Gadd45a and Gadd45b protect hematopoietic cells from UV-induced apoptosis via distinct signaling pathways, including p38 activation and JNK inhibition

GADD45A: With or without you

The growth arrest and DNA damage inducible (GADD)45 family includes three small and ubiquitously distributed proteins (GADD45A, GADD45B, and GADD45G) that regulate numerous cellular processes associated with stress signaling and injury response. Here, we provide a comprehensive review of the current literature investigating GADD45A, the first discovered member of the family. We first depict how its levels are regulated by a myriad of genotoxic and non-genotoxic stressors, and through the combined action of intricate transcriptional, posttranscriptional, and even, posttranslational mechanisms. GADD45A is a recognized tumor suppressor and, for this reason, we next summarize its role in cancer, as well as the different mechanisms by which it regulates cell cycle, DNA repair, and apoptosis. Beyond these most well-known actions, GADD45A may also influence catabolic and anabolic pathways in the liver, adipose tissue and skeletal muscle, among others. Not surprisingly, GADD45A may trigger AMP-activated protein kinase activity, a master regulator of metabolism, and is known to act as a transcriptional coregulator of numerous nuclear receptors. GADD45A has also been reported to display a cytoprotective role by regulating inflammation, fibrosis and oxidative stress in several organs and tissues, and is regarded an important contributor for the development of heart failure. Overall data point to that GADD45A may play an important role in metabolic, neurodegenerative and cardiovascular diseases, and also autoimmune-related disorders. Thus, the potential mechanisms by which dysregulation of GADD45A activity may contribute to the progression of these diseases are also reviewed below.

Artesunate improves glucose and lipid metabolism in db/db mice by regulating the metabolic profile and the MAPK/PI3K/Akt signalling pathway

BACKGROUND

Diabetes is a metabolic disorder characterized by chronic hyperglycaemia. Chronic metabolic abnormalities and long-term hyperglycaemia may result in a wide range of acute and chronic consequences. Previous studies have demonstrated that artesunate(ART) has antidiabetic, anti-inflammatory, antiatherosclerotic, and other beneficial effects, but the specific regulatory mechanism is not completely clear.

AIM

This study investigated the effects of ART on metabolic disorders in type 2 diabetes mellitus (T2DM) model db/db mice and explored the underlying mechanisms involved.

METHODS

C57BL/KsJ-db/db mice were used to identify the targets and molecular mechanism of ART. Metabolomic methods were used to evaluate the efficacy of ART in improving T2DM-related metabolic disorders. Network pharmacology and transcriptomic sequencing were used to analyse the targets and pathways of ART in T2DM. Finally, molecular biology experiments were performed to verify the key targets and pathways selected by network pharmacology and transcriptomic analyses.

RESULTS

After a 7-week ART intervention (160 mg/kg), the glucose and lipid metabolism levels of the db/db mice improved. Additionally, the oxidative stress indices, namely, the MDA and SOD levels, significantly improved (p<0.01). Linoleic acid and glycerophospholipid metabolism, amino acid metabolism, bile acid synthesis, and purine metabolism disorders in db/db mice were partially corrected after ART treatment. Network pharmacology analysis identified important targets of ART for the treatment of metabolic disorders in T2DM . These targets are involved in key signalling pathways, including the highest scores observed for the PI3K/Akt signalling pathway. Transcriptomic analysis revealed that ART could activate the MAPK signalling pathway and two key gene targets, HGK and GADD45. Immunoblotting revealed that ART increases p-PI3K, p-AKT, Glut2, and IRS1 protein expression and suppresses the phosphorylation of p38, ERK1/2, and JNK, returning HGK and GADD45 to their preartesunate levels.

CONCLUSION

Treatment of db/db mice with 160 mg/kg ART for 7 weeks significantly reduced fasting blood glucose and lipid levels. It also improved metabolic imbalances in amino acids, lipids, purines, and bile acids, thereby improving metabolic disorders. These effects are achieved by activating the PI3K/AKT pathway and inhibiting the MAPK pathway, thus demonstrating the efficacy of the drug.

Boron Derivatives Inhibit the Proliferation of Breast Cancer Cells and Affect Tumor-Specific T Cell Activity In Vitro by Distinct Mechanisms

Breast cancer is the most frequently diagnosed cancer among women worldwide. Despite the initial clinical response obtained with the widely used conventional chemotherapy, an improved prognosis for breast cancer patients has been missing in the clinic because of the high toxicity to normal cells, induction of drug resistance, and the potential immunosuppressive effects of these agents. Therefore, we aimed to investigate the potential anti-carcinogenic effect of some boron derivatives (sodium pentaborate pentahydrate (SPP) and sodium perborate tetrahydrate (SPT)), which showed a promising effect on some types of cancers in the literature, on breast cancer cell lines, as well as immuno-oncological side effects on tumor-specific T cell activity. These findings suggest that both SPP and SPT suppressed proliferation and induced apoptosis in MCF7 and MDA-MB-231 cancer cell lines through downregulation of the monopolar spindle-one-binder (MOB1) protein. On the other hand, these molecules increased the expression of PD-L1 protein through their effect on the phosphorylation level of Yes-associated protein (Phospho-YAP (Ser127). In addition, they reduced the concentrations of pro-inflammatory cytokines such as IFN-γ and cytolytic effector cytokines such as sFasL, perforin, granzyme A, Granzyme B, and granulysin and increased the expression of PD-1 surface protein in activated T cells. In conclusion, SPP, SPT, and their combination could have growth inhibitory (antiproliferative) effects and could be a potential treatment for breast cancer. However, their stimulatory effects on the PD-1/PD-L1 signaling pathway and their effects on cytokines could ultimately account for the observed repression of the charging of specifically activated effector T cells against breast cancer cells.

Multi-Omics Analysis Reveals the Potential Effects of Maternal Dietary Restriction on Fetal Muscle Growth and Development

In terms of fetal muscle growth, development, and health, maternal nutrition is a crucial influence, although the exact biochemical mechanism by which this occurs is still not fully understood. To examine the potential impacts of maternal dietary restriction on fetal muscle development, the sheep maternal dietary restriction model was developed for this study. In our study, 12 pregnant ewes were evenly split into two experimental groups and fed either 75% or 100% of a maternal nutrient. In addition, a multi-omics analysis was used to study the embryonic longissimus dorsis on gestational days (GD) 85 and 135. The fetal weight at GD 135 was significantly below normal due to the maternal restricted diet (p < 0.01). When fetuses were exposed to the dietary deficit, 416 mRNAs and 40 proteins were significantly changed. At GD 85, the multi-omics analysis revealed that maternal dietary restriction led to a significant up-regulation of the cell cycle regulator CDK2 gene in the cellular senescence signaling pathway, and the results of the qRT-PCR were similar to the multi-omics analysis, which showed that SIX1, PAX7, the cell cycle factors CDK4 and CDK6, and the BCL-2 apoptosis factor were up-regulated and several skeletal muscle marker genes, such as MYF5 and MyoD were down-regulated. At GD 135, maternal dietary restriction blocks the muscle fiber differentiation and maturation. The multi-omics analysis revealed that the TEAD1 gene was in the Hippo signaling pathway, the muscle marker genes MYF5 and MyoG were significantly down-regulated, and the TEAD1 binding of the down-regulated VGLL3 gene might be potential mechanisms affecting myofiber differentiation and maturation. Knocking down the CDK2 gene could inhibit the proliferation of primary embryonic myoblasts, and the expression levels of cell cycle regulatory factors CDK4 and CDK6 were significantly changed. Under low nutrient culture conditions, the number of myoblasts decreased and the expression of CDK2, CDK6, MYF5, PAX7 and BCL-2 changed, which was in perfect agreement with the multi-omics analysis. All of the findings from our study helped to clarify the potential effects of maternal dietary restriction on fetal muscle growth and development. They also provided a molecular foundation for understanding the molecular regulatory mechanisms of maternal nutrition on fetal muscle growth and development, as well as for the development of new medications and the management of related metabolic diseases.

