Cytokine-stimulated phosphorylation of GSK-3 is primarily dependent upon PKCs, not PKB

The GSK3β/Mcl-1 axis is regulated by both FLT3-ITD and Axl and determines the apoptosis induction abilities of FLT3-ITD inhibitors

Acute myeloid leukemia (AML) patients with FLT3-ITD mutations are associated with poor prognosis. FLT3-ITD inhibitors are developed and result in transient disease remission, but generally resistance develops. We propose that resistance occurs due to apoptosis evasion. We compared the abilities of five clinically used FLT3-ITD inhibitors, namely, midostaurin, crenolanib, gilteritinib, quizartinib, and sorafenib, to induce apoptosis. These drugs inhibit FLT3-ITD and induce apoptosis. Apoptosis induction is associated with GSK3β activation, Mcl-1 downregulation, and Bim upregulation. Sorafenib-resistant MOLM-13/sor cells have the secondary D835Y mutation and increased Axl signaling pathway with cross-resistance to quizartinib. Gilteritinib and crenolanib inhibit both FLT3-ITD and Axl and induce apoptosis in MOLM-13/sor cells, in which they activate GSK3β and downregulate Mcl-1. Inactivation of GSK3β through phosphorylation and inhibitors blocks apoptosis and Mcl-1 reduction. The Axl/GSK3β/Mcl-1 axis works as a feedback mechanism to attenuate apoptosis of FLT3-ITD inhibition. Homoharringtonine decreases the protein levels of Mcl-1, FLT3-ITD, and Axl. Moreover, it synergistically induces apoptosis with gilteritinib in vitro and prolongs survival of MOLM-13/sor xenografts. The GSK3β/Mcl-1 axis works as the hub of FLT3-ITD inhibitors and plays a critical role in resistance against FLT3-ITD AML-targeted therapy.

Interleukin-4 Boosts Insulin-Induced Energy Deposits by Enhancing Glucose Uptake and Lipogenesis in Hepatocytes

Type 2 diabetes mellitus (T2DM), with dysregulated hepatic gluconeogenesis as the major cause of fasting hyperglycemia, is closely associated with chronic inflammation. We previously demonstrated interleukin-4 (IL-4) improves insulin sensitivity and glucose tolerance while reducing lipid deposits. The present study examined the in vitro effects of IL-4 on insulin signaling molecules, glucose uptake, and lipid metabolism in hepatocytes, as well as in vivo effects on hepatic adiposity, for elucidating the roles of IL-4 in hepatic energy metabolism. Potential interaction between IL-4 and insulin in regulating hepatic metabolism was also investigated. Our results showed that IL-4 enhanced Akt and GSK-3α/β phosphorylations, which in turn promoted glycogen synthesis. IL-4 not only potentiated basal glucose uptake by upregulating glucose transporter 2 expression but also promoted insulin-induced glucose uptake. Additionally, IL-4 increased triglyceride contents through facilitating free fatty acid uptake and expression/activity of lipogenic enzymes. The major effects of IL-4 on the liver were to promote energy storage by boosting insulin-stimulated glucose uptake and lipid synthesis. This study provides evidence to implicate the novel roles of IL-4 in mediating hepatic glucose and lipid metabolism, interactions between immune responses and metabolic homeostasis, and the involvement of IL-4 in metabolic abnormalities.

Resibufogenin suppresses transforming growth factor-β-activated kinase 1-mediated nuclear factor-κB activity through protein kinase C-dependent inhibition of glycogen synthase kinase 3

Resibufogenin (RB), one of the major active compounds of the traditional Chinese medicine Chansu, has received considerable attention for its potency in cancer therapy. However, the anticancer effects and the underlying mechanisms of RB on pancreatic cancer remain elusive. Here, we found that RB inhibited the viability and induces caspase‐dependent apoptosis in human pancreatic cancer cells Panc‐1 and Aspc. Resibufogenin‐induced apoptosis was through inhibition of constitutive nuclear factor‐κB (NF‐κB) activity and its target genes’ expression, which was caused by downregulation of transforming growth factor‐β‐activated kinase 1 (TAK1) levels and suppression of IκB kinase activity in Panc‐1 and Aspc cells. This induction of TAK1‐mediated NF‐κB inactivation by RB was associated with increased glycogen synthase kinase‐3 (GSK‐3) phosphorylation and subsequent suppression of its activity. Moreover, RB‐induced GSK‐3 phosphorylation/inactivation acted through activation of protein kinase C but not Akt. Finally, RB suppressed human pancreatic tumor xenograft growth in athymic nude mice. Thus, our findings reveal a novel mechanism by which RB suppresses TAK1‐mediated NF‐κB activity through protein kinase C‐dependent inhibition of GSK‐3. Our findings provide a rationale for the potential application of RB in pancreatic cancer therapy.

