Chemotherapeutic resistance in breast cancer, whether acquired or intrinsic, remains a major clinical obstacle. Thus, increasing tumor cell sensitivity to chemotherapeutic agents will be helpful in improving the clinical management of breast cancer. In the present study, we found an induction of HO-1 expression in doxorubicin (DOX)-treated MDA-MB-231 human breast adenocarcinoma cells, which showed insensitivity to DOX treatment. Knockdown HO-1 expression dramatically upregulated the incidence of MDA-MB-231 cell death under DOX treatment, indicating that HO-1 functions as a critical contributor to drug resistance in MDA-MB-231 cells. We further observed that DOX exposure induced a cytoprotective autophagic flux in MDA-MB-231 cells, which was dependent on HO-1 induction. Moreover, upregulation of HO-1 expression required the activation of both signal transducer and activator of transcription (STAT)3 and its upstream regulator, protein kinase Src. Abrogating Src ⁄ STAT3 pathway activation attenuated HO-1 and autophagy induction, thus increasing the chemosensitivity of MDA-MB-231 cells. Therefore, we conclude that Src ⁄ STAT3-dependent HO-1 induction protects MDA-MB-231 breast cancer cells from DOX-induced death through promoting autophagy. In the following study, we further demonstrated the contribution of Src ⁄ STAT3 ⁄ HO-1 ⁄ autophagy pathway activation to DOX resistance in another breast cancer cell line, MDA-MB-468, which bears a similar phenotype to MDA-MB-231 cells. Therefore, activation of Src ⁄ STAT3 ⁄ HO-1 ⁄ autophagy signaling pathway might play a general role in protecting certain subtypes of breast cancer cells from DOX-induced cytotoxicity. Targeting this signaling event may provide a potential approach for overcoming DOX resistance in breast cancer therapeutics. B reast cancer is the most common malignant disease for Western women.(1) Early detection of breast cancer has improved the prognosis for patients with primary disease confined to the breast but the prognosis for patients with advanced metastatic breast cancer remains poor, which is often due to poor response to standard chemotherapy that is mainly based on anthracyclines and taxanes. Significant advances in the understanding of the mechanisms of anti-cancer drug resistance have not been paralleled by the introduction of novel strategies to circumvent or avoid resistance in clinical practice. Thus, increasing tumor cell sensitivity to these chemotherapeutic agents is an attractive goal towards improving the therapeutic efficacy of breast cancer, and modulation of tumor-specific signaling pathways may provide a different and complementary approach.Heme oxygenase (HO), the rate-limiting enzyme in heme degradation, catalyzes the oxidation of heme to generate several biologically active molecules: carbon monoxide (CO), biliverdin and ferrous ion.(2) Among the three isoforms of the HO family, HO-1 is widely expressed at low levels in most tissues under steady state and is highly inducible under a variety of chemical and physical cellular stresses.(...

Epidemiological and clinical studies have increasingly shown that fine particulate matter (PM2.5) is associated with a number of pathological respiratory diseases, such as bronchitis, asthma, and chronic obstructive pulmonary disease, which share the common feature of airway inflammation induced by particle exposure. Thus, understanding how PM2.5 triggers inflammatory responses in the respiratory system is crucial for the study of PM2.5 toxicity. In the current study, we found that exposing human bronchial epithelial cells (immortalized Beas-2B cells and primary cells) to PM2.5 collected in the winter in Wuhan, a city in southern China, induced a significant upregulation of VEGFA (vascular endothelial growth factor A) production, a signaling event that typically functions to control chronic airway inflammation and vascular remodeling. Further investigations showed that macroautophagy/autophagy was induced upon PM2.5 exposure and then mediated VEGFA upregulation by activating the SRC (SRC proto-oncogene, non-receptor tyrosine kinase)-STAT3 (signal transducer and activator of transcription 3) pathway in bronchial epithelial cells. By exploring the upstream signaling events responsible for autophagy induction, we revealed a requirement for TP53 (tumor protein p53) activation and the expression of its downstream target DRAM1 (DNA damage regulated autophagy modulator 1) for the induction of autophagy. These results thus extend the role of TP53-DRAM1-dependent autophagy beyond cell fate determination under genotoxic stress and to the control of proinflammatory cytokine production. Moreover, PM2.5 exposure strongly induced the activation of the ATR (ATR serine/threonine kinase)-CHEK1/CHK1 (checkpoint kinase 1) axis, which subsequently triggered TP53-dependent autophagy and VEGFA production in Beas-2B cells. Therefore, these findings suggest a novel link between processes regulating genomic integrity and airway inflammation via autophagy induction in bronchial epithelial cells under PM2.5 exposure.