Protective interaction of human phagocytic APC subsets with Cryptococcus neoformans induces genes associated with metabolism and antigen presentation

Cryptococcal meningitis is the most common cause of meningitis among HIV/AIDS patients in sub-Saharan Africa, and worldwide causes over 223,000 cases leading to more than 181,000 annual deaths. Usually, the fungus gets inhaled into the lungs where the initial interactions occur with pulmonary phagocytes such as dendritic cells and macrophages. Following phagocytosis, the pathogen can be killed or can replicate intracellularly. Previous studies in mice showed that different subsets of these innate immune cells can either be antifungal or permissive for intracellular fungal growth. Our studies tested phagocytic antigen-presenting cell (APC) subsets from the human lung against C. neoformans. Human bronchoalveolar lavage was processed for phagocytic APCs and incubated with C. neoformans for two hours to analyze the initial interactions and fate of the fungus, living or killed. Results showed all subsets (3 macrophage and 3 dendritic cell subsets) interacted with the fungus, and both living and killed morphologies were discernable within the subsets using imaging flow cytometry. Single cell RNA-seq identified several different clusters of cells which more closely related to interactions with C. neoformans and its protective capacity against the pathogen rather than discrete cellular subsets. Differential gene expression analyses identified several changes in the innate immune cell's transcriptome as it kills the fungus including increases of TNF-α (TNF) and the switch to using fatty acid metabolism by upregulation of the gene FABP4. Also, increases of TNF-α correlated to cryptococcal interactions and uptake. Together, these analyses implicated signaling networks that regulate expression of many different genes - both metabolic and immune - as certain clusters of cells mount a protective response and kill the pathogen. Future studies will examine these genes and networks to understand the exact mechanism(s) these phagocytic APC subsets use to kill C. neoformans in order to develop immunotherapeutic strategies to combat this deadly disease.

Expression of Human Mutant Preproinsulins Induced Unfolded Protein Response, Gadd45 Expression, JAK-STAT Activation, and Growth Inhibition in Drosophila

Mutations in the insulin gene (INS) are frequently associated with human permanent neonatal diabetes mellitus. However, the mechanisms underlying the onset of this genetic disease is not sufficiently decoded. We induced expression of two types of human mutant INSs in Drosophila using its ectopic expression system and investigated the resultant responses in development. Expression of the wild-type preproinsulin in the insulin-producing cells (IPCs) throughout the larval stage led to a stimulation of the overall and wing growth. However, ectopic expression of human mutant preproinsulins, hINSC96Y and hINSLB15YB16delinsH, neither of which secreted from the β-cells, could not stimulate the Drosophila growth. Furthermore, neither of the mutant polypeptides induced caspase activation leading to apoptosis. Instead, they induced expression of several markers indicating the activation of unfolded protein response, such as ER stress-dependent Xbp1 mRNA splicing and ER chaperone induction. We newly found that the mutant polypeptides induced the expression of Growth arrest and DNA-damage-inducible 45 (Gadd45) in imaginal disc cells. ER stress induced by hINSC96Y also activated the JAK-STAT signaling, involved in inflammatory responses. Collectively, we speculate that the diabetes-like growth defects appeared as a consequence of the human mutant preproinsulin expression was involved in dysfunction of the IPCs, rather than apoptosis.

Inhibiting calpain 1 and 2 in cyclin G associated kinase-knockout mice mitigates podocyte injury

Evidence for reduced expression of cyclin G associated kinase (GAK) in glomeruli of patients with chronic kidney disease was observed in the Nephroseq human database, and GAK was found to be associated with the decline in kidney function. To examine the role of GAK, a protein that functions to uncoat clathrin during endocytosis, we generated podocyte-specific Gak-knockout mice (Gak-KO), which developed progressive proteinuria and kidney failure with global glomerulosclerosis. We isolated glomeruli from the mice carrying the mutation to perform messenger RNA profiling and unearthed evidence for dysregulated podocyte calpain protease activity as an important contributor to progressive podocyte damage. Treatment with calpain inhibitor III specifically inhibited calpain-1/-2 activities, mitigated the degree of proteinuria and glomerulosclerosis, and led to a striking increase in survival in the Gak-KO mice. Podocyte-specific deletion of Capns1, essential for calpain-1 and calpain-2 activities, also improved proteinuria and glomerulosclerosis in Gak-KO mice. Increased podocyte calpain activity-mediated proteolysis of IκBα resulted in increased NF-κB p65-induced expression of growth arrest and DNA-damage-inducible 45 beta in the Gak-KO mice. Our results suggest that loss of podocyte-associated Gak induces glomerular injury secondary to calcium dysregulation and aberrant calpain activation, which when inhibited, can provide a protective role.

Loss of the spectraplakin gene Short stop induces a DNA damage response in Drosophila epithelia

Epithelia are an eminent tissue type and a common driver of tumorigenesis, requiring continual precision in cell division to maintain tissue structure and genome integrity. Mitotic defects often trigger apoptosis, impairing cell viability as a tradeoff for tumor suppression. Identifying conditions that lead to cell death and understanding the mechanisms behind this response are therefore of considerable importance. Here we investigated how epithelia of the Drosophila wing disc respond to loss of Short stop (Shot), a cytoskeletal crosslinking spectraplakin protein that we previously found to control mitotic spindle assembly and chromosome dynamics. In contrast to other known spindle-regulating genes, Shot knockdown induces apoptosis in the absence of Jun kinase (JNK) activation, but instead leads to elevated levels of active p38 kinase. Shot loss leads to double-strand break (DSB) DNA damage, and the apoptotic response is exacerbated by concomitant loss of p53. DSB accumulation is increased by suppression of the spindle assembly checkpoint, suggesting this effect results from chromosome damage during error-prone mitoses. Consistent with DSB induction, we found that the DNA damage and stress response genes, Growth arrest and DNA damage (GADD45) and Apoptosis signal-regulating kinase 1 (Ask1), are transcriptionally upregulated as part of the shot-induced apoptotic response. Finally, co-depletion of Shot and GADD45 induced significantly higher rates of chromosome segregation errors in cultured cells and suppressed shot-induced mitotic arrest. Our results demonstrate that epithelia are capable of mounting molecularly distinct responses to loss of different spindle-associated genes and underscore the importance of proper cytoskeletal organization in tissue homeostasis.

DNA damage and health effects in juvenile haddock (Melanogrammus aeglefinus) exposed to PAHs associated with oil-polluted sediment or produced water

The research objective was to study the presence of DNA damages in haddock exposed to petrogenic or pyrogenic polyaromatic hydrocarbons (PAHs) from different sources: 1) extracts of oil produced water (PW), dominated by 2-ring PAHs; 2) distillation fractions of crude oil (representing oil-based drilling mud), dominated by 3-ring PAHs; 3) heavy pyrogenic PAHs, mixture of 4/5/6-ring PAHs. The biological effect of the different PAH sources was studied by feeding juvenile haddock with low doses of PAHs (0.3-0.7 mg PAH/kg fish/day) for two months, followed by a two-months recovery. In addition to the oral exposure, a group of fish was exposed to 12 single compounds of PAHs (4/5/6-ring) via intraperitoneal injection. The main endpoint was the analysis of hepatic and intestinal DNA adducts. In addition, PAH burden in liver, bile metabolites, gene and protein expression of CYP1A, GST activity, lipid peroxidation, skeletal deformities and histopathology of livers were evaluated. Juvenile haddock responded quickly to both intraperitoneal injection and oral exposure of 4/5/6-ring PAHs. High levels of DNA adducts were detected in livers three days after the dose of the single compound exposure. Fish had also high levels of DNA adducts in liver after being fed with extracts dominated by 2-ring PAHs (a PW exposure scenario) and 3-ring PAHs (simulating an oil exposure scenario). Elevated levels of DNA adducts were observed in the liver of all exposed groups after the 2 months of recovery. High levels of DNA adduct were found also in the intestines of individuals exposed to oil or heavy PAHs, but not in the PW or control groups. This suggests that the intestinal barrier is very important for detoxification of orally exposures of PAHs.

