Sunitinib inhibits catecholamine synthesis and secretion in pheochromocytoma tumor cells by blocking VEGF receptor 2 via PLC-γ-related pathways.
Sunitinib is an oral, small molecule multitargeted receptor tyrosine kinase inhibitor with antiangiogenic and antitumor activity that primarily targets vascular endothelial growth factor receptors (VEGFRs). Although sunitinib is an active agent for the treatment of malignant pheochromocytomas, it is unclear whether sunitinib acts through only antiangiogenic mechanisms or also directly targets tumor cells. We previously showed that sunitinib directly induced apoptosis of PC-12 cells. To further confirm these direct effects, we examined the effects of sunitinib on tyrosine hydroxylase (TH) (the rate-limiting enzyme in catecholamine biosynthesis) activity and catecholamine secretion in PC-12 cells and the underlying mechanisms. Sunitinib inhibited TH activity in a dose-dependent manner, and decreased TH protein levels. Consistent with this finding, sunitinib decreased TH phosphorylation at Ser(31) and Ser(40) and significantly decreased catecholamine secretion. VEGFR-2 knockdown attenuated these effects, including inhibition of TH activity and catecholamine secretion, suggesting that they were mediated by VEGFR-2. Sunitinib significantly decreased phospholipase C (PLC)-γ phosphorylation and subsequent protein kinase C (PKC) activity. Because Ser(40) phosphorylation significantly affects TH activity and is known to be regulated by PKC, sunitinib may inhibit Ser(40) phosphorylation via the VEGFR-2/PLC-γ/PKC pathway. Additionally, sunitinib markedly decreased the activity of extracellular signal-regulated kinase (ERK), but not c-Jun NH(2)-terminal kinase or p38 mitogen-activated protein kinase. Therefore, sunitinib may reduce TH Ser(31) phosphorylation through inhibition of the VEGFR-2/PLC-γ/PKC/Raf/mitogen-activated protein kinase/extracellular signal-regulated kinase kinase/ERK pathway. Sunitinib also significantly reduced inositol 1,4,5-trisphosphate production. However, because PC-12 cells do not precisely reflect the pathogenesis of malignant cells, we confirmed the key findings in a human neuroblastoma cell line, SK-N-SH. In conclusion, sunitinib directly inhibits catecholamine synthesis and secretion in pheochromocytoma PC-12 cells.
Department of Molecular Laboratory Medicine, Graduate School of Comprehensive Human Sciences, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan.
Yuichi
Y
Aita
Kiyo-aki
KA
Ishii
Yuria
Y
Saito
Tatsuhiko
T
Ikeda
Yasushi
Y
Kawakami
Hitoshi
H
Shimano
Hisato
H
Hara
Kazuhiro
K
Takekoshi
D020533:Angiogenesis Inhibitors / Q000494:pharmacology*; D000818:Animals; D015153:Blotting, Western; D002395:Catecholamines / Q000096:biosynthesis* / Q000378:metabolism*; D045744:Cell Line, Tumor; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D015544:Inositol 1,4,5-Trisphosphate / Q000096:biosynthesis; D016716:PC12 Cells; D010673:Pheochromocytoma / Q000378:metabolism; D051966:Phospholipase C gamma / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D011758:Pyrroles / Q000494:pharmacology*; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D040262:Receptors, Vascular Endothelial Growth Factor / Q000037:antagonists & inhibitors*; D015398:Signal Transduction / Q000187:drug effects; D000077210:Sunitinib; D014446:Tyrosine 3-Monooxygenase / Q000378:metabolism
D020533:Angiogenesis Inhibitors; D002395:Catecholamines; D007211:Indoles; D011758:Pyrroles; D034741:RNA, Small Interfering; D015544:Inositol 1,4,5-Trisphosphate; D014446:Tyrosine 3-Monooxygenase; D040262:Receptors, Vascular Endothelial Growth Factor; D011493:Protein Kinase C; D048049:Extracellular Signal-Regulated MAP Kinases; D051966:Phospholipase C gamma; D000077210:Sunitinib