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During wound healing and tissue repair the dermal fibroblast-to-myofibroblast transdifferentiation plays an important role, transforming growth factor-β1 (TGF-β1) is considered to be the main stimuli factor of transdifferentiation. MicroRNAs (miRNAs) have recently emerged as key post-transcriptional regulators of gene expression. The involvement of miRNAs and their roles in TGF-β1-induced myofibroblast transdifferentiation remains to be determined in detail. The current study found that the expression of miR-146a was upregulated in human dermal fibroblasts cells in response to TGF-β1 stimulation in dose-dependent manner by quantitative RT-PCR. Bioinformatic analyses predict that signaling effectors mothers against decapentaplegic protein 4 (SMAD4) is a miR-146a target gene. Luciferase assay demonstrated that miR-146a mimics suppressed SMAD4 3'-UTR reporter construct activity. Furthermore, miR-146a overexpression in dermal fibroblast did not decrease target mRNA levels, but significantly reduced target protein expression. In addition, dermal fibroblasts transfected with miR-146a mimics exhibited attenuated TGF-β1 -induced α-smooth muscle actin (α-SMA) expression compared with the control. This study demonstrated that miR-146a may function as a novel negative regulator to modulate myofibroblast transdifferentiation during TGF-β1 induction by targeting SMAD4.

These results suggest that miR-146a may be involved in negatively regulating H. pylori-induced PTGS2 expression in human gastric epithelial cells.

Two catalytic subunits of the IKK complex, IKKα and IKKβ, trigger NF-κB activation as well as NF-κB-independent signaling events under both physiological and pathological conditions. Here we identified the NF-κB-unrelated cytoprotective function of IKKα in promoting autophagy by triggering p53 transactivation and upregulation of its downstream autophagic mediator, DRAM1, in the arsenite-treated hepatoma cells, which responses depended on IKKα kinase activity. Furthermore, IKKα triggered p53/DRAM1-dependent autophagy by inducing CHK1 activation and CHK1/p53 interaction. Interestingly, after provoking autophagy, IKKα could be specifically recognized by the autophagic machinery via directly binding with LC3B, resulting in selective degradation of IKKα by autophagy. Unexpectedly, the selectivity of autophagic sequestration towards IKKα was mediated by novel mechanism independent of the classical LC3-interacting regions (LIRs) within IKKα, while C-terminal arm of LIR was involved in mediating IKKα/LC3B interaction. Taken together, we conclude that IKKα attenuates arsenite-induced apoptosis by inducing p53-dependent autophagy, and then selective feedback degradation of IKKα by autophagy contributes to the cytotoxic response induced by arsenite.

Our previous studies revealed that GADD45α is a liable protein, which undergoes MDM2-dependent constitutive ubiquitination and degradation in resting HepG2 hepatoma cells. Arsenite exposure induces ribosomal stress responses mediated by the ribosomal protein S7, which can block MDM2 activity and result in GADD45α accumulation and cell apoptosis. In the present study, we found that one of the catalytic subunits of IκB kinase (IKK), IKKβ, exerted a novel IKKα- and NF-κB-independent function in stabilizing MDM2 and therefore contributed to ubiquitination-dependent degradation of GADD45α in resting HepG2 cells. Arsenite stimulation induced transactivation of p53, which formed a complex with its downstream target, Ets-1, and then synergistically repressed IKKβ transcription, reduced MDM2 stability, and ultimately removed the inhibitory effect of MDM2 on GADD45α induction. In addition, DAPK1 functioned as an upstream protein kinase triggering p53/Ets-1-dependent IKKβ and MDM2 reduction and GADD45α accumulation, thus promoting apoptosis in HepG2 cells. Subsequent studies further revealed that the activation of the DAPK1/p53/Ets-1/IKKβ/MDM2/GADD45α cascade was a common signaling event in mediating apoptosis of diverse cancer cells induced by arsenite and other tumor therapeutic agents. Therefore, we conclude that data in the current study have revealed a novel role for IKKβ in negatively regulating GADD45α protein stability and the contribution of p53-dependent IKKβ reduction to mediating cancer cell apoptosis.

Our previous studies reveal that GADD45α is a liable proapoptotic protein, which undergoes MDM2 dependent constitutive ubiquitination and degradation in resting cancer cells. Under chemotherapeutic agents (such as arsenite, 5-Fu, VP-16) exposure, DAPK1 functions as novel p53 kinase, which induces phosphorylation of p53 at Ser15 and transactivates p53 target, Ets-1, to synergistically repress IKKβ dependent MDM2 stability, and ultimately removes the inhibitory effect of MDM2 on GADD45α, resulting in GADD45α accumulation and cell apoptosis. In the current study, we observed a strong induction of ISG20L1 expression in several cancer cell lines under exposure of arsenite and other chemotherapeutic agents. Surprisingly, although originally identified as a transcriptional target of p53, ISG20L1 induction was not controlled by p53. Instead, ISG20L1 functioned as upstream activator of p53 by interacting with DAPK1 and play an essential role in determining the ability of DAPK1/p53 complex formation and the subsequent activation of Ets-1/IKKβ/MDM2/GADD45α cascade. Therefore, our findings have revealed novel function of ISG20L1 in mediating cancer cell apoptosis induced by chemotherapeutic agents via modulating activation of the DAPK1/p53 dependent cell death pathway.