Metals and low dose IR: Molecular effects of combined exposures using HepG2 cells as a biological model

Uranium mining sites produce residues rich in metals and radionuclides, that may contaminate all environmental matrices, exposing human and non-human biota to low doses of ionizing radiation (LDIR) and to the chemical toxicity of several metals. To date, experimental and radio-epidemiological studies do not provide conclusive evidence of LDIR induced cancer. However, co-exposures (LDIR plus other contaminants), may increase the risks. To determine the potential for genotoxic effects in human cells induced by the exposure to LDIR plus metals, HEPG2 cells were exposed to different concentrations of a uranium mine effluent for 96 h. DNA damage was evaluated using the comet assay and changes in the expression of tumor suppressor and oncogenes were determined using qPCR. Results show that effluent concentrations higher than 5%, induce significant DNA damage. Also, a significant under-expression of ATM and TP53 genes and a significant overexpression of GADD45a gene was observed. Results show that the exposure to complex mixtures cannot be disregarded, as effects were detected at very low doses. This study highlights the need for further studies to clarify the risks of exposure to LDIR along with other stressors, to fully review the IR exposure risk limits established for human and non-human biota.

GADD45B Promotes Glucose-Induced Renal Tubular Epithelial-Mesenchymal Transition and Apoptosis via the p38 MAPK and JNK Signaling Pathways

Growth arrest and DNA damage-inducible beta (GADD45B) is closely linked with cell cycle arrest, DNA repair, cell survival, or apoptosis in response to stress and is known to regulate the mitogen-activated protein kinase (MAPK) pathway. Here, using an RNA sequencing approach, we determined that GADD45B was significantly upregulated in diabetic kidneys, which was accompanied by renal tubular epithelial-mesenchymal transition (EMT) and apoptosis, as well as elevated MAPK pathway activation. In vitro, GADD45B expression in cultured human kidney proximal tubular epithelial cells (HK-2 cells) was also stimulated by high glucose (HG). In addition, overexpression of GADD45B in HK-2 cells exacerbated renal tubular EMT and apoptosis and increased p38 MAPK and c-Jun N-terminal kinases (JNK) activation, whereas knockdown of GADD45B reversed these changes. Notably, the activity of extracellular regulated kinase (ERK) was not affected by GADD45B expression. Furthermore, inhibitors of p38 MAPK (SB203580) and JNK (SP600125) alleviated HG‐ and GADD45B overexpression-induced renal tubular epithelial-mesenchymal transition and apoptosis. These findings indicate a role of GADD45B in diabetes-induced renal tubular EMT and apoptosis via the p38 MAPK and JNK pathways, which may be an important mechanism of diabetic kidney injury.

Identification of biomarkers in common chronic lung diseases by co-expression networks and drug-target interactions analysis

Background

asthma, chronic obstructive pulmonary disease (COPD), and idiopathic pulmonary fibrosis (IPF) are three serious pulmonary diseases that contain common and unique characteristics. Therefore, the identification of biomarkers that differentiate these diseases is of importance for preventing misdiagnosis. In this regard, the present study aimed to identify the disorders at the early stages, based on lung transcriptomics data and drug-target interactions.

Methods

To this end, the differentially expressed genes were found in each disease. Then, WGCNA was utilized to find specific and consensus gene modules among the three diseases. Finally, the disease-disease similarity was analyzed, followed by determining candidate drug-target interactions.

Results

The results confirmed that the asthma lung transcriptome was more similar to COPD than IPF. In addition, the biomarkers were found in each disease and thus were proposed for further clinical validations. These genes included RBM42, STX5, and TRIM41 in asthma, CYP27A1, GM2A, LGALS9, SPI1, and NLRC4 in COPD, ATF3, PPP1R15A, ZFP36, SOCS3, NAMPT, and GADD45B in IPF, LRRC48 and CETN2 in asthma-COPD, COL15A1, GIMAP6, and JAM2 in asthma-IPF and LMO7, TSPAN13, LAMA3, and ANXA3 in COPD-IPF. Finally, analyzing drug-target networks suggested anti-inflammatory candidate drugs for treating the above mentioned diseases.

Conclusion

In general, the results revealed the unique and common biomarkers among three chronic lung diseases. Eventually, some drugs were suggested for treatment purposes.

GADD45B Transcript Is a Prognostic Marker in Papillary Thyroid Carcinoma Patients Treated With Total Thyroidectomy and Radioiodine Therapy

Currently, there is a lack of efficient recurrence prediction methods for papillary thyroid carcinoma (PTC). In this study, we enrolled 202 PTC patients submitted to total thyroidectomy and radioiodine therapy with long-term follow-up (median = 10.7 years). The patients were classified as having favorable clinical outcome (PTC-FCO, no disease in the follow-up) or recurrence (PTC-RE). Alterations in BRAF, RAS, RET, and TERT were investigated (n = 202) and the transcriptome of 48 PTC (>10 years of follow-up) samples was profiled. Although no mutation was associated with the recurrence risk, 68 genes were found as differentially expressed in PTC-RE compared to PTC-FCO. Pathway analysis highlighted a potential role of cancer-related pathways, including signal transduction and FoxO signaling. Among the eight selected genes evaluated by RT-qPCR, SLC2A4 and GADD45B showed down-expression exclusively in the PTC-FCO group compared to non-neoplastic tissues (NT). Increased expression of GADD45B was an independent marker of shorter disease-free survival [hazard ratio (HR) 2.9; 95% confidence interval (CI95) 1.2-7.0] in our cohort and with overall survival in the TCGA dataset (HR = 4.38, CI95 1.2-15.5). In conclusion, GADD45B transcript was identified as a novel prognostic marker candidate in PTC patients treated with total thyroidectomy and radioiodine therapy.

New Uracil Analogs with Exocyclic Methylidene Group as Potential Anticancer Agents

BACKGROUND

Hybrid molecules combining uracil skeleton with methylidene exo-cyclic group were designed in the search for novel anticancer drug candidates.

OBJECTIVE

Two series of racemic 5-methylidenedihydrouracils, either 1,3-disubstituted or 1,3,6-trisubstituted were synthesized and tested for their possible cytotoxic activity against two cancer cell lines (HL-60 and MCF-7) and two healthy cell lines (HUVEC and MCF-10A). The most cytotoxic analogs were re-synthesized as pure enantiomers. The analog designated as U-332 [(R)-3-(4-bromophenyl)-1-ethyl-5-methylidene-6-phenyldihydrouracil], which had a very low IC50 value in HL-60 cell line (0.77μM) and was the most selective towards cancer cells was chosen for further experiments on HL-60 cell line, in order to determine the possible mechanism involved in its antineoplastic action.

METHODS

Cytotoxic activities of compound was assessed by the MTT assay. In order to explore the mechanism of U-332 activity, we performed quantitative real-time PCR analysis of p53 and p21 genes. Apoptosis, cell proliferation and DNA damage in HL-60 cells were determined using the flow cytometry. The ability of U-332 to determine GADD45ɑ protein level in HL-60 cells incubated with U-332 was analyzed by ELISA test.

RESULTS

U-332 was shown to generate excessive DNA damage (70% of the cell population), leading to p53 activation, resulting in p21 down-regulation and a significant increase of GADD45α protein, responsible for the cell cycle arrest in G2/M phase.

CONCLUSION

U-332 can be used as a potential lead compound in the further development of novel uracil analogs as anticancer agents.

Menstrual blood derived mesenchymal stem cells combined with Bushen Tiaochong recipe improved chemotherapy-induced premature ovarian failure in mice by inhibiting GADD45b expression in the cell cycle pathway

BACKGROUND

To investigate the therapeutic effects of menstrual blood derived mesenchymal stem cells (MB-MSCs) combined with Bushen Tiaochong recipe (BSTCR) on epirubicin induced premature ovarian failure (POF) in mice.

METHODS

Twenty-four female C57BL/6 mice of 6-8 weeks were intraperitoneally injected with epirubicin to induce POF, and then they were randomized into 4 groups of 6 mice each and treated with PBS, MB-MSCs, BSTCR, and MB-MSCs combined with BSTCR, respectively. Six mice of the same age were used as controls. Vaginal smear, TUNEL and hematoxylin-eosin staining were to observe estrous cycles, ovarian cell apoptosis and follicles. Enzyme-linked immunosorbent analysis determined serum estradiol, follicle-stimulating hormone (FSH) and anti-Müllerian hormone (AMH) levels. RT-qPCR and Western Blot analysis were to determine GADD45b, CyclinB1, CDC2 and pCDC2 expressions.

