Role of ERp57 in the signaling and transcriptional activity of STAT3 in a melanoma cell line

Chromatin immunoprecipitation in M14 melanoma cells showed that the protein ERp57 (endoplasmic reticulum protein 57) binds to DNA in the proximity of STAT3 in a subset of STAT3-regulated genes. In the same cells, IL-6 induced a significant increase of the expression of one of these genes, i.e. CRP. Upon depletion of ERp57 by RNA interference, the phosphorylation of STAT3 on tyrosine 705 was decreased, and the IL-6-induced activation of CRP expression was completely suppressed. In vitro experiments showed that ERp57 is also required for the binding of STAT3 to its consensus sequence on DNA. Thus ERp57, previously shown to associate with STAT3 in the cytosol and in the nuclear STAT3-containing enhanceosome, is a necessary cofactor for the regulation of at least a subset of STAT3-dependent genes, probably intervening both at the site of STAT3 phosphorylation and at the nuclear level.     

Design and discovery of novel quinazolinedione-based redox modulators as therapies for pancreatic cancer

Background

Altered cellular bioenergetics and oxidative stress are emerging hallmarks of most cancers including pancreatic cancer. Elevated levels of intrinsic reactive oxygen species (ROS) in tumors make them more susceptible to exogenously induced oxidative stress. Excessive oxidative insults overwhelm their adaptive antioxidant capacity and trigger ROS-mediated cell death. Recently, we have discovered a novel class of quinazolinediones that exert their cytotoxic effects by modulating ROS-mediated signaling.

Methods

Cytotoxic potential was determined by colorimetric and colony formation assays. An XF24 Extracellular Flux Analyzer, and colorimetric and fluorescent techniques were used to assess the bioenergetics and oxidative stress effects, respectively. Mechanism was determined by Western blots.

Results

Compound 3a (6-[(2-acetylphenyl)amino]quinazoline-5,8-dione) was identified through a medium throughput screen of ~ 1000 highly diverse in-house compounds and chemotherapeutic agents for their ability to alter cellular bioenergetics. Further structural optimizations led to the discovery of a more potent analog, 3b (6-[(3-acetylphenyl)amino]quinazoline-5,8-dione) that displayed anti-proliferative activities in low micromolar range in both drug-sensitive and drug-resistant cancer cells. Treatment with 3b causes Akt activation resulting in increased cellular oxygen consumption and oxidative stress in pancreatic cancer cells. Moreover, oxidative stress induced by 3b promoted activation of stress kinases (p38/JNK) resulting in cancer cell death. Treatment with antioxidants was able to reduce cell death confirming ROS-mediated cytotoxicity.

Conclusion

In conclusion, our novel quinazolinediones are promising lead compounds that selectively induce ROS-mediated cell death in cancer cells and warrant further preclinical studies.

General significance

Since 3b (6-[(3-acetylphenyl)amino]quinazoline-5,8-dione) exerts Akt-dependent ROS-mediated cell death, it might provide potential therapeutic options for chemoresistant and Akt-overexpressing cancers.     

Angoline: A selective IL-6/STAT3 signaling pathway inhibitor isolated from Zanthoxylum nitidum

STAT3 signaling pathway is an important target for human cancer therapy. Thus, the identification of small-molecules that target STAT3 signaling will be of great interests in the development of anticancer agents. The aim of this study was to identify novel inhibitors of STAT3 pathway from the roots of Zanthoxylum nitidum (Roxb.) DC. The bioassay-guided fractionation of MeOH extract of Z. nitidum using a STAT3-responsive gene reporter assay led to the isolation of angoline (1) as a potent and selective inhibitor of the STAT3 signaling pathway (IC₅₀ = 11.56 μM). Angoline inhibited STAT3 phosphorylation and its target gene expression and consequently induced growth inhibition of human cancer cells with constitutively activated STAT3 (IC₅₀ = 3.14–4.72 μM). This work provided a novel lead for the development of anti-cancer agents targeting the STAT3 signaling pathway.     

