New insights into early molecular events in colon cancer

For the first time, distinct gene expression profiles have been demonstrated in patients with colonic adenomas with low grade dysplasia. The detailed molecular analysis was made possible by laser mediated microdissection (LMM) of colonic crypts of normal and adenomotous colonic cryosections. This was followed by RNA arbitrarily primed polymerase chain reaction (RAP-PCR) and then use of cDNA expression arrays.

LMM was used to isolate colonic crypts of normal and adenomatous mucosa from six different patients. RAP-PCR was performed to screen mRNA populations and to generate hybridisation probes for cDNA expression arrays. Differential expression was then confirmed at the protein level by immunohistochemistry.

Upregulation of proliferation associated genes ras-oncogene related p21-rac1, mitogen activated protein kinase (MAPK) p38α and interferon γ receptor were found. Downregulation of apoptosis related genes (FAST kinase and p53) and thrombospondin 2 were also found. One of the pathways thought to be activated in the development of colonic tumours is RAS/MAPK pathway which plays an important role in the regulation of proliferation and transcription. This study showed that p21-rac1 and MAPK p38 may be candidate genes potentially involved in key mechanisms leading to colon cancer.

The combination of laser microdissection with RAP-PCR and cDNA expression to analyse adenomas with low grade dysplasia enables the understanding of gene expression of cells in their actual tissue environment. The technique offers further possibilities in histomolecular analysis and an understanding of the initial steps in development of colon cancer.