PPAR-γ Activation Inhibits Angiogenesis by Blocking ELR+CXC Chemokine Production in Non-small Cell Lung Cancer

Abstract

Activation of peroxisome proliferator-activated receptor-γ (PPAR-γ) results in inhibition of tumor growth in various types of cancers, but the mechanism(s) by which PPAR-γ induces growth arrest has not been completely defined. In a recent study, we demonstrated that treatment of A549 (human non small cell lung cancer cell line) tumor-bearing SCID mice with PPAR-γ ligands troglitazone (Tro) and pioglitazone significantly inhibits primary tumor growth. In this study, immunohistochemical analysis of Tro-treated and Pio-treated tumors with factor VIII antibody revealed a significant reduction in blood vessel density compared to tumors in control animals, suggesting inhibition of angiogenesis. Further analysis showed that treatment of A549 cells in vitro with Tro or transient transfection of A549 cells with constitutively active PPAR-γ (VP16-PPAR-γ) construct blocked the production of the angiogenic ELR +CXC chemokines IL-8 (CXCL8), ENA-78 (CXCL5), Gro-α (CXCL1). Similarly, an inhibitor of NF-ΚB activation (PDTC) also blocked CXCL8, CXCL5, CXCL1 production, consistent with their NF-ΚB-dependent regulation. Conditioned media from A549 cells induce human microvascular endothelial cell (HMVEC) chemotaxis. However, conditioned media from Tro-treated A549 cells induced significantly less HMVEC chemotaxis compared to untreated A549 cells. Furthermore, PPAR-γ activation inhibited NF-ΚB transcriptional activity, as assessed by TransAM reporter gene assay. Collectively, our data suggest that PPAR-γ ligands can inhibit tumor-associated angiogenesis by blocking the production of ELR+CXC chemokines, which is mediated through antagonizing NF-ΚB activation. These antiangiogenic effects likely contribute to the inhibition of primary tumor growth by PPAR-γ ligands.

Keywords

• PPAR-γ
• NSCLC
• angiogenesis
• CXC chemokines
• NF-ΚB