NF1 gene loss of heterozygosity and expression analysis in sporadic colon cancer.

Colon cancer tumorigenesis is a multistep process of mutation accumulation in a number of oncogenes and tumour suppressor genes. NF1 gene protein, neurofibromin, acts as a tumour suppressor by turning the active form of Ras into an inactive form. This molecular switch has an important role in the control of the cell cycle and differentiation, and changes in Ras activity are present in many different cancers. This is the first study to investigate the role of NF1 in sporadic colon cancer. We investigated loss of heterozygosity (LOH) at the NF1 locus. Real time reverse transcription-polymerase chain reaction was used to determine NF1 mRNA expression in tumours and corresponding normal tissue. Expression of neurofibromin was analysed by immunohistochemistry. Relative ratio of NF1 mRNA type I and II isoform expression was also examined. LOH of the NF1 gene was detected in 20.7% of heterozygous samples. NF1 mRNA expression was significantly increased in tumour tissue compared with corresponding normal tissue (p = 0.04291). There was a statistically significant increase in NF1 type I isoform expression (p = 0.0005) in tumour tissue compared with corresponding normal colon tissue. NF1 isoform type II was predominantly expressed in normal tissue while the NF1 isoform type I prevailed in tumour samples. The transition from dominant expression of isoform type II in normal mucous tissue 15 cm away from the tumour to dominant expression of isoform type I in tumour tissue itself was detected. Total neurofibromin expression increased as tumours were more advanced but expression of wild-type neurofibromin remained the same. Our findings suggest that the NF1 gene may play a role in the development and progression of colon cancer and the NF1 gene may be a potential tumour marker and a new potential target for colon cancer therapy.