Exploring the Molecular Mechanisms of Human Cytoglobin and its Role in Cancer

Cytoglobin (Cygb), a recently discovered globin, is found in low levels in most human tissues. It currently has undefined functions, but theories include scavenging free radicals and redox regulation. It is implicated in cancer and evidence suggests the protein has bimodal functions, acting as a tumour suppressor under normoxic conditions and an oncogene under hypoxic conditions. Additionally, Cygb is proposed to be involved in cancer therapy resistance by protecting tumour cells from harsh environments including high free radical levels generated with chemotherapeutics. The effects of different conditions and interactions were tested on the protein to better understand the protein’s reaction to environments including NiR (nitrite reductase), lipid and liposome interactions and NOD (nitric oxide dioxygenase). The WT protein was compared to results gathered from two mutants: H81A and L46W. H81 mutation was selected as it affects NiR activity in neuroglobin and L46 affects NOD activity in myoglobin (Mb) and haemoglobin (Hb). In addition to tests on the three proteins, investigations were undertaken on CYGB (WT and mutant) transfected MCF7 and HEK293S cell lines whereby reactions to stimuli such as H2O2 and chemotherapeutics were observed. Cell proliferation and survival assays including crystal violet were used to assess the extent of the effect. Results indicated significant levels of protection afforded to cells transfected with CYGB when exposed to H2O2 whereby these cells had much higher EC50 than the control cells. When exposed to chemotherapeutics, L46W appeared to reduce the cytoprotection. The oxidation rate of liposomes was significantly improved in the H81A mutant and slightly decreased in L46W where it mirrored the absorbance patterns of Mb. Lipid binding did not occur in L46W. Further investigation of the in-cell work conducted in this study, replicated in stable-transfected cell lines, would improve understanding of the role of cytoglobin in protecting cells from oxidative stress.