Expression of myoglobin by tumor cells and its role in progression of malignancy

The review examines available literature data on the expression of myoglobin in various tumors and tumor cell lines of non-muscle nature, and the effect of hypoxia, reactive oxygen and nitrogen species, hormones, growth factors, gender and age on this process. The influence of tumor myoglobin on processes occurring in cells – oxidative stress, inhibition of mitochondrial respiration by nitric oxide and fatty acid metabolism is also analyzed, both in the case of intrinsic endogenous (ectopic) expression of small amounts (~1 µM) of myoglobin and overexpression of the protein (~150 µM) via the myoglobin gene embedded in the tumour cell genome. It is concluded that hypoxia-induced intrinsic expression of low concentrations of myoglobin, due to its ability to utilise reactive oxygen and nitrogen species that can damage tumour cells, ensures their better survival, promoting tumour progression and metastasis. Accordingly, this myoglobin expression is generally associated with a more aggressive tumour type and poor prognosis for the course and outcome of the disease, and may thus serve as a “marker” of an aggressive malignancy. In contrast, artificial overexpression of myoglobin can significantly inhibit tumour development and improve disease course by switching cancer cell metabolism from tumour-specific glycolysis to oxidative phosphorylation inherent in healthy tissue. Myoglobin overexpression may thus be an effective therapeutic tool in oncology.