Cr (VI) induced mitophagy via the interaction of HMGA2 and PARK2

A novel HMGA2/MPC-1/mTOR signaling pathway promotes cell growth via facilitating Cr (VI)-induced glycolysis

Mitochondrial Pyruvate Carrier 1 (MPC1) is localized on mitochondrial outer membrane to mediate the transport of pyruvate from cytosol to mitochondria. It is also well known to act as a tumor suppressor. Hexavalent chromium (Cr (VI)) contamination poses a global challenge due to its high toxicity and carcinogenesis. This research was intended to probe the potential mechanism of MPC1 in the effect of Cr (VI)-induced carcinogenesis. First, Cr (VI)-treatments decreased the expression of MPC1 in vitro and in vivo. Overexpression of MPC1 inhibited Cr (VI)-induced glycolysis and migration in A549 cells. Then, high mobility group A2 (HMGA2) protein strongly suppressed the transcription of MPC1 by binding to its promoter, and HMGA2/MPC1 axis played an important role in oxidative phosphorylation (OXPHOS), glycolysis and cell migration. Furthermore, endoplasmic reticulum (ER) stress made a great effect on the interaction between HMGA2 and MPC1. Finally, the mammalian target of the rapamycin (mTOR) was determined to mediate MPC1-regulated OXPHOS, aerobic glycolysis and cell migration. Collectively, our data revealed a novel HMGA2/MPC-1/mTOR signaling pathway to promote cell growth via facilitating the metabolism reprogramming from OXPHOS to aerobic glycolysis, which might be a potential therapy for cancers.

Effects of hexavalent chromium on mitochondria and their implications in carcinogenesis

Hexavalent chromium (Cr(VI)) is a well-known occupational and environmental human carcinogen. The cellular effect of Cr(VI) is complex and often nonspecific due to its ability to modulate multiple cellular targets. The toxicity of Cr(VI) is strongly linked to the generation of reactive oxygen species (ROS) during its reduction process. ROS can cause oxidation of cellular macromolecules, such as proteins, lipids, and DNA, thereby altering their functions. A major genotoxic effect of Cr(VI) that contributes to carcinogenesis is the formation of DNA adducts, which can lead to DNA damage. Modulations of cellular signaling pathways and epigenetics may also contribute to the carcinogenic effects of Cr(VI). Cr(VI) has a major impact on many aspects of mitochondrial biology, including oxidative phosphorylation, mitophagy, and mitochondrial biogenesis. These effects have the potential to alter the trajectory of Cr(VI)-induced carcinogenic process. This perspective article summarizes current understandings of the effect of Cr(VI) on mitochondria and discusses the future directions of research in this area, particularly with regard to carcinogenesis.

Role of NF-κB signaling pathway in hexavalent chromium-induced hepatotoxicity

Hexavalent chromium Cr (VI) is a primary human carcinogen with damaging toxic effects on multiple organs. Cr (VI) exposure can induce hepatotoxicity through oxidative stress, but its exact mechanism of action was still unclear. In our study, a model of acute Cr (VI) induced liver injury was established by exposing mice to different concentrations (0, 40, 80, and 160 mg/kg) of Cr (VI); RNA-seq was used to characterize changes in liver tissue transcriptome of C57BL/6 mice after exposing to 160 mg/kg Bw of Cr (VI). Changes in liver tissue structures, proteins, and genes were observed by hematoxylin and eosin (H&E), western blot, immunohistochemistry and RT-PCR. After Cr (VI) exposure, abnormal liver tissue structure, hepatocyte injury, and hepatic inflammatory response were observed in mice in a dose-dependent manner. RNA-seq transcriptome results indicated that oxidative stress, apoptosis, and inflammatory response pathways were increased after Cr (VI) exposure; KEGG pathway analysis found that activation of NF-κB signaling pathway was significantly upregulated. Consistent with the RNA-seq results, immunohistochemistry showed that Cr (VI) exposure resulted in infiltrating of Kupffer cells and neutrophils, increasing expression of inflammatory factors (TNF-α, IL-6, IL-1β), and activating of NF-κB signaling pathways (p-IKKα/β and p-p65). However, ROS inhibitor, N-acetyl-L-cysteine (NAC), could reduce infiltration of Kupffer cells and neutrophils and expression of inflammatory factors. Besides, NAC could inhibit NF-κB signaling pathway activation, and alleviate Cr (VI)-induced liver tissue damage. Our findings strongly suggested that inhibition of ROS by NAC might help in the development of new strategies for Cr (VI)-associated liver fibrosis. Our findings revealed for the first time that Cr (VI) induced liver tissue damage through the inflammatory response mediated by the NF-κB signaling pathway, and inhibition of ROS by NAC might help in the development of new strategies for Cr (VI)-associated hepatotoxicity.

