Cadmium-induced Activation of Stress Signaling Pathways, Disruption of Ubiquitin-dependent Protein Degradation and Apoptosis in Primary Rat Sertoli Cell-Gonocyte Cocultures

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 coculture system 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 polyubiquitinated proteins (HMW-polyUb) as well as alterations in proteasome activity. Robust activation of cellular stress response, measured through the increased phosphorylation of stress-activated protein kinase/c-jun N-terminal kinase and p38, paralleled the accumulation of HMW-polyUb. In addition, p53, a key regulatory protein, was upregulated 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 effect 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.

Cadmium Renal Toxicity <i>via</i> Apoptotic Pathways

“…19) Moreover, cadmium causes an increase in intracellular p53 protein levels and/or phosphorylated p53 protein levels in several cells. [57][58][59][60][61][62][63][64][65] These observations also support our findings that the p53-mediated pathway is one of the critical pathways for inducing apoptosis in chronic cadmium-exposed proximal tubular cells in the kidney.…”

Impact of inorganic nutrients on maintenance of genomic stability

“…Furthermore, other trace minerals may impact on genome stability. For instance, exposure to cadmium and lead has been reported to compromise the repair of oxidative DNA damage [Bolin et al, 2006, Yu et al, 2008. It will be important for future studies to reach a mechanistic understanding of how inorganic nutrients, either at nutritional or supranutritional levels, modulate DNA damage response and carcinogenesis.…”

Cadmium toxicity is caused by accumulation of p53 through the down-regulation of Ube2d family genes in vitro and in vivo

“…Ubiquitinated proteins that are not degraded by the proteasome can accumulate and cause toxic cell damage. Previous studies have shown that Cd increases the accumulation of ubiquitinated proteins in several cell lines, such as mouse neuronal HT4 cells (Figueiredo-Pereira et al, 2002), rat sertoli cell-gonocyte cocultures (Yu et al, 2008) and rat proximal tubule cells (Thévenod and Friedmann, 1999). These findings suggest that Cd may cause toxic cell damage through the accumulation of unnecessary proteins.…”