Evidence that PKCα inhibition in Dalton's Lymphoma cells augments cell cycle arrest and mitochondrial-dependent apoptosis.

Protein kinase Cα (PKCα), belonging to ser/thr protein kinase, perform various biological functions. Overexpression of PKCα has been observed in multiple human malignancies including lymphoma. However, the molecular pathogenesis and involvement of PKCα in Non-Hodgkin lymphoma (NHL) are not clearly understood. Hence, deciphering the role of PKCα in NHL management may provide a better therapeutic option. In the present study, we used selective pharmacological inhibitors Gö6976 and Ro320432 that potentially inhibit PKCα-mediated signaling in DL cells, resulting in the inhibition of cell growth and mitochondrial-dependent apoptosis. PKCα inhibition by these inhibitors also displays cell cycle arrest at the G1 phase and causes growth retardation of DL cells. Our results extended the mechanism of PKCα in NHL, and provided potential implications for its therapy.

MiR-706 alleviates white matter injury via downregulating PKCα/MST1/NF-κB pathway after subarachnoid hemorrhage in mice.

Increasing numbers of patients with spontaneous subarachnoid hemorrhage(SAH) who recover from surgery and intensive care management still live with cognitive impairment after discharge, indicating the importance of white matter injury at the acute stage of SAH. In the present study, standard endovascular perforation was employed to establish an SAH mouse model, and a microRNA (miRNA) chip was used to analyze the changes in gene expression in white matter tissue after SAH. The data indicate that 17 miRNAs were downregulated, including miR-706, miR-669a-5p, miR-669p-5p, miR-7116-5p and miR-195a-3p, while 13 miRNAs were upregulated, including miR-6907-5p, miR-5135, miR-6982-5p, miR-668-5p, miR-8119. Strikingly, miR-706 was significantly downregulated with the highest fold change. Further experiments confirmed that miR-706 could alleviate white matter injury and improve neurological behavior, at least partially by inhibiting the PKCα/MST1/NF-κB pathway and the release of inflammatory cytokines. These results might provide a deeper understanding of the pathophysiological processes in white matter after SAH, as well as potential therapeutic strategies for the translational research.

All-trans retinoic acid and protein kinase C α/ß1 inhibitor combined treatment targets cancer stem cells and impairs breast tumor progression.

Breast cancer is the leading cause of cancer death among women worldwide. Blocking a single signaling pathway is often an ineffective therapy, especially in the case of aggressive or drug-resistant tumors. Since we have previously described the mechanism involved in the crosstalk between Retinoic Acid system and protein kinase C (PKC) pathway, the rationale of our study was to evaluate the effect of combining all-trans-retinoic acid (ATRA) with a classical PCK inhibitor (Gö6976) in preclinical settings. Employing hormone-independent mammary cancer models, Gö6976 and ATRA combined treatment induced a synergistic reduction in proliferative potential that correlated with an increased apoptosis and RARs modulation towards an anti-oncogenic profile. Combined treatment also impairs growth, self-renewal and clonogenicity potential of cancer stem cells and reduced tumor growth, metastatic spread and cancer stem cells frequency in vivo. An in-silico analysis of "Kaplan-Meier plotter" database indicated that low PKCα together with high RARα mRNA expression is a favorable prognosis factor for hormone-independent breast cancer patients. Here we demonstrate that a classical PKC inhibitor potentiates ATRA antitumor effects also targeting cancer stem cells growth, self-renewal and frequency.

Curcumin suppresses the malignancy of non-small cell lung cancer by modulating the circ-PRKCA/miR-384/ITGB1 pathway.

