PKCε-mediated c-Met endosomal processing directs fluctuant c-Met-JNK-paxillin signaling for tumor progression of HepG2

Hepatocyte growth factor (HGF) induced c-Met signaling play critical roles in the progression of hepatocellular carcinoma (HCC). However, c-Met targeting approaches suffered resistance and side effect, thus identification of more suitable downstream targets is needed. Recently, we demonstrated HGF-induced fluctuant ERK/paxillin signaling within 24 h. We further examined the underlying mechanisms for fluctuant c-Met/JNK/paxillin signal cascade within 12 h. HGF-induced phosphotylation of c-Met, JNK, and paxillin (Ser178) shared a common fluctuation pattern characterized by an initial peak at 0.5 h, a middle drop at 4 h, and a later peak at 10 h. Dynasore, the inhibitor of dynamin, suppressed HGF-induced c-Met internalization and phosphorylation of JNK and paxillin (Ser178) at 0.5 h, indicating that endosome formation is required for initial signal enhancement. Further, depletion of PKC epsilon not only enhanced HGF-induced phosphorylation of JNK and paxillin (Ser178) but also prevented c-Met degradation at 0.5 h, suggesting that PKC epsilon mediated c-Met degradation for signal declination. On the other hand, HGF induced colocalizations of both phosphorylated JNK and paxillin with the endosomal recycling protein GGA3 at 10 h and depletion of GGA3 abolished membrane recycling of c-Met and phosphorylation of JNK/paxillin at the same time point. Interestingly, HGF induced GGA3 phosphorylation in a PKC epsilon-dependent manner during 0.5-4 h, which is associated with c-Met degradation in the same period. Finally, HGF-induced cell migration, invasion and intrahepatic metastasis of HepG2 were prevented by the inhibitors of endocytosis. Our results suggest that critical endosomal components are promising therapeutic targets for preventing HGF-induced progression of HCC. (C) 2015 Elsevier Inc All rights reserved.