MNK1 and MNK2 regulation in HER2-overexpressing breast cancer lines

University of Virginia, Charlottesville, Virginia, United States
Journal of Biological Chemistry (Impact Factor: 4.57). 03/2007; 282(7):4243-52. DOI: 10.1074/jbc.M607368200
Source: PubMed


MAPK-interacting protein kinases 1 and 2 (MNK1 and MNK2) function downstream of p38 and ERK MAPK, but there are large gaps in our knowledge of how MNKs are regulated and function. As proteins activated in the HER2/Ras/Raf/ERK pathway, the MNKs are of potential interest in HER2-overexpressing cancers. We utilized a panel of breast cell lines (HCC1419, AU565, SKBR3, MCF7, and MCF10A), three of which overexpress HER2, to characterize the amounts and activation status of MNKs and other pathway enzymes (ERKs and RSKs) in these cells. We generated a phosphospecific antibody to Thr(P)-214 in the T-loop of MNKs and found that phosphorylations of both Thr-209 and Thr-214 in human MNK1 are required for activation. Increased phosphorylation and activity of the MNKs correlate with HER2 overexpression, and inhibition of the MNKs reduces colony formation in soft agar. Our work identifies the MNKs as potential therapeutic targets for breast cancer treatments.

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    • "We also found that Mnk2a can bind and phosphorylate both p38a and p38b, but not p38g or p38d, suggesting that Mnk2a has specificity toward these two substrates (Figures 4A, 4B, and S6F–S6H). We further confirmed that the kinase activity of Mnk2a is required for activation of p38a and its target genes because both the Mnk2aKD or application of the Mnk1/Mnk2 kinase inhibitor CGP 57380 (Knauf et al., 2001; Chrestensen et al., 2007) inhibited these activities (Figures S6B and 6). Taken together, these results indicate that Mnk2 kinase activity is required for the activation of p38-MAPK and its downstream targets. "
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    ABSTRACT: The kinase Mnk2 is a substrate of the MAPK pathway and phosphorylates the translation initiation factor eIF4E. In humans, MKNK2, the gene encoding for Mnk2, is alternatively spliced yielding two splicing isoforms with differing last exons: Mnk2a, which contains a MAPK-binding domain, and Mnk2b, which lacks it. We found that the Mnk2a isoform is downregulated in breast, lung, and colon tumors and is tumor suppressive. Mnk2a directly interacts with, phosphorylates, activates, and translocates p38α-MAPK into the nucleus, leading to activation of its target genes, increasing cell death and suppression of Ras-induced transformation. Alternatively, Mnk2b is pro-oncogenic and does not activate p38-MAPK, while still enhancing eIF4E phosphorylation. We further show that Mnk2a colocalization with p38α-MAPK in the nucleus is both required and sufficient for its tumor-suppressive activity. Thus, Mnk2a downregulation by alternative splicing is a tumor suppressor mechanism that is lost in some breast, lung, and colon tumors.
    Cell Reports 04/2014; 7(2). DOI:10.1016/j.celrep.2014.03.041 · 8.36 Impact Factor
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    • "Despite increased understanding of Mnk structure and function, little progress has been made with the discovery of pharmacological Mnk inhibitors. So far three Mnk inhibitors have been reported: CGP052088 [75], CGP57380 [76-79], and Cercosporamide [80] (Figure 4). These compounds have mainly served as chemical biological tools for Mnk target validation. "
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    Oncotarget 02/2012; 3(2):118-31. DOI:10.18632/oncotarget.453 · 6.36 Impact Factor
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    • "We used untreated MCF-7 human breast cancer cells as positive controls for ER-α and ER-β protein and SKBR3 human breast cancer cells (Chrestensen et al. 2007) as positive controls for HER2 (human epidermal growth factor receptor 2) protein. "
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