Role of Opioid Receptors Signaling in Remote Electrostimulation--Induced Protection against Ischemia/Reperfusion Injury in Rat Hearts

Aims

Our previous studies demonstrated that remote electro-stimulation (RES) increased myocardial GSK3 phosphorylation and attenuated ischemia/ reperfusion (I/R) injury in rat hearts. However, the role of various opioid receptors (OR) subtypes in preconditioned RES-induced myocardial protection remains unknown. We investigated the role of OR subtype signaling in RES-induced cardioprotection against I/R injury of the rat heart.

Methods & Results

Male Spraque-Dawley rats were used. RES was performed on median nerves area with/without pretreatment with various receptors antagonists such as opioid receptor (OR) subtype receptors (KOR, DOR, and MOR). The expressions of Akt, GSK3, and PKCε expression were analyzed by Western blotting. When RES was preconditioned before the I/R model, the rat's hemodynamic index, infarction size, mortality and serum CK-MB were evaluated. Our results showed that Akt, GSK3 and PKCε expression levels were significantly increased in the RES group compared to the sham group, which were blocked by pretreatment with specific antagonists targeting KOR and DOR, but not MOR subtype. Using the I/R model, the duration of arrhythmia and infarct size were both significantly attenuated in RES group. The mortality rates of the sham RES group, the RES group, RES group + KOR antagonist, RES group + DOR/MOR antagonists (KOR left), RES group + DOR antagonist, and RES group + KOR/MOR antagonists (DOR left) were 50%, 20%, 67%, 13%, 50% and 55%, respectively.

Conclusion

The mechanism of RES-induced myocardial protection against I/R injury seems to involve multiple target pathways such as Akt, KOR and/or DOR signaling.

The cysteine-rich core domain of REIC/Dkk-3 is critical for its effect on monocyte differentiation and tumor regression

Reduced expression in immortalized cells (REIC)/Dickkopf (Dkk)-3 is a tumor-suppressor gene and has been studied as a promising therapeutic gene for cancer gene therapy. Intratumoral injection of an adenovirus vector carrying the human REIC/Dkk-3 gene (Ad-REIC) elicits cancer cell-specific apoptosis and anticancer immune responses. The cytokine-like effect of secretory REIC/Dkk-3 on the induction of dendritic cell (DC)-like cell differentiation from monocytes plays a role in systemic anticancer immunity. In the present study, we generated recombinant full-length and N-terminally truncated REIC/Dkk-3 to characterize the biological activity of the protein. During the purification procedure, we identified a 17 kDa cysteine-rich stable product (C17-REIC) showing limited degradation. Further analysis showed that the C17-REIC domain was sufficient for the induction of DC-like cell differentiation from monocytes. Concomitant with the differentiation of DCs, the REIC/Dkk-3 protein induced the phosphorylation of glycogen synthase kinase 3β (GSK-3β) and signal transducers and activators of transcription (STAT) at a level comparable to that of granulocyte/macrophage colony-stimulating factor. In a mouse model of subcutaneous renal adenocarcinoma, intraperitoneal injection of full-length and C17-REIC proteins exerted anticancer effects in parallel with the activation of immunocompetent cells such as DCs and cytotoxic T lymphocytes in peripheral blood. Taken together, our results indicate that the stable cysteine-rich core region of REIC/Dkk-3 is responsible for the induction of anticancer immune responses. Because REIC/Dkk-3 is a naturally circulating serum protein, the upregulation REIC/Dkk-3 protein expression could be a promising option for cancer therapy.

Cytokine-induced monocyte MMP-1 is negatively regulated by GSK-3 through a p38 MAPK-mediated decrease in ERK1/2 MAPK activation