HMGA2 mediates Cr (VI)-induced metabolic reprogramming through binding to mitochondrial D-Loop region

Hexavalent chromium [Cr (VI)] exists environmentally and occupationally. It has been shown to pose a carcinogenic hazard in certain occupations. This study was to investigate the role of high mobility group A2 (HMGA2) in Cr (VI)-induced metabolism reprogramming from oxidative phosphorylation (OXPHOS) to glycolysis in A549 and HELF cells. First, knockdown of HMGA2 by siHMGA2 significantly attenuated Cr (VI)-reduced expression of OXPHOS-related proteins (COX IV and ND1) and mitochondrial mass, indicating that HMGA2 was involved in Cr (VI)-reduced OXPHOS. Overexpression of HMGA2 by transfection of HMGA2-DNA plasmids reduced the expression of COX IV, ND1 and mitochondrial mass, suggesting the negative role of HMGA2 in OXPHOS. Secondly, both CCCP, the inhibitor of mitochondrial function, and the ER stress inhibitor, 4-phenylbutyric acid (4-PBA), decreased the level of HMGA2, indicating that the interaction of mitochondrial dysfunction and ER stress resulted in Cr (VI)-induced HMGA2 expression. Further study demonstrated that ER stress/HMGA2 axis mediated the metabolism rewiring from OXPHOS to aerobic glycolysis. Notably, Cr (VI) induced the accumulation of HMGA2 proteins in mitochondria and ChIP assay demonstrated that HMGA2 proteins could bind to D-loop region of mitochondrial DNA (mtDNA), which provided the proof for HMGA2-modulating OXPHOS. Taken together, our results suggested that the interaction of mitochondria and ER stress-enhanced HMGA2 played an important role in Cr (VI)-induced metabolic reprogramming from OXPHOS to glycolysis by binding directly to D-loop region of mtDNA. This work informs on the potential mode of action for Cr (VI)-induced tumors and builds on growing evidence regarding the contribution of cellular metabolic disruption contributing to carcinogenicity.

HMGA2 expression defines a subset of human AML with immature transcriptional signature and vulnerability to G2/M inhibition

High-mobility group AT-hook 2 (HMGA2) is a nonhistone chromatin-binding protein that is normally expressed in stem cells of various tissues and aberrantly detected in several tumor types. We recently observed that one-fourth of human acute myeloid leukemia (AML) specimens express HMGA2, which associates with a very poor prognosis. We present results indicating that HMGA2+ AMLs share a distinct transcriptional signature representing an immature phenotype. Using single-cell analyses, we showed that HMGA2 is expressed in CD34+ subsets of stem cells and early progenitors, whether normal or derived from AML specimens. Of interest, we found that one of the strongest gene expression signatures associated with HMGA2 in AML is the upregulation of G2/M checkpoint genes. Whole-genome CRISPR/Cas9 screening in HMGA2 overexpressing cells further revealed a synthetic lethal interaction with several G2/M checkpoint genes. Accordingly, small molecules that target G2/M proteins were preferentially active in vitro and in vivo on HMGA2+ AML specimens. Together, our findings suggest that HMGA2 is a key functional determinant in AML and is associated with stem cell features, G2/M status, and related drug sensitivity.

