Molecular characterization of autophagic and apoptotic signaling induced by sorafenib in liver cancer cells

Sorafenib is the unique accepted molecular targeted drug for the treatment of patients in advanced stage of hepatocellular carcinoma. The current study evaluated cell signaling regulation of endoplasmic reticulum (ER) stress, c-Jun-N-terminal kinase (JNK), Akt, and 5′AMP-activated protein kinase (AMPK) leading to autophagy and apoptosis induced by sorafenib. Sorafenib induced early (3–12 hr) ER stress characterized by an increase of ^Ser51P-eIF2α/eIF2α, C/EBP homologous protein (CHOP), IRE1α, and sXBP1, but a decrease of activating transcription factor 6 expression, overall temporally associated with the increase of ^{Thr183,Tyr185}P-JNK1/2/JNK1/2, ^Thr172P-AMPKα, ^Ser413P-Foxo3a, ^Thr308P-AKt/AKt and ^Thr32P-Foxo3a/Foxo3a ratios, and reduction of ^Ser2481P-mammalian target of rapamycin (mTOR)/mTOR and protein translation. This pattern was related to a transient increase of tBid, Bim _EL, Beclin-1, Bcl-xL, Bcl-2, autophagy markers, and reduction of myeloid cell leukemia-1 (Mcl-1) expression. The progressive increase of CHOP expression, and reduction of ^Thr308P-AKt/AKt and ^Ser473P-AKt/AKt ratios were associated with the reduction of autophagic flux and an additional upregulation of Bim _EL expression and caspase-3 activity (24 hr). Small interfering-RNA (si-RNA) assays showed that Bim, but not Bak and Bax, was involved in the induction of caspase-3 in sorafenib-treated HepG2 cells. Sorafenib increased autophagic and apoptotic markers in tumor-derived xenograft model. In conclusion, the early sorafenib-induced ER stress and regulation of JNK and AMPK-dependent signaling were related to the induction of survival autophagic process. The sustained drug treatment induced a progressive increase of ER stress and PERK-CHOP-dependent rise of Bim _EL, which was associated with the shift from autophagy to apoptosis. The kinetic of Bim _EL expression profile might also be related to the tight balance between AKt- and AMPK-related signaling leading to Foxo3a-dependent BIM _EL upregulation.