Cyclin B1 proteolysis via p38 MAPK signaling participates in G2 checkpoint elicited by arsenite

P38 kinase in gastrointestinal cancers

Gastrointestinal cancers are a leading cause of cancer morbidity and mortality worldwide with 4.2 million new cases and 3.2 million deaths estimated in 2020. Despite the advances in primary and adjuvant therapies, patients still develop distant metastases and require novel therapies. Mitogen‑activated protein kinase (MAPK) cascades are crucial signaling pathways that regulate many cellular processes, including proliferation, differentiation, apoptosis, stress responses and cancer development. p38 Mitogen Activated Protein Kinases (p38 MAPKs) includes four isoforms: p38α (MAPK14), p38β (MAPK11), p38γ (MAPK12), and p38δ (MAPK13). p38 MAPK was first identified as a stress response protein kinase that phosphorylates different transcriptional factors. Dysregulation of p38 pathways, in particular p38γ, are associated with cancer development, metastasis, autophagy and tumor microenvironment. In this article, we provide an overview of p38 and p38γ with respect to gastrointestinal cancers. Furthermore, targeting p38γ is also discussed as a potential therapy for gastrointestinal cancers.

TAT-OSBP-1-MKK6(E), a novel TAT-fusion protein with high selectivity for human ovarian cancer, exhibits anti-tumor activity

To improve the selectivity of TAT-fusion proteins for targeted cancer therapy, we developed a novel TAT-based target-specific fusion protein, TAT-OSBP-1-MKK6(E), and evaluated its selectivity and anti-tumor activity in vitro and in vivo. The fusion protein containing TAT-OSBP-1-MKK6(E) has three functional domains: (1) the protein transduction domain of TAT, (2) the human ovarian cancer HO8910 cell-specific binding peptide (OSBP-1) and (3) the potential anti-tumor effector domain of MKK6(E). The transduction efficiency, selectivity, cytotoxicity and apoptotic effect of TAT-OSBP-1-MKK6(E) were examined using immunofluorescence, CCK8 assay and flow cytometry. The in vivo anti-tumor efficacy and target specificity of the fusion protein were evaluated using a nude mouse model with subcutaneous xenografts of human ovarian cancer HO8910 cells. Tumor-bearing mice were divided into three treatment groups that received tail vein injections of TAT-OSBP-1-MKK6(E), TAT-OSBP-1 or normal saline. Tumor growth inhibition was determined by tumor volume, weight and morphology. The distribution and apoptotic effect of TAT-OSBP-1-MKK6(E) were assessed by immunohistochemical staining and TUNEL assays. TAT-OSBP-1-MKK6(E) can be selectively internalized into human ovarian cancer HO8910 cells, rather than normal ovarian OSE cells. In vivo, the fusion protein was mainly expressed in the tumor xenograft, but not in ovary or liver tissues. As a result, TAT-OSBP-1-MKK6(E) significantly induced growth inhibition and apoptosis of tumor cells in vitro and in vivo, with limited effects in normal cells and tissues. TAT-OSBP-1-MKK6(E) treatment can selectively target HO8910 cells in vitro and in vivo, leading to growth inhibition and apoptosis of tumor cells. As such, TAT-OSBP-1-MKK6(E) may be a potential approach for ovarian cancer target therapy.

Chaetoglobosin K induces apoptosis and G2 cell cycle arrest through p53-dependent pathway in cisplatin-resistant ovarian cancer cells

Adverse side effects and acquired resistance to conventional platinum based chemotherapy have become major impediments in ovarian cancer treatment, and drive the development of more selective anticancer drugs. Chaetoglobosin K (ChK) was shown to have a more potent growth inhibitory effect than cisplatin on two cisplatin-resistant ovarian cancer cell lines, OVCAR-3 and A2780/CP70, and was less cytotoxic to a normal ovarian cell line, IOSE-364, than to the cancer cell lines. Hoechst 33342 staining and Flow cytometry analysis indicated that ChK induced preferential apoptosis and G2 cell cycle arrest in both ovarian cancer cells with respect to the normal ovarian cells. ChK induced apoptosis through a p53-dependent caspase-8 activation extrinsic pathway, and caused G2 cell cycle arrest via cyclin B1 by increasing p53 expression and p38 phosphorylation in OVCAR-3 and A2780/CP70 cells. DR5 and p21 might play an important role in determining the sensitivity of normal and malignant ovarian cells to ChK. Based on these results, ChK would be a potential compound for treating platinum-resistant ovarian cancer.

