Colon-26 cancer-induced skeletal muscle wasting is IKKbeta/IkappaBalpha-dependent and NF-kappaB-Independent
Cornwell, Evangeline Wang
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Existing data suggest that NF-kappaB signaling is a key regulator of cancer-induced skeletal muscle wasting. However, identification of the components of this signaling pathway and of the NF-kappaB transcription factors that regulate wasting is far from complete. In muscles of C26 tumor-bearing mice, overexpression of dominant-negative (d.n.) IKKbeta and the IkappaBalpha-super repressor blocked wasting by 69% and 41%, respectively. In contrast, overexpression of d.n. IKKalpha or d.n. NIK did not block C26-induced muscle wasting. Surprisingly, overexpression of d.n. RelA (p65) or d.n. c-Rel did not significantly affect muscle wasting. Genome-wide mRNA expression arrays showed upregulation of many genes previously implicated in muscle atrophy. To test if these upregulated genes were direct targets of NF-kappaB transcription factors, we compared genome-wide p65 binding to DNA in control and cachectic muscle using chromatin immunoprecipitation-sequencing (ChiP-seq). Bioinformatic analysis of ChiP-sequencing data from control and C26 muscles did not show p65 binding peaks in the upregulated genes as reflected by the expression arrays. The p65 ChiP-seq data are consistent with our finding of no significant change in protein binding to an NF-kappaB oligonucleotide in an electrophoretic mobility shift assay (EMSA), no activation of an NF-kappaB-dependent reporter, and no effect of d.n. p65 overexpression in muscles of tumor-bearing mice. Taken together, these data support the idea that although inhibition of IkappaBalpha, and particularly IKKbeta, blocks cancer-induced muscle wasting, the alternative NF-kappaB signaling pathway is not required. In addition, the downstream NF-kappaB transcription factors are not involved in gene regulation during atrophy. These data are consistent with the growing body of literature showing that there are NF-kappaB-independent activities of IKKbeta and IkappaBalpha that regulate physiological processes.
Thesis (Ph.D.)--Boston University