Elucidation of the signal transduction events leading to the production of MMPs by monocytes/macrophages may provide insights into the mechanisms involved in the destruction of connective tissue associated with chronic inflammatory lesions. Here, we show that GSK-3 is a negative regulator of cytokine-induced MMP-1 production by monocytes. Inhibition of monocyte GSK-3 pharmacologically with SB216763 or GSK-3β siRNA caused a significant enhancement of MMP-1 by TNF-α- and GM-CSF-activated monocytes, indicating that induction of MMP-1 by TNF-α and GM-CSF involved phosphorylation/inactivation of GSK-3. TNF-α- and GM-CSF-induced phosphorylation of GSK-3 and subsequent MMP-1 production was blocked with the PKC inhibitor Gö6976 but not by the AKT1/2 inhibitor AKT VIII, showing that cytokine phosphorylation of GSK-3 occurs primarily through a PKC pathway. Inhibition of GSK-3 resulted in decreased phosphorylation of p38 MAPK with a corresponding increase in phosphorylation of ERK1/2 MAPK. Enhanced MMP-1 production by treatment with SB216763 was a result of increased ERK1/2 activation, as demonstrated by inhibition of MMP-1 by PD98059, a specific ERK1/2 inhibitor. Conversely, the p38 MAPK inhibitor SB203580 enhanced cytokine activation of ERK1/2 and the production of MMP-1 similar to that of SB216763. These findings demonstrate that the degree of cytokine-mediated phosphorylation/inhibition of GSK-3 determines the level of MMP-1 production through a mechanism involving decreased activation of p38 MAPK, a negative regulator of ERK1/2 required for cytokine-induced production of MMP-1 by monocytes.

SIL1 Rescued Bip Elevation-Related Tau Hyperphosphorylation in ER Stress

Endoplasmic reticulum (ER) stress has been indicated in the early stage of Alzheimer's disease (AD), in which tau hyperphosphorylation is one major pathological alteration. The elevation of binding immunoglobulin protein (Bip), an important ER chaperon, was reported in AD brain. It is important to study the roles of ER-related chaperons in tau hyperphosphorylation. In this research, increased Bip was found in the brains of the AD model mice (Tg2576) compared to the age-matched control mice. Meanwhile, deficiency of SIL1, an important co-chaperon of Bip, was observed in brains of Tg2576 mice and in ER stress both in vivo and in vitro. Then, we transfected Bip-EGFP plasmid into HEK293 cells stably expressing the longest human tau (HEK293/tau) or N2a cells and found that increased Bip induced tau hyperphosphorylation via activating glycogen synthase kinase-3β (GSK-3β), an important tau kinase, and increased the association with tau and GSK-3β. When we overexpressed SIL1 in Bip-transfected HEK293/tau cells and thapsigargin-treated HEK293/tau cells, significantly reduced tau hyperphosphorylation and GSK-3β activation were observed. These results suggested the important roles of ER-related chaperons, Bip and SIL1, in AD-like tau hyperphosphorylation.

PKCβ positively regulates RANKL-induced osteoclastogenesis by inactivating GSK-3β

Protein kinase C (PKC) family members phosphorylate a wide variety of protein targets and are known to be involved in diverse cellular signaling pathways. However, the role of PKC in receptor activator of NF-κB ligand (RANKL) signaling has remained elusive. We now demonstrate that PKCβ acts as a positive regulator which inactivates glycogen synthase kinase-3β (GSK-3β) and promotes NFATc1 induction during RANKL-induced osteoclastogenesis. Among PKCs, PKCβ expression is increased by RANKL. Pharmacological inhibition of PKCβ decreased the formation of osteoclasts which was caused by the inhibition of NFATc1 induction. Importantly, the phosphorylation of GSK-3β was decreased by PKCβ inhibition. Likewise, down-regulation of PKCβ by RNA interference suppressed osteoclast differentiation, NFATc1 induction, and GSK-3β phosphorylation. The administration of PKC inhibitor to the RANKL-injected mouse calvaria efficiently protected RANKL-induced bone destruction. Thus, the PKCβ pathway, leading to GSK-3β inactivation and NFATc1 induction, has a key role in the differentiation of osteoclasts. Our results also provide a further rationale for PKCβ's therapeutic targeting to treat inflammation-related bone diseases.

Loss of TRIM62 expression is an independent adverse prognostic factor in acute myeloid leukemia

BACKGROUND

Tripartite motif (TRIM)-62 is a putative tumor suppressor gene whose role in leukemia is unknown.

MATERIALS AND METHODS

We evaluated the effect of TRIM62 protein expression in patients with acute myeloid leukemia (AML). We used reverse-phase protein array methodology to determine TRIM62 levels in leukemia-enriched protein samples from 511 patients newly diagnosed with AML.

RESULTS

TRIM62 levels in AML cells were significantly lower than in normal CD34-positive cells, suggesting that TRIM62 loss might be involved in leukemogenesis, but was not associated with specific karyotypic abnormalities or Nucleophosmin (NPM1), Fms-like Tyrosine Kinase-3 (FLT3), or rat sarcoma viral oncogene (RAS) mutational status. Low TRIM62 levels were associated with shorter complete remission duration and significantly shorter event-free and overall survival rates, particularly among patients with intermediate-risk cytogenetics. In that AML subgroup, age and TRIM62 levels were the most powerful independent prognostic factors for survival. TRIM62 protein levels further refined the risk associated with NPM1 and FLT3 mutational status. TRIM62 loss was associated with altered expression of proteins involved in leukemia stem cell homeostasis (β-catenin and Notch), cell motility, and adhesion (integrin-β3, ras-related C3 botulinum toxin substrate [RAC], and fibronectin), hypoxia (Hypoxia-inducible factor 1-alpha [HIF1α], egl-9 family hypoxia-inducible factor 1 [Egln1], and glucose-regulated protein, 78 kDa [GRP78]), and apoptosis (B-cell lymphoma-extra large (BclXL) and caspase 9).

