Retinoblastoma protein dephosphorylation is an early event of cellular response to prooxidant conditions

The modification of intracellular redox conditions with diethylmaleate (DEM ), a glutathione-depleting agent, induces a p53-independent growth arrest m ediated by the accumulation of p21(waf1) mRNA and protein. The same treatme nt also induces the retinoblastoma protein (pRb) dephosphorylation. This de phosphorylation (i) is very fast, being observed already 5 min after the ex posure of the cells to DEM, (ii) is dependent on the prooxidant effects of DEM, being prevented by the treatment with N-acetylcysteine and (iii) is co mpletely reversible, since the rephosphorylation of pRb is promptly obtaine d upon the removal of the glutathione-depleting agent from the culture medi um. The dephosphorylation of pRb is independent of the accumulation of p21( waf1) induced by DEM; in fact, p21(waf1) levels start to increase much late r after DEM treatment and accordingly cyclin-dependent kinase activities ar e not yet induced when pRb is already dephosphorylated following DEM treatm ent. Finally, pRb dephosphorylation is catalyzed by phosphatases activated by DEM treatment. (C) 2000 Federation of European Biochemical Societies.