Requirement of protein kinase C micro activation and calpain-mediated proteolysis for arachidonic acid-stimulated adhesion of MDA-MB-435 human mammary carcinoma cells to collagen type IV

The roles of intracellular proteolysis in cardiac ischemia-reperfusion injury

Ischemic heart disease remains a leading cause of human mortality worldwide. One form of ischemic heart disease is ischemia-reperfusion injury caused by the reintroduction of blood supply to ischemic cardiac muscle. The short and long-term damage that occurs due to ischemia-reperfusion injury is partly due to the proteolysis of diverse protein substrates inside and outside of cardiomyocytes. Ischemia-reperfusion activates several diverse intracellular proteases, including, but not limited to, matrix metalloproteinases, calpains, cathepsins, and caspases. This review will focus on the biological roles, intracellular localization, proteolytic targets, and inhibitors of these proteases in cardiomyocytes following ischemia-reperfusion injury. Recognition of the intracellular function of each of these proteases includes defining their activation, proteolytic targets, and their inhibitors during myocardial ischemia-reperfusion injury. This review is a step toward a better understanding of protease activation and involvement in ischemic heart disease and developing new therapeutic strategies for its treatment.

A protein kinase D inhibitor suppresses AKT on T cells and antagonizes cancer immunotherapy by anti-PD-1

Antibodies that block the interaction between PD-1 and PD-1 ligands (anti-PD-1) are in clinical use for the treatment of cancer, yet their efficacy is limited. Pre-approved therapies that enhance the effect of anti-PD-1 in combination are beneficial. Small-molecule inhibitors that attenuate T cell receptor signaling are reported to prevent T cell exhaustion and induce memory T cells with stem cell potential, resulting in a durable effector T cell response in combination with anti-PD-1. In search of such targets, we focused on protein kinase D (PKD), which is suggested to be suppressive in both tumor growth and TCR signaling. We report that CRT0066101, a PKD inhibitor (PKDi), suppressed the growth of mouse tumors at a sub-micromolar concentration in vitro. Despite its inhibitory effects on tumors, a single treatment of tumor-bearing mice with PKDi did not inhibit, but rather accelerated tumor growth, and reversed the therapeutic effect of anti-PD-1. Mice treated with PKDi showed reduced T cell infiltration and defects in the generation of effector T cells, compared to those treated with anti-PD-1, suggesting that PKDi inhibited ongoing antitumor responses. Mechanistically, PKDi inhibited phosphorylation of AKT, a primary checkpoint that is reactivated by anti-PD-1. In conclusion, PKD is fundamentally required for T cell reactivation by anti-PD-1; therefore, inhibition of PKD is not appropriate for combination therapy with anti-PD-1. On the other hand, a single dose of PKDi was shown to strongly suppress experimental autoimmunity in mice, indicating that PKDi could be useful for the treatment of immune-related adverse events that are frequently reported in anti-PD-1 therapy.

Systematic interaction of plasma albumin with the efficacy of chemotherapeutic drugs

Albumin, as the most abundant plasma protein, plays an integral role in the transport of a variety of exogenous and endogenous ligands in the bloodstream and extravascular spaces. For exogenous drugs, especially chemotherapeutic drugs, binding to and being delivered by albumin can significantly affect their efficacy. Meanwhile, albumin can also bind to many endogenous ligands, such as fatty acids, with important physiological significance that can affect tumor proliferation and metabolism. In this review, we summarize how albumin with unique properties affects chemotherapeutic drugs efficacy from the aspects of drug outcome in blood, toxicity, tumor accumulation and direct or indirect interactions with fatty acids, plus application of albumin-based carriers for anti-tumor drug delivery.

