Aberrations in the Retinoblastoma susceptibility gene in tumours from South Africa oesophageal cancer patients

Abstract

Little is known about the genetic events occurring in oesophageal cancer and very few studies have been undertaken to analyse oesophageal tumours from South African patients in this regard. Inactivation of numerous tumour suppressor genes, including the Rb gene, has been implicated in oesophageal tumourigenesis in different populations. This study had two objectives. The first was to develop a procedure for the simultaneous extraction of DNA and RNA from small (ca. 25mg) oesophageal biopsy samples. The procedure developed here has proven to be rapid, cost effective and consistently produced excellent yields of high-quality DNA and RNA. It has to be determined, however, whether long-term storage affects the integrity of the isolated RNA. The second and primary objective of this study was to determine whether the Rb gene is involved in oesophageal tumourigenesis in South African patients. Loss of Heterozygosity analysis using a VNTR marker in intron 20 and a microsatellite marker in intron 4 of the Rb gene revealed that Rb-allelic loss had occurred n 50% of the thirty-three patients analysed. Furthermore, microsatellite instability was demonstrated at the intron 4 marker in 15% of the patients analysed. Mutation screening of exons 17 and 21 of the Rb gene, frequently mutated in oesophageal tumours from Chinese patients, in twenty samples using the mutation screening techniques of SSCP and heteroduplex analysis, followed by DNA sequencing of putative positives, revealed no positive mutations. However, the high percentage of allelic loss found suggests that the /lb gene is inactivated in the progression of South African oesophageal tumours. Furthermore, the microsatellite instability suggests that defective DNA repair may also play a role in oesophageal tumourigenesis.