PD-L1 confers glioblastoma multiforme malignancy via Ras binding and Ras/Erk/EMT activation.

Glioblastoma multiforme (GBM) is the most aggressive primary brain tumor due to the lack of effective therapeutic drugs. Cancer therapy targeting programmed cell death protein 1 (PD-1) or programmed death ligand-1 (PD-L1) is of revolutionary. However, the role of intrinsic PD-L1, which determines immune-therapy outcomes, remains largely unclear. Here we demonstrated an oncogenic role of PD-L1 via binding and activating Ras in GBM cells. RNA-sequencing transcriptome data revealed that PD-L1 significantly altered gene expression enriched in cell growth/migration/invasion pathways in human GBM cells. PD-L1 overexpression and knockout or knockdown demonstrated that PD-L1 promoted GBM cell proliferation and migration in vitro and in vivo. Mechanistically, PD-L1 prominently activated epithelial mesenchymal transition (EMT) process in a MEK/Erk- but not PI3K/Akt-dependent manner. Further, we identified intracellular interactions of PD-L1 and H-Ras, which led to Ras/Erk/EMT activation. Finally, we demonstrated that PD-L1 overexpression promoted while knockdown abolished GBM development and invasion in orthotopic GBM models of rodents. Taken together, we found that intracellular PD-L1 confers GBM cell malignancy and aggressiveness via binding Ras and activating the downstream Erk-EMT signaling. Thus, these results shed important insights in improving efficacy of immune therapy for GBM as well as other malignant tumors.

Advances in Hypoxia-Mediated Mechanisms in Hepatocellular Carcinoma.

Hepatocellular carcinoma (HCC) is the fifth most common and the third most deadly malignant tumor worldwide. Hypoxia and related oxidative stress are heavily involved in the process of HCC development and its therapies. However, direct and accurate measurement of oxygen concentration and evaluation of hypoxic effects in HCC prove difficult. Moreover, the hypoxia-mediated mechanisms in HCC remain elusive. Here, we summarize recent major evidence of hypoxia in HCC lesions shown by measuring partial pressure of oxygen (pO2), the clinical importance of hypoxic markers in HCC, and recent advances in hypoxia-related mechanisms and therapies in HCC. For the mechanisms, we focus mainly on the roles of oxygen-sensing proteins (i.e., hypoxia-inducible factor and neuroglobin) and hypoxia-induced signaling proteins (e.g., matrix metalloproteinases, high mobility group box 1, Beclin 1, glucose metabolism enzymes, and vascular endothelial growth factor). With respect to therapies, we discuss mainly YQ23, sorafenib, 2-methoxyestradiol, and celastrol. This review focuses primarily on the results of clinical and animal studies.

Piperlongumine suppresses bladder cancer invasion via inhibiting epithelial mesenchymal transition and F-actin reorganization.

Piperlongumine (PL), a natural alkaloid isolated from longer pepper plants, is recently found to be a potent selective anti-cancer compound. We first tested its anti-cancer effects on bladder cancer, the fifth most common and aggressive cancer worldwide, to further explore the therapeutic spectrum and molecular mechanisms of PL. PL significantly suppressed bladder cancer cell proliferation, the transition of G2/M phase to next phase, migration/invasion in vitro and bladder cancer growth/development in vivo. PL markedly elevated reactive oxygen species (ROS) and the administration of antioxidants abolished PL induced cell proliferation inhibition, G2/M phase arrest and migration suppression on bladder cancer cells. In vivo studies demonstrated that PL inhibited epithelial mesenchymal transition with profoundly decreased level of Slug, ß-catenin, ZEB1 and N-Cadherin. Further, we first reported PL effects on cytoskeleton with prominently reduced lamellipodia formation and decreased F-actin intensity in bladder cancer cells. Taken together, our results first revealed that PL suppressed bladder cancer proliferation and migration in vivo and in vitro, suggesting novel mechanism underlying PL's anti-cancer effect and providing a new anticancer drug strategy for bladder cancer therapy.

Piperlongumine induces apoptotic and autophagic death of the primary myeloid leukemia cells from patients via activation of ROS-p38/JNK pathways.