CONCLUSION

Low TRIM62 levels, consistent with a tumor suppressor role, represent an independent adverse prognostic factor in AML.

Lipid raft-mediated Akt signaling as a therapeutic target in mantle cell lymphoma

Recent evidence shows that lipid raft membrane domains modulate both cell survival and death. Here, we have found that the phosphatidylinositol-3-kinase (PI3K)/Akt signaling pathway is present in the lipid rafts of mantle cell lymphoma (MCL) cells, and this location seems to be critical for full activation and MCL cell survival. The antitumor lipids (ATLs) edelfosine and perifosine target rafts, and we found that ATLs exerted in vitro and in vivo antitumor activity against MCL cells by displacing Akt as well as key regulatory kinases p-PDK1 (phosphatidylinositol-dependent protein kinase 1), PI3K and mTOR (mammalian TOR) from lipid rafts. This raft reorganization led to Akt dephosphorylation, while proapoptotic Fas/CD95 death receptor was recruited into rafts. Raft integrity was critical for Ser473 Akt phosphorylation. ATL-induced apoptosis appeared to correlate with the basal Akt phosphorylation status in MCL cell lines and primary cultures, and could be potentiated by the PI3K inhibitor wortmannin, or inhibited by the Akt activator pervanadate. Classical Akt inhibitors induced apoptosis in MCL cells. Microenvironmental stimuli, such as CD40 ligation or stromal cell contact, did not prevent ATL-induced apoptosis in MCL cell lines and patient-derived cells. These results highlight the role of raft-mediated PI3K/Akt signaling in MCL cell survival and chemotherapy, thus becoming a new target for MCL treatment.

Sea urchin akt activity is Runx-dependent and required for post-cleavage stage cell division

In animal development following the initial cleavage stage of embryogenesis, the cell cycle becomes dependent on intercellular signaling and controlled by the genomically encoded ontogenetic program. Runx transcription factors are critical regulators of metazoan developmental signaling, and we have shown that the sea urchin Runx gene runt-1, which is globally expressed during early embryogenesis, functions in support of blastula stage cell proliferation and expression of the mitogenic genes pkc1, cyclinD, and several wnts. To obtain a more comprehensive list of early runt-1 regulatory targets, we screened a Strongylocentrotus purpuratus microarray to identify genes mis-expressed in mid-blastula stage runt-1 morphants. This analysis showed that loss of Runx function perturbs the expression of multiple genes involved in cell division, including the pro-growth and survival kinase Akt (PKB), which is significantly underexpressed in runt-1 morphants. Further genomic analysis revealed that Akt is encoded by two genes in the S. purpuratus genome, akt-1 and akt-2, both of which contain numerous canonical Runx target sequences. The transcripts of both genes accumulate several fold during blastula stage, contingent on runt-1 expression. Inhibiting Akt expression or activity causes blastula stage cell cycle arrest, whereas overexpression of akt-1 mRNA rescues cell proliferation in runt-1 morphants. These results indicate that post-cleavage stage cell division requires Runx-dependent expression of akt.

Mediating effects of aryl-hydrocarbon receptor and RhoA in altering brain vascular integrity: the therapeutic potential of statins

We have demonstrated previously that focal adhesion kinase (FAK)/RhoA alteration by the aryl-hydrocarbon receptor (AhR) agonist 3-methylcholanthrene (3MC) is involved in the antimigratory effects of 3MC in human umbilical vascular endothelial cells. Here, we identified that signaling properties and molecular mechanisms of RhoA/β-catenin were both implicated in alterations to blood-brain barrier integrity. The mechanisms of action were the down-regulation of integrin, the extracellular matrix, and adherens junction stability. PTEN phosphorylation by 3MC-mediated AhR/RhoA activation increased the proteasomal degradation of β-catenin through PKCδ/pGSK3β-mediated β-catenin phosphorylation; the crucial roles of AhR/RhoA in this process were verified by using gain- or loss-of-function experiments. The decrease in β-catenin led to decreased expression of fibronectin and α5β1 integrin. Additionally, protein interactions among FAK, VE-cadherin, vinculin, and β-actin were simultaneously decreased, resulting in adherens junction instability. Novel functional TCF/LEF1 binding sites in the promoter regions of fibronectin and α5/β1 integrin were identified by electrophoretic mobility shift and chromatin immunoprecipitation assays. The results indicate that the binding activities of β-catenin decreased in mouse cerebrovascular endothelial cells treated with 3MC. In addition, simvastatin and pravastatin treatment reversed 3MC-mediated alterations in mouse cerebrovascular endothelial cells by RhoA inactivation, and the in vitro findings were substantiated by an in vivo blood-brain barrier assay. Thus, endothelial barrier dysfunction due to 3MC occurs through AhR/RhoA-mediated β-catenin down-regulation, which is reversed by simvastatin treatment in vivo.

