ALTERATION IN MUCIN GENE-EXPRESSION AND BIOLOGICAL PROPERTIES OF HT29COLON-CANCER CELL SUBPOPULATIONS

Previous studies from our laboratory have shown that HT29 cells select ed by adaptation to methotrexate (HT29-MTX) express mature mucins that differ in their immunoreactivity to antibodies against gastric mucin and in the level of one of two major gastric mucin MUC5AC (MUC5) mRNA compared with parental HT29 cells. In this study, we examined the expr ession of another major gastric mucin, MUC6 mRNA, as web as that of MU C2, -3 and -5 mRNAs in HT29-MTX cells. We also exmained their relation ship to mucin-related antigen expression and biological properties of the cells such as adhesion to matrigel and E-selectin and in vitro inv asiveness, liver colonising activity and degree of differentiation of nude mouse xenograft. Slot blot and Northern analysis revealed markedl y increased levels of MUC5 mRNA but no change in MUC6 mRNA level in HT 29-MTX cells compared with parental HT29 cells which express barely de tectable levels of MUC6 mRNA. A nuclear run-on study showed that MUC5 mRNA was up-regulated at the transcriptional level. The marked increas e in MUC5 mRNA was associated with a significant increase in the expre ssion of human gastric mucin and apomucin antigens in HT29-MTX cells. When the adhesive capacity of two cell lines was compared, HT29-MTX ce lls showed significantly lower adhesion to E-selectin consistent with their lower expression of sialyl Le(x) and sialyl Le(a) antigens compa red with HT29 cells. HT29-MTX cells also showed lower adhesive capacit y to matrigel than HT29 cells. Interestingly, HT29-MTX cells exhibited significantly decreased liver colonisation capacity in nude mice foll owing splenic vein injection. Furthermore, nude mouse xenograft tumour s produced by HT29-MTX cells exhibited a significantly greater degree of differentiation, consisting of mucin-secreting glands than those pr oduced by HT29 cells. In conclusion, these results indicate a shift of predominantly colonic-type mucins to the gastric type, specifically t he surface epithelial cell type (MUC5) but not the mucous neck cell or antral gland type (MUC6) in HT29-MTX cells and strongly suggest that altered regulation of mucin genes and the degree of differentiation in cancer cells may be responsible for the altered biological behaviour of these cells. Copyright (C) 1996 Elsevier Science Ltd