Transforming growth factor (TGF)-β promotes epithelial-mesenchymal transition and cell invasion of cancer cells in part through the small GTPase RAC1. Since RAC1 can signal through reactive oxygen species (ROS), we probed the role of the ROS-producing NADPH oxidase (NOX) and p38 mitogen-activated protein kinase (MAPK) in mediating TGF-β1/RAC1-driven random cell migration (chemokinesis). Although the NOX isoforms NOX2, 4, 5, 6, and RAC1 were readily detectable by RT-PCR in pancreatic ductal adenocarcinoma (PDAC)-derived Panc1 and Colo357 cells, only NOX4 and RAC1 were expressed at higher levels comparable to those in peripheral blood monocytes. TGF-β1 treatment resulted in upregulation of NOX4 (and NOX2) and rapid intracellular production of ROS. To analyze whether RAC1 functions through NOX and ROS to promote cell motility, we performed real-time cell migration assays with xCELLigence® technology in the presence of the ROS scavenger N-acetyl-L-cysteine (NAC) and various NOX inhibitors. NAC, the NOX4 inhibitor diphenylene iodonium or small interfering RNA (siRNA) to NOX4, and the NOX2 inhibitor apocynin all suppressed TGF-β1-induced chemokinesis of Panc1 and Colo357 cells as did various inhibitors of RAC1 used as control. In addition, we showed that blocking NOX4 or RAC1 function abrogated phosphorylation of p38 MAPK signaling by TGF-β1 and that inhibition of p38 MAPK reduced TGF-β1-induced random cell migration, while ectopic expression of a kinase-active version of the p38 activating kinase MKK6 was able to partially rescue the decline in migration after RAC1 inhibition. Our data suggest that TGF-β1-induced chemokinesis in PDAC cells is mediated through a RAC1/NOX4/ROS/p38 MAPK cascade.
Research Areas and Centers
- Academic Focus: Center for Brain, Behavior and Metabolism (CBBM)