AIM: To investigate the effects of piperlongumine (PL), an anticancer alkaloid from long pepper plants, on the primary myeloid leukemia cells from patients and the mechanisms of action. METHODS: Human BM samples were obtained from 9 patients with acute or chronic myeloid leukemias and 2 patients with myelodysplastic syndrome (MDS). Bone marrow mononuclear cells (BMMNCs) were isolated and cultured. Cell viability was determined using MTT assay, and apoptosis was examined with PI staining or flow cytometry. ROS levels in the cells were determined using DCFH-DA staining and flow cytometry. Expression of apoptotic and autophagic signaling proteins was analyzed using Western blotting. RESULTS: PL inhibited the viability of BMMNCs from the patients with myeloid leukemias (with IC50 less than 20 µmol/L), but not that of BMMNCs from a patient with MDS. Furthermore, PL (10 and 20 µmol/L) induced apoptosis of BMMNCs from the patients with myeloid leukemias in a dose-dependent manner. PL markedly increased ROS levels in BMMNCs from the patients with myeloid leukemias, whereas pretreatment with the antioxidant N-acetyl-L-cysteine abolished PL-induced ROS accumulation and effectively reduced PL-induced cytotoxicity. Moreover, PL markedly increased the expression of the apoptotic proteins (Bax, Bcl-2 and caspase-3) and autophagic proteins (Beclin-1 and LC3B), and phosphorylation of p38 and JNK in BMMNCs from the patients with myeloid leukemias, whereas pretreatment with the specific p38 inhibitor SB203580 or the specific JNK inhibitor SP600125 partially reversed PL-induced ROS production, apoptotic/autophagic signaling activation and cytotoxicity. CONCLUSION: Piperlongumine induces apoptotic and autophagic death of the primary myeloid leukemia cells from patients via activation of ROS-p38/JNK pathways.

The Binding of PD-L1 and Akt Facilitates Glioma Cell Invasion Upon Starvation via Akt/Autophagy/F-Actin Signaling.

Glioma, especially glioblastoma, is pathologically characterized by high aggressiveness, which largely contributed to the ineffectiveness of current therapies. It has been recently reported that intrinsic PD-L1 can regulate tumor malignancy, whereas underlying mechanisms remain mostly unclear. Here, we report a novel mechanism by which PD-L1 promotes glioma cell infiltration. In orthotopic glioma models, PD-L1 expression was up-regulated predominantly in glioma cells in the infiltrating front. For PD-L1-overexpressed glioma cells, PI3K/Akt and actin regulations were among the top six most altered signaling pathways as detected by RNA-sequencing. PD-L1 significantly activated Akt/F-actin signaling while suppressed autophagic signaling upon cell starvation. Mechanistically, PD-L1 preferentially bound to Akt among various PI3K/Akt signaling proteins. Serial truncation identified the interaction between the 128-237aa fragment of PD-L1 and the 112-480aa fragment of Akt, which facilitates the membrane translocation/activation of Akt, and was unaffected by Perifosin (specific p-Akt inhibitor targeting Akt PH-domain). Taken together, our data indicate that in glioma cells, PD-L1 is induced to prevent autophagic cytoskeleton collapse via Akt binding/activation, facilitating glioma cell invasion upon starvation stress.

The Prognostic and Therapeutic Value of PD-L1 in Glioma.

Glioma is the most common type of primary brain tumors. After standard treatment regimen (surgical section, radiotherapy and chemotherapy), the average survival time remains merely around 14 months for glioblastoma (grade IV glioma). Recent immune therapy targeting to the immune inhibitory checkpoint axis, i.e., programmed cell death protein 1 (PD-1) and its ligand PD-L1 (i.e., CD274 or B7-H1), has achieved breakthrough in many cancers but still not in glioma. PD-L1 is considered a major prognostic biomarker for immune therapy in many cancers, with anti-PD-1 or anti-PD-L1 antibodies being used. However, the expression and subcellular distribution of PD-L1 in glioma cells exhibits great variance in different studies, severely impairing PD-L1's value as therapeutic and prognostic biomarker in glioma. The role of PD-L1 in modulating immune therapy is complicated. In addition, endogenous PD-L1 plays tumorigenic roles in glioma development. In this review, we summarize PD-L1 mRNA expression and protein levels detected by using different methods and antibodies in human glioma tissues in all literatures, and we evaluate the prognostic value of PD-L1 in glioma. We also summarize the relationships between PD-L1 and immune cell infiltration in glioma. The mechanisms regulating PD-L1 expression and the oncogenic roles of endogenous PD-L1 are discussed. Further, the therapeutic results of using anti-PD-1/PD-L1 antibodies or PD-L1 knockdown are summarized and evaluated. In summary, current results support that PD-L1 is not only a prognostic biomarker of immune therapy, but also a potential therapeutic target for glioma.

Neuroglobin boosts axon regeneration during ischemic reperfusion via p38 binding and activation depending on oxygen signal.

