The role of autophagy in metal-induced urogenital carcinogenesis

Molecular mechanistic approach to reveal decitabine's effect on DNMT gene modulation and its inhibitory role in heavy metal-induced proliferation in urinary bladder cancer cell line

Heavy metals are pervasive environmental and occupational carcinogens known to induce uncontrolled cell proliferation. They influence a number of cellular processes, including proliferation, metabolism, apoptosis, and carcinogenesis. Among the several underlying mechanisms of carcinogenesis, metal-induced aberrant modulation of DNA methyltransferase (DNMT) activity may play crucial role. In this context, our study explored the proliferative and/or cytotoxic effects of heavy metals on the T24 urinary bladder cancer cell line. Additionally, we evaluated the effects of heavy metals and the chemotherapeutic agent decitabine on DNMT expression and activity. For investigative purposes, T24 cells were exposed to different heavy metals; namely, lead (Pb), chromium (Cr), cadmium (Cd), nickel (Ni), and arsenic (As) at concentrations ranging from 0.5 to 32 μM for 24, 48, and 72 h, as well as to decitabine (1 to 64 μM) for 72 h. Post-incubation, cell proliferation and migration increased, and mitochondrial membrane potential decreased significantly in the presence of heavy metals, especially Cr and Cd. Moreover, in the presence of Cr and Cd, expression of DNMT1 and DNMT3b genes enhanced significantly. Furthermore, decitabine treatment effectively inhibited Cd- and Cr-induced proliferation and downregulated expression of DNMT genes. In conclusion, heavy metals such as Cd and Cr may contribute to urinary bladder carcinogenesis through DNMT upregulation, while decitabine showedprotective effects by suppressing DNMT expression and inhibiting cell proliferation.

Long-Term Impact of Cr(VI) Exposure in Swiss Albino Mice: ROS-Driven Modulation of Autophagy and Cellular Fate

Hexavalent chromium [Cr(VI)], due to its high solubility and permeability, is significantly more toxic than trivalent chromium [Cr(III)] as it generates reactive oxygen species (ROS) during cellular reduction. Industrial discharges have led to increasing Cr(VI) contamination in surface and groundwater, posing serious environmental and public health concerns. In our previous study, we demonstrated that exposure to 5 ppm Cr(VI) for 4 and 8 months adversely affected body weight, water consumption, and liver function in Swiss albino mice. Histological analyses revealed tissue alterations, disrupted DNA repair gene expression in liver tissue, and a marked increase in apoptotic gene expression after 8 months of exposure. Building on these findings, we employed the same Cr(VI) concentration (5 ppm via drinking water) over 4 and 8 months in the present study. Our results showed a significant increase in ROS generation in the liver, brain, and kidney tissues at both time intervals. Additionally, the presence of autophagolysosomes was markedly elevated after chronic Cr(VI) exposure in each tissue. We also observed altered expression patterns of key autophagy-related genes (Atg5, Beclin1, and Lc3) and mTor in these tissues. Immunohistochemical analysis further confirmed a significant increase in LC3B expression after 4 months of exposure. Our findings suggest that heightened intracellular oxidative stress triggers a protective autophagy response, mediated via mTOR signaling, to maintain cellular integrity. However, prolonged toxic insult and ROS accumulation may eventually shift pro-survival autophagy toward apoptotic cell death in the liver and brain tissues.

Sohlh2 Promotes the Progression of Hepatocellular Carcinoma via TGM2-Mediated Autophagy