BACKGROUND: Curcumin exerts a suppressive effect in tumor growth by acting as a modulator of multiple molecular targets. Circular RNA hsa_circ_0007580 (circ-PRKCA) accelerates the tumorigenesis of non-small cell lung cancer (NSCLC). However, whether curcumin can regulate circ-PRKCA to inhibit NSCLC progression is unclear. METHODS: Cell viability, colony formation, apoptosis, migration, and invasion were analyzed using Cell Counting Kit-8 (CCK-8), plate clone, flow cytometry, or transwell assay. Expression of circ-PRKCA, microRNA (miR)-384, and ITGB1 mRNA (integrin subunit beta 1) mRNA were detected by quantitative real-time polymerase chain reaction (qRT-PCR). Curcumin repressed NSCLC growth through regulating circ-PRKCA expression was validated by xenograft assay. The targeting relationship between circ-PRKCA or ITGB1 and miR-384 was verified by dual-luciferase reporter assay. The level of ITGB1 protein was measured by western blotting. RESULTS: Circ-PRKCA and ITGB1 expression were elevated in NSCLC tissues and cells, but miR-384 had an opposing tendency. After curcumin treatment, the expression tendency of circ-PRKCA, miR-384, and ITGB1 in NSCLC cells was overturned. Furthermore, curcumin impeded viability, colony formation, migration, invasion, and accelerated apoptosis of NSCLC cells, but these impacts were partially reversed by circ-PRKCA elevation, miR-384 downregulation, or ITGB1 overexpression. Also, the inhibitory effect of curcumin on xenograft tumor was further enhanced after circ-PRKCA knockdown. Notably, circ-PRKCA regulated ITGB1 expression through sponging miR-384 in curcumin-treated NSCLC cells. CONCLUSIONS: Curcumin inhibited NSCLC growth through downregulating circ-PRKCA, which regulated ITGB1 expression by adsorbing miR-384. This study provided a new mechanism to understand how curcumin inhibited the progression of NSCLC.

Lophira alata Suppresses Phorbol Ester-Mediated Increase in Cell Growth via Inhibition of Protein Kinase C-α/Akt in Glioblastoma Cells.

BACKGROUND: Medicinal plants serve as sources of compounds used to treat other types of cancers. The root of the plant Lophira alata (Ochnaceae) has been used as a component of traditional herbal decoctions administered to cancer patients in southwestern Nigeria. However, the mechanism of the cytotoxic effects of Lophira alata alone or in the presence of phorbol ester has not been investigated in brain tumor cells. OBJECTIVE: This study aimed to examine the cytotoxic potential of the methanolic fraction of Lophira alata root on malignant glioma invasive cellular growth and survival. METHODS: The methanolic fraction of Lophira alata (LAM) was subjected to high-performance liquid chromatography to determine the fingerprints of the active molecules. The antiproliferative effects of Lophira alata were assessed using the MTT and LDH assays. Protein immunoblots were carried out to test the effects of Lophira alata, alone or in the presence of phorbol ester, on survival signaling pathways, such as Akt, mTOR, and apoptotic markers such as PARP and caspases. RESULTS: The methanolic fraction of Lophira alata (LAM) induced a concentration-dependent and time-dependent decrease in glioma cell proliferation. In addition, LAM attenuated phorbol ester-mediated signaling of downstream targets such as Akt/mTOR. Gene silencing using siRNA targeting PKC-alpha attenuated LAM-mediated downregulation of Akt. In addition, LAM induced both PARP and caspase cleavages. The HPLC fingerprint of the fraction indicates the presence of flavonoids. CONCLUSION: LAM decreases cell proliferation and induces apoptosis in glioma cell lines and thus could serve as a therapeutic molecule in the management of gliomas.

Coronavirus disease 2019 (COVID-19), human erythrocytes and the PKC-alpha/-beta inhibitor chelerythrine -possible therapeutic implication.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) causes COVID-19. Until now, diverse drugs have been used for the treatment of COVID-19. These drugs are associated with severe side effects, e.g. induction of erythrocyte death, named eryptosis. This massively affects the oxygen (O2) supply of the organism. Therefore, three elementary aspects should be considered simultaneously: (1) a potential drug should directly attack the virus, (2) eliminate virus-infected host cells and (3) preserve erythrocyte survival and functionality. It is known that PKC-α inhibition enhances the vitality of human erythrocytes, while it dose-dependently activates the apoptosis machinery in nucleated cells. Thus, the use of chelerythrine as a specific PKC-alpha and -beta (PKC-α/-ß) inhibitor should be a promising approach to treat people infected with SARS-CoV-2.

