Stimulation of Transglutaminase Activity by GM1‐Ganglioside and α‐Sialylcholesterol in Superior Cervical and Nodose Ganglia Excised from Adult Rat

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Abstract
Changes in transglutaminase (TG) activity in superior cervical ganglia (SCG) and nodose ganglia (NG) excised from adult rats were examined following application of selected membrane transport‐altering agents, including GM1‐ganglioside (GM1) and α‐sialylcholesterol (α‐SC). Although TG activity of freshly dissected SCG and NG was relatively low, it increased gradually during 30 min of incubation, and it stayed at this elevated level for 2 h. Addition of α‐SC at its maximal effective concentration, 20 μM, stimulated TG activity more than eightfold in SCG and more than twofold in NG by 30 min. Addition of GM1 at its most effective concentration, 5 nM, had similar effects, but of lesser magnitude. Cydoheximide, a potent inhibitor of protein biosynthesis, did not affect the GM1‐or α‐SC‐evoked increases in ganglionic TG activity, suggesting that enzyme activation rather than synthesis of new enzyme was occurring. The stimulation of TG activity in both ganglia caused by either GM1 or α‐SC was associated with a decrease in Km and an increase in Vmax values. Addition of cholera toxin B. which specifically masks the oligosaccharide chain of GM1. reduced the GM1‐induced increase in TG activity by approximately 60% in SCG and 88% in NG. The α‐SC‐induced increase in TG activity was only partially mimicked by free cholesterol. Although application of either dibutyryl cyclic AMP or dibutyryl cyclic GMP produced little change in TG activity of either ganglion, phorbol ester clearly inhibited the enzymic activity. Because TG is a calcium‐dependent enzyme, we measured 45Ca2+ influx into either ganglion, and found that it was reduced by GM1 and a‐SC in SCG and by α‐SC in NG. The GM1‐induced decrease in 45Ca2+ influx was prevented by cholera toxin B in SCG, whereas the α‐SC‐induced decrease was not mimicked by cholesterol in either ganglion. These results suggest that the sialic acid moiety of GM1 and α‐SC is responsible for the activation of ganglionic TG and that activation may occur via a protein kinase C‐regulated pathway linked with calcium ion movement.

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