A role of mitogen and stress-activated protein kinase 1/2 in survival of lipopolysaccharide-stimulated RAW 264.7 macrophages

Mitogen- and Stress-Activated Protein Kinase 1 Regulates Status Epilepticus-Evoked Cell Death in the Hippocampus

Mitogen-activated protein kinase (MAPK) signaling has been implicated in a wide range of neuronal processes, including development, plasticity, and viability. One of the principal downstream targets of both the extracellular signal-regulated kinase/MAPK pathway and the p38 MAPK pathway is Mitogen- and Stress-activated protein Kinase 1 (MSK1). Here, we sought to understand the role that MSK1 plays in neuroprotection against excitotoxic stimulation in the hippocampus. To this end, we utilized immunohistochemical labeling, a MSK1 null mouse line, cell viability assays, and array-based profiling approaches. Initially, we show that MSK1 is broadly expressed within the major neuronal cell layers of the hippocampus and that status epilepticus drives acute induction of MSK1 activation. In response to the status epilepticus paradigm, MSK1 KO mice exhibited a striking increase in vulnerability to pilocarpine-evoked cell death within the CA1 and CA3 cell layers. Further, cultured MSK1 null neurons exhibited a heighted level of N-methyl-D-aspartate-evoked excitotoxicity relative to wild-type neurons, as assessed using the lactate dehydrogenase assay. Given these findings, we examined the hippocampal transcriptional profile of MSK1 null mice. Affymetrix array profiling revealed that MSK1 deletion led to the significant (>1.25-fold) downregulation of 130 genes and an upregulation of 145 genes. Notably, functional analysis indicated that a subset of these genes contribute to neuroprotective signaling networks. Together, these data provide important new insights into the mechanism by which the MAPK/MSK1 signaling cassette confers neuroprotection against excitotoxic insults. Approaches designed to upregulate or mimic the functional effects of MSK1 may prove beneficial against an array of degenerative processes resulting from excitotoxic insults.

Accelerated apoptotic death and in vivo turnover of erythrocytes in mice lacking functional mitogen- and stress-activated kinase MSK1/2

The mitogen- and stress-activated kinase MSK1/2 plays a decisive role in apoptosis. In analogy to apoptosis of nucleated cells, suicidal erythrocyte death called eryptosis is characterized by cell shrinkage and cell membrane scrambling leading to phosphatidylserine (PS) externalization. Here, we explored whether MSK1/2 participates in the regulation of eryptosis. To this end, erythrocytes were isolated from mice lacking functional MSK1/2 (msk^−/−) and corresponding wild-type mice (msk^+/+). Blood count, hematocrit, hemoglobin concentration and mean erythrocyte volume were similar in both msk^−/− and msk^+/+ mice, but reticulocyte count was significantly increased in msk^−/− mice. Cell membrane PS exposure was similar in untreated msk^−/− and msk^+/+ erythrocytes, but was enhanced by pathophysiological cell stressors ex vivo such as hyperosmotic shock or energy depletion to significantly higher levels in msk^−/− erythrocytes than in msk^+/+ erythrocytes. Cell shrinkage following hyperosmotic shock and energy depletion, as well as hemolysis following decrease of extracellular osmolarity was more pronounced in msk^−/− erythrocytes. The in vivo clearance of autologously-infused CFSE-labeled erythrocytes from circulating blood was faster in msk^−/− mice. The spleens from msk^−/− mice contained a significantly greater number of PS-exposing erythrocytes than spleens from msk^+/+ mice. The present observations point to accelerated eryptosis and subsequent clearance of erythrocytes leading to enhanced erythrocyte turnover in MSK1/2-deficient mice.

Mitogen- and stress-activated kinase 1-mediated histone H3 phosphorylation is crucial for cell transformation

Mitogen- and stress-activated kinase 1 (MSK1) belongs to a family of dual protein kinases that are activated by either extracellular signal-regulated kinase or p38 mitogen-activated protein kinases in response to stress or mitogenic extracellular stimuli. The physiologic role of MSK1 in malignant transformation and cancer development is not well understood. Here, we report that MSK1 is involved in 12-O-tetradecanoylphorbol-13-acetate (TPA)-induced or epidermal growth factor (EGF)-induced neoplastic transformation of JB6 Cl41 cells. H89, a potent inhibitor of MSK1, strongly suppressed TPA-induced or EGF-induced cell transformation. When cells overexpressing wild-type MSK1 were treated with TPA or EGF, colony formation increased substantially compared with untreated cells or cells that did not overexpress MSK1. In contrast, MSK1 COOH terminal or NH(2) terminal dead dominant negative mutants dramatically suppressed cell transformation. Introduction of small interfering RNA-MSK1 into JB6 Cl41 cells resulted in suppressed TPA-induced or EGF-induced cell transformation. In addition, cell proliferation was inhibited in MSK1 knockdown cells compared with MSK1 wild-type cells. In wild-type MSK1-overexpressing cells, activator protein (AP-1) activation increased after TPA or EGF stimulation, whereas AP-1 activation decreased in both MSK1 dominant-negative mutants and in MSK1 knockdown cells. Moreover, TPA-induced or EGF-induced phosphorylation of histone H3 at Ser(10) was increased in wild-type cells but the induced phosphorylation was abolished in MSK1 dominant-negative mutant or MSK1 knockdown cells. Thus, MSK1 is required for tumor promoter-induced cell transformation through its phosphorylation of histone H3 at Ser(10) and AP-1 activation.