Cd2+-Induced Alteration of the Global Proteome of Human Skin Fibroblast Cells

Cadmium (Cd2+) is a toxic heavy metal and a well-known human carcinogen. The toxic effects of Cd2+ on biological systems are diverse and thought to be exerted through a complex array of mechanisms. Despite the large number of studies aimed to elucidate the toxic mechanisms of action of Cd2+, few have been targeted toward investigating the ability of Cd2+ to disrupt multiple cellular pathways simultaneously and the overall cellular responses toward Cd2+ exposure. In this study, we employed a quantitative proteomic method, relying on stable isotope labeling by amino acids in cell culture (SILAC) and LC–MS/MS, to assess the Cd2+-induced simultaneous alterations of multiple cellular pathways in cultured human skin fibroblast cells. By using this approach, we were able to quantify 2931 proteins, and 400 of them displayed significantly changed expression following Cd2+ exposure. Our results unveiled that Cd2+ treatment led to the marked upregulation of several antioxidant enzymes (e.g., metallothionein-1G, superoxide dismutase, pyridoxal kinase, etc.), enzymes associated with glutathione biosynthesis and homeostasis (e.g., glutathione S-transferases, glutathione synthetase, glutathione peroxidase, etc.), and proteins involved in cellular energy metabolism (e.g., glycolysis, pentose phosphate pathway, and the citric acid cycle). Additionally, we found that Cd2+ treatment resulted in the elevated expression of two isoforms of dimethylarginine dimethylaminohydrolase (DDAH I and II), enzymes known to play a key role in regulating nitric oxide biosynthesis. Consistent with these findings, we observed elevated formation of nitric oxide in human skin (GM00637) and lung (IMR-90) fibroblast cells following Cd2+ exposure. The upregulation of DDAH I and II suggests a role of nitric oxide synthesis in Cd2+-induced toxicity in human cells.