Regulation of Transmembrane Signaling by Ganglioside GM1 :

Abstract : Interaction of antibodies to ganglioside GM1 with Neuro2a cells was studied to investigate the role of GM1 in cell signaling. Binding of anti‐GM1 to Neuro2a cells induced the formation of 3H‐inositol phosphates (3H‐IPs) and elevated the intracellular Ca2+ concentration [Ca2+]i. The rise in [Ca2+]i was due to the influx of Ca2+ from the extracellular medium and release from intracellular Ca2+ pools. The Ca2+ influx pathway did not allow the permeation of Na+ or K+. The influx was inhibited by amiloride, a specific blocker of T‐type Ca2+, channels, whereas nifedipine and diltiazem, blockers of L‐type Ca2+ channels, did not have any effect. Thus, anti‐GM1 appears to activate a T‐type Ca2+ channel in Neuro2a cells. The intracellular Ca2+ release was inhibited by pretreatment of cells with neomycin sulfate, phorbol dibutyrate, and pertussis toxin (PTx), which also inhibited the 3H‐IP formation in Neuro2a cells. Addition of caffeine neither elevated the [Ca2+]i nor affected the anti‐GM1‐induced [Ca2+]i rise. The data reveal that the binding of anti‐GM1 to Neuro2a cells activates phospholipase C via a PTx‐sensitive G protein, which leads to formation of IPs and release of Ca2+ from inositol trisphosphate‐sensitive pool of endoplasmic reticulum. Anti‐GM1 also arrested the differentiation of Neuro2a cells in culture and significantly stimulated their proliferation. This stimulatory effect of anti‐GM1 on cell proliferation was blocked by amiloride but not by PTx, suggesting that the influx of Ca2+ was essentially required for cell proliferation. Our data suggest a role for GM1 in the regulation of transmembrane signaling events and cell growth.