Low expression of ORF4, a dominant negative variant of peroxisome proliferator-activated receptor gamma, in colorectal adenocarcinoma.

Peroxisome proliferator-activated receptor gamma (PPARgamma) agonists have been demonstrated to exert an inhibitory effect on cell growth, and to induce the cell differentiation and apoptosis of colorectal cancer cells. PPARgamma was therefore proposed as a therapeutic target. Recently, a variant of PPARgamma which functions as a dominant negative (ORF4) was described. Expression of this protein may prevent PPARgamma ligand efficiency in colon cancer treatment. In an effort to evaluate the importance of this variant, we determined the expression level of PPARgamma and that of the splicing variant ORF4 in a series of 28 human colon adenocarcinomas relative to paired normal mucosa by real-time PCR. PPARgamma expression was found to be heterogeneous among tumors. ORF4 was also expressed, but represented <10% of the PPARgamma transcripts. This low level was also found in several human colon cancer cell lines treated or not with a specific PPARgamma ligand in preparations of isolated human colonic epithelial cells and in mouse colon. We conclude that ORF4 expression is a general phenomenon, and that its low level should not affect the efficiency of selective PPARgamma modulators in colon cancer treatment.

The PPAR(gamma) K422Q mutation does not contribute to troglitazone inefficiency in colon cancer treatment.

Peroxisome proliferator-activated receptor gamma (PPAR(gamma)) ligands inhibit cell growth of colorectal cancer cells in most experimental models, but no significant effect could be observed in patients with colorectal cancer. We therefore, screened human colorectal tumors to determine the prevalence of the PPAR(gamma) K422Q loss-of-function mutation, recently identified in 50% of colonic cancer cell lines. A sensitive allele-specific real-time amplification assay was developed and 170 colorectal primary tumors and 12 liver metastasis were analyzed. We did not find the K422Q mutation in any of these samples. We can therefore exclude this alteration as a mechanism of resistance to PPAR(gamma) ligands in patients with colon cancer.

Growth inhibitory effect of celecoxib and rofecoxib on human colorectal carcinoma cell lines.

BACKGROUND: Epidemiological studies have revealed a protective effect of NSAIDs, which principally target cyclooxygenase (COX)-1 and COX-2, on the development of colorectal cancer. Increased expression of COX-2 was shown in colorectal adenocarcinoma. However, some effects were shown to be COX-independent. Here, we compared two selective COX-2 inhibitors for their effect on the growth of colorectal tumour cells in vitro. MATERIALS AND METHODS: Fifteen tumour cell lines were characterized for COX-1 and COX-2 expression by Western blot and RT-PCR. The effect of celecoxib and rofecoxib on their growth was assessed by staining of DNA with crystal violet. RESULTS: COX-2 expression varied among cell lines, whereas COX-1 was always expressed. Rofecoxib displayed a limited dose-related effect on cell proliferation, whereas celecoxib strongly inhibited cell growth at high concentrations. Both effects appeared COX-2-independent. CONCLUSION: Rofecoxib, which is devoid of apoptotic effect at high concentration but efficient at pharmacological concentrations, revealed a potential new mechanism of action of NSAIDs towards colorectal cancer.