INDUCTION OF DIFFERENTIATION OF COLON CANCER CELLS

Sodium butyrate induces a more differentiated and less tumorigenic phenotype of HT-29 human colon carcinoma cells in vitro. We have cloned a cDNA library of sequences expressed in HT-29 cells and have developed a computerized scanning and image processing system to quantitate the relative level of expression of each of 4000 members of this library in tissue biopsies or cells in culture. We will also produce two new more extensive cDNA libraries from cell lines which stably differentiated during treatment of HT-29 cells with butyrate. These cell lines, 16E and 19A, each exhibit properties of different lineages of colon cell differentiation (mucin secretion and vectorial transport), and these properties continue to be expressed in the absence of inducer. These libraries will be produced in the bacterial expression vector Lambdagt11. Utilizing all three libraries and the computer-linked methodology we have developed, we will identify sequences which are altered in expression during treatment with sodium butyrate, the time course of such alterations and association with acquisition of various traits characteristic of a more differentiated phenotype, the time necessary for commitment to such changes during butyrate treatment, and the stability and reversal of such changes after withdrawal of butyrate. In a continuation and extension of work we have done on expression of proto-onc sequences in the stably differentiated cell lines, we will investigate the expression of proto-onc sequences of the myc and ras gene family in these experiments. We will also determine the time course of change in gene expression in two other human colon carcinoma cell lines, SW480 and SW1116, during butyrate treatment in order to determine if similar changes are consistently observed in these other lines. Finally, a monoclonal antibody which recognizes the peptide of colon mucin will be used to isolate this mRNA from one of the Lambdagt11 libraries, and subsequently study the effects of sodium butyrate on expression of this gene in the experiments outlined.