Expression of plasminogen activator inhibitor type 1 (PAI-1) by HT-29di human large bowel carcinoma cells is modulated as a function of epithelial differentiation

Abstract

Highly differentiated epithelial populations (36% mucin-producing cells; sixfold increase in alkaline phosphatase activity; development of flat, substrate-adherent, entero-cytic foci) were induced upon in vitro exposure of HT-29di human colon carcinoma cells to sodium butyrate (NaB). 1,25-dihydroxyvitamin D 3 [1,25-(OH) 2D 3] (10 −7 M) and the ionophore A23187 (0.5 μM) significantly augmented (two to threefold) NaB-induced HT-29di differentiation, whereas 1,25-(OH) 2D 3 or A23187 alone were not effective. Induction reflected specific changes in protein abundance, involving, most notably, a differentiation-associated increase in the expression and substrate-deposition of a 47-kDa protein with pI/mw two-dimensional map coordinates and immunochemical properties identical to that of plasminogen activator inhibitor type 1 (PAI-1), a major regulator of the pericellular proteolytic cascade. Culture of HT-29di cells in medium of either high (2.5 mM) or low (0.25 mM) Ca 2+ concentration did not affect the incidence of ‘spontaneous’ differentiation, although NaB-induced goblet cell and enterocytic maturation was Ca 2+-dependent. The inability of 1,25-(OH) 2D 3, A23187 or modulated Ca 2+ levels alone (i.e., in the absence of NaB) to effect differentiation of HT-29di cells and the Ca 2+-dependence of the NaB response indicate that NaB and Ca 2+ act co-operatively to induce colonic epithelial maturation in vitro.