Siyang Song

Cytosporone B is an agonist for nuclear orphan receptor Nur77

Nuclear orphan receptor Nur77 has important roles in many biological processes. However, a physiological ligand for Nur77 has not been identified. Here, we report that the octaketide cytosporone B (Csn-B) is a naturally occurring agonist for Nur77. Csn-B specifically binds to the ligand-binding domain of Nur77 and stimulates Nur77-dependent transactivational activity towards target genes including Nr4a1 (Nur77) itself, which contains multiple consensus response elements allowing positive autoregulation in a Csn-B-dependent manner. Csn-B also elevates blood glucose levels in fasting C57 mice, an effect that is accompanied by induction of multiple genes involved in gluconeogenesis. These biological effects were not observed in Nur77-null (Nr4a1-/-) mice, which indicates that Csn-B regulates gluconeogenesis through Nur77. Moreover, Csn-B induced apoptosis and retarded xenograft tumor growth by inducing Nur77 expression, translocating Nur77 to mitochondria to cause cytochrome c release. Thus, Csn-B may represent a promising therapeutic drug for cancers and hypoglycemia, and it may also be useful as a reagent to increase understanding of Nur77 biological function.

The Ets Transcription Factor GABP Is a Component of the Hippo Pathway Essential for Growth and Antioxidant Defense

The transcriptional coactivator Yes-associated protein (YAP) plays an important role in organ-size control and tumorigenesis. However, how Yap gene expression is regulated remains unknown. This study shows that the Ets family member GABP binds to the Yap promoter and activates YAP transcription. The depletion of GABP downregulates YAP, resulting in a G1/S cell-cycle block and increased cell death, both of which are substantially rescued by reconstituting YAP. GABP can be inactivated by oxidative mechanisms, and acetaminophen-induced glutathione depletion inhibits GABP transcriptional activity and depletes YAP. In contrast, activating YAP by deleting Mst1/Mst2 strongly protects against acetaminophen-induced liver injury. Similar to its effects on YAP, Hippo signaling inhibits GABP transcriptional activity through several mechanisms. In human liver cancers, enhanced YAP expression is correlated with increased nuclear expression of GABP. Therefore, we conclude that GABP is an activator of Yap gene expression and a potential therapeutic target for cancers driven by YAP.

Kinases Mst1 and Mst2 positively regulate phagocytic induction of reactive oxygen species and bactericidal activity

Mitochondria need to be juxtaposed to phagosomes for the synergistic production of ample reactive oxygen species (ROS) in phagocytes to kill pathogens. However, how phagosomes transmit signals to recruit mitochondria has remained unclear. Here we found that the kinases Mst1 and Mst2 functioned to control ROS production by regulating mitochondrial trafficking and mitochondrion-phagosome juxtaposition. Mst1 and Mst2 activated the GTPase Rac to promote Toll-like receptor (TLR)-triggered assembly of the TRAF6-ECSIT complex that is required for the recruitment of mitochondria to phagosomes. Inactive forms of Rac, including the human Rac2D57N mutant, disrupted the TRAF6-ECSIT complex by sequestering TRAF6 and substantially diminished ROS production and enhanced susceptibility to bacterial infection. Our findings demonstrate that the TLR-Mst1-Mst2-Rac signaling axis is critical for effective phagosome-mitochondrion function and bactericidal activity.Summary Mitochondria need to be juxtaposted to phagosomes to synergistically produce ample reactive oxygen species (ROS) in phagocytes for pathogens killing. However, how phagosomes transmit signal to recruit mitochondria remains unclear. Here, we report that the kinases Mst1 and Mst2 function to control ROS production by regulating mitochondrial trafficking and mitochondrion-phagosome juxtaposition. Mst1 and Mst2 activate Rac GTPase to promote Toll-like receptor (TLR)-triggered assembly of the TRAF6-ECSIT complex that is required for mitochondrial recruitment to phagosomes. Inactive forms of Rac, including the human Rac2D57N mutant, disrupt the TRAF6-ECSIT complex by sequestering TRAF6, and severely dampen ROS production and greatly increase susceptibility to bacterial infection. These findings demonstrate the TLR-Mst1-Mst2-Rac signalling axis to be critical for effective phagosome-mitochondrion function and bactericidal activity.

