title: Inhibition of autophagy enhances sunitinib-induced cytotoxicity in rat pheochromocytoma PC12 cells.
abstract: Sunitinib is an oral multitargeted receptor tyrosine kinase inhibitor with antiangiogenic and antitumor activity that mainly targets vascular endothelial growth factor receptors, and recently, it has been shown to be an active agent for the treatment of malignant pheochromocytomas. Previously, we demonstrated that sunitinib directly inhibited mTORC1 signaling in rat pheochromocytoma PC12 cells. Although autophagy is a highly regulated cellular process, its relevance to cancer seems to be complicated. It is of note that inhibition of mTORC1 is a prerequisite for autophagy induction. Indeed, direct mTORC1 inhibition initiates ULK1/2 autophosphorylation and subsequent Atg13 and FIP200 phosphorylation, inducing autophagy. Here, we demonstrated that sunitinib significantly increased the levels of LC3-II, concomitant with a decrease of p62 in PC12 cells. Following sunitinib treatment, immunofluorescent imaging revealed a marked increased punctate LC3-II distribution. Furthermore, Atg13 knockdown significantly reduced its protein level, which in turn abolished sunitinib-induced autophagy. Moreover, inhibition of autophagy by siRNAs targeting Atg13 or by pharmacological inhibition with ammonium chloride, enhanced both sunitinib-induced apoptosis and anti-proliferation. Thus, sunitinib-induced autophagy is dependent on the suppression of mTORC1 signaling and the formation of ULK1/2-Atg13-FIP200 complexes. Inhibition of autophagy may be a promising therapeutic option for improving the anti-tumor effect of sunitinib.
authors.affiliation: Department of Endocrine Surgery, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Japan.
authors.forename: Tatsuhiko
authors.initials: T
authors.lastname: Ikeda
authors.forename: Kiyo-Aki
authors.initials: KA
authors.lastname: Ishii
authors.forename: Yuria
authors.initials: Y
authors.lastname: Saito
authors.forename: Masahiro
authors.initials: M
authors.lastname: Miura
authors.forename: Aoi
authors.initials: A
authors.lastname: Otagiri
authors.forename: Yasushi
authors.initials: Y
authors.lastname: Kawakami
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Shimano
authors.forename: Hisato
authors.initials: H
authors.lastname: Hara
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Takekoshi
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000378:metabolism; D000310:Adrenal Gland Neoplasms / Q000378:metabolism / Q000473:pathology*; D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001343:Autophagy / Q000187:drug effects*; D000071183:Autophagy-Related Proteins; D007211:Indoles / Q000494:pharmacology*; D000076222:Mechanistic Target of Rapamycin Complex 1; D008869:Microtubule-Associated Proteins / Q000378:metabolism; D058990:Molecular Targeted Therapy; D046912:Multiprotein Complexes; D016716:PC12 Cells; D010673:Pheochromocytoma / Q000378:metabolism / Q000473:pathology*; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000037:antagonists & inhibitors*; D011758:Pyrroles / Q000494:pharmacology*; D051381:Rats; D015398:Signal Transduction / Q000187:drug effects; D000077210:Sunitinib; D058570:TOR Serine-Threonine Kinases
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D020533:Angiogenesis Inhibitors; D000970:Antineoplastic Agents; D000071183:Autophagy-Related Proteins; D007211:Indoles; D000076222:Mechanistic Target of Rapamycin Complex 1; D008869:Microtubule-Associated Proteins; D046912:Multiprotein Complexes; D017346:Protein Serine-Threonine Kinases; D011505:Protein-Tyrosine Kinases; D011506:Proteins; D011758:Pyrroles; D000077210:Sunitinib; D058570:TOR Serine-Threonine Kinases; C534291:ATG13 protein, human; C526109:Anxa3 protein, rat; C407704:RB1CC1 protein, human