Translocation of protein kinase C-betaII in astrocytes requires organized actin cytoskeleton and is not accompanied by synchronous RACK1 relocation

PKCβII activation requires nuclear trafficking for phosphorylation and Mdm2-mediated ubiquitination

PKCβII, a conventional PKC family member, plays critical roles in the regulation of a variety of cellular functions. Here, we employed loss-of-function approaches and mutants of PKCβII with altered phosphorylation and protein interaction behaviors to identify the cellular mechanisms underlying the activation of PKCβII. Our results show that 3-phosphoinositide-dependent protein kinase-1 (PDK1)-mediated constitutive phosphorylation of PKCβII at the activation loop (T500) is required for phorbol ester-induced nuclear entry and subsequent Mdm2-mediated ubiquitination of PKCβII, whereas ubiquitination of PKCβII is required for the PDK1-mediated inducible phosphorylation of PKCβII at T500 in the nucleus. After moving out of the nucleus, PKCβII interacts with actin, undergoes inducible mTORC2-mediated phosphorylation at the turn motif (T641), interacts with clathrin, and then translocates to the plasma membrane. This overall cascade of cellular events intertwined with the phosphorylation at critical residues and Mdm2-mediated ubiquitination in the nucleus and along with interactions with actin and clathrin plays roles that encompass the core processes of PKC activation.

Redox Modulations, Antioxidants, and Neuropsychiatric Disorders

Although antioxidants, redox modulations, and neuropsychiatric disorders have been widely studied for many years, the field would benefit from an integrative and corroborative review. Our primary objective is to delineate the biological significance of compounds that modulate our redox status (i.e., reactive species and antioxidants) as well as outline their current role in brain health and the impact of redox modulations on the severity of illnesses. Therefore, this review will not enter into the debate regarding the perceived medical legitimacy of antioxidants but rather seek to clarify their abilities and limitations. With this in mind, antioxidants may be interpreted as natural products with significant pharmacological actions in the body. A renewed understanding of these often overlooked compounds will allow us to critically appraise the current literature and provide an informed, novel perspective on an important healthcare issue. In this review, we will introduce the complex topics of redox modulations and their role in the development of select neuropsychiatric disorders.

PKCβII acts downstream of chemoattractant receptors and mTORC2 to regulate cAMP production and myosin II activity in neutrophils

mTORC2 has been shown to be involved in cytoskeletal regulation, but the mechanisms by which this takes place are poorly understood. This study shows that PKCβII is specifically required for mTORC2-dependent activation of adenylyl cyclase 9 and back retraction during neutrophil chemotaxis to chemoattractants.

Chemotaxis is a process by which cells polarize and move up a chemical gradient through the spatiotemporal regulation of actin assembly and actomyosin contractility, which ultimately control front protrusions and back retractions. We previously demonstrated that in neutrophils, mammalian target of rapamycin complex 2 (mTORC2) is required for chemoattractant-mediated activation of adenylyl cyclase 9 (AC9), which converts ATP into cAMP and regulates back contraction through MyoII phosphorylation. Here we study the mechanism by which mTORC2 regulates neutrophil chemotaxis and AC9 activity. We show that inhibition of protein kinase CβII (PKCβII) by CPG53353 or short hairpin RNA knockdown severely inhibits chemoattractant-induced cAMP synthesis and chemotaxis in neutrophils. Remarkably, PKCβII-inhibited cells exhibit specific and severe tail retraction defects. In response to chemoattractant stimulation, phosphorylated PKCβII, but not PKCα, is transiently translocated to the plasma membrane, where it phosphorylates and activates AC9. mTORC2-mediated PKCβII phosphorylation on its turn motif, but not its hydrophobic motif, is required for membrane translocation of PKCβII. Inhibition of mTORC2 activity by Rictor knockdown not only dramatically decreases PKCβII activity, but it also strongly inhibits membrane translocation of PKCβII. Together our findings show that PKCβII is specifically required for mTORC2-dependent AC9 activation and back retraction during neutrophil chemotaxis.

