT) is strongly up-regulated in most human cancers. hTERT expression is regulated by different transcription factors, such as c-Myc, Mad1 and Sp1. In this study, we demonstrated that 15d-PG J2 and rosiglitazone (an endogenous and synthetic peroxisome proliferators activated receptor γ (PPARγ) ligand, respectively) inhibited hTERT expression and telomerase activity in CaCo-2 colon cancer cells. Moreover, both ligands inhibited c-Myc protein expression and its E-box DNA binding activity. Additionally, Mad1 protein expression and its E-box DNA binding activity were strongly increased by 15d-PG J2 and, to a lesser extent, by rosiglitazone. Sp1 transcription factor expression and its GC-box DNA binding activity were not affected by both PPARγ ligands. Results obtained by transient transfection of CaCo-2 cells with pmaxFP-Green-PRL plasmid constructs containing the functional hTERT core promoter (including one E-box and five GC-boxes) and its E-box deleted sequences, cloned upstream of the green fluorescent protein reporter gene, demonstrated that 15d-PG J2, and with minor effectiveness, rosiglitazone, strongly reduced hTERT core promoter activity. E-boxes for Myc/Mad/Max binding showed a higher activity than GC-boxes for Sp1. By using GW9662, an antagonist of PPARγ, we demonstrated that the effects of 15d-PG J2 are completely PPARγ independent, whereas the effects of rosiglitazone on hTERT expression seem to be partially PPARγ independent. The regulation of hTERT expression by 15d-PG J2 and rosiglitazone, through the modulation of the Myc/Max/Mad1 network, may represent a new mechanism of action of these substances in inhibiting cell proliferation.