Swertia chirayita suppresses the growth of non-small cell lung cancer A549 cells and concomitantly induces apoptosis via downregulation of JAK1/STAT3 pathway

Lung carcinoma is the leading cause of cancer-related mortalities worldwide, and present therapeutical interventions are not successful enough to treat this disease in many cases. Recent years have witnessed a surge in exploring natural compounds for their antiproliferative efficacy to expedite the characterization of novel anticancer chemotherapeutics. Swertia chirayita is a valued medicinal herb and possess intrinsic pharmaceutical potential. However, elucidation of its anticancer effects at molecular levels remains unclear and needs to be investigated. We assessed the anticancer and apoptotic efficacy of S. chirayita ethanolic extract (Sw-EtOH) on non-small cell lung cancer (NSCLC) A549 cells during this exploratory study. The results elucidated that S. chirayita extract induced toxic effects within lung cancer cells by ~1 fold during cytotoxicity and LDH release assay at a 400 μg/ml concentration. Sw-EtOH extract elevates the level of ROS, resulting in the disruption of Δψm and release of cytosolic cytochrome c by 3.15 fold. Activation of caspases-3, -8 & -9 also escalated by ~1 fold, which further catalyze the augmentation of PARP cleavage (~3 folds), resulting in a four-fold increase in Sw-EtOH induced apoptosis. The gene expression analysis further demonstrated that Sw-EtOH extracts inhibited JAK1/STAT3 signaling pathway by down-regulating the levels of JAK1 and STAT3 to nearly half a fold. Treatment of Sw-EtOH modulates the expression level of various STAT3 associated proteins, including Bcl-XL, Bcl-2, Mcl-1, Bax, p53, Fas, Fas-L, cyclinD1, c-myc, IL-6, p21 and p27 in NSCLC cells. Thus, our study provided a strong impetus that Sw-EtOH holds the translational potential of being further evaluated as efficient cancer therapeutics and a preventive agent for the management of NSCLC.     

Activation of STAT3 stimulates AHSP expression in K562 cells

Studies on the chaperone proteinα-hemoglobin stabilizing protein(AHSP)reveal that abundant AHSP in erythroid cells enhance the cells’tolerance to oxidative stress imposed by excessα-hemoglobin in pathological conditions.However,the potential intracellular modulation of AHSP expression itself in response to oxidative stress is still unknown.The present study examined the effect and molecular mechanism of STAT3,an oxidative regulator,on the expression of AHSP.AHSP expression increased in K562 cells upon cytokine IL-6-induced STAT3 activation and decreased in STAT3 knock-down K562 cells.Regulation of AHSP in oxidative circumstance was then examined inα-globin-overloaded K562 cells,and real-time PCR showed strengthened expression of both AHSP and STAT3.ChIP analysis showed binding of STAT3 to AHSP promoter and binding was significantly augmented with IL6 stimulation and uponα-globin overexpression.Dual luciferase reporter assays of the wildtype and mutated SB3 element,an IL-6RE site,in the AHSP promoter in K562 cells highlighted the direct regulatory effect of STAT3 on AHSP gene.Finally,direct binding of STAT3 to SB3 site of AHSP promoter was confirmed with EMSA assays.Our work reveals an adaptive AHSP regulation mediated by the redox-sensitive STAT3 signaling pathway,and provides clues to the therapeutic strategy for AHSP enhancement.     

Minocycline binds and inhibits LYN activity to prevent STAT3-meditated metastasis of colorectal cancer

Colorectal cancer (CRC) is one of the most common malignancies worldwide. Metastasis is a major cause of CRC recurrence and mortality. Several antibiotic drugs have been reported to exert potential anticancer activities, however, whether and how the tetracycline antibiotic minocycline exhibit tumor suppressive effect on CRC remains unknown. Here, we found that minocycline markedly inhibits the epithelial-mesenchymal transition (EMT) process and metastasis of CRC cells both in vitro and in vivo. Using chemical proteomics screening combined with docking analysis and site-directed mutagenesis, we identified LYN as a direct bind target of minocycline, and Ala255 of LYN is required for minocycline binding. Mechanistically, minocycline binding inactivates LYN, leading to STAT3 inactivation and EMT suppression, thereby inhibits CRC metastasis. Tissue microarray analysis further confirmed the clinical relevance of LYN-STAT3 axis in the EMT and progression of CRC. In addition to CRC, minocycline also significantly prevents EMT process and inhibits the metastasis of several other cancer types. Our findings elucidate the mechanism of action of minocycline for the inhibition of CRC metastasis by LYN binding, and suggest that repurposing minocycline may represent a promising strategy for the treatment of advanced CRC and other cancer types.     