Diabetes-induced increased oxidative stress in cardiomyocytes is sustained by a positive feedback loop involving Rho kinase and PKCβ2

We previously reported that acute inhibition of the RhoA/Rho kinase (ROCK) pathway normalized contractile function of diabetic rat hearts, but the underlying mechanism is unclear. Protein kinase C (PKC) β(2) has been proposed to play a major role in diabetic cardiomyopathy at least in part by increasing oxidative stress. Further evidence suggests that PKC positively regulates RhoA expression through induction of inducible nitric oxide synthase (iNOS) in diabetes. However, in preliminary studies, we found that inhibition of ROCK itself reduced RhoA expression in diabetic hearts. We hypothesized that there is an interaction between RhoA/ROCK and PKCβ(2) in the form of a positive feedback loop that sustains their activation and the production of reactive oxygen species (ROS). This was investigated in cardiomyocytes isolated from diabetic and control rat hearts, incubated with or without cytochalasin D or inhibitors of ROCK, RhoA, PKCβ(2), or iNOS. Inhibition of RhoA and ROCK markedly attenuated the diabetes-induced increases in PKCβ(2) activity and iNOS and RhoA expression in diabetic cardiomyocytes, while having no effect in control cells. Inhibition of PKCβ(2) and iNOS also normalized RhoA expression and ROCK overactivation, whereas iNOS inhibition reversed the increase in PKCβ(2) activity. Each of these treatments also normalized the diabetes-induced increase in production of ROS. Actin cytoskeleton disruption attenuated the increased expression and/or activity of all of these targets in diabetic cardiomyocytes. These data suggest that, in the diabetic heart, the RhoA/ROCK pathway contributes to contractile dysfunction at least in part by sustaining PKCβ(2) activation and ROS production via a positive feedback loop that requires an intact cytoskeleton.

Identification of novel small molecule activators of nuclear factor-κB with neuroprotective action via high-throughput screening

Neuronal noncytokine-dependent p50/p65 nuclear factor-κB (the primary NF-κB complex in the brain) activation has been shown to exert neuroprotective actions. Thus neuronal activation of NF-κB could represent a viable neuroprotective target. We have developed a cell-based assay able to detect NF-κB expression enhancement, and through its use we have identified small molecules able to up-regulate NF-κB expression and hence trigger its activation in neurons. We have successfully screened approximately 300,000 compounds and identified 1,647 active compounds. Cluster analysis of the structures within the hit population yielded 14 enriched chemical scaffolds. One high-potency and chemically attractive representative of each of these 14 scaffolds and four singleton structures were selected for follow-up. The experiments described here highlighted that seven compounds caused noncanonical long-lasting NF-κB activation in primary astrocytes. Molecular NF-κB docking experiments indicate that compounds could be modulating NF-κB-induced NF-κB expression via enhancement of NF-κB binding to its own promoter. Prototype compounds increased p65 expression in neurons and caused its nuclear translocation without affecting the inhibitor of NF-κB (I-κB). One of the prototypical compounds caused a large reduction of glutamate-induced neuronal death. In conclusion, we have provided evidence that we can use small molecules to activate p65 NF-κB expression in neurons in a cytokine receptor-independent manner, which results in both long-lasting p65 NF-κB translocation/activation and decreased glutamate neurotoxicity.

Changes in gene expression and cellular architecture in an ovarian cancer progression model

BACKGROUND

Ovarian cancer is the fifth leading cause of cancer deaths among women. Early stage disease often remains undetected due the lack of symptoms and reliable biomarkers. The identification of early genetic changes could provide insights into novel signaling pathways that may be exploited for early detection and treatment.

METHODOLOGY/PRINCIPAL FINDINGS

Mouse ovarian surface epithelial (MOSE) cells were used to identify stage-dependent changes in gene expression levels and signal transduction pathways by mouse whole genome microarray analyses and gene ontology. These cells have undergone spontaneous transformation in cell culture and transitioned from non-tumorigenic to intermediate and aggressive, malignant phenotypes. Significantly changed genes were overrepresented in a number of pathways, most notably the cytoskeleton functional category. Concurrent with gene expression changes, the cytoskeletal architecture became progressively disorganized, resulting in aberrant expression or subcellular distribution of key cytoskeletal regulatory proteins (focal adhesion kinase, α-actinin, and vinculin). The cytoskeletal disorganization was accompanied by altered patterns of serine and tyrosine phosphorylation as well as changed expression and subcellular localization of integral signaling intermediates APC and PKCβII.

