Dynamics of an incoherent feedforward loop drive ERK-dependent pattern formation in the early Drosophila embryo

Positional information in developing tissues often takes the form of stripes of gene expression that mark the boundaries of a particular cell type or morphogenetic process. How stripes form is still in many cases poorly understood. Here we use optogenetics and live-cell biosensors to investigate one such pattern: the posterior stripe of brachyenteron (byn) expression in the early Drosophila embryo. This byn stripe depends on interpretation of an upstream signal - a gradient of ERK kinase activity - and the expression of two target genes tailless (tll) and huckebein (hkb) that exert antagonistic control over byn . We find that high or low doses of ERK signaling produce either transient or sustained byn expression, respectively. These ERK stimuli also regulate tll and hkb expression with distinct dynamics: tll transcription is rapidly induced under both low and high stimuli, whereas hkb transcription converts graded ERK inputs into an output switch with a variable time delay. Antagonistic regulatory paths acting on different timescales are hallmarks of an incoherent feedforward loop architecture, which is sufficient to explain transient or sustained byn dynamics and adds temporal complexity to the steady-state model of byn stripe formation. We further show that an all-or-none stimulus can be 'blurred' through intracellular diffusion to non-locally produce a stripe of byn gene expression. Overall, our study provides a blueprint for using optogenetic inputs to dissect developmental signal interpretation in space and time.

Piperlongumine induces autophagy in biliary cancer cells via reactive oxygen species-activated Erk signaling pathway

Biliary cancer (BC) is an aggressive neoplasm with high mortality. BC can be categorized into three groups: Intrahepatic cholangiocarcinoma (CCA; also known as bile duct cancer), extrahepatic cholangiocarcinoma and gallbladder cancer. Due to its heterogeneity and aggressiveness, the response to current chemotherapy and radiotherapy methods in patients with BC is poor. Therefore, there is an urgent requirement to develop drugs to treat BC. Piperlongumine (PL), a naturally occurring small molecule isolated from Piper longum L., exhibits anticancer activity by inducing reactive oxygen species (ROS) production. In the present study, the effects of PL on cell proliferation, cell cycle, apoptosis and autophagy in BC cells were investigated. PL induced BC cell death in a concentration‑ and time‑dependent manner by inducing ROS production. PL induced cell cycle arrest in CCA cells (HuCCT‑1) and gallbladder cancer cells (OCUG‑1) cells, but with distinct cell cycle distribution profiles. PL caused G2/M cell cycle arrest in HuCCT‑1 cells, and G0/G1 cell cycle arrest in OCUG‑1 cells. PL induced apoptosis and autophagy; PL treatment induced accumulation of LC3‑II in a concentration‑ and time‑dependent manner. The Erk signaling pathway appeared to be involved in autophagy induction. Application of the ROS scavenger, N‑acetyl‑l‑cysteine, to BC cells attenuated the cell death, cell cycle arrest, apoptosis and autophagy induced by PL treatment. These findings indicated that PL may be a potential agent for BC treatment in the future.

C-terminus of ETA/ETB receptors regulate endothelin-1 signal transmission

The dimerization of the G protein-coupled receptors for endothelin-1 (ET-1), endothelin A receptor (ETA) and endolethin B receptor (ETB), is well established. However, the signaling consequences of the homodimerization and heterodimerization of ETA and ETB is not well understood. Here, we demonstrate that peptides derived from the C-termini of these receptors regulate the signaling capacity of ET-1. The C-termini of the ETA and ETB receptors are believed to consist of three α-helices, which may serve as points of interaction between the receptors. The third α-helix in the C-terminus is of particular interest because of its amphipathic nature. In a cell line expressing only the ETA receptor, expression of residues Y430-S442, representing the third helix of the ETB C-terminus, leads to a dramatic increase in the signaling induced by ET-1. In contrast, in a cell line containing only ETB , Y430-S442 has an antagonistic effect, slightly reducing the ET-1 induced signal. Computational docking results suggest that the α-helical ETB -derived peptide binds to the second and third intracellular loops of the ETA receptor consistent with the alteration of its signaling capacity. Our results described here provide important insight into ETA /ETB receptor interactions and possibly a new approach to regulate specific G protein-coupled receptor signal transmission.

Role of ERK map kinase and CRM1 in IL-1beta-stimulated release of HMGB1 from cortical astrocytes

Reactive astrocytes are traditionally thought to impede brain plasticity after stroke. However, we previously showed that reactive astrocytes may also contribute to stroke recovery, partly via the release of a nuclear protein called high-mobility group box 1 (HMGB1). Here, we investigate the mechanisms that allow stimulated astrocytes to release HMGB1. Exposure of rat primary astrocytes to IL-1beta for 24 h elicited a dose-dependent HMGB1 response. Immunostaining and western blots of cell lysates showed increased intracellular levels of HMGB1. Western blots confirmed that IL-1beta induced a release of HMGB1 into astrocyte conditioned media. MAP kinase signaling was involved. Levels of phospho-ERK were increased by IL-1beta, and the MEK/ERK inhibitor U0126 decreased HMGB1 upregulation in the stimulated astrocytes. Since HMGB1 is a nuclear protein, the role of the nuclear protein exporter, chromosome region maintenance 1 (CRM1), was assessed as a candidate mechanism for linking MAP kinase signaling to HMGB1 release. IL-1beta increased CRM1 expression in concert with a translocation of HMGB1 from nucleus into cytoplasm. Blockade of IL-1beta-stimulated HMGB1 release with the ERK inhibitor U0126 was accompanied by a downregulation of CRM1. Our findings reveal that IL-1beta stimulates the release of HMGB1 from activated astrocytes via ERK MAP kinase and CRM1 signaling. These data suggest a novel pathway by which inflammatory cytokines may enhance the ability of reactive astrocytes to release prorecovery mediators after stroke.