The influence of type I collagen on the growth and differentiation of the human colonic adenocarcinoma cell line HT-29 in vitro

HT-29 Human colonic adenocarcinoma cells when grown on a plastic substratum were anaplastic in appearance and failed to express any morphological or biochemical features that were characteristic of intestinal differentiation. Growth of HT-29 cells subcutaneously in the flank of immune deprived mice gave rise to morphologically heterogeneous tumors which were poorly differentiated but contained approximately 11% of cells with an intestinal phenotype: these showed features typical of cell polarization with well-developed microvilli, tight junctional complexes and desmosomes between adjacent cells. The transfer of cells from plastic onto either a fixed (designated 'non-released') or floating (designated 'released') type I collagen gel induced some morphological features typical of intestinal differentiation; for example goblet-like cells were observed after 9 days, but biochemical markers of differentiation were expressed only modestly. The continued subculture of HT-29 cells on collagen type I gels, which were either attached to the plastic or floating in the medium, induced some morphological features of intestinal differentiation and changes in the activity of brush border-associated enzymes. Alkaline phosphatase activity was enhanced from 1.3 x 10(-3) mumoles/mg/min for cells cultured on plastic substrata to 2.1 x 10(-3) mumoles/mg/min when gels were non-released, and 2.9 x 10(-3) mumoles/mg/min when gels were released after 12 days of culture. This was confirmed by electron microscopical visualization of alkaline phosphatase activity. Elevated levels of aminopeptidase activity were also observed on day 12 (plastic = 26 milliunits/mg; non-released gel = 41 milliunits/mg; released gel = 36 milliunits/mg). Similarly, changes occurred in the secretion of carcinoembryonic antigen from 0.96 x 10(-2) micrograms/mg/48 hours by cells cultured on plastic to 2.3 x 10(-2) micrograms/mg/48 hours by cells cultured on floating collagen gels. The effects of permitting HT-29 cells to undergo polarization were tested by culture on inert filter inserts: morphological features of intestinal differentiation were observed although this did not occur until after 21 days. These studies show that optimization of the growth conditions of anaplastic cells in vitro may provide cultures more representative of the tumor in vivo. This model system may be useful for cell biological and pharmacological studies of colon carcinoma.