Evaluating the current status of protein kinase C (PKC)-protein kinase D (PKD) signalling axis as a novel therapeutic target in ovarian cancer

Ovarian cancer, especially high grade serous ovarian cancer is one of the most lethal gynaecological malignancies with high relapse rate and patient death. Notwithstanding development of several targeted treatment and immunotherapeutic approaches, researchers fail to turn ovarian cancer into a manageable disease. Protein kinase C (PKC) and protein kinase D (PKD) are families of evolutionarily conserved serine/threonine kinases that can be activated by a plethora of extracellular stimuli such as hormones, growth factors and G-protein coupled receptor agonists. Recent literature suggests that a signalling cascade initiated by these two protein kinases regulates a battery of cellular and physiological processes involved in tumorigenesis including cell proliferation, migration, invasion and angiogenesis. In an urgent need to discover novel therapeutic interventions against a deadly pathology like ovarian cancer, we have discussed the status quo of PKC/PKD signalling axis in context of this disease. Additionally, apart from discussing the structural properties and activation mechanisms of PKC/PKD, we have provided a comprehensive review of the recent reports on tumor promoting functions of PKC isoforms and discussed the potential of PKC/PKD signalling axis as a novel target in this lethal pathology. Furthermore, in this review, we have discussed the significance of several recent clinical trials and development of small molecule inhibitors that target PKC/PKD signalling axis in ovarian cancer.

The L1 cell adhesion molecule affects protein kinase D1 activity in the cerebral cortex in a mouse model of Alzheimer's disease

Alzheimer's disease (AD) is characterized by deposition of β-amyloid protein (Aβ), neurofibrillary tangles and cognitive deficits resulting from neuronal cell death. In search for the molecular underpinnings of the disease, we were interested in the relationship between Aβ, L1 cell adhesion molecule and protein kinase D1 (PKD1), which are not only implicated in neural development and functional maintenance in the adult, but are also neuroprotective under pathological conditions. Based on our observations that L1 and phosphorylated, i.e. activated, protein kinase PKD1 (pPKD1) co-localize in cultured neurons, we investigated the functional relationship between L1 and pPKD1 in the frontal lobe of an AD human cortical tissue microarray, and found increased and positively correlating levels of both molecules when compared to a non-affected human brain. Also in the APP_SWE mouse model of AD, L1 and pPKD1 levels were increased in the frontal lobe. To investigate whether L1 influences PKD1-based functions in AD, cultured cortical neurons were stressed with either H₂O₂ or oligomeric Aβ_1-42, in the presence or absence of recombinant L1 extracellular domain, and PKD1 phosphorylation was measured. As indicated by the cell viability assay, L1 maintained neuronal survival under oxidative stress and under application of oligomeric Aβ_1-42, when PKD1 activity was inhibited, suggesting that L1 ameliorates some aspects of Aβ_1-42 pathology in parallel with reducing PKD1 function.

CCR2 Chemokine Receptors Enhance Growth and Cell-Cycle Progression of Breast Cancer Cells through SRC and PKC Activation

Basal-like breast cancers are an aggressive breast cancer subtype, which often lack estrogen receptor, progesterone receptor, and Her2 expression, and are resistant to antihormonal and targeted therapy, resulting in few treatment options. Understanding the underlying mechanisms that regulate progression of basal-like breast cancers would lead to new therapeutic targets and improved treatment strategies. Breast cancer progression is characterized by inflammatory responses, regulated in part by chemokines. The CCL2/CCR2 chemokine pathway is best known for regulating breast cancer progression through macrophage-dependent mechanisms. Here, we demonstrated important biological roles for CCL2/CCR2 signaling in breast cancer cells. Using the MCF10CA1d xenograft model of basal-like breast cancer, primary tumor growth was significantly increased with cotransplantation of patient-derived fibroblasts expressing high levels of CCL2, and was inhibited with CRISP/R gene ablation of stromal CCL2. CRISP/R gene ablation of CCR2 in MCF10CA1d breast cancer cells inhibited breast tumor growth and M2 macrophage recruitment and validated through CCR2 shRNA knockdown in the 4T1 model. Reverse phase protein array analysis revealed that cell-cycle protein expression was associated with CCR2 expression in basal-like breast cancer cells. CCL2 treatment of basal-like breast cancer cell lines increased proliferation and cell-cycle progression associated with SRC and PKC activation. Through pharmacologic approaches, we demonstrated that SRC and PKC negatively regulated expression of the cell-cycle inhibitor protein p27KIP1, and are necessary for CCL2-induced breast cancer cell proliferation. IMPLICATIONS: This report sheds novel light on CCL2/CCR2 chemokine signaling as a mitogenic pathway and cell-cycle regulator in breast cancer cells.

Protein kinase D signaling in cancer: A friend or foe?