Cerebral ischemia causes severe cell death or injury including axon breakdown or retraction in the brain. Axon regeneration is crucial for the functional recovery of injured neurons or brains after ischemia/reperfusion (I/R); however, this process has been proved extremely difficult in adult brains and there is still no effective therapy for it. Here we reported that neuroglobin (Ngb), a novel oxygen-binding or sensor protein existing predominantly in neurons or brains, functions as a driving factor for axon regeneration during I/R. Ngb was upregulated and accumulated in growth cones of ischemic neurons in primary cultures, rat, and human brains, correlating positively to the elevation of axon-regeneration markers GAP43, neurofilament-200, and Tau-1. Ngb overexpression promoted while Ngb knockdown suppressed axon regeneration as well as GAP43 expression in neurons during oxygen-glucose deprivation/reoxygenation (OGD/Re). By using specific pharmacological inhibitors, we identified p38 MAPK as the major downstream player of Ngb-induced axon regeneration during OGD/Re. Mechanistically, Ngb directly bound to and activated p38 in neurons upon OGD/Re. Serial truncation and point mutation of Ngb revealed that the 7-105 aa fragment of Ngb was required and the oxygen-binding site (His64) of Ngb was the major regulatory site for its p38 interaction/activation. Finally, administration of exogenous TAT-Ngb peptides significantly enhanced axon regeneration in cultured neurons upon OGD/Re. Taken together, Ngb promotes axon regeneration via O2-Ngb-p38-GAP43 signaling during I/R. This novel mechanism suggests potential therapeutic applications of Ngb for ischemic stroke and other related axonopathy.

Piperlongumine selectively kills hepatocellular carcinoma cells and preferentially inhibits their invasion via ROS-ER-MAPKs-CHOP.

Hepatocellular carcinomas (HCC) are highly malignant and aggressive tumors lack of effective therapeutic drugs. Piperlongumine (PL), a natural product isolated from longer pepper plants, is recently identified as a potent cytotoxic compound highly selective to cancer cells. Here, we reported that PL specifically suppressed HCC cell migration/invasion via endoplasmic reticulum (ER)-MAPKs-CHOP signaling pathway. PL selectively killed HCC cells but not normal hepatocytes with an IC50 of 10-20 µM while PL at much lower concentrations only suppressed HCC cell migration/invasion. PL selectively elevated reactive oxygen species (ROS) in HCC cells, which activated or up-regulated downstream PERK/Ire 1α/Grp78, p38/JNK/Erk and CHOP subsequently. Administration of antioxidants completely abolished PL's effects on cell death and migration/invasion. However, pharmacological inhibition of ER stress-responses or MAPKs signaling pathways with corresponding specific inhibitors only reversed PL's effect on cell migration/invasion but not on cell death. Consistently, knocking-down of CHOP by RNA interference only reversed PL-suppressed HCC cell migration. Finally, PL significantly suppressed HCC development and activated the ER-MAPKs-CHOP signaling pathway in HCC xenografts in vivo. Taken together, PL selectively killed HCC cells and preferentially inhibited HCC cell migration/invasion via ROS-ER-MAPKs-CHOP axis, suggesting a novel therapeutic strategy for the highly malignant and aggressive HCC clinically.

Neuroglobin - recent developments.

Neuroglobin (Ngb), a monomeric hexacoordinated heme protein of 17 kDa, was identified in 2000 in the nervous system. Accumulative evidence has proved that Ngb is an endogenous neuroprotective molecule against ischemic/hypoxic insults and oxidative stresses, and in most ischemic conditions, Ngb is up-regulated. The underlying mechanisms, however, are not fully clarified. Here we review the recent experimental findings, mainly focusing on the mechanisms of Ngb's protection and induction during ischemic/hypoxic conditions, the roles of Ngb in astrocytes and tumors, as well as Ngb's function in neurite outgrowth.

Piperlongumine inhibits migration of glioblastoma cells via activation of ROS-dependent p38 and JNK signaling pathways.

Piperlongumine (PL) is recently found to kill cancer cells selectively and effectively via targeting reactive oxygen species (ROS) responses. To further explore the therapeutic effects of PL in cancers, we investigated the role and mechanisms of PL in cancer cell migration. PL effectively inhibited the migration of human glioma (LN229 or U87 MG) cells but not normal astrocytes in the scratch-wound culture model. PL did not alter EdU(+)-cells and cdc2, cdc25c, or cyclin D1 expression in our model. PL increased ROS (measured by DCFH-DA), reduced glutathione, activated p38 and JNK, increased IκBα, and suppressed NFκB in LN229 cells after scratching. All the biological effects of PL in scratched LN229 cells were completely abolished by the antioxidant N-acetyl-L-cysteine (NAC). Pharmacological administration of specific p38 (SB203580) or JNK (SP600125) inhibitors significantly reduced the inhibitory effects of PL on LN229 cell migration and NF κ B activity in scratch-wound and/or transwell models. PL prevented the deformation of migrated LN229 cells while NAC, SB203580, or SP600125 reversed PL-induced morphological changes of migrated cells. These results suggest potential therapeutic effects of PL in the treatment and prevention of highly malignant tumors such as glioblastoma multiforme (GBM) in the brain by suppressing tumor invasion and metastasis.