Introduction

Abstract

Specific stresses induce specific as well as overlapping stress responses. Oxidants, UV radiation, metals and lymphotoxin share the fact that they play dual roles in biological systems, on the one hand serving as key cellular activators or chemical cofactors, raising essential second messengers, and on the other hand leading potentially to DNA damage and cell death by apoptosis or necrosis. Low-dose oxidants activate cell proliferation and contribute to antiinfectious defense Low-dose metals and low-dose tumor necrosis factor are essential in the regulation of proteins involved in antioxidant defenses such as SOD and metallothionins, respectively, while their toxic effects at high concentrations will overcome the induced protective mechanisms Genotoxic agents in general evoke a series of events leading to the activation of a wide group of genes with various functions among which many are also rapidly induced by mitogenic stimulation. UV radiation and mitogens for example induce both shared and specific kinase phosphorylation cascades and similarly enhance both shared and specific gene expression. To prevent DNA damage, the cells have evolved a number of protective mechanisms including DNA repair, cell cycle arrest and apoptosis and the activation of p53 may play a pivotal role in the type of responses observed following DNA damage.