HNK‐1 carbohydrate synthesis in retinoic acid‐induced P19 cells

Sulfoglucuronyl carbohydrate (SGC) reactive with HNK-1 antibody are expressed on glycoproteins and on glycolipids (SGGLs) in the nervous system. The interaction of SGC with SGC-binding protein-1 (SBP-1) has been implicated in the regulation of neurite outgrowth and cell-migration during development. To define the cell-specific expression and function of SGC, SGC synthesis on glycoproteins and glycolipids was studied in embryonal carcinoma P19 cells after induction with retinoic acid (RA). With RA, P19 cells differentiate to neuron-like cells with axonal and dendritic processes. The uninduced cells express SSEA-1 glycoproteins, but are SGC negative. After RA, the induced neuronal population strongly expresses SGC-glycoproteins. The appearance of SGC is accompanied by a 16-fold up-regulation in the activity of GlcNAc-Tr (Lc3 synthase), which synthesizes the key intermediate LcOse3Cer, for lacto- and neolacto-glycolipids. Despite up-regulation of Lc3 synthase, the levels of SGGLs were not significantly up-regulated after RA induction. Instead, the levels of other neolactoglycolipids, such as SSEA-1 and disialosyl-nLcOse4Cer, were up-regulated. Treatment with RA also induced four fold higher synthesis of SBP-1, which was specifically localized in neuron-like cells along with SGC, similar to that in vivo. The results indicate that the induction of SGC in RA-treated P19 neuronal cells is mostly due to SGC on glycoproteins and not SGGLs. The coordinated induction of SBP-1 along with the SGC-glycoproteins in the same cells support the hypothesis that their interaction is important in neurite outgrowth.