APE1/Ref-1 prevents oxidative inactivation of ERK for G1-to-S progression following lead acetate exposure

Apurinic/apyrimidinic endonuclease 1 (APE1)/redox effector factor-1 is a multifunctional enzyme involved in DNA base excision repair and protein redox regulation. Previously, we have showed that lead acetate (Pb) elicits EGFR activation to initiate the SFK/PKCα/Ras/Raf-1/MKK1/2/ERK signaling cascade functioning against genotoxicity. Here, we explore whether APE1 and reactive oxygen species (ROS) affect ERK signaling and cell cycle progression following Pb exposure. We found that Pb induced APE1 expression and ROS generation in CL3 human lung cancer cells. The Pb-elicited ROS levels and cytotoxicity were further enhanced by introducing small interfering RNA specific for APE1 (siAPE1). E3330, an inhibitor of APE1 redox activity, also augmented the ROS levels and cytotoxicity in Pb-treated cells. Intriguingly, the capability of Pb to activate ERK was abolished under siAPE1 or E3330 co-treatments; conversely, forced expression of APE1 up-regulated the ERK activation by Pb or serum in both Cys65-redox activity dependent and independent manners. Moreover, APE1 formed complex with ERK2, and its redox activity could rescue ERK oxidative inactivation. APE1 redox activity also facilitated the Cyclin D1 expression and G1-to-S progression following Pb exposure. In summary, the results indicate that APE1 is a direct redox regulator of ERK for maintaining the kinase activity to promote cell proliferation.

Cytotoxic and Genotoxic effects of Arsenic and Lead on Human Adipose Derived Mesenchymal Stem Cells (AMSCs)

Arsenic and lead, known to have genotoxic and mutagenic effects, are ubiquitously distributed in the environment. The presence of arsenic in drinking water has been a serious health problem in many countries. Human exposure to these metals has also increased due to rapid industrialization and their use in formulation of many products. Liposuction material is a rich source of stem cells. In the present study cytotoxic and genotoxic effects of these metals were tested on adipose derived mesenchymal stem cells (AMSCs). Cells were exposed to 1-10 μg/ml and 10-100 μg/ml concentration of arsenic and lead, respectively, for 6, 12, 24 and 48 h. The cytotoxic effects were measured by neutral red uptake assay, while the genotoxic effects were tested by comet assay. The growth of cells decreased with increasing concentration and the duration of exposure to arsenic. Even the morphology of cells was changed; they became round at 10 μg /ml of arsenic. The cell growth was also decreased after exposure to lead, though it proved to be less toxic when cells were exposed for longer duration. The cell morphology remained unchanged. DNA damage was observed in the metal treated cells. Different parameters of comet assay were investigated for control and treated cells which indicated more DNA damage in arsenic treated cells compared to that of lead. Intact nuclei were observed in control cells. Present study clearly demonstrates that both arsenic and lead have cytotoxic and genotoxic effects on AMSCs, though arsenic compared to lead has more deleterious effects on AMSCs.

Design, synthesis, and characterization of a highly effective Hog1 inhibitor: a powerful tool for analyzing MAP kinase signaling in yeast

The Saccharomyces cerevisiae High-Osmolarity Glycerol (HOG) pathway is a conserved mitogen-activated protein kinase (MAPK) signal transduction system that often serves as a model to analyze systems level properties of MAPK signaling. Hog1, the MAPK of the HOG-pathway, can be activated by various environmental cues and it controls transcription, translation, transport, and cell cycle adaptations in response to stress conditions. A powerful means to study signaling in living cells is to use kinase inhibitors; however, no inhibitor targeting wild-type Hog1 exists to date. Herein, we describe the design, synthesis, and biological application of small molecule inhibitors that are cell-permeable, fast-acting, and highly efficient against wild-type Hog1. These compounds are potent inhibitors of Hog1 kinase activity both in vitro and in vivo. Next, we use these novel inhibitors to pinpoint the time of Hog1 action during recovery from G(1) checkpoint arrest, providing further evidence for a specific role of Hog1 in regulating cell cycle resumption during arsenite stress. Hence, we describe a novel tool for chemical genetic analysis of MAPK signaling and provide novel insights into Hog1 action.

