Cadmium-induced alterations of gene expression in human cells

We have reported the changes in gene expression in human HeLa cells exposed to a low concentration (5 μM) of Cd. In the present study, cells exposed to a higher concentration of Cd were analyzed using a DNA microarray with 9182 human cDNA probes, in an attempt to obtain a comprehensive view on the biological effects of Cd. After a 6 h exposure to 50 μM Cd, 48 genes were up-regulated 2.5-fold or greater and 14 genes were down-regulated to 40% or less. Marked up-regulation of genes coding for metallothioneins, anti-oxidant proteins, and heat shock proteins was observed. Cd appeared to repress cell proliferation by modulating genes involved in multiple pathways. Cd also affected a number of genes related to apoptosis. Interestingly, it appeared that a series of genes were regulated to accelerate the intrinsic pathway of apoptosis, while others were directed to suppress the extrinsic pathway. Of these, rapid and transient induction of the TR3 gene was noted as a possible key process in Cd-induced apoptosis. Effects on several genes that may reflect mechanistic backgrounds of Cd toxicity were also observed. The present study disclosed a complex pleiotypic response of human cells to Cd, which was composed of a variety of changes in gene expression directed to defense, growth arrest, recovery from damage, apoptosis and so on.