Absence of FHIT expression is associated with apoptosis inhibition in colorectal cancer

Abstract

The fragile histidine triad (FHIT) gene, a candidate tumor suppressor gene located at 3p14.2, has been shown to be involved in the carcinogenesis of many human tissues, including digestive tract tissues. However, the expression and the role of the FHIT in the initiation and the development of the colorectal cancer (CRC) are poorly understood. We have shown that the FHIT gene exhibits significantly decreased expression in human CRC compared to colorectal adenoma and normal colorectal tissue by tissue microarray (TMA). The positive rate of FHIT gene expression in normal colorectal tissue, adenoma and adenocarcinoma were 93.75%, 68.75% and 46.25%, respectively. We show this decreased expression to be significantly correlated with the progression of colorectal carcinoma (P<0.05) as well as with differentiation and lymph node metastasis (P<0.05). We detected two somatic alterations in the FHIT gene in human CRC. The presence of this mutation correlated significantly with decreased FHIT expression in the human CRC. In our present study we tested the hypothesis that the decreased FHIT expression resulted in apoptosis inhibition associated with abnormal expression of apoptosis related proteins. To test this hypothesis we did a series of experiments. In the first test, we assessed apoptosis status using a standard TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick-end-labeling) assay by comparing FHIT-positive CRC vs. FHIT-negative CRC. In the second experiment, the protein expression of the FHIT and other apoptosis related proteins (Bax, Bcl-2 and Survivin) were measured in human CRC by TMA. Our combined results demonstrate the mutation in the FHIT gene significantly reduced FHIT expression in human CRC. Both TUNEL and TMA experiments demonstrated significantly inhibited apoptosis by down-regulation of Bax and the up-regulation of Survivin and Bcl-2. Collectively, these studies identify the mechanism by which an important tumor suppressor gene, FHIT is inactivated specifically in human CRC contributing to our understanding of the mechanism of colorectal carcinogenesis.