Carcinogenesis Advance Access originally published online on February 6, 2008
Carcinogenesis 2008 29(4):704-712; doi:10.1093/carcin/bgn031
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Macrophage inhibitory cytokine-1 activates AKT and ERK-1/2 via the transactivation of ErbB2 in human breast and gastric cancer cells
1 Molecular Cancer Research Center, Korea Research Institute of Bioscience and Biotechnology, Daejeon, Republic of Korea
2 Department of Life Science, Sookmyung Women's University, Seoul, Republic of Korea
3 Department of Biology, Chungnam National University, Daejeon, Republic of Korea
4 Department of Biochemistry and Research Institute of Life Science, College of Natural Sciences, Kangwon National University, Chuncheon 200-701, Republic of Korea
* To whom correspondence should be addressed. Tel: +82 33 250 8519; Fax: +82 33 242 0459; Email: jhlee36{at}kangwon.ac.kr
Macrophage inhibitory cytokine-1 (MIC-1) is a member of the transforming growth factor-β superfamily, which is overexpressed in a variety of human cancers, including breast and gastric cancer. The function of MIC-1 in cancer remains controversial and its signaling pathways remain poorly understood. In this study, we demonstrate that MIC-1 induces the transactivation of ErbB2 in SK-BR-3 breast and SNU-216 gastric cancer cells. MIC-1 induced a significant phosphorylation of Akt and ERK-1/2, and also effected an increase in the levels of tyrosine phosphorylation of ErbB1, ErbB2 and ErbB3 in SK-BR-3 and SNU-216 cells. The treatment of these cells with AG825 and AG1478, inhibitors specific for ErbB2 tyrosine kinase, resulted in the complete abolition of MIC-1-induced Akt and ERK-1/2 phosphorylation. Furthermore, the small-interfering RNA-mediated downregulation of ErbB2 significantly reduced not only the phosphorylation of Akt and ERK-1/2 but also the invasiveness of the cells induced by MIC-1. Our results show that ErbB2 activation performs a crucial function in MIC-1-induced signaling pathways. Further investigations revealed that MIC-1 induced the expression of the hypoxia inducible factor-1
protein and the expression of its target genes, including vascular endothelial growth factor, via the activation of the mammalian target of rapamycin (mTOR) signaling pathway. Stimulation of SK-BR-3 with MIC-1 profoundly induces the phosphorylation of mTOR and its downstream substrates, including p70S6K and 4E-BP1. Collectively, these results show that MIC-1 may participate in the malignant progression of certain human cancer cells that overexpress ErbB2 through the transactivation of ErbB2 tyrosine kinase.
Abbreviations: EGFR, epidermal growth factor receptor; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; HIF-1, hypoxia inducible factor-1; MIC-1, macrophage inhibitory cytokine-1; mTOR, mammalian target of rapamycin; PI3K, phosphatidylinositol-3 kinase; rMIC-1, recombinant MIC-1; siRNA, small-interfering RNA; TGF-β, transforming growth factor-β; VEGF, vascular endothelial growth factor
Received August 15, 2007; revised January 6, 2008; accepted January 26, 2008.