IL-6-induced Enhancement of c-Myc Translation in Multiple Myeloma Cells

• Published in: The Journal of biological chemistry 2011-01, Vol.286 (1), p.67-78
• Main Authors: Shi, Yijiang, Frost, Patrick, Hoang, Bao, Benavides, Angelica, Gera, Joseph, Lichtenstein, Alan
• Format: Article
• Language: English
• Subjects: Cytokine Action; hnRNP A1; Interleukin; Interleukin 6; Multiple Myeloma; Myc; Translation Control; Translation Regulation
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M110.153221

Prior work indicates that IL-6 can stimulate c-Myc expression in multiple myeloma (MM) cells, which is independent of effects on transcription and due to enhanced translation mediated by an internal ribosome entry site in the 5′-UTR of the c-Myc RNA. The RNA-binding protein hnRNP A1 (A1) was also critical to IL-6-stimulated translation. Because A1 shuttles between nucleus and cytoplasm, we investigated whether the ability of IL-6 to enhance Myc translation was mediated by stimulation of A1 shuttling. In MM cell lines and primary specimens, IL-6 increased A1 cytoplasmic localization. In contrast, there was no effect on the total cellular levels of A1. Use of a dominant negative A1 construct, which prevents endogenous A1 from nucleus-to-cytoplasm transit, prevented the ability of IL-6 to enhance Myc internal ribosome entry site activity, Myc protein expression, and MM cell growth. IL-6-stimulated cytoplasmic localization was mediated by alterations in the C-terminal M9 peptide of A1, and this correlated with the ability of IL-6 to induce serine phosphorylation of this domain. A p38 kinase inhibitor prevented IL-6-induced A1 phosphorylation. Thus, IL-6 activates c-Myc translation in MM cells by inducing A1 phosphorylation and cytoplasmic localization in a p38-dependent fashion. These data suggest A1 as a potential therapeutic target in MM.