Inflammation-associated genes and genetic variations in colorectal cancer
Sammanfattning: Colorectal cancer is a major cause of morbidity and mortality around the world, each year affecting about one million individuals worldwide. The disease is characterized by an accumulation of genetic alterations, and a sequence of events leading to the development of an invasive and metastasising tumour. Chronic or dysregulated inflammation may contribute to tumour initiation and progression via the release and activity of various mediators – e.g. cytokines, prostaglandins, inducible nitric oxide synthase (NOS2), matrix metalloproteinases (MMPs), and vascular endothelial growth factors (VEGF). In the present thesis, genes and genetic alterations controlling these events were analysed and discussed within the context of colorectal cancer.Prostaglandins, being generated from arachidonic acid in reactions dependent on cyclooxygenases (COX-1, COX-2), have been implicated in carcinogenesis of many organs. Since the quite recent characterization of the terminal and specific prostaglandin synthases, which act downstream of COX enzymes, the search for molecular targets which selectively suppress individual prostanoids has been intensified. In papers I-II, the role and regulation of inducible prostaglandin E2 (PGE2) synthase - mPGES-1 - were explored within the context of intestinal cancer. mPGES-1 was genetically deleted in the ApcMin/+ mouse - yielding marked suppression of PGE2 generation in intestinal and tumour tissue. However, a shift towards enhanced generation of non-PGE2 prostanoids was observed in mPGES-1 knock out mice, and these mice developed more and larger instestinal tumours. These results therefore indicate that targeting mPGES-1 may paradoxically promote tumourigenesis, most likely by secondary effects on other potentially pro-tumoural mediators. We also explored the relation of the commonly mutated APC gene and mPGES-1 in colon tumour cells, and found that high expression of mPGES-1 was associated with the presence of wild type APC. Rather than by regulating putative β-catenin/Tcf binding sites of the mPGES-1 promoter, APC seems to influence the stabilisation of mPGES-1 mRNA.In papers III-V, the possible contribution of variations in regulatory regions of genes encoding NOS2, MMPs, and VEGF, was assessed in populations of colorectal cancer patients and healthy control individuals. A single nucleotide insertion (1G/2G) at -1607 upstream the transcription start site of the MMP-1 gene was identified to be a susceptibility factor for colorectal cancer development, although no relation with disease characteristics was observed. Except for a rather uncommon combination of two individual polymorphisms of the VEGF gene, investigated genetic variations of VEGF, other MMPs, and NOS2, were not associated with colorectal cancer susceptibility or clinicopathological characteristics. We therefore suggest that other molecular events play more significant roles for the dysregulation of these genes in colorectal tumours.In summary, accumulating evidence, including the results here presented, suggest significant albeit complex roles of inflammation-induced genes and mediators in colorectal tumourigenesis. The present results may aid in identifying or excluding potential biomarkers and drug targets within cancer-related inflammation.
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