Cytoglobin is important in the progression of oral squamous cell carcinoma but the molecular and cellular basis remain to be elucidated. In the current study, we develop a new cell model to study the function of cytoglobin in oral squamous carcinoma and response to cisplatin. Transcriptomic profiling showed cytoglobin mediated changes in expression of genes related to stress response, redox metabolism, mitochondrial function, cell adhesion, and fatty acid metabolism. Cellular and biochemical studies show that cytoglobin expression results in changes to phenotype associated with cancer progression including: increased cellular proliferation, motility and cell cycle progression. Cytoglobin also protects cells from cisplatin-induced apoptosis and oxidative stress with levels of the antioxidant glutathione increased and total and mitochondrial reactive oxygen species levels reduced. The mechanism of cisplatin resistance involved inhibition of caspase 9 activation and cytoglobin protected mitochondria from oxidative stress-induced fission. To understand the mechanism behind these phenotypic changes we employed lipidomic analysis and demonstrate that levels of the redox sensitive and apoptosis regulating cardiolipin are significantly up-regulated in cells expressing cytoglobin. In conclusion, our data shows that cytoglobin expression results in important phenotypic changes that could be exploited by cancer cells in vivo to facilitate disease progression.

BackgroundFibrosis is a physiological response to cellular injury in the liver and is mediated by the activation of hepatic stellate cells resulting in the replacement of hepatocytes with extracellular matrix comprised principally of collagen 1 to form a hepatic scar. Although the novel hexaco-ordinated globin cytoglobin was identified in activated hepatic stellate cells more than 10 years ago, its role in stellate cell biology and liver fibrosis remains enigmatic.ResultsIn the current study, we investigated the role of different extracellular matrix proteins in stellate cell proliferation, activation (alpha smooth muscle actin expression and retinoic acid uptake) and cytoglobin expression. Our results demonstrate that cytoglobin expression is correlated with a more quiescent phenotype of stellate cells in culture and that cytoglobin is regulated by the extracellular matrix through integrin signalling dependent on activation of focal adhesion kinase.ConclusionsAlthough further studies are required, we provide evidence that cytoglobin is a negative regulator of stellate cell activation and therefore may represent a novel target for anti-fibrotic treatments in the future.Electronic supplementary materialThe online version of this article (doi:10.1186/s13069-015-0032-y) contains supplementary material, which is available to authorized users.

Cytoglobin has been implicated in a range of pathological conditions including fibrosis and cancer, where cytoglobin expression is linked to hypoxia- and drug-resistance. One disease where there is evidence of a role for cytoglobin is head and neck squamous cell carcinoma, a disease with a poor prognosis and where clinical resistance to platinum-based drugs is common. In the current study, we demonstrate that 3D-culture of head and neck cancer cells (PE/CA-PJ41, Liv-22K) and normal oral keratinocyte cells (NOK-hTERT) results in changes in sensitivity to cisplatin cytotoxicity compared to 2D-cultures. Relative to 2D-cultures, 3D-cultures of PE/CA-PJ41 and NOK-hTERT cells demonstrated increased cisplatin resistance. In contrast, 3D-cultures of Liv-22K cells were more sensitive to cisplatin. Evidence for cisplatin genotoxicity was observed in the form of GADD45A activation in PE/CA-PJ41 cells but not the other two cell types investigated. Furthermore, DNA-strand breaks were also detected by the alkaline comet assay in PE/CA-PJ41 cells although levels were not significantly affected by 3D-culture. Cytoglobin expression levels were elevated by 3D-culture in all three cell lines investigated and there were also changes in expression of genes related to cell division (MKI57, GJB6), cell adhesion (CDH1), stress response (NFkB, NQO1) and apoptosis (Casp3) but these changes were cell line specific. We also observed consistent transcriptional activation of HIF1a in 3D-cultures of all three cell lines, suggestive of hypoxic conditions in spheroids. In support of a direct role of hypoxia in cytoglobin induction, the HIF1a stabiliser cobalt chloride also induced cytoglobin expression in spheroids. Transcriptomic profiling of PE/CA-PJ41 cells over-expressing cytoglobin identified 121 differentially regulated genes, when cells were cultured under hypoxic conditions. Major changes identified included, upregulation of G1/S cell cycle regulation as well as wnt- and RhoGTPase-signalling pathways. In conclusion, 3D-cultures are a useful model to further study the biological function of cytoglobin in head and neck cancer and we provide evidence that further supports a role for cytoglobin in hypoxia-dependent cellular proliferation and phenotypic changes that could contribute to cisplatin resistance in vivo.