Growth-inhibition of ht29 cells exposed to N-methylformamide correlates with altered expression of alpha-6/beta-4 integrin

The anticancer agent N-methylformamide (NMF) suppresses the expression of the c-myc proto-oncogene in human colon carcinoma cells while increasing the doubling time and reducing tumorigenicity in these cells. However, the mechanism by which NMF exerts its effects has remained unclear. We compared the expression of c-myc and of other growth-regulated genes (p53, beta-actin) to that of the H3 histone gene, which is specifically expressed in S-phase cells, in HT29 human colon carcinoma cells maintained in vitro or in nude mice. The growth fraction of the cell populations in the presence or absence of NMF was also evaluated at different days of growth by flow cytometric analysis. To assess whether prolonged exposure to NMF might induce a different phenotype in human carcinoma cells, the expression of alpha6, beta1, and beta4 integrin subunits were evaluated. The data indicate that NMF treatment induces a reduction in the growth fraction of HT29 colon carcinoma cells accompanied by a reduction in c-myc, H3 histone, p53, and beta-actin gene expression, and that prolonged exposure to NMF induces elevated expresssion of alpha6/beta4 integrin receptor, These data suggest that NMF-induced reduction of the proliferative capacity supports a different 'maturation status' of colon carcinoma cells which is defined by an elevated expression of the alpha6/beta4 integrin.