Gambogic acid inhibits Hsp90 and deregulates TNF-α/NF-κB in HeLa cells.

Gambogic acid (GB) is an important anti-cancer drug candidate, but the target protein by which it exerts its anti-cancer effects has not been identified. This study is the first to show that GB inhibits heat shock protein 90 (Hsp90) and down-regulates TNF-α/NF-κB in HeLa cells. The effects of GB on Hsp90 were studied by characterizing its physical interactions with Hsp90 upon binding, the noncompetitive inhibition of Hsp90 ATPase activity, and the degradation of Hsp90 client proteins (i.e., Akt, IKK) in HeLa cells. GB seems to bind to the N-terminal ATP-binding domain of Hsp90. Additionally, GB suppresses the activation of TNF-α/NF-κB and decreases XIAP expression levels and the ratio of Bcl-2/Bax, which in turn induces HeLa cell apoptosis. Thus, GB represents a promising therapeutic agent for cancer; it may also be useful as a probe to increase understanding of the biological functions of Hsp90.

Two new spirooxindole alkaloids from rhizosphere strain Streptomyces sp. xzqh-9.

Two new spirooxindole alkaloids spindomycins A (1) and B (2) were isolated from rhizosphere strain Streptomyces sp. xzqh-9. Their structures were elucidated by comprehensive spectroscopic analyses of NMR and MS data. The absolute configurations of 1 and 2 were determined by experimental and theoretical calculation of electronic circular dichroism (ECD). Antitumor, lactate dehydrogenase, and tyrosine kinase inhibitory activities of two compounds were evaluated, while only spindomycin B (2) exhibited weak inhibitory activity against tyrosine kinase Bcr-Abl.

Gambogic acid protects from endotoxin shock by suppressing pro-inflammatory factors in vivo and in vitro

ObjectiveGambogic acid (GBA) targeted Heat shock protein 90 (Hsp90) and prohibited TNF-α/NF-κB signaling pathway. It can be inferred that the anti-inflammatory activity of GBA results from inhibiting the cytokine production via NF-κB signaling pathway. We used the RAW264.7 cell line and the endotoxin shock mouse model to confirm the hypothesis that GBA protects mice from endotoxin shock by suppressing cytokine synthesis.MethodRAW264.7 cells were cultured and the endotoxin shocked mice model was constructed. ELISA was employed to evaluate the change of cytokine secretion levels. The effects of GBA on the activation of NF-κB signaling pathway were also determined by western blot and immune-fluorescent analysis. Cell viability was determined by MTT assay, and the cell migration was tested by wound healing assay.ResultOur results demonstrated that GBA significantly inhibited the LPS-induced release of pro-inflammatory factors both in cell lines and mice serum, thereby protecting mice from endotoxin shock. Furthermore, we observed that the reduction of inflammatory cytokines interleukin 1-beta, interleukin 6 and TNF-α resulted from the Hsp90’s client protein IKK degradation and the suppression of NF-κB pathway. Moreover, GBA suppressed the migration of LPS-induced RAW264.7 cells.ConclusionOur results indicate that GBA has a potential both as an antitumor and anti-inflammatory therapeutic agent.

Hsp90 interacts with AMPK and mediates acetyl-CoA carboxylase phosphorylation

Heat shock protein 90 (Hsp90) serves to stabilise and correctly fold multiple significant client proteins associated with cell proliferation and cell survival. However, little is known about the Hsp90 client proteins that regulate cell metabolism. Here, we describe a unique ability of Hsp90 to regulate the stability and activity of AMP-activated kinase (AMPK), a key sensor of cellular energy status. Hsp90 is found to interact with AMPK and to maintain its AMP-activated kinase activity, which in turn is required for the phosphorylation of its substrate, acetyl-CoA carboxylase (ACC), the key enzyme in fatty acid metabolism. Our binding analysis reveals that both the γ subunit and the α subunit of AMPK bind to Hsp90 with a high affinity. We demonstrate that Hsp90 inhibitors, including geldanamycin (GA) and mycoepoxydiene (MED), can induce the dissociation of AMPK from Hsp90, and cause a significant decrease in phosphorylation of AMPK and ACC. Furthermore, we demonstrate that shRNAs of Hsp90 can efficiently suppress the activation of AMPK. These findings not only establish a novel interaction between Hsp90 and AMPK but also suggest a new mechanism for regulating tumour cell fatty acid metabolism.