Thr 163 phosphorylation causes Mcl-1 stabilization when degradation is independent of the adjacent GSK3-targeted phosphodegron, promoting drug resistance in cancer

The antiapoptotic Bcl-2 family member Mcl-1 is a PEST protein (containing sequences enriched in proline, glutamic acid, serine, and threonine) and is subject to rapid degradation via multiple pathways. Impaired degradation leading to the maintenance of Mcl-1 expression is an important determinant of drug resistance in cancer. Phosphorylation at Thr 163 in the PEST region, stimulated by 12-O-tetradecanoylphorbol acetic acid (TPA)-induced activation of extracellular signal-regulated kinase (ERK), is associated with Mcl-1 stabilization in BL41-3 Burkitt lymphoma cells. This contrasts with the observation that Thr 163 phosphorylation in normal fibroblasts primes glycogen synthase kinase (GSK3)-induced phosphorylation at Ser 159, producing a phosphodegron that targets Mcl-1 for degradation. In the present follow-up studies in BL41-3 cells, Mcl-1 degradation was found to be independent of the GSK3-mediated pathway, providing a parallel to emerging findings showing that Mcl-1 degradation through this pathway is lost in many different types of cancer. Findings in Mcl-1-transfected CHO cells corroborated those in BL41-3 cells in that the GSK3-targeted phosphodegron did not play a major role in Mcl-1 degradation, and a phosphomimetic T163E mutation resulted in marked Mcl-1 stabilization. TPA-treated BL41-3 cells, in addition to exhibiting Thr 163 phosphorylation and Mcl-1 stabilization, exhibited an ∼10-fold increase in resistance to multiple chemotherapeutic agents, including Ara-C, etoposide, vinblastine, or cisplatin. In these cancer cells in which Mcl-1 degradation is not dependent on the GSK3/phosphodegron-targeted pathway, ERK activation and Thr 163 phosphorylation are associated with pronounced Mcl-1 stabilization and drug resistance – effects that can be suppressed by inhibition of ERK activation.

Phosphoproteomic analysis of AT1 receptor-mediated signaling responses in proximal tubules of angiotensin II-induced hypertensive rats

The signaling mechanisms underlying the effects of angiotensin II in proximal tubules of the kidney are not completely understood. Here we measured signal protein phosphorylation in isolated proximal tubules using pathway-specific proteomic analysis in rats continuously infused with pressor or non-pressor doses of angiotensin II over a 2-week period. Of the 38 phosphoproteins profiled, 14 were significantly altered by the pressor dose. This included increased phosphorylation of the protein kinase C isoenzymes, PKCα and PKCβII, and the glycogen synthase kinases, GSK3α and GSK3β. Phosphorylation of the cAMP-response element binding protein 1 and PKCδ were decreased, whereas PKCɛ remained unchanged. By contrast, the phosphorylation of only seven proteins was altered by the non-pressor dose, which increased that of PKCα, PKCδ, and GSKα. Phosphorylation of MAP kinases, ERK1/2, was not increased in proximal tubules in vivo by the pressor dose, but was in proximal tubule cells in vitro. Infusion of the pressor dose decreased, whereas the non-pressor dose of angiotensin II increased the phosphorylation of the sodium and hydrogen exchanger 3 (NHE-3) in membrane fractions of proximal tubules. Losartan largely blocked the signaling responses induced by the pressor dose. Thus, PKCα and PKCβII, GSK3α and GSK3β, and cAMP-dependent signaling pathways may have important roles in regulating proximal tubular sodium and fluid transport in Ang II-induced hypertensive rats.

