Apical release of base-labile fatty acyl groups commensurate with stimulation of glycoprotein sialosyl Lewis(a) secretion in colorectal carcinoma cells.
The rate of polarized secretion of a putative adhesion ligand, sialosyl Lewis(a) (19-9), by SW1116 colorectal carcinoma cells is stimulated at least 20-fold after pre-incubation with, and the incorporation of, retinoic acid (RA). In order to investigate the possible involvement of fatty acylation in the export of the epitope, purified ligands from carcinoma-cell membranes, membrane subfractions and media were analyzed during RA-induced secretion. Incorporation of radioactivity from (3H)palmitate into membrane subfractions and purified sialosyl Lewis(a) antigenic molecular species of M(r) > 150,000 (SiaLeams) was stimulated by RA treatment. Most of the intracellular lipid radioactivity which bound to solid-phase 19-9 antibody behaved chromatographically, either like ganglioside or like NH2 OH-labile acyl groups, but most of the (3H) bound to SiaLeams of post-incubation media behaved like base-labile fatty acyl groups, or free fatty acid. Release of base-labile lipid radioactivity after 3 hr (associated with antigen) was almost exclusively into the apical media of membrane inserts. Gas-liquid chromatography/mass spec. analyses of purified Sialeams revealed the presence of palmitate (16:0), as well as stearate (18:0) and oleate (18:1) fatty acyl groups. Our results suggest that fatty acylation of SiaLeams may be co-ordinated with alterations in glycosylation and participate in directing these molecules to the apical surface. Lipid analyses were consistent with ganglioside chaperonage of SiaLeams to the apical surface, where N-fatty-acylated gangliosides remain for the most part integrated into the bilayer, but some oxyester or thioester bonds may be cleaved to permit release of SiaLeams to the apical medium.
Liepkalns
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Department of Biochemistry (Biochemistry of Cellular Transport, CNRS), University of Paris XI, Orsay, France.
Eboue
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D
Kuksis
A
A
Beringer
T
T
Icard-Liepkalns
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C
D000215:Acylation; D002849:Chromatography, Gas; D015179:Colorectal Neoplasms / Q000378:metabolism*; D004591:Electrophoresis, Polyacrylamide Gel; D005227:Fatty Acids / Q000378:metabolism*; D005455:Fluorescent Antibody Technique; D006023:Glycoproteins / Q000378:metabolism; D006801:Humans; D016256:Lewis X Antigen / Q000378:metabolism*; D013058:Mass Spectrometry; D019308:Palmitic Acid; D010169:Palmitic Acids / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
D005227:Fatty Acids; D006023:Glycoproteins; D016256:Lewis X Antigen; D010169:Palmitic Acids; D019308:Palmitic Acid; D014212:Tretinoin