RESULTS

Epirubicin treatment resulted in a decrease in the number of primordial, primary, secondary and antral follicles, an increase in the number of atretic follicles and ovarian cell apoptosis, a decrease in estradiol and AMH levels, an increase in FSH levels, and estrous cycle arrest. However, MB-MSCs combined with BSTCR rescued epirubicin induced POF through down-regulating GADD45b and pCDC2 expressions, and up-regulating CyclinB1 and CDC2 expressions. The combined treatment showed better therapeutic efficacy than BSTCR or MB-MSCs alone.

CONCLUSIONS

MB-MSCs combined with BSTCR improved the ovarian function of epirubicin induced POF mice, which might be related to the inhibition of GADD45b expression and the promotion of CyclinB1 and CDC2 expressions. The combined treatment had better therapeutic efficacy than BSTCR or MB-MSCs alone.

Radioprotective effect of newly synthesized toll-like receptor 5 agonist, KMRC011, in mice exposed to total-body irradiation

Exposure to ionizing radiation leads to severe damages in radiosensitive organs and induces acute radiation syndrome, including effects on the hematopoietic system and gastrointestinal system. In this study, the radioprotective ability of KMRC011, a novel toll-like receptor 5 (TLR5) agonist, was investigated in C57BL6/N mice exposed to lethal total-body gamma-irradiation. In a 30-day survival study, KMRC011-treated mice had a significantly improved survival rate compared with control after 11 Gy total-body irradiation (TBI), and it was found that the radioprotective activity of KMRC011 depended on its dosage and repeated treatment. In a 5-day short-term study, we demonstrated that KMRC011 treatment stimulated cell proliferation and had an anti-apoptotic effect. Furthermore, KMRC011 increased the expressions of genes related to DNA repair, such as Rad21, Gadd45b, Sod2 and Irg1, in the small intestine of lethally irradiated mice. Interestingly, downregulation of NF-κB p65 in the mouse intestine by KMRC011 treatment was observed. This data indicated that KMRC011 exerted a radioprotective activity partially by regulating NF-κB signaling. Finally, peak expression levels of G-CSF, IL-6, IFN-γ, TNF-α and IP-10 induced by KMRC011 treatment were different depending on the route of administration and type of cytokine. These cytokines could be used as candidate biomarkers for the evaluation of KMRC011 clinical efficacy. Our data indicated that KMRC011 has radioprotective activity in lethally irradiated mice and may be developed as a therapeutic agent for radioprotection.

ALK5 signaling pathway mediates neurogenesis and functional recovery after cerebral ischemia/reperfusion in rats via Gadd45b

Transforming growth factor β (TGF-β) serves critical functions in brain injury, especially in cerebral ischemia; however, apart from its neuroprotective effects, its role in regulating neurogenesis is unclear. TGF-β acts in different ways; the most important, canonical TGF-β activity involves TGF-β receptor I (TβRI) or the activin receptor-like kinase 5 (ALK5) signaling pathway. ALK5 signaling is a major determinant of adult neurogenesis. In our previous studies, growth arrest and DNA damage protein 45b (Gadd45b) mediated axonal plasticity after stroke. Here, we hypothesized that ALK5 signaling regulates neural plasticity and neurological function recovery after cerebral ischemia/reperfusion (I/R) via Gadd45b. First, ALK5 expression was significantly increased in middle cerebral artery occlusion/reperfusion (MCAO/R) rats. Then, we knocked down or overexpressed ALK5 with lentivirus (LV) in vivo. ALK5 knockdown reduced axonal and dendritic plasticity, with a concomitant decrease in neurological function recovery. Conversely, ALK5 overexpression significantly increased neurogenesis as well as functional recovery. Furthermore, ALK5 mediated Gadd45b protein levels by regulating Smad2/3 phosphorylation. Finally, ALK5 coimmunoprecipitated with Gadd45b. Our results suggested that the ALK5 signaling pathway plays a critical role in mediating neural plasticity and neurological function recovery via Gadd45b after cerebral ischemia, representing a new potential target for cerebral I/R injury.

Gadd45b Acts as Neuroprotective Effector in Global Ischemia-Induced Neuronal Death

PURPOSE

Transient global ischemia arising in human due to cardiac arrest causes selective, delayed neuronal death in hippocampal CA1 and cognitive impairment. Growth arrest and DNA-damage-inducible protein 45 beta (Gadd45b) is a wellknown molecule in both DNA damage-related pathogenesis and therapies. Emerging evidence suggests that Gadd45b is an anti-apoptotic factor in nonneuronal cells and is an intrinsic neuroprotective molecule in neurons. However, the mechanism of Gadd45b pathway is not fully examined in neurodegeneration associated with global ischemia.

METHODS

Rats were subjected to transient global ischemia by the 4-vessel occlusion or sham operation. The animals were sacrificed at 24 hours, 48 hours, and 7 days after ischemia. The hippocampal CA1 was microdissected and processed to examine mRNA and protein level. To assess neuronal death, tissue sections were cut and processed for Fluoro-Jade and Nissl staining.

RESULTS

Here we show that ischemic insults increase abundance of Gadd45b and brain-derived neurotrophic factor, a known target of Gadd45 mediated demethylation, in selectively-vulnerable hippocampal CA1 neurons. We further show that knockdown of Gadd45b increases abundance of a pro-apoptotic Bcl-2 family member Bax while decreasing the antiapoptotic protein Bcl-2, which together promote neuronal death.

CONCLUSION

These findings document a protective role of Gadd45b against neuronal insults associated with global ischemia and identify Gadd45b as a potential therapeutic target for the amelioration of hippocampal neurodegeneration.

Fluorescent labeling of CRISPR/Cas9 RNP for gene knockout in HSPCs and iPSCs reveals an essential role for GADD45b in stress response

CRISPR/Cas9-mediated gene editing of stem cells and primary cell types has several limitations for clinical applications. The direct delivery of ribonucleoprotein (RNP) complexes consisting of Cas9 nuclease and guide RNA (gRNA) has improved DNA- and virus-free gene modifications, but it does not enable the essential enrichment of the gene-edited cells. Here, we established a protocol for the fluorescent labeling and delivery of CRISPR/Cas9-gRNA RNP in primary human hematopoietic stem and progenitor cells (HSPCs) and induced pluripotent stem cells (iPSCs). As a proof of principle for genes with low-abundance transcripts and context-dependent inducible expression, we successfully deleted growth arrest and DNA-damage-inducible β (GADD45B). We found that GADD45B is indispensable for DNA damage protection and survival in stem cells. Thus, we describe an easy and efficient protocol of DNA-free gene editing of hard-to-target transcripts and enrichment of gene-modified cells that are generally difficult to transfect.

Identification of key pathways and genes in lung carcinogenesis

The present study aimed to identify key pathways and genes in the pathogenesis of lung cancer. The GSE10072 dataset was downloaded from the Gene Expression Omnibus database. Protein-protein interaction data were collected from Human Protein Reference Database, and 201 pathways were downloaded from the Kyoto Encyclopedia of Genes and Genomes database. Signaling network impact analysis was performed to identify enriched pathways, followed by the construction of a pathway-pathway crosstalk network. Benzopyrene was used to treat normal human lung cells at concentrations of 0.01, 0.1, 1 and 10 µM, and cell viability was measured. Furthermore, growth arrest and DNA damage inducible β (GADD45B), p53, cyclin B, Akt and nuclear factor (NF)-κB protein levels were also measured via western blotting. Impact analysis identified 11 enriched lung cancer-associated KEGG pathways, including 'complement and coagulation cascades', 'ECM-receptor interaction', 'P53 signaling pathway', 'cell adhesion molecules' and 'focal adhesion'. In addition, cell cycle, 'drug metabolism-cytochrome P450', 'metabolic pathways', 'pathways in cancer', 'focal adhesion' and 'antigen processing and presentation' were central in the pathway-pathway cross-talk network. Furthermore, the upregulated gene GADD45B was associated with three of the pathways, including an activated pathway ('MAPK signaling pathway') and two repressed pathways ('cell cycle' and 'P53 pathway'). Western blotting demonstrated that the expression of NF-κB, Akt and GADD45B increased over time in lung cells treated with benzopyrene, whereas the expression levels of cyclin B and P53 decreased. In conclusion, GADD45B may contribute to lung carcinogenesis via affecting the MAPK, P53 signaling and cell cycle pathways.

