Induction of intracellular signalling by cyclic glycerophosphates and their deoxy analogues

Cyclic glycerophosphates can be formed by enzymic degradation of phospholip ids. They have only recently attracted attention, and their physiological f unction is still obscure. In this study, we have searched for signalling fu nctions of the natural 1,3-cyclic and 1,2-cyclic glycerophosphates, their d eoxy analogues, and the phenyl esters of the 1,3-cyclic phosphates. Linear sn-glycerol 3-phosphate and glycerol 2-phosphate served as the control comp ounds. Each of the six-membered ring cyclic phosphates tested induced rapid intracellular tyrosine phosphorylation in CHO and NIH-3T3 cells when appli ed extracellularly at a concentration of 0.5-4 mu M. The phosphorylated int racellular proteins had molecular masses of approximate to 35 kDa, approxim ate to 45 kDa, 60-70 kDa and approximate to 120 kDa. The five-membered ring cyclic phosphates had a similar effect, but at an external concentration o f 2-10 mu M, while sn-glycerol 3-phosphate and glycerol 2-phosphate had no effect.. The six-membered cyclic phosphates also induced rapid threonine ph osphorylation in CHO cells of approximate to 18-kDa, approximate to 35-kDa, and approximate to 38-kDa proteins. Further experiments indicated that the cyclic phosphates partition rapidly into the cell cytosol where they activ ate kinases, including mitogen-activated protein kinase. When their intrace llular level increases, dephosphorylation presumably takes place. This patt ern may account for the signalling profile of cyclic phosphates and suggest s that they may take part in processes associated with cell differentiation .