Oesophageal Cancer Research – Prof Monique Zaahl
Title of the project
Molecular characterisation of the promoter region of genes of the iron metabolism pathway in Oesophageal Cancer patients
Iron is a trace element that is required by almost every living organism. It is used in a variety of cellular functions, and as a result, changes in iron homeostasis within the body can have important clinical consequences. A combination of factors such as nutrition, environment and genetics play a role in the control of iron levels within an individual. Normal iron levels within the body are required for a variety of metabolic functions, including haemoglobin synthesis, immune system functioning and anti-tumour activity. Iron is an essential cofactor in heme and nonheme-containing enzymes, but ferrous iron (Fe2+) generates free radicals that can damage DNA strands and change the structure of the DNA, leading to the development of cancer. In normal circumstances, loss of iron from a target cell results in anti-tumour activity, which is reduced when there is excess iron present. For this reason, iron can be said to have an indirect carcinogenic effect on cells. Increased levels of iron can also inhibit the growth of tumouricidal-activated macrophages. Homeostatic regulation of ferrous iron levels is important for physiological processes while preventing the toxicity associated with iron overload, which can lead to other disorders.
The role of iron as a potential risk factor for the development of OC was previously described in Black South African patients who had dietary iron overload as a result of drinking traditional beer brewed in non-galvanised steel drums. The involvement of iron in the development of other cancers such as liver cancer has also been previously studied and attributed to dietary iron overload. Further studies using rat models showed that iron supplementation could be indicated as a risk factor for developing OC. Studies have also shown that an increase in dietary iron plays a role in the development of OC in groups other than the Black South African population.
OC occurs in high frequencies around the world and is one of the leading causes of cancer-related deaths worldwide. It has a particularly high incidence in areas of France, Japan, China, Iran, Italy and South Africa. Oesphageal cancer is common in Africa, particularly in the Transkei region of South Africa. Environmental factors such as smoking, alcohol consumption, dietary factors, nitrosamines, mycotoxins and infections such as the human papillomavirus are thought to play a role in the development of the disease, but these factors can vary markedly from one geographic region to another.
The human genome is a system regulated at many different levels. Transcriptional regulation is the first, and arguably the most important, step in the process of gene expression. This process is governed by the presence of specific cis-regulatory regions (cis-motifs) residing within the promoter of that gene and the functional interactions between the products of specific regulatory genes (transcription factors-TFs) and these cis-motif. A large number of cis-elements have been associated with specific expression patterns in response to constitutive, developmental, tissue-specific, hormonal and environmental regulation. The promoter regions of genes are responsible for regulating the level of gene activity on different tissues, at certain stages during development and/or in response to a variety of conditions that may affect the cell.
Understanding gene regulation and the subsequent analysis of cis-motifs in promoters can be a demanding endeavour. It is therefore necessary to explore new technologies such as the use of various bioinformatic tools to attempt to formulate putative predictions on how specific cis-motifs residing in these regions may influence the expression patterns of specific genes or groups of genes.
Most genetic disorders of iron metabolism are caused by iron overload rather than iron deficiency. The accumulation of excessive amounts of iron in the body results in damage to various organs such as the liver, pancreas, heart, and other endocrine organs. It is therefore clear that iron is essential for many cellular pathways and needs to be regulated, in order to avoid the toxicity associated with excess iron. An excess of iron has previously been demonstrated to result in increased tumourigenesis, oesophageal injury and inflammation. We aim to characterize the promoter region of 16 genes involved in the iron metabolism pathway, in Black South African patients with Oesophageal Cancer (OC). This will be achieved by a comprehensive in silico analysis approach to identify specific motifs potentially involved in the regulation of the genes involved in this pathway. Functional analysis of these regions will then be performed in order to elucidate the specific mechanisms of gene regulation. The functional significance of previously identified variants, associated with OC, will be investigated using luciferase reporter gene constructs. In silico analyses have revealed a conserved genomic region within 9 of the 16 genes investigated. Transcription factors of interest within this region were selected on the basis of their known involvement in transcriptional regulation, tissue specificity and involvement in the iron regulatory pathway. In vitro analysis of the selected transcription factors will be performed in order to attempt to elucidate their role in the regulation of the 9 iron genes under investigation. Elucidation of the role of iron in cancer development and how these genes are regulated should contribute to better treatment and counseling of these cancer patients.
- N.J. Strickland, T. Matsha, R.T. Erasmus and M.G. Zaahl, Molecular analysis of Ceruloplasmin in a South African cohort presenting with oesophageal cancer, Int. J. Cancer: 131, 623–632 (2012) © 2011 UICC