Inhibition of porcine reproductive and respiratory syndrome virus by PKC inhibitor dequalinium chloride in vitro.

As a severe disease characterized by reproductive failure and respiratory distress, porcine reproductive and respiratory syndrome (PRRS) is one of the most leading threats to the swine industry worldwide. Highly evolving porcine reproductive and respiratory syndrome virus (PRRSV) strains with distinct genetic diversity make the current vaccination strategy much less cost-effective and thus urge alternative protective host directed therapeutic approaches. RACK1-PKC-NF-κB signalling axis was suggested as a potential therapeutic target for PRRS control, therefore we tested the inhibitory effect of PKC inhibitor dequalinium chloride (DECA) on the PRRSV infection in vitro. RT-qPCR, western blot, Co-IP and cytopathic effect (CPE) observations revealed that DECA suppressed PRRSV infection and protected Marc-145 cells and porcine alveolar macrophages (PAMs) from severe cytopathic effects, by repressing the PKCα expression, the interaction between RACK1 and PKCα, and subsequently the NF-κB activation. In conclusion, the data presented in this study shed more light on deeper understanding of the molecular pathogenesis upon PRRSV infection and more importantly suggested DECA as a potential promising drug candidate for PRRS control.

The specific PKC-α inhibitor chelerythrine blunts costunolide-induced eryptosis.

Costunolide, a natural sesquiterpene lactone, has multiple pharmacological activities such as neuroprotection or induction of apoptosis and eryptosis. However, the effects of costunolide on pro-survival factors and enzymes in human erythrocytes, e.g. glutathione and glucose-6-phosphate dehydrogenase (G6PDH) respectively, have not been studied yet. Our aim was to determine the mechanisms underlying costunolide-induced eryptosis and to reverse this process. Phosphatidylserine exposure was estimated from annexin-V-binding, cell volume from forward scatter in flow cytometry, and intracellular glutathione [GSH]i from high performance liquid chromatography. The oxidized status of intracellular glutathione and enzyme activities were measured by spectrophotometry. Treatment of erythrocytes with costunolide dose-dependently enhanced the percentage of annexin-V-binding cells, decreased the cell volume, depleted [GSH]i and completely inhibited G6PDH activity. The effects of costunolide on annexin-V-binding and cell volume were significantly reversed by pre-treatment of erythrocytes with the specific PKC-α inhibitor chelerythrine. The latter, however, had no effect on costunolide-induced GSH depletion. Costunolide induces eryptosis, depletes [GSH]i and inactivates G6PDH activity. Furthermore, our study reveals an inhibitory effect of chelerythrine on costunolide-induced eryptosis, indicating a relationship between costunolide and PKC-α. In addition, chelerythrine acts independently of the GSH depletion. Understanding the mechanisms of G6PDH inhibition accompanied by GSH depletion should be useful for development of anti-malarial therapeutic strategies or for synthetic lethality-based approaches to escalate oxidative stress in cancer cells for their sensitization to chemotherapy and radiotherapy.

Protein exchange is reduced in calcium-independent epithelial junctions.

Desmosomes are cell-cell junctions that provide mechanical integrity to epithelial and cardiac tissues. Desmosomes have two distinct adhesive states, calcium-dependent and hyperadhesive, which balance tissue plasticity and strength. A highly ordered array of cadherins in the adhesive interface is hypothesized to drive hyperadhesion, but how desmosome structure confers adhesive state is still elusive. We employed fluorescence polarization microscopy to show that cadherin order is not required for hyperadhesion induced by pharmacologic and genetic approaches. FRAP experiments in cells treated with the PKCα inhibitor Gö6976 revealed that cadherins, plakoglobin, and desmoplakin have significantly reduced exchange in and out of hyperadhesive desmosomes. To test whether this was a result of enhanced keratin association, we used the desmoplakin mutant S2849G, which conferred reduced protein exchange. We propose that inside-out regulation of protein exchange modulates adhesive function, whereby proteins are "locked in" to hyperadhesive desmosomes while protein exchange confers plasticity on calcium-dependent desmosomes, thereby providing rapid control of adhesion.

