Evidence for early signaling events in stomatin-induced differentiation ofTetrahymena vorax

The mechanism of stomatin-induced differentiation of Tetrahymena vorax was investigated by in vivo protease degradation of cell surface proteins, the direct measurement of products formed from the activation of phospholipase C, and the use of an array of signal transduction inhibitors/activators. Th e data indicate that a surface-exposed protein is required for stomatin to signal the cells to differentiate and that the cells are committed to the d ifferentiation pathway within two hours after exposure to stomatin. Analysi s of radiolabeled polyphosphoinositols and inositol lipids from control and stomatin-treated populations in the presence of 10 mM LiCl were consistent with a rapid activation of phospholipase C. Within five min following addi tion of stomatin, this resulted in an increase in polyphosphoinositols and a concomitant decrease in the relative amounts of phosphatidylinositol bisp hosphate and phosphatidylinositol trisphosphate.