Celecoxib promotes c-FLIP degradation through Akt-independent inhibition of GSK3

Celecoxib is a COX-2 inhibitor that reduces the risk of colon cancer. However, the basis for its cancer chemopreventive activity is not fully understood. In this study, we defined a mechanism of celecoxib action based on degradation of cellular FLICE-inhibitory protein (c-FLIP), a major regulator of the death receptor pathway of apoptosis. c-FLIP protein levels are regulated by ubiquitination and proteasome-mediated degradation. We found that celecoxib controlled c-FLIP ubiquitination through Akt-independent inhibition of glycogen synthase kinase-3 (GSK3), itself a candidate therapeutic target of interest in colon cancer. Celecoxib increased the levels of phosphorylated GSK3, including the α and β forms, even in cell lines, where phosphorylated Akt levels were not increased. Phosphoinositide 3-kinase inhibitors abrogated Akt phosphorylation as expected but had no effect on celecoxib-induced GSK3 phosphorylation. In contrast, protein kinase C (PKC) inhibitors abolished celecoxib-induced GSK3 phosphorylation, implying that celecoxib influenced GSK3 phosphorylation through a mechanism that relied upon PKC and not Akt. GSK3 blockade either by siRNA or kinase inhibitors was sufficient to attenuate c-FLIP levels. Combining celecoxib with GSK3 inhibition enhanced attenuation of c-FLIP and increased apoptosis. Proteasome inhibitor MG132 reversed the effects of GSK3 inhibition and increased c-FLIP ubiquitination, confirming that c-FLIP attenuation was mediated by proteasomal turnover as expected. Our findings reveal a novel mechanism through which the regulatory effects of c-FLIP on death receptor signaling are controlled by GSK3, which celecoxib acts at an upstream level to control independently of Akt.

Prevention of cytokine withdrawal-induced apoptosis by Mcl-1 requires interaction between Mcl-1 and Bim

Growth factor withdrawal from hemopoietic cells results in activation of the mitochondrial pathway of apoptosis. Members of the Bcl-2 family regulate this pathway, with anti-apoptotic members counteracting the effects of pro-apoptotic members. We investigated the effect on Mcl-1 function of mutation at a conserved threonine 163 residue (T163) in its proline, glutamate, serine, and threonine rich (PEST) region. Under normal growth conditions, Mcl-1 half-life increased with alteration of T163 to glutamic acid, but decreased with mutation to alanine. However, both T163 mutants exhibited greater pro-survival effects compared with the wild type, which can be explained by an increased stability of the T163A mutant in cytokine-starved conditions. Both the mutant forms exhibited prolonged binding to pro-apoptotic Bim in cytokine-deprived cells. The extent to which Mcl-1 mutants were able to exert their anti-apoptotic effects correlated with their ability to associate with Bim. We further observed that primary bone marrow derived macrophages survived following cytokine withdrawal as long as Bim and Mcl-1 remained associated. In our study, we were unable to detect a role for GSK-3-mediated regulation of Mcl-1 expression. Based on these results we propose that upon cytokine withdrawal, survival of hemopoietic cells depends on association between Mcl-1 and Bim. Furthermore, alteration of T163 of Mcl-1 may change the protein such that its association with Bim is affected, resulting in prolonged association and increased survival.

An enigmatic tail of CD28 signaling

CD28 costimulation regulates a wide range of cellular processes, from proliferation and survival to promoting the differentiation of specialized T-cell subsets. Since first being identified over 20 years ago, CD28 has remained a subject of intense study because of its profound consequences on T cell function and its potential for therapeutic manipulation. In this review we highlight the signaling cascades initiated by the major signaling motifs in CD28, focusing on PI-3 kinase-dependent and -independent pathways and how these are linked to specific cellular outcomes. Recent studies using gene targeted knockin mice have clarified the relative importance of these motifs on in vivo immune responses; however, much remains to be elucidated. Understanding the mechanism behind costimulation holds great potential for development of new clinically relevant reagents, a fact beginning to be realized with the advent of drugs that prevent CD28 ligation and signaling.

Development of a platelet-activating factor antagonist for HIV-1 associated neurocognitive disorders

The neuroregulatory activities of PMS-601, a platelet activating factor antagonist, were investigated in laboratory and animal models of HIV-1 encephalitis (HIVE). For the former, PMS-601 reduced monocyte-derived macrophage pro-inflammatory secretions, multinucleated giant cell (MGC) formation, and neuronal loss independent of antiretroviral responses. PMS-601 treatment of HIVE severe combined immunodeficient mice showed reduced microgliosis, MGCs and neurodegeneration. These observations support the further development of PMS-601 as an adjunctive therapy for HIV-1 associated neurocognitive disorders.