Identification, characterization, and comparison of n-alkanols and anesthetics binding to the C1b subdomain of protein kinase cα: similar function with different binding sites.

Protein kinase C (PKC) is a family of lipid-activated enzymes involved in anesthetic preconditioning signaling pathways. Previously, n-alkanols and general anesthetics have been found to activate PKC by binding to the kinase C1B subdomain. In the present study, we attempt to ascertain the molecular mechanism and interaction mode of human PKCα C1B subdomain with a variety of exogenous n-alkanols and volatile general anesthetics as well as endogenous activator phorbol ester (PE) and co-activator diacylglycerol (DG). Systematic bioinformatics analysis identifies three spatially vicinal sites on the subdomain surface to potentially accommodate small-molecule ligands, where the site 1 is a narrow, amphipathic pocket, the site 2 is a wide, flat and hydrophobic pocket, and the site 3 is a rugged, polar pocket. Further interaction modeling reveals that site 1 is the cognate binding region of natural PE activator, which can moderately simulate the kinase activity in an independent manner. The short-chain n-alkanols are speculated to also bind at the site to competitively inhibit PE-induced kinase activation. The long-chain n-alkanols and co-activator DG are found to target site 2 in a nonspecific manner, while the volatile anesthetics prefer to interact with site 3 in a specific manner. Since the site 1 is composed of two protein loops that are also shared by sites 2 and 3, binding of n-alkanols, DG and anesthetics to sites 2 and 3 can trigger a conformational displacement on the two loops, which enlarges the pocket size and changes the pocket configuration of site 1 through an allosteric mechanism, consequently enhancing kinase activation by improving PE affinity to the site.

Cooperative Blockade of PKCα and JAK2 Drives Apoptosis in Glioblastoma.

The mTOR signaling is dysregulated prominently in human cancers including glioblastoma, suggesting mTOR as a robust target for therapy. Inhibitors of mTOR have had limited success clinically, however, in part because their mechanism of action is cytostatic rather than cytotoxic. Here, we tested three distinct mTOR kinase inhibitors (TORKi) PP242, KU-0063794, and sapanisertib against glioblastoma cells. All agents similarly decreased proliferation of glioblastoma cells, whereas PP242 uniquely induced apoptosis. Apoptosis induced by PP242 resulted from off-target cooperative inhibition of JAK2 and protein kinase C alpha (PKCα). Induction of apoptosis was also decreased by additional on-target inhibition of mTOR, due to induction of autophagy. As EGFR inhibitors can block PKCα, EGFR inhibitors erlotinib and osimertinib were tested separately in combination with the JAK2 inhibitor AZD1480. Combination therapy induced apoptosis of glioblastoma tumors in both flank and in patient-derived orthotopic xenograft models, providing a preclinical rationale to test analogous combinations in patients. SIGNIFICANCE: These findings identify PKCα and JAK2 as targets that drive apoptosis in glioblastoma, potentially representing a clinically translatable approach for glioblastoma.

Involvement of miR-200b-PKCα signalling in pulmonary hypertension in cor pulmonale model.

The right ventricle (RV) enlargement and pulmonary fibrosis are involved in cor pulmonale. The role of miR-200b in cor pulmonale is less well understood. This study was designed to evaluate the regulatory roles of miR-200b in cor pulmonale. Cor pulmonary mouse model was built via monocrotaline injection of monocrotaline (MCT). The expression of miR-200b in the lungs, RV and left ventricle (LV) are using real-time polymerase chain reaction. The transthoracic echocardiography was employed to determine the effects of miR-200b mimics and Gö6976 injection on MCT mice. The protein levels of protein kinase C α (PKCα), collagen, and fibronectin in the lung, RV, and LV in the mice with and without miR-200b mimics and Gö6976 injection were evaluated using western blot. The expression of miR-200b decreased in MCT mice, while there was no difference in LV. Both the miR-200b mimics and Gö6976 injection reversed the muscularization in the pulmonary artery, reversed RV hypertrophy, reduced RV systolic pressure, wall thickness and pulmonary fibrosis. The injection of miR-200b can reduce the PKCα expression in the lung, RV, and LV. This study confirmed the down-regulation of miR-200b in cor pulmonale. The reverse effects of miR-200b in the present study may provide a potential tool for cor pulmonary treatment.