Liver cancer is the third leading cause of cancer-related deaths worldwide, with hepatocellular carcinoma (HCC) accounting for 85% of liver cancer-related deaths. Autophagy controls HCC cell growth, invasion, metastasis, drug resistance, and stemness. Spermatogenesis and oogenesis basic helix-loop-helix transcription factor 2 (Sohlh2) can bind to the E-boxes in the promoter regions of target genes, which are involved in multiple neoplasms. In this study, Sohlh2 was highly expressed in HCC tissues and was related to poor prognosis. Moreover, Sohlh2 overexpression promoted the proliferation, migration, invasion, and metastasis of HCC cells in vivo and in vitro. However, Sohlh2 silencing inhibited proliferation, migration, invasion, and metastasis of HCC cells in vivo and in vitro. Mechanistically, Sohlh2 could bind to the promoter of TGM2 and enhance its transcriptional activity, thereby enhancing the autophagy of HCC cells. Furthermore, Sohlh2 protein levels were positively associated with TGM2 expression in HCC tissues. Taken together, these results demonstrate that Sohlh2 can promote HCC progression via TGM2-mediated autophagy, implying that Sohlh2 is a promising candidate for HCC treatment.

Role of PERK-Mediated Endoplasmic Reticulum Stress in Ferroptosis Caused by Hexavalent Chromium in Chicken Hepatocytes

This study aimed to investigate whether Cr(VI) can induce ferroptosis in chicken hepatocytes and determine the role of PERK-mediated endoplasmic reticulum stress (ERS). First, a model of Cr(VI) poisoning was established by exposing chicken hepatocytes to Cr(VI). The levels of ferroptosis-related proteins, meanwhile, GSH, SOD, MDA, and lipid ROS, were measured. Furthermore, the expression of GRP78 and PERK proteins was examined. Changes in ERS and ferroptosis were evaluated by silencing the PERK gene. Results showed that Cr(VI) led to the accumulation of lipid ROS, decreased expression of GPX4 and HSP27, increased expression of COX2, and induced ferroptosis in chicken hepatocytes. Exposure to Cr(VI) increased the protein expression of GRP78 and PERK, and silencing of PERK worsened Cr(VI)-induced ferroptosis. In conclusion, Cr(VI) can induce ferroptosis in chicken hepatocytes, and PERK plays an important role as a negative regulator.

Does the Presence of Heavy Metals Influence the Gene Expression and Oxidative Stress in Bladder Cancer?

Heavy metal toxicity is associated with cancer progression. Studies have reported the relation between some metal ions and bladder cancer (BC). Direct influence of such agents in bladder carcinogenesis is still needed. Total 49 BC patients were included in the study. Level of Pb, Cr, Hg and Cd, oxidative stress markers, and gene expression of Bcl-2, Bax, IL-6, AKT, and P38 genes were detected in cancer and non-cancerous tissues obtained from bladder cancer patients. Concentrations of Pb, Cr, and Cd were significantly elevated in cancer tissues than normal, while Hg level was significantly increased in normal tissue than cancer. MDA level was significantly higher and SOD activity was lower in the cancer tissues compared to non-cancerous. The expressions of Bcl-2, IL-6, AKT, and P38 were significantly increased in the cancer tissues than in normal tissues while Bax level was significantly increased in non-cancerous tissue than in cancer tissue. In cancer tissue, there were significant correlations between Cr level with expression of Bax, AKT, and P38 while Cd level was significantly correlate with Bax, IL-6, AKT, and P38expression. The correlation between Cr and Cd with the expression of Bax, IL-6, AKT, and P38 may indicate a carcinogenic role of these metals on progression of bladder cancer.

The dynamic face of cadmium-induced Carcinogenesis: Mechanisms, emerging trends, and future directions

Cadmium (Cd) is a malleable element with odorless, tasteless characteristics that occurs naturally in the earth's crust, underground water, and soil. The most common reasons for the anthropological release of Cd to the environment include industrial metal mining, smelting, battery manufacturing, fertilizer production, and cigarette smoking. Cadmium-containing products may enter the environment as soluble salts, vapor, or particle forms that accumulate in food, soil, water, and air. Several epidemiological studies have highlighted the association between Cd exposure and adverse health outcomes, especially renal toxicity, and the impact of Cd exposure on the development and progression of carcinogenesis. Also highlighted is the evidence for early-life and even maternal exposure to Cd leading to devastating health outcomes, especially the risk of cancer development in adulthood. Several mechanisms have been proposed to explain how Cd mediates carcinogenic transformation, including epigenetic alteration, DNA methylation, histone posttranslational modification, dysregulated non-coding RNA, DNA damage in the form of DNA mutation, strand breaks, and chromosomal abnormalities with double-strand break representing the most common DNA form of damage. Cd induces an indirect genotoxic effect by reducing p53's DNA binding activity, eventually impairing DNA repair, inducing downregulation in the expression of DNA repair genes, which might result in carcinogenic transformation, enhancing lipid peroxidation or evasion of antioxidant interference such as catalase, superoxide dismutase, and glutathione. Moreover, Cd mediates apoptosis evasion, autophagy activation, and survival mechanisms. In this review, we decipher the role of Cd mediating carcinogenic transformation in different models and highlight the interaction between various mechanisms. We also discuss diagnostic markers, therapeutic interventions, and future perspectives.

