The generation of PD-L1 and PD-L2 in cancer cells: From nuclear chromatin reorganization to extracellular presentation

The immune checkpoint blockade (ICB) targeting on PD-1/PD-L1 has shown remarkable promise in treating cancers. However, the low response rate and frequently observed severe side effects limit its broad benefits. It is partially due to less understanding of the biological regulation of PD-L1. Here, we systematically and comprehensively summarized the regulation of PD-L1 from nuclear chromatin reorganization to extracellular presentation. In PD-L1 and PD-L2 highly expressed cancer cells, a new TAD (topologically associating domain) (chr9: 5,400,000-5,600,000) around CD274 and CD273 was discovered, which includes a reported super-enhancer to drive synchronous transcription of PD-L1 and PD-L2. The re-shaped TAD allows transcription factors such as STAT3 and IRF1 recruit to PD-L1 locus in order to guide the expression of PD-L1. After transcription, the PD-L1 is tightly regulated by miRNAs and RNA-binding proteins via the long 3'UTR. At translational level, PD-L1 protein and its membrane presentation are tightly regulated by post-translational modification such as glycosylation and ubiquitination. In addition, PD-L1 can be secreted via exosome to systematically inhibit immune response. Therefore, fully dissecting the regulation of PD-L1/PD-L2 and thoroughly detecting PD-L1/PD-L2 as well as their regulatory networks will bring more insights in ICB and ICB-based combinational therapy.

Nitrosative Stress as a Modulator of Inflammatory Change in a Model of Takotsubo Syndrome

Previous studies have shown that patients with Takotsubo syndrome (TS) have supranormal nitric oxide signaling, and post-mortem studies of TS heart samples revealed nitrosative stress. Therefore, we first showed in a female rat model that isoproterenol induces TS-like echocardiographic changes, evidence of nitrosative stress, and consequent activation of the energy-depleting enzyme poly(ADP-ribose) polymerase-1. We subsequently showed that pre-treatment with an inhibitor of poly(ADP-ribose) polymerase-1 ameliorated contractile abnormalities. These findings thus add to previous reports of aberrant β-adrenoceptor signaling (coupled with nitric oxide synthase activation) to elucidate mechanisms of impaired cardiac function in TS and point to potential methods of treatment.

Changes in the NFκB and E-cadherin expression are associated to diabetic nephropathy inPsammomys obesus

Diabetes mellitus is a major leading cause of end-stage renal failure, characterized by kidney inflammation and glomerular dysfunction, in worldwide. Kidney inflammation is associated to modifications in the expression levels of pro-inflammatory molecules, such as nuclear factor-κB (NFκB) and adhesion molecules, such as E-cadherin, leading to glomerular dysfunction. However, the relationships between these two processes in human diabetic nephropathy remain an open question. Since Psammomys obesus is an ideal animal model to study diabetes mellitus temporal evolution, we have used this model to study the correlation between kidney structural changes and modification on the expression levels of NFκB and E-cadherin over time. We have demonstrated that, after induction of diabetes metillus with a high energy diet (HED), P. obesus develops the characteristic symptoms of human disease. In detail, at the third month nuclear factor NFκB is expressed in the kidney of diabetic P. obesus and structural renal changes, such as mesangial expansion or interstitial fibrosis, are detectable; at 6 months, thickening of glomerular basement membrane, glomerular sclerosis, and tubular atrophy occurs; at 9 months, symptoms of the final stages of the disease, such as down expression of E-cadherin, happens. As a result of these observations we proposed that NFκB activation and E-cadherin down-expression are interlinked on diabetic kidney disease (DKD).

Transcriptional regulation of tenascin genes

Extracellular matrix proteins of the tenascin family resemble each other in their domain structure, and also share functions in modulating cell adhesion and cellular responses to growth factors. Despite these common features, the 4 vertebrate tenascins exhibit vastly different expression patterns. Tenascin-R is specific to the central nervous system. Tenascin-C is an “oncofetal” protein controlled by many stimuli (growth factors, cytokines, mechanical stress), but with restricted occurrence in space and time. In contrast, tenascin-X is a constituitive component of connective tissues, and its level is barely affected by external factors. Finally, the expression of tenascin-W is similar to that of tenascin-C but even more limited. In accordance with their highly regulated expression, the promoters of the tenascin-C and -W genes contain TATA boxes, whereas those of the other 2 tenascins do not. This article summarizes what is currently known about the complex transcriptional regulation of the 4 tenascin genes in development and disease.

Claudin-2 as a mediator of leaky gut barrier during intestinal inflammation

The epithelial tight junction determines the paracellular water and ion movement in the intestine and also prevents uptake of larger molecules, including antigens, in an uncontrolled manner. Claudin-2, one of the 27 mammalian claudins regulating that barrier function, forms a paracellular channel for small cations and water. It is typically expressed in leaky epithelia like proximal nephron and small intestine and provides a major pathway for the paracellular transport of sodium, potassium, and fluid. In intestinal inflammation (Crohn's disease, ulcerative colitis), immune-mediated diseases (celiac disease), and infections (HIV enteropathy), claudin-2 is upregulated in small and large intestine and contributes to diarrhea via a leak flux mechanism. In parallel to that upregulation, other epithelial and tight junctional features are altered and the luminal uptake of antigenic macromolecules is enhanced, for which claudin-2 may be partially responsible through induction of tight junction strand discontinuities.

