Basic And Clinical Studies On The Effects Of Peroxisome Proliferator-activated Receptor γ On Biological Behaviors Of Human Colorectal Cancer

Objective: To investigate the expressions and correlations with clinico -pathological data of peroxisome proliferator-activated receptor y and PTEN and to explore their potent clinical significances in human colorectal cancer. Methods: 139 colorectal cancer, 18 adenomatou polyps and 50 para-cancer benign mucosas paraffin embedded blocks were accumulated and made into 4 tissue microarrays(TMA) blocks which including 104, 72, 130 and 54 cores respectively. Expressions of PPARγ and PTEN were detected by using immuno -histochemical staing to tissue microarray.Results: Histologic appearance was well preserved in every dots of the TMA. Significant differences of expressions of PPARγ and PTEN were not found among colorectal cancer, adenomas and normal mucosa (P=0.207, P=0.250). Correlations between PTEN expression and histological grade (P=0.006) or distant metastasis (P=0.015) were demonstrated in this cohort tissues.Conclusions: Being a new molecular biological technique, tissue microarray will have a pivotal role in cancer research. The distortions of PPARγ and PTEN protein expressions may not involve in the coloncarcinogenesis and may not be seemed as early dignositic markers. Colorectal cancers with low expression or deletion of PTEN were faciliated to advanced stage differentiation and metastasis and PTEN expression may be a potent prognostic factor.Objective: To investigate the expression of peroxisome proliferator-activated receptor y (PPARy) and the inhibitory effect of activation of PPARy on cells growth in colorectal cancer cell line HT-29, and to explore whether PPARy ligand effect on PTEN expression involve in reducing the viability of HT-29 cells.Methods: The expressions of PPARy mRNA and protein in HT-29 were determined by reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting, respectively. Furthermore, the effects of PPARy agonists, 15d-PGJ2 and rosiglitazone, on cell growth were investigated by MTT and soft agarose clonogenic assays. The apoptosis was detected by fluorescence microscope, TUNEL staining and flow-cytometric using CaspSCREEN? Flowcytometric Apoptosis Detection Kit. The expressions of caspase-3 in HT-29 cells before and after treatment with PPARy ligands were determined by immunohistochemical staining. The expressions of PTEN and p-Aktl protein were detected by Western blotting.Results: The results of RT-PCR and western blot showed that PPARy mRNA and protein were expressed in HT-29 cells. The agonists of PPARy,15d-PGJ2 and rosiglitazone, could reduce the viability of HT-29 in a dose and time -dependent manner and inhibit its anchorage-dependent and anchorage -independent growth. In addition, fluorescence microscope and TUNEL results demonstrated that the typical apoptosis morphology changes were emerged after treatment with 10 umol/L 15d-PGJ2 or rosiglitazone for 48h. Significant differences were found by FCM assay after compared the control group with the cells treated with PPARy ligands, which showed that the percentage of apoptosis of cells treated with 10 umol/L rosiglitazone or 15d-PGJ2 for 24h and 48h were 14.8±0.8%, 28.5±1.3% or 15±0.7% and 40±1.2% while the cells without treatment were 3.8±0.4% and 8.8±0.4%. The IHC results manifested that the expression rates of caspase-3 were increased after treatment with rosiglitazone and 15d-PGJ2, which showed positive correlation with apoptosis. The cell cycle analysis detected by FCM using PI stainig showed that the ratio of Go/Gi phase cells increased after incubated with 10 umol/L rosiglitazone or 15d-PGJ2 for 24h and 48h. In addition, western blotting analysis confirmed upregulation of PTEN protein expression and downregulation of p-Aktl protein expression when PPARy was activated. Conclusions: PPARy was expressed in colorectal cancer cell line HT-29. Activation of PPARy can inhibit HT-29 cells growth through inducement of apoptosis and cell cycle arrest. One of the mechanisms which can affect the viability of HT-29 is that activation of PPARy can upregulate the expressionof PTEN and then inhibit the PI3K pathway. The present results suggest that PPARy could be seemed as one of the new theraputic target of colorectal cancers in human.