Loss of Gadd45b accelerates BCR-ABL-driven CML

Gadd45b is a member of Gadd45 stress sensor protein family that also includes Gadd45a & Gadd45g. To investigate the effect of Gadd45b in bcr-abl oncogene driven chronic myeloid leukemia (CML) development, syngeneic wild type lethally irradiated mice were reconstituted with either wild type or Gadd45b null myeloid progenitors transduced with a retroviral vector expressing BCR-ABL. Loss of Gadd45b was observed to accelerate BCR-ABL driven CML development with shortened median mouse survival time. BCR-ABL Gadd45b deficient CML progenitors exhibited increased proliferation and decreased apoptosis, associated with hyper-activation of c-Jun NH₂-terminal kinase and Stat5. These results provide novel evidence that gadd45b, like gadd45a, functions as a suppressor of BCR-ABL driven leukemia, albeit via a different mechanism.

Brazilin induces T24 cell death through c-Fos and GADD45β independently regulated genes and pathways

Purified Brazilin from Sappan wood extract has been reported with significant antitumor effect, especially on human T24 cells and bladder cancer mouse models. Brazilin can significantly induce expression of c-Fos and GADD45β and transfection expression of c-Fos and GADD45β in T24 cells can induce significant cell morphology changes, reduced viability and cell death, while transfection of siRNA-c-Fos and siRNA-GADD45β can reverse the induced cell death. Co-transfection of both c-Fos and GADD45β into T24 cells resulted in a significantly additive effect when compared to single transfection with only c-Fos or GADD45β. Meanwhile, transfection of interfering siRNA-c-Fos or siRNA-GADD45β can partially rescue the cell viability and siRNA co-transfection showed increased rescue rate. The transfection expression and interference with pcDNA3.1-c-Fos/siRNA-c-Fos or pcDNA3.1-GADD45β/siRNA-GADD45β did not affect each other's expression. Moreover, analysis of c-Fos and GADD45β regulated genes and signal pathways showed that no common regulated genes or pathways were present. All the results indicated that c-Fos and GADD45β mediate independent Brazilin-inducible genes and pathways. © 2018 IUBMB Life, 70(11):1101-1110, 2018.

Gadd45a gene silencing by RNAi promotes cell proliferation and inhibits apoptosis and senescence in skin squamous cell carcinoma through the p53 signaling pathway

Skin squamous cell carcinoma (SCC) is generally considered as nonaggressive lesions and mainly caused by ultraviolet (UV) radiation. Gadd45a is a key component protecting skin against UV-induced tumors. For that, the study aims to investigate the mechanism of Gadd45a gene silencing on cell proliferation, apoptosis, and senescence in nude mice with skin SCC through the p53 signaling pathway. Healthy nude mice was collected as the normal group and 40 nude mouse models of skin SCC were successfully established as the model group, which were sub-divided into five groups. The incidence, size, and weight of SCC tumor of nude mice were observed. The mRNA expression of Gadd45a, Cyclin B1, MMP-2, Bcl-2, and Bax were determined by RT-qPCR. Cell viability, cell cycle and apoptosis, cell senescence were detected by MTT assay, flow cytometry, and β-galactosidase staining, respectively. The levels of inflammatory factors and vascular endothelial growth factor (VEGF) were detected by using ELISA. The protein expression rate of mutant p53 was detected by immunohistochemistry. Mice transfected with siGadd45a showed increased tumor incidence, size, and weight. Cells transfected with siGadd45a showed decrease in expression of Gadd45a and Bax; and increase in expression of Cyclin B1, MMP-2, and Bcl-2, expression of mutant p53, IL-1α, IL-1β, IL-6, TNF-α, and VEGF. Cell apoptosis and senescence were inhibited, while cell viability and proliferation were promoted after siGadd45a treatment. The results reveal that Gadd45a silencing increases tumor cell proliferation and reduces apoptosis and senescence through the p53 signaling pathway in skin SCC.

Down-regulation of GADD45A enhances chemosensitivity in melanoma

Melanoma is a malignant skin cancer with considerable drug resistance. Increased expression of DNA repair genes have been reported in melanoma, and this contributes to chemotherapy resistance. GADD45A is involved in DNA repair, cell cycle arrest and apoptosis in response to physiologic or environmental stresses. In this study, we investigated the role of GADD45A in chemotherapy response. Firstly, the mRNA expression of profiled DNA repair genes in cisplatin-treated melanoma cells was detected by RT2 profilerTM PCR array. We found the expression of GADD45A upregulated in a dose- and time- dependent manner. In addition, suppression of GADD45A sensitized melanoma cells to cisplatin and enhanced cisplatin-induced DNA damage. Flow cytometry revealed that downregulating GADD45A released cells from cisplatin-induced G2/M arrest and increased apoptosis. By using a MEK inhibitor, GADD45A was shown to be regulated by MAPK-ERK pathway following cisplatin treatment. Thus, the induction of GADD45A might play important roles in chemotherapy response in human melanoma cancer and could serve as a novel molecular target for melanoma therapy.

GADD45 family proteins suppress JNK signaling by targeting MKK7

Growth arrest and DNA damage-inducible 45 (GADD45) family genes encode related proteins, including GADD45α, GADD45β, and GADD45γ. In HeLa cells, expression of GADD45 members is differentially regulated under a variety of environmental conditions, but thermal and genotoxic stresses induce the expression of all genes. The heat shock response of GADD45β is mediated by the heat shock transcription factor 1 (HSF1), and GADD45β is necessary for heat stress survival. Heat and genotoxic stress-induced activation of c-Jun N-terminal kinase (JNK) is suppressed by the expression of GADD45 proteins. GADD45 proteins bind the JNK kinase mitogen-activated protein kinase kinase 7 (MKK7) and inhibit its activity, even under normal physiological conditions. Our findings indicate that GADD45 essentially suppresses the MKK7-JNK pathway and suggest that differentially expressed GADD45 family members fine-tune stress-inducible JNK activity.

Gadd45a deficiency accelerates BCR-ABL driven chronic myelogenous leukemia

The Gadd45a stress sensor gene is a member in the Gadd45 family of genes that includes Gadd45b & Gadd45g. To investigate the effect of GADD45A in the development of CML, syngeneic wild type lethally irradiated mice were reconstituted with either wild type or Gadd45a null myeloid progenitors transduced with a retroviral vector expressing the 210-kD BCR-ABL fusion oncoprotein. Loss of Gadd45a was observed to accelerate BCR-ABL driven CML resulting in the development of a more aggressive disease, a significantly shortened median mice survival time, and increased BCR-ABL expressing leukemic stem/progenitor cells (GFP+Lin- cKit+Sca+). GADD45A deficient progenitors expressing BCR-ABL exhibited increased proliferation and decreased apoptosis relative to WT counterparts, which was associated with enhanced PI3K-AKT-mTOR-4E-BP1 signaling, upregulation of p30C/EBPa expression, and hyper-activation of p38 and Stat5. Furthermore, Gadd45a expression in samples obtained from CML patients was upregulated in more indolent chronic phase CML samples and down regulated in aggressive accelerated phase CML and blast crisis CML. These results provide novel evidence that Gadd45a functions as a suppressor of BCR/ABL driven leukemia and may provide a unique prognostic marker of CML progression.

