Cytokine signaling to the cell cycle

Toxicity and speciation of inorganic arsenics and their adverse effects on in vivo endpoints and oxidative stress in the marine medaka Oryzias melastigma

Here, we investigate the effects of acute and chronic exposure to arsenate (AsV) and arsenite (AsIII) in the marine medaka Oryzias melastigma. In vivo effects, biotransformation, and oxidative stress were studied in marine medaka exposed to the two inorganic arsenics for 4 or 28 days. An investigation of embryonic development revealed no effect on in vivo parameters, but the hatching rate increased in the group exposed to AsIII. Exposure to AsIII also caused the greatest accumulation of arsenic in medaka. For acute exposure, the ratio of AsV to AsIII was higher than that of chronic exposure, indicating that bioaccumulation of inorganic arsenic can induce oxidative stress. The largest increase in oxidative stress was observed following acute exposure to AsIII, but no significant degree of oxidative stress was induced by chronic exposure. During acute exposure to AsV, the increase in the enzymatic activity of glutathione-S-transferase (GST) was twice as high compared with exposure to AsIII, suggesting that GST plays an important role in the initial detoxification process. In addition, an RNA-seq-based ingenuity pathway analysis revealed that acute exposure to AsIII may be related to cell-cycle progression. A network analysis using differentially expressed genes also revealed a potential link between the generation of inflammatory cytokines and oxidative stress due to arsenic exposure.

Studies on Human Cultured Fibroblasts and Cutaneous Squamous Cell Carcinomas Suggest That Overexpression of Histone Variant H2A.J Promotes Radioresistance and Oncogenic Transformation

Background: Cellular senescence in response to ionizing radiation (IR) limits the replication of damaged cells by causing permanent cell cycle arrest. However, IR can induce pro-survival signaling pathways that reduce the extent of radiation-induced cytotoxicity and promote the development of radioresistance. The differential incorporation of histone variant H2A.J has profound effects on higher-order chromatin organization and on establishing the epigenetic state of radiation-induced senescence. However, the precise epigenetic mechanism and function of H2A.J overexpression in response to IR exposure still needs to be elucidated. Methods: Primary (no target, NT) and genetically modified fibroblasts overexpressing H2A.J (H2A.J-OE) were exposed to 20 Gy and analyzed 2 weeks post-IR for radiation-induced senescence by immunohistochemistry and immunofluorescence microscopy. Transcriptome signatures were analyzed in (non-)irradiated NT and H2A.J-OE fibroblasts by RNA sequencing. Since H2A.J plays an important role in the epidermal homeostasis of human skin, the oncogenic potential of H2A.J was investigated in cutaneous squamous cell carcinoma (cSCC). The tissue microarrays of cSCC were analyzed for H2A.J protein expression pattern by automated image analysis. Results: In response to radiation-induced DNA damage, the overexpression of H2A.J impairs the formation of senescence-associated heterochromatin foci (SAHF), thereby inhibiting the SAHF-mediated silencing of proliferation-promoting genes. The dysregulated activation of cyclins and cyclin-dependent kinases disturbs cell cycle arrest in irradiated H2A.J-OE fibroblasts, thereby overcoming radiation-induced senescence. Comparative transcriptome analysis revealed significantly increased WNT16 signaling in H2A.J OE fibroblasts after IR exposure, promoting the fundamental mechanisms of tumor development and progression, including the activation of the epithelial-mesenchymal transition. The quantitative analysis of cSCCs revealed that undifferentiated tumors are associated with high nuclear H2A.J expression, related with greater oncogenic potential. Conclusion: H2A.J overexpression induces radioresistance and promotes oncogenic transformation through the activation of WNT16 signaling pathway functions. H2A.J-associated signatures may improve risk stratification by identifying patients with more aggressive cSCC who may require radiotherapy with increased doses.

EpoR stimulates rapid cycling and larger red cells during mouse and human erythropoiesis

The erythroid terminal differentiation program couples sequential cell divisions with progressive reductions in cell size. The erythropoietin receptor (EpoR) is essential for erythroblast survival, but its other functions are not well characterized. Here we use Epor-/- mouse erythroblasts endowed with survival signaling to identify novel non-redundant EpoR functions. We find that, paradoxically, EpoR signaling increases red cell size while also increasing the number and speed of erythroblast cell cycles. EpoR-regulation of cell size is independent of established red cell size regulation by iron. High erythropoietin (Epo) increases red cell size in wild-type mice and in human volunteers. The increase in mean corpuscular volume (MCV) outlasts the duration of Epo treatment and is not the result of increased reticulocyte number. Our work shows that EpoR signaling alters the relationship between cycling and cell size. Further, diagnostic interpretations of increased MCV should now include high Epo levels and hypoxic stress.

P38 MAPK/AKT signalling is involved in IL-33-mediated anti-apoptosis in childhood acute lymphoblastic leukaemia blast cells

BACKGROUND

Acute lymphoblastic leukaemia (ALL) is often characterized by broad clinical and biological heterogeneity, as well as recurrent genetic aberrations. Despite remarkable improvements in the treatment outcome in paediatric ALL over the past several decades, it remains a leading cause of morbidity and mortality among children. Cytokines have been extensively studied in haematologic diseases; however, the mechanisms by which cytokines contribute to ALL pathogenesis remain poorly understood.

METHODS

IL-33 levels were measured by enzyme-linked immunosorbent assay (ELISA). IL1RL1 expression on ALL cell surface was accessed by flow cytometry. Expression of phosphorylated p38 MAPK, p38, pAKT, AKT and GAPDH were quantified by western blot. Cell survival signals were evaluated by apoptosis using flow cytometry.

