MK2 plays an important role for the increased vascular permeability that follows thermal injury

Effect of Inhibiting p38 on HuR Involving in β-AChR Post-transcriptional Mechanisms in Denervated Skeletal Muscle

Previous studies reported that RNA-binding protein human antigen R (HuR) mediates changes in the stability of AChR β-subunit mRNA after skeletal muscle denervation; also, p38 pathway regulated the stability of AChR β-subunit mRNA in C2C12 myotubes. However, the relationship between HuR and p38 in regulating the stability of AChR β-subunit mRNA have not been clarified. In this study, we wanted to examine the effect of inhibiting p38 on HuR in denervated skeletal muscle. Denervation model was built and 10% DMSO or SB203580 were administered respectively follow denervation. Tibialis muscles were collected in 10% DMSO-administered contralateral (undenervated) leg, 10% DMSO-administered denervated leg, SB203580-administered contralateral (undenervated) leg, and SB203580-administered denervated leg, respectively. P38 protein, β-AChR mRNA and protein, HuR protein, β-AChR mRNA stability, and HuR binding with AChR β-subunit mRNAs were measured. Results demonstrated that the administration of SB203580 can inhibit the increase of β-AChR protein expression and mRNA expression and stability, and RNA-binding protein human antigen R (HuR) expression, in cytoplasmic and nuclear fractions in skeletal muscle cells following denervation. Importantly, we observed that SB203580 also inhibited the increased level of binding activity between HuR and AChR β-subunit mRNAs following denervation. Collectively, these results suggested that inhibition of p38 can post-transcriptionally inhibit β-AChR upregulation via HuR in denervated skeletal muscle.

p38 MAPK-MK2 pathway regulates the heat-stress-induced accumulation of reactive oxygen species that mediates apoptotic cell death in glial cells

Previous studies have demonstratedf that heat stress can induce injury of the central nervous system and lead to neuronal cell apoptosis. However, the molecular mechanisms underlying these cellular changes remain unclear. In the present study, flow cytometry was used to investigate heat-stress-induced apoptosis, and caspase-3 activation was also assessed in neurons. The role of reactive oxygen species (ROS) accumulation in the heat-stress-induced apoptosis of neurons was demonstrated using the antioxidant drug manganese (III) tetrakis (4-benzoic acid)porphyrin. The present study presents evidence that heat stress induces mitogen-activated protein kinase (MAPK) activation in rat malignant glioma F98 cells. Following the inhibition of different MAPKs with a range of specific inhibitors, SB203580 (an inhibitor of p38 MAPK), but not PD98059 (an inhibitor of extracellular signal-regulated kinases) or SP600125 (an inhibitor of c-Jun N-terminal kinases), diminished the production of ROS and apoptosis, and prevented activation of the p38-downstream kinase MAPK-activated protein kinase 2 (MK2) in neurons. Inhibiting MK2 with dominant negative adenoviral constructs or a specific inhibitor significantly decreased normal and heat-stress-induced ROS accumulation and cell apoptosis, whereas inhibition of another kinase downstream of p38 MAPK, MAPK-activated protein kinase 5, by transfection with another adenoviral construct did not exert the same effects. Taken together, these findings indicate that heat stress stimulation induces p38-MK2 pathway activation, which exerts a pro-apoptotic effect by regulating ROS accumulation in neurons.

Viral activation of stress-regulated Rho-GTPase signaling pathway disrupts sites of mRNA degradation to influence cellular gene expression

Viruses are useful tools that often reveal previously unrecognized levels of control within a cell. By studying the oncogenic Kaposi's sarcoma-associated herpesvirus (KSHV), we discovered a new signaling axis in endothelial cells (ECs) that links actin cytoskeleton dynamics to post-transcriptional control of gene expression. Translational repression and rapid decay of mRNAs containing AU-rich elements (AREs) occurs in cytoplasmic RNA granules known as processing bodies (PBs). Rho-GTPase activity influences PB dynamics but mechanistic details remain obscure. We have previously shown that the KSHV Kaposin B protein blocks the degradation of ARE-mRNAs that encode potent cytokines and angiogenic factors, at least in part by preventing PB formation. Moreover, Kaposin B is sufficient to cause marked alterations in endothelial cell physiology including the formation of long parallel actin stress fibers and accelerated migration and angiogenic phenotypes. All of these phenotypes depend on Kaposin B-mediated activation of a non-canonical signaling pathway comprising the stress-inducible kinase MK2, hsp27, p115RhoGEF and RhoA. Accelerated endothelial cell migration and angiogenesis depends on the subsequent activation of the RhoA-dependent kinase ROCK, but PB disruption is ROCK-independent. In this Commentary, we discuss implications of the activation of this signaling axis, and propose mechanistic links between RhoA activation and PB dynamics.

Doxycycline hyclate protects lipopolysaccharide-induced endothelial barrier dysfunction by inhibiting the activation of p38 mitogen-activated protein kinase

Doxycycline hyclate (DOX-h) attenuates inflammatory conditions independent of its antimicrobial effect. This study aimed to observe the effects of DOX-h on lipopolysaccharide (LPS)-induced endothelial barrier dysfunction. The endothelial monolayer permeability of human umbilical vein endothelial cells (HUVECs) was monitored by transendothelial electrical resistance (TEER). The phosphorylation of mitogen-activated protein kinases (MAPKs) and the arrangement of F-actin were detected. The results showed that both pretreatment and simultaneous treatment with DOX-h markedly attenuated the LPS-induced reduction in TEER and the disorganization of F-actin on HUVECs in a dose- and time-dependent manner. LPS mediated the phosphorylation of all three MAPKs (p38, extracellular signal-regulated kinase (ERK)1/2, and c-Jun N-terminal kinase (JNK)), but DOX-h was only able to inhibit the LPS-induced phosphorylation of p38 and JNK. The data further suggested that DOX-h alleviated LPS-evoked TEER reduction and F-actin redistribution by inhibiting the phosphorylation of p38 and its downstream target, heat shock protein (HSP)27. Thus, DOX-h attenuates LPS-induced endothelial barrier dysfunction via inhibition of the p38 MAPK-HSP27-F-actin pathway.