A microarray approach to detect chromosome 18 deletions in colorectal cancer

Conventional techniques have identified Chromosome 18 as having the highest frequency of deletion in colorectal cancer (CRC); it is the likely site of a causative tumour suppressor gene inactivated by deletion in CRC carcinogenesis. These techniques have not however accurately identified the deleted region that is likely to contain the causative tumour suppressor gene. A high-resolution technique, microarray comparative genomic hybridisation (CGH) was utilised, directly comparing normal DNA against tumour DNA for differences. The microarray was designed and constructed to target chromosome 18 at the highest resolution with a complete 'tiling path' of 860 overlapping BAC clones to represent this region. The accuracy of the constructed micro array and comparative genomic hybridisation technique was confmned by analysis of normal against normal DNA and a cell line with a known large deletion and amplification. Micro array CGH wa.s performed on 47 cell lines and 69 primary cancers, identifying deletions in 81% of the cell lines and 55% of the primary cancers. Three minimal regions of deletion were identified, spanning only 371kb to 3.5 Mh. Two of the minimal regions of deletion were common to 92% of all deletions in the cell lines and 79% of primary cancers. The other minimal region of deletion was common to 92% of all deletions in the cell lines and 63% in the primary cancers. Fluorescent in situ hybridisation (FISH) confirmed the presence and location ofthese minimal deletions. The 3 minimal regions of deletion contained only 8 genes; including 3 strong candidate tumour suppressor genes, SMAD 7, CADHERIN 7 and CADHERIN 19. SMAD 7 is part of the tumour growth factor (TGF) cascade, a potent inhibitor of cell growth and inducer of apoptosis, important in colorectal carcinogenesis. The CADHERINS are involved in intercellular adhesion, disturbance of which is a prerequisite for invasion and metastasis of tumour cells.EThOS - Electronic Theses Online ServiceGBUnited Kingdo