Toxoplasma gondii induces prolonged host epidermal growth factor receptor signalling to prevent parasite elimination by autophagy: Perspectives for in vivo control of the parasite.

Toxoplasma gondii causes retinitis and encephalitis. Avoiding targeting by autophagosomes is key for its survival because T. gondii cannot withstand lysosomal degradation. During invasion of host cells, T. gondii triggers epidermal growth factor receptor (EGFR) signalling enabling the parasite to avoid initial autophagic targeting. However, autophagy is a constitutive process indicating that the parasite may also use a strategy operative beyond invasion to maintain blockade of autophagic targeting. Finding that such a strategy exists would be important because it could lead to inhibition of host cell signalling as a novel approach to kill the parasite in previously infected cells and treat toxoplasmosis. We report that T. gondii induced prolonged EGFR autophosphorylation. This effect was mediated by PKCα/PKCß âž” Src because T. gondii caused prolonged activation of these molecules and their knockdown or incubation with inhibitors of PKCα/PKCß or Src after host cell invasion impaired sustained EGFR autophosphorylation. Addition of EGFR tyrosine kinase inhibitor (TKI) to previously infected cells led to parasite entrapment by LC3 and LAMP-1 and pathogen killing dependent on the autophagy proteins ULK1 and Beclin 1 as well as lysosomal enzymes. Administration of gefitinib (EGFR TKI) to mice with ocular and cerebral toxoplasmosis resulted in disease control that was dependent on Beclin 1. Thus, T. gondii promotes its survival through sustained EGFR signalling driven by PKCα/ß âž” Src, and inhibition of EGFR controls pre-established toxoplasmosis.

A novel form of glycolytic metabolism-dependent cardioprotection revealed by PKCα and ß inhibition.

KEY POINTS: Acute hyperglycaemia at the time of a heart attack worsens the outcome for the patient. Acute hyperglycaemia is not limited to diabetic patients and can be due to a stress response in non-diabetics. This study suggests that the damaging cardiac effects of hyperglycaemia can be reversed by selective PKC inhibition. If PKCα/ß isoforms are inhibited, then high glucose itself becomes protective against ischaemic damage. Selective PKC inhibition may therefore be a useful therapeutic tool to limit the damage that can occur during a heart attack by stress-induced hyperglycaemia. ABSTRACT: Hyperglycaemia has a powerful association with adverse prognosis for patients with acute coronary syndromes (ACS). Previous work shows that high glucose prevents ischaemic preconditioning and causes electrical and mechanical disruption via protein kinase C α/ß (PKCα/ß) activation. The present study aimed to: (i) determine whether the adverse clinical association of hyperglycaemia in ACS can be replicated in preclinical cellular models of ACS and (ii) determine the importance of PKCα/ß activation to the deleterious effect of glucose. Freshly isolated rat, guinea pig or rabbit cardiomyocytes were exposed to simulated ischaemia after incubation in the presence of normal (5 mm) or high (20 mm) glucose in the absence or presence of small molecule or tat-peptide-linked PKCαß inhibitors. In each of the four conditions, the following hallmarks of cardioprotection were recorded using electrophysiology or fluorescence imaging: cardiomyocyte contraction and survival, action potential stability and time to failure, intracellular calcium and ATP, mitochondrial depolarization, ischaemia-sensitive leak current, and time to Kir 6.2 opening. High glucose alone resulted in decreased cardiomyocyte contraction and survival; however, it also imparted cardioprotection in the presence of PKCα/ß inhibitors. This cardioprotective phenotype displayed improvements in all of the measured parameters and decreased myocardium damage during whole heart coronary ligation experiments. High glucose is deleterious to cellular and whole-heart models of simulated ischaemia, in keeping with the clinical association of hyperglycaemia with an adverse outcome in ACS. PKCαß inhibition revealed high glucose to show a cardioprotective phenotype in this setting. The results of the present study suggest the potential for the therapeutic application of PKCαß inhibition in ACS associated with hyperglycaemia.

