Expression of PPARγ is reduced by medium supplementation with L-glutamine in human colorectal Caco-2 cells

Peroxisome proliferator-activated receptor-gamma (PPARgamma) belongs to the nuclear hormone receptor family. This receptor is implicated in colon cell differentiation and in colon cancer. Receptor activation by specific agonists has been shown to protect against colon cancer progression. PPARgamma protein content within cells is modulated by several mechanisms, including proteasome degradation, activation of Wnt signalling pathways and presence of fermentation products such as butyrate. Herein, we investigated the impact of L-glutamine on PPARgamma expression during the differentiation of Caco-2 cells grown in medium containing dialyzed fetal calf serum supplemented or not with L-glutamine. Using RT-PCR and Western blotting, we demonstrated that PPARgamma expression was decreased when L-glutamine was added to the medium. Using immunohistochemistry, we demonstrated that PPARgamma immunostaining was mainly found in cytoplasm when cells were cultured with L-glutamine while it was found in nuclei and cytoplasm when cells were grown without the addition of L-glutamine. Supershift retardation assays demonstrated a decrease of PPARgamma binding onto consensus peroxisome proliferator response element. We concluded that L-glutamine modulated PPARgamma expression in Caco-2 cells.