CONCLUSIONS/SIGNIFICANCE

Our studies have identified genes that are aberrantly expressed during MOSE cell neoplastic progression. We show that early stage dysregulation of actin microfilaments is followed by progressive disorganization of microtubules and intermediate filaments at later stages. These stage-specific, step-wise changes provide further insights into the time and spatial sequence of events that lead to the fully transformed state since these changes are also observed in aggressive human ovarian cancer cell lines independent of their histological type. Moreover, our studies support a link between aberrant cytoskeleton organization and regulation of important downstream signaling events that may be involved in cancer progression. Thus, our MOSE-derived cell model represents a unique model for in depth mechanistic studies of ovarian cancer progression.

Tagging of functional ribosomes in living cells by HaloTag® technology

Ribosomal proteins and ribosomal associated proteins are complicated subjects to target and study because of their high conservation through evolution which led to highly structured and regulated proteins. Tagging of ribosomal proteins may allow following of protein synthesis in vivo and isolating translated mRNAs. HaloTag® is a new technology which allows detection in living cells, biochemical purification, and localization studies. In the present work, we tested HaloTag®-based ribosomal tagging. We focused on eIF6 (eukaryotic Initiation Factor 6 free 60S ribosomal marker), RACK1 (Receptor for Activated C Kinase 1; 40S and polysomes, not nuclear), and rpS9 (40S ribosomes, both in the nucleus and in the cytoplasm). Experiments performed on HEK293 cells included ribosomal profiles and Western blot on the fractions, purification of HaloTag® proteins, and fluorescence with time-lapse microscopy. We show that tagged proteins can be incorporated on ribosomes and followed by time-lapse microscopy. eIF6 properly accumulates in the nucleolus, and it is redistributed upon actinomycin D treatment. RACK1 shows a specific cytoplasmic localization, whereas rpS9 is both nucleolar and cytoplasmic. However, efficiency of purification varies due to steric hindrances. In addition, the level of overexpression and degradation may vary upon different constructs. In summary, HaloTag® technology is highly suitable to ribosome tagging, but requires prior characterization for each construct.

Effect of interleukin-1β on the expression of actin isoforms in cultured mouse astroglia

Cytokines are soluble mediators that are thought to act as communication signals between astroglia and neighboring neural cells. They are both released by, and act on, astroglia. It is hypothesized that it is this effect on astroglia that may be important in widespread phenomena including traumatic brain injury, inflammation, and scar formation. In this article, we examine the effect of mouse recombinant interleukin-1β (IL-1β) on the morphology, organization, and expression of glial fibrillary acidic protein (GFAP) and actin isoforms in cultured mouse astroglia. This study shows that the majority of the astroglia treated with IL-1β acquire long processes. Immunofluorescence staining shows that there are no remarkable changes in the organization of GFAP, F-actin, α-smooth muscle (α-sm) actin, and β-actin isoforms. In fluorescent microplate assay, the short-term treated astroglia (range, 1-2 days) show an increase in the intensity of GFAP and β-actin isoform over the level observed in untreated control, whereas no remarkable changes are observed in the intensity of α-sm actin isoform. In the case of long-term treatment (range, 4-8 days), the intensity of GFAP and α-sm actin isoform progressively decreases below the level of untreated control. In addition, the intensity of β-actin isoform increases above the control level. These results have been confirmed by immunoblotting experiments. The upregulation of β-actin isoform may be important in limiting the noxious effects of an inflammatory reaction. This gives credence to the hypothesis that it might be possible to modulate astroglial effects on neuronal inflammation and scar formation with appropriate therapies.

Astrocytes refill intracellular Ca2+ stores in the absence of cytoplasmic [Ca2+] elevation: a functional rather than a structural ability

Capacitative Ca(2+) entry (CCE) is a phenomenon triggered by depletion of Ca(2+) content in intracellular stores (ICS). Data about this phenomenon in astrocytes are limited. We analyzed CCE in astrocytes by means of fura-2 based digital imaging. We found that in astrocytes CCE is not associated with an increase of cytosolic Ca(2+) concentration ([Ca(2+)](i)), although ICS are efficiently refilled. We used Mn(2+), thapsigargin and prolonged ATP exposure to show that CCE is not associated with cytosolic diffusion of Ca(2+) entering astrocytes. Our data suggest that the ion is being quickly sequestered in the ICS by the smooth endoplasmic reticulum Ca(2+)-ATP-ase (SERCA). Several experiments were carried out with the goal of failing the efficient uptake in the endoplasmic reticulum (ER). In fact, inhibition of SERCA activity, increased extracellular [Ca(2+)](i) or pharmacologic potentiation of CCE all caused [Ca(2+)](i) elevation during CCE, suggesting that the control of this phenomenon could have physiologic and pathological relevance. The molecular components involved in CCE have been proposed to be organized in a multi-molecular complex tethered by cytoskeleton components and arranged via a secretion coupling model. We show here that the efficient routing of Ca(2+) into the ICS in astrocytes is not affected by disruption of cytoskeleton organization or Golgi's function, but it is instead linked to the high efficiency of SERCA. We conclude that depleted ICS in astrocytes are efficiently refilled by CCE activation, although Ca(2+) influx is not accompanied by elevation of [Ca(2+)](i). This ability seems to be functional rather than structural in nature.