4-Carbonyl-2,6-dibenzylidenecyclohexanone derivatives as small molecule inhibitors of STAT3 signaling pathway

Inhibition of STAT3 signaling pathway is proposed to be a promising strategy for cancer treatment. In this study, a series of 4-carbonyl-2,6-dibenzylidenecyclohexanone derivatives were prepared and evaluated as anticancer agents. The most potent compound 13r was discovered to exhibit antiproliferative activity against a broad rang of cancer cell lines and relatively low cytotoxicity against normal human cells. Besides, 13r effectively suppressed STAT3 expression as well as phosphorylation, and surface plasmon resonance analysis confirmed the direct interaction of 13r with STAT3. Docking simulation showed that 13r could inhibit STAT3 by targeting SH2 domain. This study provided evidence for these compounds to be further developed as antitumor agents through inhibition of the STAT3 pathway.     

Axotomy induces axonogenesis in hippocampal neurons through STAT3

After axotomy of embryonic hippocampal neurons in vitro, some of the axotomized axons lose their identity, and new axons arise and grow. This axotomy-induced axonogenesis requires importin, suggesting that some injury-induced signals are transported via axons to elicit axonogenesis after axotomy. In this study, we show that STAT3 is activated in response to axotomy. Because STAT3 was co-immunoprecipitated with importin β in the axotomized neurons, we suggest that STAT3 is retrogradely transported as molecular cargo of importin α/β heterodimers. Indeed, inhibition of importin α binding with STAT3 resulted in the attenuation of axonogenesis. Silencing STAT3 blocked the axonogenesis, demonstrating that STAT3 is necessary for axotomy-induced axonogenesis. Furthermore, the overexpression of STAT3 enhanced axotomy-induced axonogenesis. Taken together, these results demonstrate that activation and retrograde transport of STAT3 in injured axons have key roles in the axotomy-induced axonogenesis of hippocampal neurons.     

Gamma-linolenic acid induces apoptosis and lipid peroxidation in human chronic myelogenous leukemia K562 cells

Various polyunsaturated fatty acids, especially gamma-linolenic acid (GLA), inhibit the growth of a variety of tumor cells. Some evidence indicates that polyunsaturated fatty acid can kill cells by apoptosis. In the current study, we tested the apoptotic effect of GLA on human chronic myelogenous leukemia K562 cells. GLA induced K562 cell death in a dose-dependent manner. Typical apoptotic nuclei were shown by staining of K562 cells with DNA-binding fluorochrome Hoechst 33342, characterized by chromatin condensation and nuclear fragmentation. Flow cytometric analysis also demonstrated that GLA caused dose-dependent apoptosis of K562 cells. The apoptosis could be inhibited by a pancaspase inhibitor (z-VAD-fmk), suggesting the involvement of caspases. Further, release of cytochrome c, activation of caspase-3 and cleavage of PARP were found in GLA-induced apoptosis. GLA treatment could also elevate lipid peroxidation in K562 cells, and antioxidant α-tocopherol could reverse the cytotoxicity of GLA. The saturated fatty acid SA, which did not exhibit significant increase in lipid peroxidation, also did not induce cytotoxicity. Intracellular GSH was also determined, and there was no marked change of GSH levels in cells after incubation with GLA compared with the control. These results demonstrate that GLA could induce apoptosis in K562 cells. Apoptosis is mediated by release of cytochrome c, activation of caspase-3. Lipid peroxidation may play a role in GLA cytotoxicity.