Cytoglobin, the Newest Member of the Globin Family, Functions as a Tumor Suppressor Gene

Abstract

Cytoglobin (CYGB) is a recently discovered vertebrate globin distantly related to myoglobin with unknown function. CYGB is assigned to chromosomal region 17q25, which is frequently lost in multiple malignancies. Previous studies failed to detect evidence for mutations in the CYGB gene. Recent studies provided preliminary evidence for increased methylation of the gene in lung cancer. Our study was aimed at investigating the role of CYGB as a tumor suppressor gene. By nested methylation-specific DNA sequencing analysis of lung and breast cancer cell lines and bronchial and mammary epithelial cell lines, we identified that methylation of a 110-bp CpG-rich segment of the CYGB promoter was correlated with gene silencing. We specifically targeted this sequence and developed a quantitative methylation-specific PCR assay, suitable for high-throughput analysis. We showed that the tumor specificity of CYGB methylation in discriminating patients with and without lung cancer, using biopsies and sputum samples. We further showed the tumor specificity of this assay with multiple other epithelial and hematologic malignancies. To show tumor suppressor activity of CYGB, we performed the following: (a) RNA interference-mediated knockdown of CYGB gene on colony formation in a CYGB expressionpositive lung cancer cell line, resulting in increased colony formation; (b) enforced gene expression in CYGB expressionnegative lung and breast cancer cell lines, reducing colony formation; and (c) identification of potential proximate targets down-stream of the CYGB genes. Our data constitute the first direct functional evidence for CYGB, the newest member of the globin family, as a tumor suppressor gene.

Cytoglobin Is Expressed in the Vasculature and Regulates Cell Respiration and Proliferation via Nitric Oxide Dioxygenation

“…The function of cytoglobin is unknown with recent studies suggesting that it acts as a tumor suppressor and protects against free radical-induced tissue injury (27,28). Biochemical studies have focused mainly on the mechanism by which diatomic ligands including NO bind and react with cytoglobin (21,29,30 ) cytoglobin, a reaction that is common to many members of the globin family (21).…”

Cytoglobin is upregulated by tumour hypoxia and silenced by promoter hypermethylation in head and neck cancer

“…The significance of such studies may not be only in the field of basic science, as the modulation of HIF1A is currently a focus for the development of novel radiosensitising drugs. The ongoing controversy of the role of CYGB has been recently highlighted by recent suggestions of its function as a tumour suppressor gene in NSCLC (Shivapurkar et al, 2008) and HNSCC , and as a prospective gene therapy (Lv et al, 2008) in the prevention of hepatocellular carcinoma after liver cirrhosis.…”

“…Furthermore, CYGB expression has recently been shown by us to be significantly downregulated in 54% sporadic non-small cell lung cancer (NSCLC) in comparison with surrounding 'normal' tissues . The potential utility of CYGB promoter methylation as a molecular biomarker in NSCLC (Shivapurkar et al, 2008) and HNSCC (Shaw et al, 2007) has also been explored. Tumour suppressor activity of CYGB has recently been shown in NSCLC and breast cancer cell lines (Shivapurkar et al, 2008).…”

“…The potential utility of CYGB promoter methylation as a molecular biomarker in NSCLC (Shivapurkar et al, 2008) and HNSCC (Shaw et al, 2007) has also been explored. Tumour suppressor activity of CYGB has recently been shown in NSCLC and breast cancer cell lines (Shivapurkar et al, 2008). Exactly what function the Cygb protein may have in aerodigestive tract squamous malignancy has not yet been elucidated.…”

Cytoglobin, a Novel Member of the Globin Family, Protects Kidney Fibroblasts against Oxidative Stress under Ischemic Conditions

“…8 The importance of the biological role of Cygb is emphasized by the high degree of sequence conservation among vertebrate globins, with mouse and human Cygb differing in only 4.7% of amino acids. 5 Although various functions have been proposed, including oxygen storage, 8 radical scavenging, 9 -11 collagen synthesis, 7,12 tumor suppression, 13 and cell respiration, 14 these were derived from in vitro studies, and no Cygb gene-manipulated animal experiments have been reported. Therefore, the biological role of Cygb in vivo remains elusive.…”