Cadmium Activates Multiple Signaling Pathways That Coordinately Stimulate Akt Activity to Enhance c-Myc mRNA Stability

TOP1 inhibition induces bifurcated JNK/MYC signaling that dictates cancer cell sensitivity

Rationale: Triple-negative breast cancer (TNBC) does not respond to anti-estrogen and anti-HER2 therapies and is commonly treated by chemotherapy. TNBC has a high recurrence rate, particularly within the first 3 years. Thus, there is an urgent clinical need to develop more effective therapies for TNBC. Topoisomerase I (TOP1) inhibitors cause DNA damage, making these drugs desirable for TNBC treatment since DNA repair machinery is defective in this subtype of breast cancer. Among the main molecular subtypes of breast cancer, the TNBC cell lines exhibited the highest TOP1 inhibition sensitivity. However, clinically used TOP1 inhibitors, such as topotecan and irinotecan, have shown limited clinical applications and the reasons remain unclear. Understanding the mechanism of differential responses to TOP1 blockade and identifying the predictive markers for cancer cell sensitivity will help further TOP1-targeted therapy for TNBC treatment and improve the clinical use of TOP1 inhibitors. Methods: Viability assays were used to evaluate breast cancer cell sensitivity to topotecan and other TOP1 inhibitors as well as TOP2 inhibitors. An in vitro-derived topotecan-resistant TNBC cell model and TNBC xenograft models were employed to confirm cancer cell response to TOP1 blockade. RNA-seq was used to identify potential predictive markers for TNBC cell response to TOP1 blockade. Western blotting and qRT-PCR were performed to measure the protein levels and RNA expression. ATAC-seq and luciferase reporter assays were used to examine MYC transcriptional regulations. The effects of MYC and JNK in cancer cell response to TOP1 inhibition were validated via loss-of-function and gain-of-function experiments. Results: We observed two distinct and diverging cancer cell responses - sensitive versus resistant to TOP1 inhibition, which was confirmed by TNBC xenograft mouse models treated by topotecan. TNBC cells exhibited bifurcated temporal patterns of ATR pathway activation upon TOP1 inhibitor treatment. The sensitive TNBC cells showed an "up then down" dynamic pattern of ATR/Chk1 signaling, while the resistant TNBC cells exhibited a "persistently up" profile. On the contrary, opposite temporal patterns of induced expression of MYC, a key regulator and effector of DNA damage, were found in TNBC cells treated by TOP1 inhibitors. Mechanistically, we showed that TOP1-induced JNK signaling upregulated MYC expression. Furthermore, pharmacological inhibition of ATR reversed TNBC cell resistance to topotecan, whereas MYC knockdown and JNK inhibition reduced cancer cell sensitivity. Conclusions: Dynamic temporal profiles of induced ATR/Chk1 and JNK activation as well as MYC expression, may predict cancer cell response to TOP1 inhibitors. JNK activation-mediated constitutive elevation of MYC expression may represent a novel mechanism governing cancer cell sensitivity to TOP1-targeting therapy. Our results may provide implications for identifying TNBC patients who might benefit from the treatment with TOP1 inhibitors.

Tumor suppressor p53 restrains cancer cell dissemination by modulating mitochondrial dynamics

Tumor suppressor p53 plays a central role in preventing tumorigenesis. Here, we unravel how p53 modulates mitochondrial dynamics to restrain the metastatic properties of cancer cells. p53 inhibits the mammalian target of rapamycin complex 1 (mTORC1) signaling to attenuate the protein level of mitochondrial fission process 1 (MTFP1), which fosters the pro-fission dynamin-related protein 1 (Drp1) phosphorylation. This regulatory mechanism allows p53 to restrict cell migration and invasion governed by Drp1-mediated mitochondrial fission. Downregulating p53 expression or elevating the molecular signature of mitochondrial fission correlates with aggressive tumor phenotypes and poor prognosis in cancer patients. Upon p53 loss, exaggerated mitochondrial fragmentation stimulates the activation of the extracellular signal-regulated kinase 1/2 (ERK1/2) signaling resulting in epithelial-to-mesenchymal transition (EMT)-like changes in cell morphology, accompanied by accelerated matrix metalloproteinase 9 (MMP9) expression and invasive cell migration. Notably, blocking the activation of mTORC1/MTFP1/Drp1/ERK1/2 axis completely abolishes the p53 deficiency-driven cellular morphological switch, MMP9 expression, and cancer cell dissemination. Our findings unveil a hitherto unrecognized mitochondria-dependent molecular mechanism underlying the metastatic phenotypes of p53-compromised cancers.

