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Int. J. Mol. Sci. 2012, 13(6), 7212-7225; doi:10.3390/ijms13067212
Article

Nec-1 Enhances Shikonin-Induced Apoptosis in Leukemia Cells by Inhibition of RIP-1 and ERK1/2

1
,
2
,
1
,
1
 and
1,*
1 Department of Medical Oncology, Sir Run Run Shaw Hospital, Zhejiang University School of Medicine, 3 East Qingchun Road, Hangzhou 310016, China 2 The Cancer Institute, The Second Affiliated Hospital, Zhejiang University School of Medicine, 88 Jiefang Road, Hangzhou 310009, China
* Author to whom correspondence should be addressed.
Received: 31 March 2012 / Revised: 23 April 2012 / Accepted: 7 June 2012 / Published: 12 June 2012
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Abstract

Necrostatin-1 (Nec-1) inhibits necroptosis by allosterically inhibiting the kinase activity of receptor-interacting protein 1 (RIP1), which plays a critical role in necroptosis. RIP1 is a crucial adaptor kinase involved in the activation of NF-κB, production of reactive oxygen species (ROS) and the phosphorylation of mitogen activated protein kinases (MAPKs). NF-κB, ROS and MAPKs all play important roles in apoptotic signaling. Nec-1 was regarded as having no effect on apoptosis. Here, we report that Nec-1 increased the rate of nuclear condensation and caspases activation induced by a low concentration of shikonin (SHK) in HL60, K562 and primary leukemia cells. siRNA-mediated knockdown of RIP1 significantly enhanced shikonin-induced apoptosis in K562 and HL60 cells. Shikonin treatment alone could slightly inhibit the phosphorylation of ERK1/2 in leukemia cells, and the inhibitory effect on ERK1/2 was significantly augmented by Nec-1. We also found that Nec-1 could inhibit NF-κB p65 translocation to the nucleus at a later stage of SHK treatment. In conclusion, we found that Nec-1 can promote shikonin-induced apoptosis in leukemia cells. The mechanism by which Nec-1 sensitizes shikonin-induced apoptosis appears to be the inhibition of RIP1 kinase-dependent phosphorylation of ERK1/2. To our knowledge, this is the first study to document Nec-1 sensitizes cancer cells to apoptosis.
Keywords: Necrostatin-1; receptor-interacting protein 1; shikonin; apoptosis; ERK1/2 Necrostatin-1; receptor-interacting protein 1; shikonin; apoptosis; ERK1/2
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Han, W.; Xie, J.; Fang, Y.; Wang, Z.; Pan, H. Nec-1 Enhances Shikonin-Induced Apoptosis in Leukemia Cells by Inhibition of RIP-1 and ERK1/2. Int. J. Mol. Sci. 2012, 13, 7212-7225.

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