OKADAIC ACID-INDUCED LENS EPITHELIAL-CELL APOPTOSIS REQUIRES INHIBITION OF PHOSPHATASE-1 AND IS ASSOCIATED WITH INDUCTION OF GENE-EXPRESSION INCLUDING P53 AND BAX

It is well established that phosphorylation and dephosphorylation are key cellular events which regulate important metabolic activities such as gene expression, cell cycle progression, and apoptosis. The polyet her fatty acid, okadaic acid has been shown previously to activate apo ptosis in a variety of cell lines. Although this marine sponge toxin i s known to inhibit protein phosphatase (PP)-2A and PP-1, it is not cer tain in most cases whether inhibition of PP-1 or PP-2A is necessary to activate apoptosis. Furthermore, it is not clear how inhibition of th ese phosphatases leads to apoptosis. Here we present evidence that inh ibition of PP-2A by okadaic acid does not activate apoptosis in the le ns system. However, when PP-1 is inhibited by okadaic acid, rabbit len s epithelial cells undergo rapid apoptosis. Associated with this proce ss is the several-fold up-regulation of the tumor suppressor gene p53 and the pro-apoptotic gene bax at both mRNA and protein levels. Analys es of the temporal pattern of expression of the two genes reveal that the up-regulation is maximized in a few hours after treatment with oka daic acid, when the majority of the treated cells become committed to apoptosis. A brief treatment of the cells with a protein synthesis inh ibitor can abolish okadaic acid-induced up-regulation of both P53 and Fax proteins. Concomitant with this inhibition, okadaic acid-induced a poptosis is also temporarily blocked. These results suggest that okada ic acid-induced expression of p53, bax, and other genes are necessary for the activation of the apoptotic programs in lens systems.