Aspertetranones A–D, Putative Meroterpenoids from the Marine Algal-Associated Fungus Aspergillus sp. ZL0-1b14

Aspertetranones A-D (1-4), four new highly oxygenated putative rearranged triketide-sesquiterpenoid meroterpenes, were isolated from the marine algal-associated fungus Aspergillus sp. ZL0-1b14. On the basis of a comprehensive spectroscopic analysis, the planar structures of aspertetranones were determined to possess an unusual skeleton in the terpenoid part. The relative and absolute configurations of the aspertetranones were assigned on the basis of NOESY analysis, X-ray crystallography, and circular dichroism spectroscopy. Compounds 1-4 were evaluated for anti-inflammatory activity in LPS-stimulated RAW264.7 macrophages. Aspertetranone D exhibited an inhibitory effect against IL-6 production with 69% inhibition at 40 μM.

Heat shock protein 90 mediates the apoptosis and autophage in nicotinic-mycoepoxydiene-treated HeLa cells

Heat shock protein 90 (Hsp90) is a fascinating target for cancer therapy due to its significant role in the crossroad of multiple signaling pathways associated with cell proliferation and regulation. Hsp90 inhibitors have the potential to be developed into anti-cancer drugs. Here, we identified nicotinic-mycoepoxydiene (NMD), a structurally novel compound as Hsp90 inhibitor to perform the anti-tumor activity. The compound selectively bound to the Hsp90 N-terminal domain, and degraded the Hsp90 client protein Akt. The degradation of Akt detained Bad in non-phosphorylation form. NMD-associated apoptosis was characterized by the formation of fragmented nuclei, poly(ADP-ribose) polymerase cleavage, cytochrome c release, caspase-3 activation, and the increased proportion of sub-G1 phase cells. Interestingly, the apoptosis was accompanied with autophagy, by exhibiting the increased expression of LC-3 and the decrease of lysosome pH value. Our findings provide a novel cellular mechanism by which Hsp90 inhibitor adjusts cell apoptosis and autophagy in vitro, suggesting that NMD not only has a potential to be developed into a novel anti-tumor pharmaceutical, but also exhibits a new mechanism in regulating cancer cell apoptosis and autophagy via Hsp90 inhibition.

Targeting BRK-Positive Breast Cancers with Small-Molecule Kinase Inhibitors

Approximately 80% of breast cancers overexpress the kinase breast tumor kinase (BRK)/protein tyrosine kinase 6, which has various oncogenic roles in breast cancer cell proliferation, survival, and migration. However, BRK inhibitors have yet to be explored as possible therapeutic tools. In this study, we used a parallel compound-centric approach to discover a new class of pharmaceutical agents, exemplified by XMU-MP-2, as potent and selective BRK inhibitors. XMU-MP-2 exhibited target-specific inhibition of BRK kinase activity and disrupted signaling pathways mediated by this activity, thereby reducing proliferation in BRK-positive breast cancer cells. In mouse xenograft models, XMU-MP-2 repressed the growth of tumors driven by oncogenic BRK, including BRK-transformed Ba/F3 cells and BRK-positive breast cancer cells. Notably, XMU-MP-2 cooperated strongly with HER2 inhibitor or ER blockade to block breast cancer cell proliferation in vitro and in vivo Overall, our findings offer a preclinical proof of concept for therapeutic targeting of the BRK kinase in breast cancer. Cancer Res; 77(1); 175-86. ©2016 AACR.