Impact of PPARγ Activation on Colon Cancer Cells and Tumor-Associated M2 Macrophages

Abstract Peroxisome proliferator-activated receptor gamma (PPARγ) is expressed in multiple tumor cells as well as macrophages, and has been identified as a putative target for the development of novel therapies against colon cancer. Stimulation of the nuclear receptor PPARγ transcriptional activity can suppress colon carcinogenesis. To understand the molecular mechanisms underlying the anti-tumorigenic effect of PPARγ, the expression of some factors known to be crucially involved in progression and metastasis of colon cancer were investigated in SW480 colon cancer cells and in vitro differentiated M2 macrophages after treatment with the PPARγ agonist rosiglitazone (100 μM). PPARγ was downregulated by decreased differentiation of colon cancer cells, and was found to be higher in M2 than M1 macrophages. Treatment with rosiglitazone reduced the expression of CXCR1, MMP-2 and CD47 in SW480 cells, and this was accompanied by decreased migration of cells after 24 h. CXCR2 and MMP-9 were downregulated by rosiglitazone treatment when SW480 cells were co-cultured with M2 macrophages. Activation of PPARγ induced CD36 upregulation in M2 macrophages, but downregulation in SW480 cells especially in the co-culture system. IL-10R1 expression was suppressed by rosiglitazone treatment in M2 macrophages cultured with or without SW480 cells. Moreover, the mRNA levels of CCR5 and its ligands CCL3 and CCL5 were all markedly reduced after PPARγ agonist treatment. These results suggest that PPARγ tumor suppressing effect could be exerted through decreasing colon cancer cell survival, proliferation and motility, increasing the phagocytic ability of tumor-associated M2 macrophages, reducing production of inflammatory mediators by neoplastic cells, and also by inhibiting immunosuppressive functions and recruitment of M2 macrophages. Overall, the present data identifies rosiglitazone as a promising chemotherapeutic agent for treatment of colon cancer. Popular science summary: Impact of PPARγ Activation on Colon Cells and Macrophages Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear protein that acts as a transcription factor. It is expressed in multiple tumor cells as well as in immune cells such as macrophages, and has been identified as a putative target for the development of novel therapies against colon cancer. Stimulation of PPARγ transcriptional activity can suppress colon carcinogenesis. To understand the molecular mechanisms underlying the anti-tumorigenic effect of PPARγ, the expression of some factors known to be crucially involved in progression and metastasis of colon cancer were investigated in SW480 colon cancer cells and in vitro differentiated M2 macrophages after treatment with the PPARγ agonist rosiglitazone. Methods Tissue culture of SW480 cells and THP-1 cells (monocyte cell line differentiated into macrophages), wound healing assay, Western blot and mRNA quantification with Q-PCR. Results PPARγ was down-regulated by decreased differentiation of colon cancer cells, and was found to be higher in M2 than M1 macrophages. Treatment with rosiglitazone reduced the expression of CXCR1, MMP-2 and CD47 in SW480 cells, and this was accompanied by decreased migration of cells after 24 h. CXCR2 and MMP-9 were downregulated by rosiglitazone treatment when SW480 cells were co-cultured with M2 macrophages. Activation of PPARγ induced CD36 upregulation in M2 macrophages, but downregulation in SW480 cells especially in the co-culture system. IL-10R1 expression was suppressed by rosiglitazone treatment in M2 macrophages cultured with or without SW480 cells. Moreover, the mRNA levels of CCR5 and its ligands CCL3 and CCL5 were all markedly reduced after PPARγ agonist treatment. Conclusions These results suggest that PPARγ tumor suppressing effect could be exerted through decreasing colon cancer cell survival, proliferation and motility, increasing the phagocytic ability of tumor-associated M2 macrophages, reducing production of inflammatory mediators by neoplastic cells, and also by inhibiting immunosuppressive functions and recruitment of M2 macrophages. Overall, the present data identifies rosiglitazone as a promising chemotherapeutic agent for treatment of colon cancer. Advisor: Anita Sjolander, Department of Laboratory Medicine-Malmo 45-ECTS Master’s Degree Project in Molecular Biology - Cellular and Molecular Immunology Department of Biology, Lund University