The different facets of protein kinases C: old and new players in neuronal signal transduction pathways

Signal transduction pathways are crucial for cell-to-cell communication. Various molecular cascades allow the translation of distinct stimuli, targeting the cell, into a language that the cell itself is able to understand, thus elaborating specific responses. Within this context, a strategic role is played by protein kinases which catalyze the phosphorylation of specific substrates. The serine/threonine protein kinase C (PKC) enzymes family (at least 10 isoforms) is implicated in the transduction of signals coupled to receptor-mediated hydrolysis of membrane phospholipids. Within this molecular pathway, protein-protein interactions play a critical role in directing the distinct activated PKCs towards selective subcellular compartments, in order to guarantee spatio-temporal and localized cellular responses. A space-specific modulation of biochemical events is particularly important during learning. Among the various mechanisms, the modulation of mRNA decay appears to be an efficient post-transcriptional way of controlling gene expression during learning, allowing changes to take place in selected neuronal regions, in particular at synaptic level. To this regard, recent studies have pointed out that PKC activation is also involved in a novel signalling cascade leading to the stabilization of specific mRNAs. This review will especially focus the attention on the implication of PKC in memory trace formation and how alterations within this molecular cascade may have consequences on physiological and pathological neuronal aging (i.e. Alzheimer's disease).

Agents that act by different mechanisms modulate the activity of protein kinase CβII isozyme in the rat spinal cord during peripheral inflammation

Hyperalgesia following unilateral complete Freund's adjuvant-induced inflammation was characterized by paw withdrawal latency to thermal stimulus. Paw withdrawal latencies were significantly shorter on the complete Freund's adjuvant-treated paw than on the contralateral paw of the complete Freund's adjuvant- and the sham-treated rats. Total cytosolic protein kinase C activity in the lumbar enlargement was unchanged on the sides of the spinal cord ipsi- and contra-lateral to the inflamed paw. Membrane-associated activities of protein kinase Calpha, protein kinase CbetaI and protein kinase Cgamma did not change significantly on the sides of the cord ipsi- and contra-lateral to the inflammation. However, membrane-associated activity of protein kinase CbetaII was increased in the cord section ipsilateral to the inflammation, suggesting that increased translocation/activation of protein kinase CbetaII is related to thermal hyperalgesia. Dextrorphan (an N-methyl-D-aspartate receptor antagonist), L-703,606 (an NK-1 receptor antagonist) and an antisense oligodeoxynucleotide for a selective knockdown of protein kinase Cbeta, reduced complete Freund's adjuvant-induced hyperalgesia, and reversed significant changes in the membrane activity of protein kinase CbetaII on the spinal cord section ipsilateral to the inflamed paw. Dextrorphan and protein kinase Cbeta antisense oligodeoxynucleotide were effective in reversing complete Freund's adjuvant-induced increase in the activity of protein kinase CbetaII ipsilateral to the inflammation at all the doses tested, but L-703,606 was effective only at the highest dose. Furthermore, in the presence of inflammatory stimulus, dextrorphan and L-703,606 did not alter the activities of membrane-associated protein kinase Calpha, protein kinase CbetaI, and protein kinase Cgamma in the section of the spinal cord ipsi- and contra-lateral to the inflammation. Protein kinase Cbeta antisense oligodeoxynucleotide had no significant effect on the membrane-associated activities of protein kinase Calpha and protein kinase Cgamma, but decreased the activities of both protein kinase CbetaI and protein kinase CbetaII and the expression of protein kinase Cbeta isozyme in the spinal cord. The data provide evidence that a common molecular event that converges to initiate and maintain hyperalgesia may include the translocation and activation of protein kinase CbetaII in the spinal dorsal horn.