Rho-kinase and PKCα Inhibition Induces Primary Cilia Elongation and Alters the Behavior of Undifferentiated and Differentiated Temperature-sensitive Mouse Cochlear Cells.

Primary cilia, regulated via distinct signal transduction pathways, play crucial roles in various cellular behaviors. However, the full regulatory mechanism involved in primary cilia development during cellular differentiation is not fully understood, particularly for the sensory hair cells of the mammalian cochlea. In this study, we investigated the effects of the Rho-kinase inhibitor Y27632 and PKCα inhibitor GF109203X on primary cilia-related cell behavior in undifferentiated and differentiated temperature-sensitive mouse cochlear precursor hair cells (the conditionally immortalized US/VOT-E36 cell line). Our results indicate that treatment with Y27632 or GF109203X induced primary cilia elongation and tubulin acetylation in both differentiated and undifferentiated cells. Concomitant with cilia elongation, Y27632 treatment also increased Hook2 and cyclinD1 expression, while only Hook2 expression was increased after treatment with GF109203X. In the undifferentiated cells, we observed an increase in the number of S and G2/M stage cells and a decrease of G1 cells after treatment with Y27632, while the opposite was observed after treatment with GF109203X. Finally, while both treatments decreased oxidative stress, only treatment with Y27632, not GF109203X, induced cell cycle-dependent cell proliferation and cell migration.

IL-17A Recruits Rab35 to IL-17R to Mediate PKCα-Dependent Stress Fiber Formation and Airway Smooth Muscle Contractility.

IL-17A is a critical proinflammatory cytokine for the pathogenesis of asthma including neutrophilic pulmonary inflammation and airway hyperresponsiveness. In this study, by cell type-specific deletion of IL-17R and adaptor Act1, we demonstrated that IL-17R/Act1 exerts a direct impact on the contraction of airway smooth muscle cells (ASMCs). Mechanistically, IL-17A induced the recruitment of Rab35 (a small monomeric GTPase) and DennD1C (guanine nucleotide exchange factor [GEF]) to the IL-17R/Act1 complex in ASMCs, resulting in activation of Rab35. Rab35 knockdown showed that IL-17A-induced Rab35 activation was essential for protein kinase Cα (PKCα) activation and phosphorylation of fascin at Ser39 in ASMCs, allowing F-actin to interact with myosin to form stress fibers and enhance the contraction induced by methacholine. PKCα inhibitor or Rab35 knockdown indeed substantially reduced IL-17A-induced stress fiber formation in ASMCs and attenuated IL-17A-enhanced, methacholine-induced contraction of airway smooth muscle. Taken together, these data indicate that IL-17A promotes airway smooth muscle contraction via direct recruitment of Rab35 to IL-17R, followed by PKCα activation and stress fiber formation.

17ß-Estradiol attenuates p38MAPK activity but not PKCα induced by angiotensin II in the brain.

17ß-Estradiol (E2) has been shown to modulate the renin-angiotensin system in hydromineral and blood pressure homeostasis mainly by attenuating angiotensin II (ANGII) actions. However, the cellular mechanisms of the interaction between E2 and angiotensin II (ANGII) and its physiological role are largely unknown. The present experiments were performed to better understand the interaction between ANGII and E2 in body fluid control in female ovariectomized (OVX) rats. The present results are the first to demonstrate that PKC/p38 MAPK signaling is involved in ANGII-induced water and sodium intake and oxytocin (OT) secretion in OVX rats. In addition, previous data from our group revealed that the ANGII-induced vasopressin (AVP) secretion requires ERK1/2 signaling. Therefore, taken together, the present observations support a novel concept that distinct intracellular ANGII signaling gives rise to distinct neurohypophyseal hormone release. Furthermore, the results show that E2 attenuates p38 MAPK phosphorylation in response to ANGII but not PKC activity in the hypothalamus and the lamina terminalis, suggesting that E2 modulates ANGII effects through the attenuation of the MAPK pathway. In conclusion, this work contributes to the further understanding of the interaction between E2 and ANGII signaling in hydromineral homeostasis, as well as it contributes to further elucidate the physiological relevance of PKC/p38 MAPK signaling on the fluid intake and neurohypophyseal release induced by ANGII.