Flavin-Containing Monooxygenases Are Conserved Regulators of Stress Resistance and Metabolism

Flavin-Containing Monooxygenases are conserved xenobiotic-detoxifying enzymes. Recent studies have revealed endogenous functions of FMOs in regulating longevity in Caenorhabditis elegans and in regulating aspects of metabolism in mice. To explore the cellular mechanisms of FMO's endogenous function, here we demonstrate that all five functional mammalian FMOs may play similar endogenous roles to improve resistance to a wide range of toxic stresses in both kidney and liver cells. We further find that stress-activated c-Jun N-terminal kinase activity is enhanced in FMO-overexpressing cells, which may lead to increased survival under stress. Furthermore, FMO expression modulates cellular metabolic activity as measured by mitochondrial respiration, glycolysis, and metabolomics analyses. FMO expression augments mitochondrial respiration and significantly changes central carbon metabolism, including amino acid and energy metabolism pathways. Together, our findings demonstrate an important endogenous role for the FMO family in regulation of cellular stress resistance and major cellular metabolic activities including central carbon metabolism.

ATAD2 expression increases [18F]Fluorodeoxyglucose uptake value in lung adenocarcinoma via AKT-GLUT1/HK2 pathway

[18F]Fluorodeoxyglucose (FDG) PET/CT imaging has been widely used in the diagnosis of malignant tumors. ATPase family AAA domain-containing protein 2 (ATAD2) plays important roles in tumor growth, invasion and metastasis. However, the relationship between [18F]FDG accumulation and ATAD2 expression remains largely unknown. This study aimed to investigate the correlation between ATAD2 expression and [18F]FDG uptake in lung adenocarcinoma (LUAD), and elucidate its underlying molecular mechanisms. The results showed that ATAD2 expression was positively correlated with maximum standardized uptake value (SUV_max), total lesion glycolysis (TLG), glucose transporter type 1 (GLUT1) expression and hexokinase2 (HK2) expression in LUAD tissues. In addition, ATAD2 knockdown significantly inhibited the proliferation, tumorigenicity, migration, [18F]FDG uptake and lactate production of LUAD cells, while, ATAD2 overexpression exhibited the opposite effects. Furthermore, ATAD2 modulated the glycometabolism of LUAD via AKT-GLUT1/HK2 pathway, as assessed using LY294002 (an inhibitor of PI3K/AKT pathway). In summary, to explore the correlation between ATAD2 expression and glycometabolism is expected to bring good news for anti-energy metabolism therapy of cancers.

Antimony enhances c-Myc stability in prostate cancer via activating CtBP2-ROCK1 signaling pathway

Antimony, one of the heavier pnictogens, is widely used in industry, and its toxicity has become a major concern. Although previous studies suggested that antimony might be a tumorigenic risk factor in several cancers, the molecular basis underlying antimony-mediated transformation remains unclear. Our results showed that the serum concentration of antimony was higher in prostate cancer specimens relative to that of benign prostate tissues, and this high serum concentration of antimony was closely associated with poorer outcome in prostate cancer patients. Additionally, we demonstrated that antimony could promote prostate cancer cell growth in vitro and in vivo. In order to gain insight into the potential mechanisms, we examined the effects of antimony exposure on downstream signaling that could contribute to tumor development. We found that low-dose antimony could regulate the expression of Ctbp2 by binding and regulating the activity of its MRE domain. Meanwhile, CtBP2 could transcriptionally regulate the expression of RhoC, which is a member of the RhoGTPase family. Subsequently, the kinase activity of ROCK1 is increased, which promotes the stability of oncogene c-Myc. Overall, our study demonstrated that antimony could enhance c-Myc protein stability and promote prostate cancer cell proliferation through activating CtBP2-ROCK1 signaling pathway. These findings also substantially highlighted the potential of targeting molecules within antimony induced CtBP2-c-Myc signaling pathway as a promising therapeutic approach for the treatment of prostate cancer.

Low-dose cadmium activates the JNK signaling pathway in human renal podocytes

Cadmium (Cd) is an environmental toxin. Our previous study demonstrated that low‑dose Cd damages the integrity of the glomerular filtration barrier (GFB); however, the underlying mechanisms are poorly understood. Podocytes are a major component of the GFB, which regulate the passage of proteins. The present study aimed to investigate the effects of low‑dose Cd on human renal podocytes (HRPs). HRPs were treated with Cd and activation of the c-Jun N-terminal kinase (JNK) pathway was examined by western blot analysis. Proliferation, viability and apoptosis of HRPs were evaluated by MTT assay, trypan blue exclusion assay and flow cytometry, respectively. The properties of HRPs were validated by immunofluorescence staining and Phalloidin‑labeling. The results indicated that 4 µM Cd may activate the JNK pathway, and increase the protein expression levels of c‑Jun and c‑Fos. However, proliferation, viability, apoptosis and alignment of the F‑actin cytoskeleton in HRPs were not significantly affected by Cd treatment, with or without SP600125 pretreatment. In addition, the expression levels of CD2‑associated protein and synaptopodin, which are differentiation markers of HRPs, remained unchanged following Cd treatment. These results indicated that low‑dose Cd activates the JNK pathway but does not significantly affect HRP function.