Cdc20 proteolysis requires p38 MAPK signaling and Cdh1-independent APC/C ubiquitination during spindle assembly checkpoint activation by cadmium

Cdc20, an activator of the anaphase promoting complex/cyclosome (APC/C) ubiquitin ligase, initiates the destruction of key mitotic regulators to facilitate mitosis, while it is negatively regulated by the spindle assembly checkpoint (SAC) to prevent premature anaphase entry. Activation of the p38 mitogen-activated protein kinase could contribute to mitotic arrest, but the underlying mechanism is unknown. Here we report a novel pathway in which the p38 signaling triggers Cdc20 destruction under SAC elicited by cadmium, a human carcinogen. We found that the cadmium-induced prometaphase arrest was linked to decreased Cdc20 and accumulated cyclin A protein levels in human cells, whereas the activity of cyclin B1-Cdk1 was unaffected. The Cdc20 half-life was markedly shortened along with its ubiquitination and degradation via 26S proteasome in cadmium-treated asynchronous or G(2)-enriched cells. Depletion of APC3 markedly suppressed the cadmium-induced Cdc20 ubiquitination and proteolysis, while depletion of Cdh1, another activator of APC/C, did not. Intriguingly, blockage of p38 activity restored the Cdc20 levels for continuing mitosis under cadmium, while inhibition of JNK activity had no effect. The cadmium-induced Cdc20 proteolysis was also suppressed during transient depletion of p38alpha or stable expression a dominant negative form of p38. Inhibition of p38 abolished the induction of Mad2-Cdc20-APC3 complex by cadmium. Moreover, forced expression of MKK6-p38 signaling could promote Cdc20 degradation in a Cdh1-independent APC/C pathway. In summary, accelerated ubiquitination and proteolysis of Cdc20 is essential for prometaphase arrest that is mediated via the p38 signaling during SAC activation.

Arsenite induces apoptosis in human mesenchymal stem cells by altering Bcl-2 family proteins and by activating intrinsic pathway

PURPOSE

Environmental exposure to arsenic is an important public health issue. The effects of arsenic on different tissues and organs have been intensively studied. However, the effects of arsenic on bone marrow mesenchymal stem cells (MSCs) have not been reported. This study is designed to investigate the cell death process caused by arsenite and its related underlying mechanisms on MSCs. The rationale is that absorbed arsenic in the blood circulation can reach to the bone marrow and may affect the cell survival of MSCs.

METHODS

MSCs of passage 1 were purchased from Tulane University, grown till 70% confluency level and plated according to the experimental requirements followed by treatment with arsenite at various concentrations and time points. Arsenite (iAs(III)) induced cytotoxic effects were confirmed by cell viability and cell cycle analysis. For the presence of canonic apoptosis markers; DNA damage, exposure of intramembrane phosphotidylserine, protein and m-RNA expression levels were analyzed.

RESULTS

iAs(III) induced growth inhibition, G2-M arrest and apoptotic cell death in MSCs, the apoptosis induced by iAs(III) in the cultured MSCs was, via altering Bcl-2 family proteins and by involving intrinsic pathway.

CONCLUSION

iAs(III) can induce apoptosis in bone marrow-derived MSCs via Bcl-2 family proteins, regulating intrinsic apoptotic pathway. Due to the multipotency of MSC, acting as progenitor cells for a variety of connective tissues including bone, adipose, cartilage and muscle, these effects of arsenic may be important in assessing the health risk of the arsenic compounds and understanding the mechanisms of arsenic-induced harmful effects.

The p38 mitogen-activated protein kinase augments nucleotide excision repair by mediating DDB2 degradation and chromatin relaxation

The p38 MAPK is a family of serine/threonine protein kinases that play important roles in cellular responses to external stress signals, e.g. UV irradiation. To assess the role of p38 MAPK pathway in nucleotide excision repair (NER), the most versatile DNA repair pathway, we determined the efficiency of NER in cells treated with p38 MAPK inhibitor SB203580 and found that p38 MAPK is required for the prompt repair of UV-induced DNA damage CPD. We further investigated the possible mechanism through which p38 MAPK regulates NER and found that p38 MAPK mediates UV-induced histone H3 acetylation and chromatin relaxation. Moreover, p38 MAPK also regulates UV-induced DDB2 ubiquitylation and degradation via phosphorylation of the target protein. Finally, our results showed that p38 MAPK is required for the recruitment of NER factors XPC and TFIIH to UV-induced DNA damage sites. We conclude that p38 MAPK regulates chromatin remodeling as well as DDB2 degradation for facilitating NER factor assembly.