Targeted knock-in mice expressing mutations of CD28 reveal an essential pathway for costimulation

Despite extensive study, the role of phosphatidylinositol 3-kinase (PI3-kinase) activation in CD28 function has been highly contentious. To definitively address this question, we generated knock-in mice expressing mutations in two critical domains of the cytoplasmic tail of CD28. Mutation of the proximal tyrosine motif interrupted PI3-kinase binding and prevented CD28-dependent phosphorylation of protein kinase B (PKB)/Akt; however, there was no detectable effect on interleukin-2 (IL-2) secretion, expression of Bcl-X(L), or on T-cell function in vivo. Furthermore, we demonstrate that signaling initiated by the C-terminal proline motif is directly responsible for tyrosine phosphorylation of phosphoinosotide-dependent kinase 1, protein kinase C theta, and glycogen synthase kinase 3beta, as well as contributing to threonine phosphorylation of PKB. T cells mutated in this domain were profoundly impaired in IL-2 secretion, and the mice had marked impairment of humoral responses as well as less severe disease manifestations in experimental allergic encephalomyelitis. These data demonstrate that the distal proline motif initiates a critical nonredundant signaling pathway, whereas direct activation of PI3-kinase by the proximal tyrosine motif of CD28 is not required for normal T-cell function.

The life of a cell: apoptosis regulation by the PI3K/PKB pathway

The activation of PI3K (phosphoinositide 3-kinase) family members is a universal event in response to virtually all cytokines, growth factors and hormones. As a result of formation of PtdIns with an added phosphate at the 3 position of the inositol ring, activation of the protein kinases PDK1 (phosphoinositide-dependent kinase 1) and PKB (protein kinase B)/Akt occurs. The PI3K/PKB pathway impinges upon a remarkable array of intracellular events that influence either directly or indirectly whether or not a cell will undergo apoptosis. In this review, the many ways in which PI3K/PKB can control these processes are summarized. Not all of the events described will necessarily play a role in any one cell type, but a subset of these events is probably essential for the survival of every cell.

Runx expression is mitogenic and mutually linked to Wnt activity in blastula-stage sea urchin embryos

Background

The Runt homology domain (Runx) defines a metazoan family of sequence-specific transcriptional regulatory proteins that are critical for animal development and causally associated with a variety of mammalian cancers. The sea urchin Runx gene SpRunt-1 is expressed throughout the blastula stage embryo, and is required globally during embryogenesis for cell survival and differentiation.

Methodology/Principal Findings

Depletion of SpRunt-1 by morpholino antisense-mediated knockdown causes a blastula stage deficit in cell proliferation, as shown by bromodeoxyuridine (BrdU) incorporation and direct cell counts. Reverse transcription coupled polymerase chain reaction (RT-PCR) studies show that the cell proliferation deficit is presaged by a deficit in the expression of several zygotic wnt genes, including wnt8, a key regulator of endomesoderm development. In addition, SpRunt-1-depleted blastulae underexpress cyclinD, an effector of mitogenic Wnt signaling. Blastula stage cell proliferation is also impeded by knockdown of either wnt8 or cyclinD. Chromatin immunoprecipitation (ChIP) indicates that Runx target sites within 5′ sequences flanking cyclinD, wnt6 and wnt8 are directly bound by SpRunt-1 protein at late blastula stage. Furthermore, experiments using a green fluorescent protein (GFP) reporter transgene show that the blastula-stage operation of a cis-regulatory module previously shown to be required for wnt8 expression (Minokawa et al., Dev. Biol. 288: 545–558, 2005) is dependent on its direct sequence-specific interaction with SpRunt-1. Finally, inhibitor studies and immunoblot analysis show that SpRunt-1 protein levels are negatively regulated by glycogen synthase kinase (GSK)-3.

Conclusions/Significance

These results suggest that Runx expression and Wnt signaling are mutually linked in a feedback circuit that controls cell proliferation during development.

Inhibition of c-jun N terminal kinase (JNK) improves functional beta cell mass in human islets and leads to AKT and glycogen synthase kinase-3 (GSK-3) phosphorylation

AIMS/HYPOTHESIS

Activation of c-jun N-terminal kinase (JNK) has been described in islet isolation and engraftment, making JNK a key target in islet transplantation. The objective of this study was to investigate if JNK inhibition with a cell-permeable TAT peptide inhibitor (L-JNKI) protects functional beta cell mass in human islets and affects AKT and its substrates in islet cells.

METHODS

The effect of L-JNKI (10 micromol/l) on islet count, mitochondrial membrane potential, glucose-stimulated insulin release and phosphorylation of both AKT and its substrates, as well as on reversal of diabetes in immunodeficient diabetic Nu/Nu mice was studied.