The P38α rs3804451 Variant Predicts Chemotherapy Response and Survival of Patients with Non-Small Cell Lung Cancer Treated with Platinum-Based Chemotherapy

The JNK and P38α pathways play an important role in the sensitivity and outcomes of chemotherapy. We hypothesize that functional single nucleotide polymorphisms (SNPs) of genes of these pathways modulate outcomes of patients with advanced non-small cell lung cancer (NSCLC) treated with first-line platinum-based chemotherapy (PBC). We selectively genotyped 11 independent, potentially functional SNPs of 9 genes in the JNK and P38α pathways first in a discovery group of 355 patients with advanced NSCLC treated with PBC, and we evaluated their associations with progression-free survival (PFS) and overall survival (OS) by Cox proportional hazards regression analysis. Then, resultant significant SNPs were further validated in a replication group of 355 patients. In both discovery and validation groups as well as their combined analysis, the MAPK14 rs3804451GA/AA genotypes showed a strong association with a reduced PFS (adjusted hazards ratio [HR]=1.39; 95% confidence interval [CI]=1.16-1.66; P=.0003) and OS (adjusted HR=1.41; 95% CI=1.11-1.80; P=.005) compared with the wild-type GG genotype. In contrast, patients with or without the MAPK14 rs3804451A allele had no significant difference in OS in response to tyrosine-kinase inhibitor treatment (adjusted HR=0.86; 95% CI=0.56-1.33; P=.505). The present study provides evidence that the MAPK14 rs3804451 G>A variant may modulate survival outcomes in patients with advanced NSCLC treated with PBC. Larger studies of additional patient populations are needed to validate our findings.

Antiproliferative and proapoptotic effects of a pyrrole containing arylthioindole in human Jurkat leukemia cell line and multidrug-resistant Jurkat/A4 cells

Recently, a series of novel arylthioindole compounds, potent inhibitors of tubulin polymerization and cancer cell growth, were synthesized. In the present study the effects of 2-(1H-pyrrol-3-yl)-3-((3,4,5-trimethoxyphenyl)thio)-1H-indole (ATI5 compound) on cell proliferation, cell cycle progression, and induction of apoptosis in human T-cell acute leukemia Jurkat cells and their multidrug resistant Jurkat/A4 subline were investigated. Treatment of the Jurkat cells with the ATI5 compound for 48 hrs resulted in a strong G2/M cell cycle arrest and p53-independent apoptotic cell death accompanied by the induction of the active form of caspase-3 and poly(ADP-ribose) polymerase-1 (PARP-1) cleavage. ATI5 treatment also caused non-cell death related mitotic arrest in multidrug resistant Jurkat/A4 cells after 48 hrs of treatment suggesting promising opportunities for the further design of pyrrole-containing ATI compounds as anticancer agents. Cell death resistance of Jurkat/A4 cells to ATI5 compound was associated with alterations in the expression of pro-survival and anti-apoptotic protein-coding and microRNA genes. More importantly, findings showing that ATI5 treatment induced p53-independent apoptosis are of great importance from a therapeutic point of view since p53 mutations are common genetic alterations in human neoplasms.

Effect of GADD45a on olaquindox-induced apoptosis in human hepatoma G2 cells: Involvement of mitochondrial dysfunction

Olaquindox, a quinoxaline 1, 4-dioxide derivative, has been widely used as a feed additive for promoting animal growth in China. The aim of present study was to investigate the effect of grow arrest and DNA damage 45 alpha (GADD45a) on olaquindox-induced apoptosis in HepG2 cells. The result showed that olaquindox induced the decrease of cell viability in a dose dependent manner. Compared to the control group, olaquindox treatment at 400 and 800μg/mL increased the expression level of GADD45a protein and reactive oxygen species (ROS) production, decreased mitochondrial membrane potential (MMP), and subsequently increased the expression of Bax while decreased the expression of Bcl-2, leading to the release of cytochrome c (Cyt c). However, knockdown of GADD45a enhanced olaquindox-induced ROS production, disrupted MMP and subsequently caused Cyt c release, then further increased olaquindox- induced cell apoptosis by increasing the activities of caspase-9, caspase-3, and poly (ADP-ribose) polymerase (PARP). In conclusion, the results revealed that GADD45a played a critical role in olaquindox-induced apoptosis in HepG2 cells, which may embrace the regulatory ability on the mitochondrial apoptosis pathway.

Cell death caused by the synergistic effects of zinc and dopamine is mediated by a stress sensor gene Gadd45b - implication in the pathogenesis of Parkinson's disease

The pathogenesis of Parkinson's disease (PD) is not completely understood, Zinc (Zn(2+) ) and dopamine (DA) have been shown to involve in the degeneration of dopaminergic cells. By microarray analysis, we identified Gadd45b as a candidate molecule that mediates Zn(2+) and DA-induced cell death; the mRNA and protein levels of Gadd45b are increased by Zn(2+) treatment and raised to an even higher level by Zn(2+) plus DA treatment. Zn(2+) plus DA treatment-induced PC12 cell death was enhanced when there was over-expression of Gadd45b and was decreased by knock down of Gadd45b. MAPK p38 and JNK signaling was able to cross-talk with Gadd45b during Zn(2+) and DA treatment. The synergistic effects of Zn(2+) and DA on PC12 cell death can be accounted for by an activation of the Gadd45b-induced cell death pathway and an inhibition of p38/JNK survival pathway. Furthermore, the in vivo results show that the levels of Gadd45b protein expression and phosphorylation of p38 were increased in the substantia nigra by the infusion of Zn(2+) /DA in the mouse brain and the level of Gadd45b mRNA is significantly higher in the substantia nigra of male PD patients than normal controls. The novel role of Gadd45b and its interactions with JNK and p38 will help our understanding of the pathogenesis of PD and help the development of future treatments for PD. Zinc and dopamine are implicated in the degeneration of dopaminergic neurons. We previously demonstrated that zinc and dopamine induced synergistic effects on PC12 cell death. Results from this study show that these synergistic effects can be accounted for by activation of the Gadd45b-induced cell death pathway and inhibition of the p38/JNK survival pathway. We provide in vitro and in vivo evidence to support a novel role for Gadd45b in the pathogenesis of Parkinson's disease.

Lack of p53 Augments Antitumor Functions in Cytolytic T Cells

Repetitive stimulation of T-cell receptor (TCR) with cognate antigen results in robust proliferation and expansion of the T cells, and also imprints them with replicative senescence signatures. Our previous studies have shown that life-span and antitumor function of T cells can be enhanced by inhibiting reactive oxygen species (ROS) or intervening with ROS-dependent JNK activation that leads to its activation-induced cell death. Because tumor suppressor protein p53 is also a redox active transcription factor that regulates cellular ROS generation that triggers downstream factor-mediating apoptosis, we determined if p53 levels could influence persistence and function of tumor-reactive T cells. Using h3T TCR transgenic mice, with human tyrosinase epitope-reactive T cells developed on p53 knockout (KO) background, we determined its role in regulating antitumor T-cell function. Our data show that as compared with h3T cells, h3T-p53 KO T cells exhibited enhanced glycolytic commitment that correlated with increased proliferation, IFNγ secretion, cytolytic capacity, expression of stemness gene signature, and decreased TGF-β signaling. This increased effector function correlated to the improved control of subcutaneously established murine melanoma after adoptive transfer of p53-KO T cells. Pharmacological inhibition of human TCR-transduced T cells using a combination of p53 inhibitors also potentiated the T-cell effector function and improved persistence. Thus, our data highlight the key role of p53 in regulating the tumor-reactive T-cell response and that targeting this pathway could have potential translational significance in adoptive T-cell therapy. Cancer Res; 76(18); 5229-40. ©2016 AACR.

Sex differences in Gadd45b expression and methylation in the developing rodent amygdala

Precise spatiotemporal epigenetic regulation of the genome facilitates species-typical development; sexual differentiation of the brain by gonadal hormones and sex chromosomes causes extensive epigenetic reprogramming of many cells in the body, including the brain, and may indirectly predispose males and females to different psychiatric conditions. We and others have demonstrated sex differences in DNA methylation, as well as in the enzymes that form, or 'write', this epigenetic modification. However, while a growing body of evidence suggests that DNA methylation undergoes rapid turnover and is dynamically regulated in vivo, to our knowledge no studies have been done investigating whether sex differences exist in the epigenetic 'erasers' during postnatal development. Here we report sex differences in the expression of growth arrest and DNA damage inducible factor β (Gadd45b), but not family members α (a) or γ (g), in the neonatal and juvenile rodent amygdala.

