ROS-Driven PKCζ Signaling as a Widely Involved Mechanism for Cancer Cell Motility and Metastasis

The enhancement of cell motility by bioactive molecules such as growth factors, hormones, and tissue factors is pivotal in cancer invasion and metastasis. However, the molecular mechanisms underlying this enhancement remain incompletely understood. In this study, we demonstrate that hepatoblastoma HepG2 cell motility is significantly increased following hepatocyte growth factor (HGF) treatment, as assessed by phagokinetic track assays, Transwell assays, and scratch assays. This enhancement is mediated by reactive oxygen species (ROS), which activate the PKCζ/Rho GTPase signaling pathway. Notably, the motility increase is markedly suppressed by superoxide dismutase (SOD), N-acetylcysteine (NAC), diphenyleneiodonium (DPI), and the PKCζ inhibitory peptide MyrPKCζ. Similar patterns of motility enhancement and its inhibition by MyrPKCζ were observed in HGF-treated colon cancer HCT116 cells, epidermal growth factor (EGF)-treated HepG2 and HCT116 cells, and transforming growth factor-β (TGF-β)-treated HepG2 cells, as evaluated using Transwell assays. Additionally, estradiol enhances the motility of breast cancer MDA-MB-231-luc cells via ROS generation and activation of the PKCζ/Rho GTPase signaling pathway, with this effect significantly suppressed by MyrPKCζ in Transwell assays. The inhibitory effect of MyrPKCζ was further confirmed in vivo, where it suppressed peritoneal invasion of HCT116 cells in NOD-SCID mice. Furthermore, in NOD-SCID mice injected with MDA-MB-231-luc cells carrying shRNA targeting PKCζ into the tail vein, doxycycline-induced shRNA expression resulted in marked suppression of pulmonary metastasis. These findings indicate that the ROS/PKCζ/Rho GTPase signaling cascade is a pivotal regulator of cancer cell motility and suggest that PKCζ represents a promising therapeutic target for preventing cancer invasion and metastasis.