Recent insights into autophagy and metals/nanoparticles exposure

Some anthropogenic pollutants, such as heavy metals and nanoparticles (NPs), are widely distributed and a major threat to environmental safety and public health. In particular, lead (Pb), cadmium (Cd), chromium (Cr), arsenic (As), and mercury (Hg) have systemic toxicity even at extremely low concentrations, so they are listed as priority metals in relation to their significant public health burden. Aluminum (Al) is also toxic to multiple organs and is linked to Alzheimer's disease. As the utilization of many metal nanoparticles (MNPs) gradually gain traction in industrial and medical applications, they are increasingly being investigated to address potential toxicity by impairing certain biological barriers. The dominant toxic mechanism of these metals and MNPs is the induction of oxidative stress, which subsequently triggers lipid peroxidation, protein modification, and DNA damage. Notably, a growing body of research has revealed the linkage between dysregulated autophagy and some diseases, including neurodegenerative diseases and cancers. Among them, some metals or metal mixtures can act as environmental stimuli and disturb basal autophagic activity, which has an underlying adverse health effect. Some studies also revealed that specific autophagy inhibitors or activators could modify the abnormal autophagic flux attributed to continuous exposure to metals. In this review, we have gathered recent data about the contribution of the autophagy/mitophagy mediated toxic effects and focused on the involvement of some key regulatory factors of autophagic signaling during exposure to selected metals, metal mixtures, as well as MNPs in the real world. Besides this, we summarized the potential significance of interactions between autophagy and excessive reactive oxygen species (ROS)-mediated oxidative damage in the regulation of cell survival response to metals/NPs. A critical view is given on the application of autophagy activators/inhibitors to modulate the systematic toxicity of various metals/MNPs.

Molecular interplay between NOX1 and autophagy in cadmium-induced prostate carcinogenesis

Chronic exposure to cadmium (Cd), a class I carcinogen, leads to malignant transformation of normal prostate epithelial cells (RWPE-1). The constant generation of Cd-induced ROS and resulting ER stress induces cellular responses that are needed for cell survival, and autophagy has an important role in this process. However, the mechanisms that regulate Cd-induced ROS and how these differ in terms of acute and chronic cadmium exposure remain unexplained. Here, we show that acute or chronic Cd exposure facilitates NOX1 assembly by activating its cytosolic regulators p47phox and p67phox in RWPE-1 cells. Upregulation of NOX1 complex proteins and generation of ROS activates unfolded protein response (UPR) via phosphorylation of protein kinase RNA-like endoplasmic reticulum kinase (PERK), eukaryotic initiation factor 2 alpha (eIF2α), and selective translation of activating transcription factor 4 (ATF4). Chronic Cd exposure constantly activates NOX1 complex and generates consistent ROS and ER stress that led to defective autophagy, wherein ATG5 expression is downregulated in contrast to acute Cd exposure. As a result, selective/defective autophagy creates depletion of autophagosome-lysosome fusion that gives a survival advantage to transforming cells, which is not available to RWPE-1 cells acutely exposed to Cd. Knockdown of key molecules in a lockstep manner directly affects the most downstream autophagy pathways in transforming cells. Overall, this study demonstrates that assembly of NOX1 complex proteins is indispensable for Cd-induced persistent ROS and controls ER stress-induced defective autophagy in mice and humans.