Possible role of glycolipid in development, cell growth regulation, and transformation.

1. A progressive branching of lacto-N-glycosyl carbohydrate chain linked to glycolipid and to band 3 protein has been observed during the development of fetal to adult human erythrocytes. A linear repeating structure of Gal beta 1 leads to 4GlcNac beta 1 leads to 3Gal was converted to a branched structure Gal beta 1 leads to 4GlcNac beta 1 leads to 3(Gal beta 1 leads to 4GlcNAc beta 1 leads to 6)Gal beta 1 leads to 4GlcNac. Some of the linear structure represents i-antigen, and some of the branched structure represents I-antigen. Such changes of carbohydrate structure in membrane coincide with the switch from fetal hemoglobin (HbF) to adult hemoglobin (HbA) synthesis, and may define the stage of differentiation in cellular function. 2) Cell-to-cell contact induces enhancement of a particular type of glycolipid synthesis (contact response). A mimic "contact response" of GM3 synthesis was observed when sparse growing culture was treated with the affinity purified anti-GM3 ganglioside Fab. The synthesis of GM3 ganglioside was enhanced severalfold, but not the synthesis of GM2, GM1, and GD1a. Growth of antibody-treated 3T3 cells was inhibited and showed reduced cell saturation density. Some cellular proteins which had specific affinity with glycolipids were released by ethidium bromide. Addition of such cellular proteins in 3T3 cell culture induced a reduction of cell saturation density. These results suggest that a particular glycolipid (contact-sensitive glycolipid) could be a receptor for a particular cell surface protein that may induce "contact inhibition." Some carbohydrate chains such as Gal beta 1 leads to #GalNAc beta 1 leads to 4Gal leads to R, which is common both to glycolipid and glycoprotein may be receptor growth stimulation from serum in vitro. Therefore, growth inhibition induced by anti-glycolipid Fab or by cell surface protein could be due to a block of the recepting growth stimulation through serum factors.