Targeted Disruption of Protein Kinase Cε Reduces Cell Invasion and Motility through Inactivation of RhoA and RhoC GTPases in Head and Neck Squamous Cell Carcinoma

摘要

Over 70% of patients with head and neck squamous cell carcinoma (HNSCC) present with locoregionally advanced stage III and IV disease. In spite of aggressive therapy, locoregional disease recurs in 60% and metastatic disease develops in 15% to 25% of patients causing a major decline in quality and length of life. Therefore, there is a need to identify and understand genes that are responsible for inducing an aggressive HNSCC phenotype. Evidence has shown that protein kinase C (PKC) ε is a transforming oncogene and may play a role in HNSCC progression. In this study, we determine the downstream signaling pathway mediated by PKCε to promote an aggressive HNSCC phenotype. RNA interference knockdown of PKCε in UMSCC11A and UMSCC36, two highly invasive and motile HNSCC cell lines with elevated endogenous PKCε levels, resulted in cells that were significantly less invasive and motile than the small interfering RNA–scrambled control transfectants; 51 ± 5% (P < 0.006) and 49 ± 3% (P < 0.010) inhibition in invasion and 69 ± 1% (P < 0.0005) and 66 ± 3% (P < 0.0001) inhibition in motility, respectively. PKCε-deficient UMSCC11A clones had reduced levels of active and serine-phosphorylated RhoA and RhoC. Moreover, constitutive active RhoA completely rescued the invasion and motility defect, whereas constitutive active RhoC completely rescued the invasion and partially rescued the motility defect of PKCε-deficient UMSCC11A clones. These results indicate that RhoA and RhoC are downstream of PKCε and critical for PKCε-mediated cell invasion and motility. Our study shows, for the first time, that PKCε is involved in a coordinated regulation of RhoA and RhoC activation, possibly through direct post-translational phosphorylation.