GROWTH AND INTESTINAL DIFFERENTIATION ARE INDEPENDENTLY REGULATED IN HT29 COLON-CANCER CELLS

The polar-planar compound hexamethylene bisacetamide (HMBA) can inhibi t HT29 colon carcinoma cell growth and induce a more benign phenotype, as defined by decreased anchorage-independent clonogenicity, loss of a cell surface malignancy marker, and decreased in vivo tumorigenicity . The principle aim of this study was to determine whether HMBA's effe cts on HT29 cell growth and biologic behavior correlate with effects o n intestinal differentiation. Parallel studies were performed with sod ium butyrate (NaBT), a potent inducer of intestinal differentiation. H T29 cell growth, proliferation, and markers of intestinal differentiat ion were assayed after short- and long-term treatment with HMBA, NaBT, or the combination. Both 5 mM HMBA and 5 mM NaBT were potent inhibito rs of monolayer growth; in combination their effects were nearly addit ive. Inhibition of DNA synthesis was detectable within 6 h of treatmen t and was preceded by down-regulation of c-myc expression. Soft agar c lonogenicity was also decreased by 90%, >99%, and >99% by HMBA, NaBT, and the combination, respectively. Despite these parallel effects on g rowth and in vitro markers of a benign phenotype, effects on intestina l differentiation were discordant. NaBT induced significant increases in membrane-associated alkaline phosphatase activity, cytosolic mucin content, PAS(+)/diastase-resistant cells, and ultrastructural evidence of intestinal cell differentiation. HMBA not only failed to induce ma rkers of intestinal differentiation, but attenuated NaBT's effects whe n used in combination. These data suggest that growth and intestinal d ifferentiation may be independently regulated in HT29 cells. They also suggest that expression of intestinal markers of differentiation is n ot a prerequisite for the acquisition of a more benign phenotype. (C) 1994 Wiley-Liss, Inc.