RESULTS

In vitro, L-JNKI reduced the islet loss in culture and protected from cell death caused by acute cytokine exposure. In vivo, treatment of freshly isolated human islets and diabetic Nu/Nu mice recipients of such islets resulted in improved functional beta cell mass. We showed that L-JNKI activates AKT and downregulates glycogen synthase kinase-3 beta (GSK-3B) in human islets exposed to cytokines, while other AKT substrates were unaffected, suggesting that a specific AKT/GSK-3B regulation by L-JNKI may represent one of its mechanisms of cytoprotection.

CONCLUSIONS/INTERPRETATION

In conclusion, we have demonstrated that targeting JNK in human pancreatic islets results in improved functional beta cell mass and in the regulation of AKT/GSK3B activity.

The protein kinase C (PKC) family of proteins in cytokine signaling in hematopoiesis

The members of the protein kinase C (PKC) family of proteins play important roles in signaling for various growth factors, cytokines, and hormones. Extensive work over the years has led to the identification of three major groups of PKC isoforms. These include the classic PKCs (PKCalpha, PKCbeta(I), PKCbeta(II), PKCgamma), the novel PKCs (PKCdelta, PKCepsilon, PKCeta, PKCmu, PKCtheta), and the atypical PKCs (PKCzeta, PKCiota/lambda). All these PKC subtypes have been shown to participate in the generation of signals for important cellular processes and to mediate diverse and, in some cases, opposing biologic responses. There is emerging evidence that these kinases also play key functional roles in the regulation of cell growth, apoptosis, and differentiation of hematopoietic cells. In this review, both the engagement of the various PKC members in cytokine and growth factor signaling and their role in the regulation of hematopoiesis are discussed.

1alpha,25-dihydroxycholecalciferol activates binding of CREB to a CRE site in the CD14 promoter and drives promoter activity in a phosphatidylinositol-3 kinase-dependent manner

1,25-dihydroxycholecalciferol, also known as 1alpha,25-dihydroxyvitamin D3 or calcitriol, regulates the differentiation and functional properties of mononuclear phagocytes. Many of these effects involve nongenomic signaling pathways, which are not fully understood. Activation of CD14 expression, a monocyte differentiation marker and coreceptor with TLR-2 for bacterial LPS, by calcitriol was shown previously to be PI-3K-dependent [1]; however, the mechanism of gene activation remained undefined. Using a transcription factor-binding array screen coupled with EMSA, we found evidence for PI-3K-dependent activation of CREB in THP-1 cells incubated with calcitriol. Furthermore, analysis of the proximal promoter of human CD14 identified regions that contained up to seven sequences, which showed significant similarity to a canonical CRE sequence, 5'-TGACGTCA-3'. Treatment of THP-1 cells with calcitriol activated CREB binding to one of these regions at Positions -37 to -55, relative to the transcription start site in a PI-3K-dependent manner. This 19-mer region also became transcriptionally active in a reporter assay in response to calcitriol, again dependent on PI-3K. Mutation of the CRE within the 19-mer abolished this activity. Taken together, these results show that calcitriol signaling, leading to activation of the CD14 promoter, involves CREB activation downstream of PI-3K.

Neurotensin phosphorylates GSK-3alpha/beta through the activation of PKC in human colon cancer cells

Neurotensin (NT), a gastrointestinal hormone, binds its receptor [neurotensin receptor (NTR)] to regulate the growth of normal and neoplastic intestinal cells; molecular mechanisms remain largely undefined. Glycogen synthase kinase-3 (GSK-3) regulates diverse cellular processes, including cell growth and apoptosis. Here, we show that NT induces the phosphorylation of GSK-3alpha/beta in the human colon cancer cell line HT29, HCT116, or SW480, which possesses high-affinity NTR. The effect of NT was blocked by inhibitors of protein kinase C (PKC), but not by inhibitors of MEK1 or phosphatidylinositol-3 kinase, suggesting a predominant role for PKC in GSK-3beta phosphorylation by NT. Pretreatment with Gö6976 (which inhibits PKCalpha and PKCbeta1) or downregulation of endogenous PKCalpha or PKCbeta1 blocked NT-mediated GSK-3beta (but not GSK-3alpha) phosphorylation. Moreover, a selective PKCbeta inhibitor, LY379196, reduced NT-mediated GSK-3beta (but not GSK-3alpha) phosphorylation, suggesting a role for PKCbeta1 in the NT-mediated phosphorylation of GSK-3beta and an undefined kinase in the NT-mediated phosphorylation of GSK-3alpha. Treatment with NT or the GSK-3 inhibitor SB216763 increased the expression of cyclin D1, a downstream effector protein of GSK-3 and a critical protein for the proliferation of various cells. Our results indicate that NT uses PKC-dependent pathways to modulate GSK-3, which may play a role in the NT regulation of intestinal cell growth.