Transcriptional Profiles in Liver from Mice Treated with Hepatotumorigenic and Nonhepatotumorigenic Triazole Conazole Fungicides: Propiconazole, Triadimefon, and Myclobutanil

Conazoles are environmental and pharmaceutical fungicides. The present study relates the toxicological effects of conazoles to alterations of gene and pathway transcription and identifies potential modes of tumorigenic action. In a companion study employing conventional toxicological bioassays ( Allen et al., 2006 ), male CD-1 mice were fed triadimefon, propiconazole, or myclobutanil in a continuous oral-dose regimen for 4, 30, or 90 days. These conazoles were found to induce hepatomegaly, to induce high levels of hepatic pentoxyresorufin-O-dealkylase activity, to increase hepatic cell proliferation, to decrease serum cholesterol, and to increase serum triglycerides. Differentially expressed genes and pathways were identified using Affymetrix GeneChips. Gene-pathway associations were obtained from the Kyoto Encyclopedia of Genes and Genomes, Biocarta, and MetaCore compendia. The pathway profiles of each conazole were different at each time point. In general, the number of altered metabolism, signaling, and growth pathways increased with time and dose and were greatest with propiconazole. All conazoles had effects on nuclear receptors as evidenced by increased expression and enzymatic activities of a series of related cytochrome P450s (CYP). A subset of altered genes and pathways distinguished the three conazoles from each other. Triadimefon and propiconazole both altered apoptosis, cell cycle, adherens junction, calcium signaling, and EGFR signaling pathways. Triadimefon produced greater changes in cholesterol biosynthesis and retinoic acid metabolism genes and in selected signaling pathways. Propiconazole had greater effects on genes responding to oxidative stress and on the IGF/P13K/AKt/PTEN/mTor and Wnt-β-catenin pathways. In conclusion, while triadimefon, propiconazole, and myclobutanil had similar effects in mouse liver on hepatomegaly, histology, CYP activities, cell proliferation, and serum cholesterol, genomic analyses revealed major differences in their gene expression profiles.

Terminal differentiation induction as DNA damage response in hematopoietic stem cells by GADD45A

Hematopoietic stem cells (HSCs) sustain lifelong blood cell regeneration by balancing their ability for self-renewal with their ability to differentiate into all blood cell types. To prevent organ exhaustion and malignant transformation, long-lived HSCs, in particular, must be protected from exogenous and endogenous stress, which cause severe DNA damage. When DNA is damaged, distinct DNA repair mechanisms and cell fate controls occur in adult HSCs compared with committed cells. Growth arrest and DNA damage-inducible 45 alpha (GADD45A) is known to coordinate a variety of cellular stress responses, indicating the molecule is an important stress mediator. So far, the function of GADD45A in hematopoietic stem and progenitor cells is controversial and appears highly dependent on the cell type and stress stimulus. Recent studies have analyzed its role in cell fate decision control of prospectively isolated HSCs and have revealed unexpected functions of GADD45A, as discussed here. The upregulation of GADD45A by DNA damage-causing conditions results in enhanced HSC differentiation, probably to efficiently eliminate aberrant HSCs from the system. These findings, in concert with a few studies on other stem cell systems, have led us to propose DNA damage-induced differentiation as a novel DNA damage response mechanism in stem cells that circumvents the fatal consequences of cumulative DNA damage in the stem cell compartment.

The protective role of Nrf2-Gadd45b against antimony-induced oxidative stress and apoptosis in HEK293 cells

Antimony (Sb) is one of the most prevalent heavy metals and frequently causes biological toxicity. However, the specific mechanisms by which Sb elicits its toxic effects remains to be fully elucidated. In this study, we found antimony trioxide (Sb2O3) caused a dose-dependent cytotoxicity against HEK293 cells, and Sb2O3-induced excessive reactive oxygen species (ROS) was closely correlated with increased cell apoptosis. Mechanistic investigation manifested that nuclear factor NF-E2-related factor 2 (Nrf2) expression and nuclear translocation were significantly induced under Sb2O3 treatment in HEK293 cells, and Nrf2 knockdown aggregated Sb2O3-induced cell apoptosis. Moreover, elevated Gadd45b expression actives the phosphorylation of MAPKs upon Sb2O3 exposure, whereas Gadd45b knockdown diminished Sb2O3-induced activation of MAPKs and promoted cell apoptosis. In the meantime, however, the antioxidant N-acetylcysteine (NAC) was found to ameliorate Nrf2 expression and nuclear translocation as well as Gadd45b expression and MAPKs activation by repressing Sb2O3-induced ROS production. More importantly, we found Gadd45b was transcriptionally enhanced by Nrf2 through binding to three canonical antioxidant response elements (AREs) within its promoter region. Either Sb2O3 or TBHQ (a selective Nrf2 activator) treatment, Gadd45b expression was significantly increased by luciferase assay. Nrf2 inhibition greatly diminished Gadd45b expression due to reduced binding of Nrf2 in Gadd45b promoter under Sb2O3 treatment. To summarize, this study demonstrated the Nrf2-Gadd45b signaling axis exhibited a protective role in Sb-induced cell apoptosis.

GADD45 proteins inhibit HIV-1 replication through specific suppression of HIV-1 transcription

GADD45 proteins are a group of stress-induced proteins and participate in various cellular pathways including cell cycle regulation, cell survival and death, DNA repair and demethylation. It was recently shown that HIV-1 infection induces the expression of GADD45 proteins. However, the effect of GADD45 on HIV-1 replication has not been studied. Here, we report that overexpression of GADD45 proteins reduces HIV-1 production through suppressing transcription from the HIV-1 LTR promoter. This inhibitory effect is specific to HIV-1, since GADD45 proteins neither inhibit the LTR promoters from other retroviruses nor reduce the production of these viruses. Knockdown of endogenous GADD45 modestly activates HIV-1 in the J-Lat A72 latency cell line, which suggests GADD45 proteins might play a role in maintaining HIV-1 latency.

Oxidative stress-induced Gadd45α inhibits trophoblast invasion and increases sFlt1/sEng secretions via p38 MAPK involving in the pathology of pre-eclampsia

BACKGROUND

Pre-eclampsia (PE) is one of the most common pregnancy-related complications. We have previously reported that growth arrest and DNA damage-inducible 45 alpha (Gadd45α) is over-expressed in trophoblasts in pre-eclamptic placentas, with an excessive activation of p38 mitogen-activated protein kinase (MAPK) and increased levels of soluble Fms-like tyrosine kinase 1 (sFlt-1) and soluble endoglin (sEng) in maternal sera. Now we further investigate how Gadd45α regulates trophoblast functions and anti-angiogenesis factors secretions during placental development in patients with PE.

METHODS

Human placental villous explants were used to verify the effects of Gadd45α and p38 MAPK in placentation. Then HRT8/SVneo cells exposed to hypoxia/reoxygenation (H/R) were employed as an oxidative stress model to investigate the effects of Gadd45α on invasion and sFlt-1/sEng secretions. Through silencing Gadd45α with lentiviral vector-based short-hairpin RNA and inhibiting p38 MAPK with SB203580, we demonstrated that Gadd45α and its downstream p38 protein played roles in the pathology of pre-eclampsia.

RESULTS

Gadd45α was found to have increased expression in H/R-treated villous explants and HTR8/SVneo cells. Gadd45α knockdown or p38 blockage could promote trophoblast outgrowth and migration in H/R-exposed villous explants, and enhance the potentials of trophoblast migration/invasion and network formation in H/R-exposed HTR8/SVneo cells. These functional changes might be related to the increased activities of MMP2/9. Meanwhile, Gadd45α knockdown or p38 inhibition also decreases sFlt-1/sEng secretions via suppressing oxidative stress.

CONCLUSIONS

Oxidative stress-induced overexpression of Gadd45α might influence the activity of MMPs through activation of p38 MAPK signaling to affect the invasion of trophoblast cells, and increase the secretions of sFlt-1/sEng, which then participate in the pathogenesis of pre-eclampsia.

