ToxSci Advance Access published online on May 6, 2008
Toxicological Sciences, doi:10.1093/toxsci/kfn087
Cadmium-induced activation of stress signaling pathways, disruption of ubiquitin-dependent protein degradation and apoptosis in primary rat Sertoli cell-gonocyte co-cultures
Dept. of Environmental and Occupational Health Sciences, University of Washington
All correspondence should be sent to: Dr. Xiaozhong Yu, Institute of Risk Analysis and Risk Communication, Dept. Environmental and Occupational Health Sciences, University of Washington, 4225 Roosevelt Way. NE, Suite #100, Seattle, WA 98105, Tel: 206-685-0465 Fax: 206-616-4875, E-mail: yuxz{at}u.washington.edu
Received December 12, 2007; revision received April 28, 2008; accepted April 28, 2008
 |
Abstract |
|---|
Cadmium (Cd) is a ubiquitous environmental pollutant that has been associated with male reproductive toxicity in both humans and animal models. The underlying mechanism of this response, however, is still uncharacterized. To address this issue, we employed a recently developed and optimized three-dimensional primary Sertoli cell-gonocyte co-culture system (SGC) and examined the time- and dose-dependent effects of Cd on morphological alterations, cell viability, activation of stress signaling pathway proteins and the disruption of the ubiquitin proteasome system (UPS). Our results demonstrated that Cd exposure lead to time- and dose-dependent morphological changes that are associated with the induction of apoptosis. In response to Cd, we also saw a disruption of the UPS as evaluated through the accumulation of high molecular weight poly-ubiquitinated proteins (HMW-polyUb) as well as alterations in proteasome activity. Robust activation of cellular stress response, measured through the increased phosphorylation of SAPK/JNK and p38, paralleled the accumulation of HMW-polyUb. In addition, p53, a key regulatory protein, was up-regulated and underwent increased ubiquitination in response to Cd. To further characterize the role of the UPS in Cd cellular response, we compared the above changes with two classic proteasomal inhibitors, lactacystin and MG132. The stress response and the accumulation of HWM-polyUb induced by Cd were consistent with the response seen with MG132, but not with lactacystin. In addition, Cd treatment resulted in a dose- and time-dependent affect on proteasome activity, but the overall Cd-induced proteasomal inhibition was unique as compared to MG132 and lactacystin. Taken together, our studies further characterize Cd-induced in vitro testicular toxicity and highlight the potential role of the UPS in this response.
Key Words: Cadmium; Sertoli cell/Gonocyte co-culture; ubiquitin proteasome system; stress signaling; male reproductive toxicity.