Regulation of Cr(VI)-Induced Premature Senescence in L02 Hepatocytes by ROS-Ca2+-NF-κB Signaling

Stress-induced premature senescence may be involved in the pathogeneses of acute liver injury. Hexavalent chromium [Cr(VI)], a common environmental pollutant related to liver injury, likely leads to premature senescence in L02 hepatocytes. However, the underlying mechanisms regarding hepatocyte premature senility in Cr(VI) exposure remain poorly understood. In this study, we found that chronic exposure of L02 hepatocytes to Cr(VI) led to premature senescence characterized by increased β-galactosidase activity, senescence-associated heterochromatin foci, G1 phase arrest, and decreased cell proliferation. Additionally, Cr(VI)-induced senescent L02 hepatocytes showed upregulated inflammation-related factors, such as IL-6 and fibroblast growth factor 23 (FGF23), which also exhibited reactive oxygen species (ROS) accumulation derived from mitochondria accompanied with increased concentration of intracellular calcium ions (Ca²⁺) and activity of nuclear factor kappa B (NF-κB). Of note is that ROS inhibition by N-acetyl-Lcysteine pretreatment not only alleviated Cr(VI)-induced premature senescence but also reduced the elevated intracellular Ca²⁺, activated NF-κB, and secretion of IL-6/FGF23. Intriguingly, the toxic effect of Cr(VI) upon premature senescence of L02 hepatocytes and increased levels of IL-6/FGF23 could be partially reversed by the intracellular Ca²⁺ chelator BAPTA-AM pretreatment. Furthermore, by utilizing the NF-κB inhibitor pyrrolidine dithiocarbamate (PDTC), we confirmed that NF-κB mediated IL-6/FGF23 to regulate the Cr(VI)-induced L02 hepatocyte premature senescence, whilst the concentration of intracellular Ca²⁺ was not influenced by PDTC. To the best of our knowledge, our data reports for the first time the role of ROS-Ca²⁺-NF-κB signaling pathway in Cr(VI)-induced premature senescence. Our results collectively shed light on further exploration of innovative intervention strategies and treatment targeting Cr(VI)-induced chronic liver damage related to premature senescence.

Inhalation cancer risk assessment for environmental exposure to hexavalent chromium: Comparison of margin-of-exposure and linear extrapolation approaches

Hexavalent chromium [Cr(VI)] exists in the ambient air at low concentrations (average upperbound ~0.1 ng/m³) yet airborne concentrations typically exceed EPA's Regional Screening Level for residential exposure (0.012 ng/m³) and other similar benchmarks, which assume a mutagenic mode of action (MOA) and use low-dose linear risk assessment models. We reviewed Cr(VI) inhalation unit risk estimates developed by researchers and regulatory agencies for environmental and occupational exposures and the underlying epidemiologic data, updated a previously published MOA analysis, and conducted dose-response modeling of rodent carcinogenicity data to evaluate the need for alternative exposure-response data and risk assessment approaches. Current research supports the role of non-mutagenic key events in the MOA, with growing evidence for epigenetic modifiers. Animal data show a weak carcinogenic response, even at cytotoxic exposures, and highlight the uncertainties associated with the current epidemiological data used in risk assessment. Points of departure from occupational and animal studies were used to determine margins of exposure (MOEs). MOEs range from 1.5 E+3 to 3.3 E+6 with a median of 5 E+5, indicating that current environmental exposures to Cr(VI) in ambient air should be considered of low concern. In this comprehensive review, the divergent results from default linear and MOE assessments support the need for more relevant and robust epidemiologic data, additional mechanistic studies, and refined risk assessment strategies.