NF-κB-Mediated MyoD Decay during Muscle Wasting Requires Nitric Oxide Synthase mRNA Stabilization, HuR Protein, and Nitric Oxide Release

Abstract

Muscle wasting (cachexia) is a consequence of chronic diseases, such as cancer, and is associated with degradation of muscle proteins such as MyoD. The cytokines tumor necrosis factor alpha and gamma interferon induce muscle degeneration by activating the transcription factor NF-κB and its target genes. Here, we show that a downstream target of NF-κB is the nitric oxide (NO) synthase gene (iNos) and suggest that NO production stimulates MyoD mRNA loss. In fact, although cytokine treatment of iNos^−/− mice activated NF-κB, it did not trigger MyoD mRNA degeneration, demonstrating that NF-κB-mediated muscle wasting requires an active iNOS-NO pathway. The induced expression of iNOS by cytokines relies on both transcriptional activation via NF-κB and increased mRNA stability via the RNA-binding protein HuR. Moreover, we show that HuR regulates iNOS expression in an AMP-activated protein kinase (AMPK)-dependent manner. Furthermore, AMPK activation results in HuR nuclear sequestration, inhibition of iNOS synthesis, and reduction in cytokine-induced MyoD loss. These results define iNOS and HuR as critical players in cytokine-induced cachexia, establishing them as potential therapeutic targets.

SUPPLEMENTAL MATERIAL

Supplemental material for this article may be found at http://mcb.asm.org/.

ACKNOWLEDGMENTS

We are grateful to Jerry Pelletier, Denis Guttridge, Maria Hatzoglou, and Paul Anderson as well as K. Van der Giessen and J. Behrmann for helpful discussions and comments on the manuscript. We thank A. B. Lassar (Harvard Medical School, Boston, Mass.) for MyoD, myogenin, and p21^Cip1 plasmids.

This work was supported by a CIHR Cancer Consortium Training Grant Fellowship Award to S.D.M., an NCIC TFF Research Fellowship to R.M., an NIH operating grant (NIH/NHGRI HG003679) to S.A.T., and CIRH operating grant Mop-57680 and an FRSQ “Subvention d'etablissement de jeune chercheur” (Frsq 23516-2760) to I.-E.G.