The heavy metal cadmium induces valosin-containing protein (VCP)-mediated aggresome formation

Abstract

Cadmium (Cd 2+ ) is a heavy metal ion known to have a long biological half-life in humans. Accumulating evidence shows that exposure to Cd 2+ is associated with neurodegenerative diseases characterized by the retention of ubiquitinated and misfolded proteins in the lesions. Here, we report that Cd 2+ directly induces the formation of protein inclusion bodies in cells. The protein inclusion body is an aggresome, a major organelle for collecting ubiquitinated or misfolded proteins. Our results show that aggresomes are enriched in the detergent-insoluble fraction of Cd 2+ -treated cell lysates. Proteomic analysis identified 145 proteins in the aggresome-enriched fractions. One of the proteins is the highly conserved valosin-containing protein (VCP), which has been shown to colocalize with aggresomes and bind ubiquitinated proteins through its N domain (#1-200). Our subsequent examination of VCP's role in the formation of aggresomes induced by Cd 2+ indicate that the C-terminal tail (#780-806) of VCP interacts with histone deacetylase HDAC6, a mediator for aggresome formation, suggesting that VCP participates in transporting ubiquitinated proteins to aggresomes. This function of VCP is impaired by inhibition of the deacetylase activity of HDAC6 or by over-expression of VCP mutants that do not bind ubiquitinated proteins or HDAC6. Our results indicate that Cd 2+ induces the formation of protein inclusion bodies by promoting the accumulation of ubiquitinated proteins in aggresomes through VCP and HDAC6. Our delineation of the role of VCP in regulating cell responses to ubiquitinated proteins has important implications for understanding Cd 2+ toxicity and associated diseases.

Involvement of ubiquitin-coding genes in cadmium-induced protein ubiquitination in human proximal tubular cells

“…Recently, Ubc was reported to be involved in arsenite-induced toxicity in mouse embryonic fibroblasts (MEFs) (Kim et al, 2015), suggesting that polyUb genes may be critical to the mechanism of metal(loid) toxicity. Cd causes the formation of protein inclusion bodies by promoting the accumulation of ubiquitinated proteins in aggresomes in HEK293 cells (Song et al, 2008), and it has been suggested that the Ub ligase FBXO6 reduces Cd toxicity by expediting degradation of misfolded proteins by the UPS in HEK293 cells (Du et al, 2014). The present study also suggests that accumulation of ubiquitinated proteins may increase Cd toxicity in HK-2 cells.…”

The small heat shock protein, HSP30, is associated with aggresome-like inclusion bodies in proteasomal inhibitor-, arsenite-, and cadmium-treated Xenopus kidney cells

“…Additionally, aggresome formation was reported in HEK293, CHO, NIH3T3, and mouse primary liver cells treated with 20 μM cadmium chloride (Song et al, 2008). To our knowledge, the induction of aggresome formation by sodium arsenite has not been reported in other systems.…”

Role of Cigarette Smoke–Induced Aggresome Formation in Chronic Obstructive Pulmonary Disease–Emphysema Pathogenesis

“…Next, we investigated the mechanism of action by which CBZ alleviates aggresome formation by examining the expression, localization, and autophagy interaction of VCP (Figures 3 and 4A), a key mediator of both proteasomal and aggresomal protein processing pathways (47,48,59,(62)(63)(64)(65)(66). VCP is not only involved in translocating proteins to microtubule organizing centers (aggresomes) (23,67), but is also responsible for segregation and unfolding of ubiquitinated proteins from aggresome bodies for presentation to the protein degradation machinery (49,64 1 aggresome bodies to assist with autophagy-mediated protein degradation, potentially by inducing its segregase/ unfoldase activity to process and present aggregated proteins to autophagosomes.…”

“…Hence, we focused on evaluating whether this dose of CBZ modulates ubiquitination and protein aggregation via valosin-containing protein (VCP), as it is known to play a critical role in autophagy-mediated protein degradation (46)(47)(48)(49). We observed that neither ubiquitinated nor total VCP protein levels were affected by short-term autophagy induction (CBZ) in the presence or absence of lysosome inhibitor ( Figure 3A).…”