Organic barn dust inhibits surfactant protein D production through protein kinase-c alpha dependent increase of GPR116.

Prolonged exposure to organic barn dusts can lead to chronic inflammation and a broad range of lung problems over time, mediated by innate immune mechanisms. The immune surfactant or collectin surfactant protein D (SP-D) is a crucial multifunctional innate immune receptor. Little work to date has examined the effect of such collectins in response to organic dusts. We provide evidence here that agricultural organic dusts can inhibit mRNA and protein expression of SP-D in a human alveolar epithelial cell line, and an in vivo mouse model. This inhibition was not a result of lipopolysaccharide (LPS) or peptidoglycans, the two most commonly cited immune active components of these dusts. We further show that inhibition of the signaling molecule protein kinase C alpha (PKCα) can reverse this inhibition implicating it as a mechanism of SP-D inhibition. Examination of the SP-D regulatory receptor GPR116 showed that its mRNA expression was increased in response to dust and inhibited by blocking PKCα, implicating it as a means of inhibiting SP-D in the lungs in response to organic dusts. This reduction shows that organic barn dust can reduce lung SP-D, thus leaving workers potentially at risk for a host of pathogens.

Bitopic Inhibition of ATP and Substrate Binding in Ser/Thr Kinases through a Conserved Allosteric Mechanism.

Protein kinases achieve substrate selective phosphorylation through their conformational flexibility and dynamic interaction with the substrate. Designing substrate selective or kinase selective small molecule inhibitors remains a challenge because of a lack of understanding of the dynamic mechanism by which substrates are selected by the kinase. Using a combination of all-atom molecular dynamics simulations and FRET sensors, we have delineated an allosteric mechanism that results in interaction among the DFG motif, G-loop, and activation loop and structurally links the nucleotide and substrate binding interfaces in protein kinase Cα and three other Ser/Thr kinases. ATP-competitive staurosporine analogues engage this allosteric switch region located just outside the ATP binding site to displace substrate binding to varying degrees. These inhibitors function as bitopic ligands by occupying the ATP binding site and interacting with the allosteric switch region. The conserved mechanism identified in this study can be exploited to select and design bitopic inhibitors for kinases.

Mineralocorticoid receptor blockade improves arginine transport and nitric oxide generation through modulation of cationic amino acid transporter-1 in endothelial cells.

Blockade of the mineralocorticoid receptor (MCR) has been shown to improve endothelial function far beyond blood pressure control. In the current studies we have looked at the effect of MCR antagonists on cationic amino acid transporter-1 (CAT-1), a major modulator of endothelial nitric oxide (NO) generation. Using radio-labeled arginine, {[3H] l-arginine} uptake was determined in human umbilical vein endothelial cells (HUVEC) following incubation with either spironolactone or eplerenone with or without silencing of MCR. Western blotting for CAT-1, PKCα and their phosphorylated forms were performed. NO generation was measured by using Griess reaction assay. Both Spironolactone and eplerenone significantly increased endothelial arginine transport, an effect which was further augmented by co-incubation with aldosterone, and blunted by either silencing of MCR or co-administration of amiloride. Following MCR blockade, we identified two bands for CAT-1. The addition of tunicamycin (an inhibitor of protein glycosylation) or MCR silencing resulted in disappearance of the extra band and prevented the increase in arginine transport. Only spironolactone decreased CAT-1 phosphorylation through inhibition of PKCα (CAT-1 inhibitor). Subsequently, incubation with either MCR antagonists significantly augmented NO2/NO3 levels (stable NO metabolites) and this was attenuated by silencing of MCR or tunicamycin. GO 6076 (PKCα inhibitor) intensified the increase of NO metabolites only in eplerenone treated cells. In conclusion spironolactone and eplerenone augment arginine transport and NO generation through modulation of CAT-1 in endothelial cells. Both MCR antagonists activate CAT-1 by inducing its glycosylation while only spironolactone inhibits PKCα.