Novel signaling axis for ROS generation during K-Ras-induced cellular transformation

Reactive oxygen species (ROS) are well known to be involved in oncogene-mediated cellular transformation. However, the regulatory mechanisms underlying ROS generation in oncogene-transformed cells are unclear. In the present study, we found that oncogenic K-Ras induces ROS generation through activation of NADPH oxidase 1 (NOX1), which is a critical regulator for the K-Ras-induced cellular transformation. NOX1 was activated by K-Ras-dependent translocation of p47 phox , a subunit of NOX1 to plasma membrane. Of note, PKC δ , when it was activated by PDPK1, directly bound to the SH3-N domain of p47 phox and catalyzed the phosphorylation on Ser348 and Ser473 residues of p47 phox C-terminal in a K-Ras-dependent manner, finally leading to its membrane translocation. Notably, oncogenic K-Ras activated all MAPKs (JNK, ERK and p38); however, only p38 was involved in p47 phox -NOX1-dependent ROS generation and consequent transformation. Importantly, K-Ras-induced activation of p38 led to an activation of PDPK1, which then signals through PKC δ , p47 phox and NOX1. In agreement with the mechanism, inhibition of p38, PDPK1, PKC δ , p47 phox or NOX1 effectively blocked K-Ras-induced ROS generation, anchorage-independent colony formation and tumor formation. Taken together, our findings demonstrated that oncogenic K-Ras activates the signaling cascade p38/PDPK1/PKC δ /p47 phox /NOX1 for ROS generation and consequent malignant cellular transformation.