CCAAT/enhancer binding protein β (C/EBPβ) regulates the transcription of growth arrest and DNA damage-inducible protein 45 β (GADD45β) in articular chondrocytes

Osteoarthritis (OA) is a whole joint disease characterized by cartilage degradation, which causes pain and disability in older adults. Our previous work showed that growth arrest and DNA damage-inducible protein 45 β (GADD45β) is upregulated in chondrocyte clusters in OA cartilage, especially in the early stage of this disease. CCAAT/enhancer binding protein β (C/EBPβ) is expressed in the hypertrophic growth plate chondrocytes and functions in synergy with GADD45β. Here, the presence and localization of these proteins was assessed by immunohistochemistry using articular cartilage from OA patients, revealing colocalization of C/EBPβ and GADD45β in OA chondrocytes. GADD45β promoter analysis was performed to determine whether C/EBPβ directly regulates GADD45β transcription. Furthermore, we analyzed the effect of C/EBPβ on Gadd45β gene regulation in articular chondrocytes in vivo and in vitro. Immunohistochemical analysis of C/ebpβ-haploinsufficient mice (C/ebpβ(+/-)) cartilage showed that C/ebpβ haploinsufficiency led to reduced Gadd45β gene expression in these cells. In vitro, we evaluated the effects of conditional C/EBPβ overexpression driven by the cartilage oligomeric matrix protein (Comp) promoter in mComp-tTA;pTRE-Tight-BI-DsRed-mC/ebpβ transgenic mice. C/EBPβ overexpression significantly stimulated Gadd45β gene expression in articular chondrocytes. Taken together, our data demonstrate that C/EBPβ plays a central role in controlling Gadd45β gene expression in these cells.

DNA-damage response gene GADD45A induces differentiation in hematopoietic stem cells without inhibiting cell cycle or survival

Hematopoietic stem cells (HSCs) maintain blood cell production life-long by their unique abilities of self-renewal and differentiation into all blood cell lineages. Growth arrest and DNA-damage-inducible 45 alpha (GADD45A) is induced by genotoxic stress in HSCs. GADD45A has been implicated in cell cycle control, cell death and senescence, as well as in DNA-damage repair. In general, GADD45A provides cellular stability by either arresting the cell cycle progression until DNA damage is repaired or, in cases of fatal damage, by inducing apoptosis. However, the function of GADD45A in hematopoiesis remains controversial. We revealed the changes in murine HSC fate control orchestrated by the expression of GADD45A at single cell resolution. In contrast to other cellular systems, GADD45A expression did not cause a cell cycle arrest or an alteration in the decision between cell survival and apoptosis in HSCs. Strikingly, GADD45A strongly induced and accelerated the differentiation program in HSCs. Continuous tracking of individual HSCs and their progeny via time-lapse microscopy elucidated that once GADD45A was expressed, HSCs differentiate into committed progenitors within 29 hours. GADD45A-expressing HSCs failed to long-term reconstitute the blood of recipients by inducing multilineage differentiation in vivo. Importantly, γ-irradiation of HSCs induced their differentiation by upregulating endogenous GADD45A. The differentiation induction by GADD45A was transmitted by activating p38 Mitogen-activated protein kinase (MAPK) signaling and allowed the generation of megakaryocytic-erythroid, myeloid, and lymphoid lineages. These data indicate that genotoxic stress-induced GADD45A expression in HSCs prevents their fatal transformation by directing them into differentiation and thereby clearing them from the system.

GADD45B mediates podocyte injury in zebrafish by activating the ROS-GADD45B-p38 pathway

GADD45 gene has been implicated in cell cycle arrest, cell survival or apoptosis in a cell type specific and context-dependent manner. Members of GADD45 gene family have been found differentially expressed in several podocyte injury models, but their roles in podocytes are unclear. Using an in vivo zebrafish model of inducible podocyte injury that we have previously established, we found that zebrafish orthologs of gadd45b were induced upon the induction of podocyte injury. Podocyte-specific overexpression of zebrafish gadd45b exacerbated edema, proteinuria and foot-process effacement, whereas knockdown of gadd45b by morpholino-oligos in zebrafish larvae ameliorated podocyte injury. We then explored the role of GADD45B induction in podocyte injury using in vitro podocyte culture. We confirmed that GADD45B was significantly upregulated during the early phase of podocyte injury in cultured human podocytes and that podocyte apoptosis induced by TGF-β and puromycin aminonucleoside (PAN) was aggravated by GADD45B overexpression but ameliorated by shRNA-mediated GADD45B knockdown. We also showed that ROS inhibitor NAC suppressed PAN-induced GADD45B expression and subsequent activation of p38 MAPK pathway in podocytes and that inhibition of GADD45B diminished PAN-induced p38 MAPK activation. Taken together, our findings demonstrated that GADD45B has an important role in podocyte injury and may be a therapeutic target for the management of podocyte injury in glomerular diseases.

Tumor cell survival pathways activated by photodynamic therapy: a molecular basis for pharmacological inhibition strategies

Photodynamic therapy (PDT) has emerged as a promising alternative to conventional cancer therapies such as surgery, chemotherapy, and radiotherapy. PDT comprises the administration of a photosensitizer, its accumulation in tumor tissue, and subsequent irradiation of the photosensitizer-loaded tumor, leading to the localized photoproduction of reactive oxygen species (ROS). The resulting oxidative damage ultimately culminates in tumor cell death, vascular shutdown, induction of an antitumor immune response, and the consequent destruction of the tumor. However, the ROS produced by PDT also triggers a stress response that, as part of a cell survival mechanism, helps cancer cells to cope with the PDT-induced oxidative stress and cell damage. These survival pathways are mediated by the transcription factors activator protein 1 (AP-1), nuclear factor E2-related factor 2 (NRF2), hypoxia-inducible factor 1 (HIF-1), nuclear factor κB (NF-κB), and those that mediate the proteotoxic stress response. The survival pathways are believed to render some types of cancer recalcitrant to PDT and alter the tumor microenvironment in favor of tumor survival. In this review, the molecular mechanisms are elucidated that occur post-PDT to mediate cancer cell survival, on the basis of which pharmacological interventions are proposed. Specifically, pharmaceutical inhibitors of the molecular regulators of each survival pathway are addressed. The ultimate aim is to facilitate the development of adjuvant intervention strategies to improve PDT efficacy in recalcitrant solid tumors.

Metformin ameliorates acetaminophen hepatotoxicity via Gadd45β-dependent regulation of JNK signaling in mice

BACKGROUND & AIMS

Acetaminophen (APAP) overdose is a leading cause of drug-induced acute liver failure. Prolonged c-Jun N-terminal kinase (JNK) activation plays a central role in APAP-induced liver injury and growth arrest, and DNA damage-inducible 45 beta (Gadd45β) is known to inhibit JNK phosphorylation. Metformin has recently been shown to have hepatoprotective effects. The aim of the present study is to investigate whether metformin mitigates APAP-induced hepatotoxicity and to ascertain the molecular basis of this effect.

METHODS

We used APAP- and/or metformin-treated Gadd45β knockout (KO) mice and wild type (WT) C57BL/6J control mice. Primary mouse hepatocytes were isolated from WT and Gadd45β KO mice were used for in vitro study.

RESULTS

Metformin pretreatment protected against APAP toxicity with decreased liver damage, and inhibited APAP-induced prolonged hepatic JNK phosphorylation in WT mice. Gadd45β expression was increased after APAP treatment, and the expression of Gadd45β was further enhanced by metformin. The effects of metformin on APAP-induced liver injury and JNK phosphorylation were abolished in Gadd45β KO mice. Notably, subtoxic doses of APAP caused cell death and sustained JNK phosphorylation in Gadd45β-deficient primary hepatocytes. In parallel, APAP increased mortality, severe liver injury, and JNK activation in Gadd45β KO mice. Interestingly, metformin administered after APAP treatment protected against APAP-evoked hepatotoxicity in WT mice, but not in Gadd45β KO mice.

CONCLUSIONS

This study is the first to demonstrate that metformin shows protective and therapeutic effects against APAP overdose-evoked hepatotoxicity via Gadd45β-dependent JNK regulation. Metformin would be a promising therapeutic strategy for treatment of APAP overdose.