RESULTS

BM samples from ALL patients at diagnosis upregulated their cell surface expression of IL1RL1, and a higher interleukin (IL)-33 level in the serum was observed as compared to the healthy individuals. Moreover, exogenous IL-33 treatment significantly inhibited apoptosis by activating p38 mitogen-activated protein kinase (MAPK) and AKT pathway, while the inhibitor for p38 MAPK, SB203580, counteracted IL-33-induced anti-apoptosis via inactivation of p38 MAPK and AKT. Furthermore, IL-33 negatively regulates cyclin B1 protein level while increasing the expression of CDK1, with SB203580 inhibiting the effect.

CONCLUSION

Our study reveals an important role for IL-33/IL1RL1 axis in supporting ALL which may represent a novel treatment for paediatric patients.KEY MESSAGESBoth IL-33 and IL1RL1 levels are upregulated in primary ALL samples.IL-33 increased both p38 MAPK and AKT activation in ALL.IL-33 promotes survival and cell cycle progression of ALL cells via activating p38 MAPK.

Hierarchy of breast cancer cells: key to reverse dormancy for therapeutic intervention

An understanding of how cancer cells adapt dormancy would allow for targeted treatment. The current literature suggests that the cancer stem cells might be the major cells with the ability to become quiescent and to resist current drug treatment. The properties of cancer stem cells and healthy stem cells are functionally similar, thereby posing a challenge to target the dormant cells. The bone marrow is particularly a challenge because the dormant breast cancer cells are close to the endosteum, which is also home to the endogenous hematopoietic stem cells. Here we discuss how research studies could bring an understanding of the cellular and molecular interactions between the cancer stem cells and cells within the bone marrow microenvironment. This will allow for intervention to reverse dormancy for targeted treatment. The treatment will require studies within the normal organ functions to ensure treatment without toxicity.

A mathematical model for a T cell fate decision algorithm during immune response

We formulate and analyze an algorithm of cell fate decision that describes the way in which division vs. apoptosis choices are made by individual T cells during an infection. Such model involves a minimal number of known biochemical mechanisms: it basically relies on the interplay between cell division and cell death inhibitors on one hand, and membrane receptors on the other. In spite of its simplicity, the proposed decision algorithm is able to account for some significant facts in immune response. At the individual level, the existence of T cells that continue to replicate in the absence of antigen and the possible occurrence of T cell apoptosis in the presence of antigen are predicted by the model. Moreover, the latter is shown to yield an emergent collective behavior, the observed delay in clonal contraction with respect to the end of antigen stimulation, which is shown to arise just from individual T cell decisions made according to the proposed mechanism.

Ghrelin promotes intestinal epithelial cell proliferation through PI3K/Akt pathway and EGFR trans-activation both converging to ERK 1/2 phosphorylation

Little is known about ghrelin's effects on intestinal epithelial cells even though it is known to be a mitogen for a variety of other cell types. Because ghrelin is released in close proximity to the proliferative compartment of the intestinal tract, we hypothesized that ghrelin may have potent pro-proliferative effect on intestinal epithelial cells as well. To test this hypothesis, we characterized the effects of ghrelin on FHs74Int and Caco-2 intestinal epithelial cell lines in vitro. We found that ghrelin has potent dose dependent proliferative effects in both cell lines through a yet to be characterized G protein coupled growth hormone secretagogue receptor (GHS-R) subtype. Consistent with above findings, cell cycle flowcytometric analyses demonstrated that ghrelin shifts cells from the G1 to S phase and thereby promotes cell cycle progression. Further characterization of subcellular events, suggested that ghrelin mediates its pro-proliferative effect through Adenylate cyclase (AC)-independent epidermal growth factor receptor (EGFR) trans-activation and PI3K-Akt phosphorylation. Both these pathways converge to stimulate MAPK, ERK 1/2 downstream. The role of ghrelin in states where intestinal mucosal injury and rapid mucosal repair occur warrants further investigation.

FOXO transcription factors enforce cell cycle checkpoints and promote survival of hematopoietic cells after DNA damage

The PI3K/AKT signaling pathway contributes to cell cycle progression of cytokine-dependent hematopoietic cells under normal conditions, and it is absolutely required to override DNA damage-induced cell cycle arrest checkpoints in these cells. Phosphatidylinositol-3-kinase (PI3K)/AKT activity also correlates with Cdk2 activity in hematopoietic cells, suggesting that Cdk2 activation may be a relevant end point for this signaling pathway. However, mediators downstream of AKT in this pathway have not been defined. The forkhead transcription factor O (FOXO) family are negatively regulated by AKT-dependent phosphorylation and are known regulators of genes affecting cell cycle progression. We show that enhanced FOXO activity replicates the effect of PI3K inhibitors in enforcing G(1) and G(2) phase arrest after DNA damage. Conversely, knockdown of endogenous FOXO proteins increased Cdk2 activity and overrode DNA damage checkpoints in cells lacking PI3K activity. Moreover, loss of FOXO activity caused an increase in sensitivity to cisplatin-induced cell death, which was associated with failure to arrest cell cycle progression in the face of DNA damage caused by this chemotherapeutic agent. These cell cycle arrests were dependent on p27 expression when mediated by FOXO3a alone, but also involve p27-independent mechanisms when promoted by endogenous FOXO proteins. Together, these observations show that FOXO proteins enforce DNA damage-induced cell cycle arrest in hematopoietic cells. Inhibition of FOXO activity by cytokine-induced PI3K/AKT signaling is sufficient to override these DNA damage-induced cell cycle checkpoints, but may negatively impact hematopoietic cell viability.