Role of peroxisome proliferator-activated receptor alpha in the control of cyclooxygenase 2 and vascular endothelial growth factor: involvement in tumor growth.

A growing body of evidence indicates that PPAR (peroxisome proliferator-activated receptor) alpha agonists might have therapeutic usefulness in antitumoral therapy by decreasing abnormal cell growth, and reducing tumoral angiogenesis. Most of the anti-inflammatory and antineoplastic properties of PPAR ligands are due to their inhibitory effects on transcription of a variety of genes involved in inflammation, cell growth and angiogenesis. Cyclooxygenase (COX)-2 and vascular endothelial growth factor (VEGF) are crucial agents in inflammatory and angiogenic processes. They also have been significantly associated to cell proliferation, tumor growth, and metastasis, promoting tumor-associated angiogenesis. Aberrant expression of VEGF and COX-2 has been observed in a variety of tumors, pointing to these proteins as important therapeutic targets in the treatment of pathological angiogenesis and tumor growth. This review summarizes the current understanding of the role of PPARalpha and its ligands in the regulation of COX-2 and VEGF gene expression in the context of tumor progression.

Peroxisome-proliferator-activated receptor alpha agonists inhibit cyclo-oxygenase 2 and vascular endothelial growth factor transcriptional activation in human colorectal carcinoma cells via inhibition of activator protein-1.

Recent evidence indicates that PPAR (peroxisome-proliferator-activated receptor) alpha ligands possess anti-inflammatory and antitumoural properties owing to their inhibitory effects on the expression of genes that are involved in the inflammatory response. However, the precise molecular mechanisms underlying these effects are poorly understood. In the present study, we show that tumour promoter PMA-mediated induction of genes that are significantly associated with inflammation, tumour growth and metastasis, such as COX-2 (cyclo-oxygenase 2) and VEGF (vascular endothelial growth factor), is inhibited by PPARalpha ligands in the human colorectal carcinoma cell line SW620. PPARalpha activators LY-171883 and WY-14,643 were able to diminish transcriptional induction of COX-2 and VEGF by inhibiting AP-1 (activator protein-1)-mediated transcriptional activation induced by PMA or by c-Jun overexpression. The actions of these ligands on AP-1 activation and COX-2 and VEGF transcriptional induction were found to be dependent on PPARalpha expression. Our studies demonstrate the existence of a negative cross-talk between the PPARalpha- and AP-1-dependent signalling pathways in these cells. PPARalpha interfered with at least two steps within the pathway leading to AP-1 activation. First, PPARalpha activation impaired AP-1 binding to a consensus DNA sequence. Secondly, PPARalpha ligands inhibited c-Jun transactivating activity. Taken together, these findings provide new insight into the anti-inflammatory and anti-tumoural properties of PPARalpha activation, through the inhibition of the induction of AP-1-dependent genes that are involved in inflammation and tumour progression.

Inhibition of activator protein 1 activation, vascular endothelial growth factor, and cyclooxygenase-2 expression by 15-deoxy-Delta12,14-prostaglandin J2 in colon carcinoma cells: evidence for a redox-sensitive peroxisome proliferator-activated receptor-gamma-independent mechanism.

Cyclooxygenase (COX)-2 and vascular endothelial growth factor (VEGF) are significantly associated with tumor growth and metastasis. Here we show that phorbol ester-mediated induction of VEGF and COX-2 expression in colon carcinoma cells is inhibited by 15-deoxy-Delta(12,14)-prostaglandin J(2) (15d-PGJ(2)). This cyclopentenone was able to inhibit activator protein1 (AP-1)-dependent transcriptional induction of COX-2 and VEGF promoters induced by phorbol 12-myristate 13-acetate (PMA) or c-Jun overexpression. 15d-PGJ(2) interfered with at least two steps within the signaling pathway leading to AP-1 activation. First, 15d-PGJ(2) impaired AP-1 binding to a consensus DNA sequence. Second, 15d-PGJ(2) selectively inhibited c-Jun NH(2) terminal kinase (JNK) but not extracellular signal-regulated kinase or p38 mitogen-activated protein kinase activation induced by PMA. This led to a decreased ability of JNK to phosphorylate c-Jun and to activate its transactivating activity. Inhibition of AP-1 activation and COX-2 or VEGF transcriptional induction by this cyclopentenone was found to be independent of peroxisome proliferator-activated receptor-gamma (PPARgamma) because it was not affected by either expression of a dominant negative form of PPARgamma or the use of a PPARgamma antagonist. In contrast, we have found that the effects of 15d-PGJ(2) on AP-1 activation may occur through its ability to induce intracellular oxidative stress. The antioxidant N-acetylcysteine significantly reversed the inhibition by 15d-PGJ(2) of AP-1 activity and COX-2 or VEGF transcriptional induction. Together, these findings provide new insight into the antitumoral properties of 15d-PGJ(2) through the inhibition of the induction of AP-1-dependent genes involved in tumor progression, such as COX-2 and VEGF.

Anti-Sa sera from patients with rheumatoid arthritis contain at least 2 different subpopulations of anti-Sa antibodies.

OBJECTIVE: Anti-Sa antibodies have been described to be a highly specific marker for rheumatoid arthritis (RA). We demonstrate the existence of 2 different subsets of anti-Sa antibodies, only one of which is specific for RA. Our objective was to purify the Sa antigen, and to achieve partial characterization of these proteins. METHODS: Saline extract and mitochondrial extract from human placenta were used as antigenic sources. Antigens were purified by immunoaffinity chromatography and studied by ELISA and immunoblotting. RESULTS: Three antigenically active bands of 68, 50, and 46 kDa were purified from the saline extract by immunoaffinity chromatography. Two other bands of 29 and 10 kDa that do not react with anti-Sa antibodies were obtained as well. The 68 kDa band was purified from a mitochondrial extract. These bands are not the same as other known mitochondrial autoantigens such as M2, M4, or M9. The amino terminal sequence of the 68 kDa Sa band is DEPKXEVP. The sequence of the 68 kDa Sa band is not compiled in the databases we searched, as either aminoterminal or internal sequence. Antibodies to 50/46 kDa anti-Sa bands detected by immunoblotting were highly specific for RA, while the 68 kDa antigen reacted in ELISA with sera from patients with RA and systemic lupus erythematosus, the latter showing a marked increase in features of RA. Antibodies directed against the 68 and 50/46 kDa Sa bands fluctuated with time, the 50/46 kDa anti-Sa antibodies present during the active period of the disease, and the 68 kDa anti-Sa antibodies during the remission period. CONCLUSION: At least 2 subsets of autoantibodies are present in anti-Sa sera, one directed against a 68 kDa Sa protein and another to the typical 50/46 bands of the Sa system.