Retinoic‐acid‐induced augmentation of molecular species carrying sialosyl lewisa antigen in colorectal‐carcinoma cell cultures

Abstract
In order to study the effects of vitamin-A metabolites on long-term carcinoma-antigen secretion, colorectal-carcinoma cells SWIII6 were cultured on membrane filters in totally synthetic media with 0 to 2.6 μM retinoic acid (RA). RA altered cell division, cell size and soluble-sialosyl Lea (S-Lea) secretion and S-Lea 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-Lea in cells and secreted 9-fold more S-Lea into culture media assayed per 24 hr by (ELISA) 19-9 monoclonal antibody binding. As total media S-Lea increased, polarity of non-lipid S-Lea antigen secretion increased toward the interior (apical) media. High-performance thin-layer immunobinding showed that ganglioside S-Lea 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 Lewisa 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-Lewisa secretion, but ganglioside Lewisa is sorted differently and retained by apical membranes.