Retinoic-acid-induced augmentation of molecular species carrying sialosyl Lewis(a) antigen in colorectal-carcinoma cell cultures.

In order to study the effects of vitamin-A metabolites on long-term carcinoma-antigen secretion, colorectal-carcinoma cells SW1116 were cultured on membrane filters in totally synthetic media with 0 to 2.6 microM retinoic acid (RA). RA altered cell division, cell size and soluble-sialosyl Le(a) (S-Le(a) secretion and S-Le(a) accumulation within cells and apical-membrane domains. Cultures treated with RA for 10-12 days grew to lower cell densities (60% of controls) and contained more protein per cell (140% of controls). RA treated cells also had 5-fold higher levels of S-Le(a) in cells and secreted 9-fold more S-Le(a) into culture media assayed per 24 hr by (ELISA) 19-9 monoclonal antibody binding. As total media S-Le(a) increased, polarity of non-lipid S-Le(a) antigen secretion increased toward the interior (apical) media. High-performance thin-layer immunobinding showed that ganglioside S-Le(a) was higher in RA-fed cells, but could not be detected in apical media of RA-fed or control cells after 24 hr. Western blots indicated that non-lipid sialosyl Lewis(a) was bound to 150- to 180-kDA molecular species principally in cells, but 210- to 300-kDa molecular species appeared in the non-lipid extract of media. Thus, the above RA alterations, monitored by 3 immunochemical techniques, include up to 9-fold stimulation of "constitutive" 150- to 300-kDa sialosyl-Lewis(a) secretion, but ganglioside Lewis(a) is sorted differently and retained by apical membranes.