Evidence for a novel functional role of astrocytes in the acute homeostatic response to high-fat diet intake in mice

Objective

Introduction of a high-fat diet to mice results in a period of voracious feeding, known as hyperphagia, before homeostatic mechanisms prevail to restore energy intake to an isocaloric level. Acute high-fat diet hyperphagia induces astrocyte activation in the rodent hypothalamus, suggesting a potential role of these cells in the homeostatic response to the diet. The objective of this study was to determine physiologic role of astrocytes in the acute homeostatic response to high-fat feeding.

Methods

We bred a transgenic mouse model with doxycycline-inducible inhibition of NFkappaB (NFκB) signaling in astrocytes to determine the effect of loss of NFκB-mediated astrocyte activation on acute high-fat hyperphagia. ELISA was used to measure the levels of markers of astrocyte activation, glial-fibrillary acidic protein (GFAP) and S100B, in the medial basal hypothalamus.

Results

Inhibition of NFκB signaling in astrocytes prevented acute high-fat diet-induced astrocyte activation and resulted in a 15% increase in caloric intake (P < 0.01) in the first 24 h after introduction of the diet.

Conclusions

These data reveal a novel homeostatic role for astrocytes in the acute physiologic regulation of food intake in response to high-fat feeding.

NFκB mediates cisplatin resistance through histone modifications in head and neck squamous cell carcinoma (HNSCC)

Cisplatin-based chemotherapy is the standard treatment of choice for head and neck squamous cell carcinoma (HNSCC). The efficiency of platinum-based therapies is directly influenced by the development of tumor resistance. Multiple signaling pathways have been linked to tumor resistance, including activation of nuclear factor kappa B (NFκB). We explore a novel mechanism by which NFκB drives HNSCC resistance through histone modifications. Post-translational modification of histones alters chromatin structure, facilitating the binding of nuclear factors that mediate DNA repair, transcription, and other processes. We found that chemoresistant HNSCC cells with active NFκB signaling respond to chemotherapy by reducing nuclear BRCA1 levels and by promoting histone deacetylation (chromatin compaction). Activation of this molecular signature resulted in impaired DNA damage repair, prolonged accumulation of histone γH2AX and increased genomic instability. We found that pharmacological induction of histone acetylation using HDAC inhibitors prevented NFκB-induced cisplatin resistance. Furthermore, silencing NFκB in HNSCC induced acetylation of tumor histones, resulting in reduced chemoresistance and increased cytotoxicity following cisplatin treatment. Collectively, these findings suggest that epigenetic modifications of HNSCC resulting from NFκB-induced histone modifications constitute a novel molecular mechanism responsible for chemoresistance in HNSCC. Therefore, targeted inhibition of HDAC may be used as a viable therapeutic strategy for disrupting tumor resistance caused by NFκB.

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Chemoresistant HNSCC cells have deacetylation of histones and active NFκB signaling.

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Histone deacetylation reduces BRCA1 levels and enhances genomic instability.

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Histone deacetylase (HDAC) inhibitors sensitize HNSCC to chemotherapy.

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NFκB signaling drives HNSCC chemoresistance by inducing histone deacetylation.

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NFκB inhibition results in histone acetylation and sensitizes HNSCC to chemotherapy.

Nrf2 activation supports cell survival during hypoxia and hypoxia/reoxygenation in cardiomyoblasts; the roles of reactive oxygen and nitrogen species

Adaptive mechanisms involving upregulation of cytoprotective genes under the control of transcription factors such as Nrf2 exist to protect cells from permanent damage and dysfunction under stress conditions. Here we explore of the hypothesis that Nrf2 activation by reactive oxygen and nitrogen species modulates cytotoxicity during hypoxia (H) with and without reoxygenation (H/R) in H9C2 cardiomyoblasts. Using MnTBap as a cell permeable superoxide dismutase (SOD) mimetic and peroxynitrite scavenger and L-NAME as an inhibitor of nitric oxide synthase (NOS), we have shown that MnTBap inhibited the cytotoxic effects of hypoxic stress with and without reoxygenation. However, L-NAME only afforded protection during H. Under reoxygenation, conditions, cytotoxicity was increased by the presence of L-NAME. Nrf2 activation was inhibited independently by MnTBap and L-NAME under H and H/R. The increased cytotoxicity and inhibition of Nrf2 activation by the presence of L-NAME during reoxygenation suggests that NOS activity plays an important role in cell survival at least in part via Nrf2-independent pathways. In contrast, O₂^−• scavenging by MnTBap prevented both toxicity and Nrf2 activation during H and H/R implying that toxicity is largely dependent on O₂^−•.To confirm the importance of Nrf2 for myoblast metabolism, Nrf2 knockdown with siRNA reduced cell survival by 50% during 4 h hypoxia with and without 2 h of reoxygenation and although cellular glutathione (GSH) was depleted during H and H/R, GSH loss was not exacerbated by Nrf2 knockdown. These data support distinctive roles for ROS and RNS during H and H/R for Nrf2 induction which are important for survival independently of GSH salvage.

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Cardiomyoblast toxicity during hypoxia is dependent on O₂^−• and NO^•.

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Nrf2 activation is important for cardiomyoblast survival during hypoxia or hypoxia/reoxygenation, but, restoration of GSH is not required.

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NOS activity is essential for the adaptation of cardiomyoblasts to hypoxia/reoxygenation but survival may be independent of Nrf2.