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

Highly differentiated epithelial populations (36% mucin-producing cell s; sixfold increase in alkaline phosphatase activity; development of f lat, substrate-adherent, entero-cytic foci) were induced upon in vitro exposure of HT-29di human colon carcinoma cells to sodium butyrate (N aB). 1,25-dihydroxyvitamin D-3 [1,25-(OH)(2)D-3] (10(-7) M) and the io nophore A23187 (0.5 mu M) significantly augmented (two to threefold) N aB-induced HT-29di differentiation, whereas 1,25-(OH)(2)D-3 or A23187 alone were not effective. Induction reflected specific changes in prot ein abundance, involving, most notably, a differentiation-associated i ncrease in the expression and substrate-deposition of a 47-kDa protein with pI/mw two-dimensional map coordinates and immunochemical propert ies 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' differe ntiation, although NaB-induced goblet cell and enterocytic maturation was Ca2+-dependent. The inability of 1,25-(OH)(2)D-3, A23187 or modula ted Ca2+ levels. alone (i.e., in the absence of NaB) to effect differe ntiation of HT-29di cells and the Ca2+-dependence of the NaB response indicate that NaB and Ca2+ act co-operatively to induce colonic epithe lial maturation in vitro.