The role of myoglobin in epithelial cancers: Insights from transcriptomics.

The muscle­associated respiratory protein myoglobin (MB) is expressed in multiple types of cancer, including breast and prostate tumors. In Kaplan­Meier analyses of the two tumor types, MB positivity is associated with favorable prognoses. Despite its well­characterized function in myocytes, the role of MB in cancer remains unclear. To study the impact of endogenous MB expression, small interfering RNA MB­knockdown cells were engineered using breast, prostate and colon cancer cell lines (MDA­MB468, LNCaP, DLD­1), and their transcriptomes were investigated using RNA­Seq at different oxygen levels. In MB­positive cells, increased expression of glycolytic genes was observed, which was possibly mediated by a higher activity of hypoxia­inducible factor 1α. In addition, the results of the gene set enrichment analysis suggested that MB contributed to fatty acid transport and turnover. MB­positive, wild­type­p53 LNCaP cells also exhibited increased expression of p53 target genes involved in cell cycle checkpoint control and prevention of cell migration. MB­positive cells expressing mutant p53 exhibited upregulation of genes associated with prolonged cancer cell viability and motility. Therefore, it was hypothesized that these transcriptomic differences may result from MB­mediated generation of nitric oxide or reactive oxygen species, thus employing established enzymatic activities of the globin. In summary, the transcriptome comparisons identified potential molecular functions of MB in carcinogenesis by highlighting the interaction of MB with key metabolic and regulatory processes.