Protein kinase D is a family of evolutionarily conserved serine/threonine kinases that belongs to the Ca⁺⁺/Calmodulin-dependent kinase superfamily. Signal transduction pathways mediated by PKD can be triggered by a variety of stimuli including G protein-coupled receptor agonists, growth factors, hormones, and cellular stresses. The regulatory mechanisms and physiological roles of PKD have been well documented including cell proliferation, survival, migration, angiogenesis, regulation of gene expression, and protein/membrane trafficking. However, its precise roles in disease progression, especially in cancer, remain elusive. A plethora of studies documented the cell- and tissue-specific expressions and functions of PKD in various cancer-associated biological processes, while the causes of the differential effects of PKD have not been thoroughly investigated. In this review, we have discussed the structural-functional properties, activation mechanisms, signaling pathways and physiological functions of PKD in the context of human cancer. Additionally, we have provided a comprehensive review of the reported tumor promoting or tumor suppressive functions of PKD in several major cancer types and discussed the discrepancies that have been raised on PKD as a major regulator of malignant transformation.

Integrative Comparison of mRNA Expression Patterns in Breast Cancers from Caucasian and Asian Americans with Implications for Precision Medicine

Asian Americans (AS) have significantly lower incidence and mortality rates of breast cancer than Caucasian Americans (CA). Although this racial disparity has been documented, the underlying pathogenetic factors explaining it are obscure. We addressed this issue by an integrative genomics approach to compare mRNA expression between AS and CA cases of breast cancer. RNA-seq data from the Cancer Genome Atlas showed that mRNA expression revealed significant differences at gene and pathway levels. Increased susceptibility and severity in CA patients were likely the result of synergistic environmental and genetic risk factors, with arachidonic acid metabolism and PPAR signaling pathways implicated in linking environmental and genetic factors. An analysis that also added eQTL data from the Genotype-Tissue Expression Project and SNP data from the 1,000 Genomes Project identified several SNPs associated with differentially expressed genes. Overall, the associations we identified may enable a more focused study of genotypic differences that may help explain the disparity in breast cancer incidence and mortality rates in CA and AS populations and inform precision medicine. Cancer Res; 77(2); 423-33. ©2016 AACR.

Involvement of Protein Kinase D1 in Signal Transduction from the Protein Kinase C Pathway to the Tyrosine Kinase Pathway in Response to Gonadotropin-releasing Hormone

The receptor for gonadotropin-releasing hormone (GnRH) belongs to the G protein-coupled receptors (GPCRs), and its stimulation activates extracellular signal-regulated protein kinase (ERK). We found that the transactivation of ErbB4 was involved in GnRH-induced ERK activation in immortalized GnRH neurons (GT1-7 cells). We found also that GnRH induced the cleavage of ErbB4. In the present study, we examined signal transduction for the activation of ERK and the cleavage of ErbB4 after GnRH treatment. Both ERK activation and ErbB4 cleavage were completely inhibited by YM-254890, an inhibitor of Gq/11 proteins. Down-regulation of protein kinase C (PKC) markedly decreased both ERK activation and ErbB4 cleavage. Experiments with two types of PKC inhibitors, Gö 6976 and bisindolylmaleimide I, indicated that novel PKC isoforms but not conventional PKC isoforms were involved in ERK activation and ErbB4 cleavage. Our experiments indicated that the novel PKC isoforms activated protein kinase D (PKD) after GnRH treatment. Knockdown and inhibitor experiments suggested that PKD1 stimulated the phosphorylation of Pyk2 by constitutively activated Src and Fyn for ERK activation. Taken together, it is highly possible that PKD1 plays a critical role in signal transduction from the PKC pathway to the tyrosine kinase pathway. Activation of the tyrosine kinase pathway may be involved in the progression of cancer.

p38 mitogen-activated protein kinase interacts with vinculin at focal adhesions during fatty acid-stimulated cell adhesion

Arachidonic acid stimulates cell adhesion by activating α2β1 integrins in a process that depends on protein kinases, including p38 mitogen activated protein kinase. Here, we describe the interaction of cytoskeletal components with key signaling molecules that contribute to the spreading of, and morphological changes in, arachidonic acid-treated MDA-MB-435 human breast carcinoma cells. Arachidonic acid-treated cells showed increased attachment and spreading on collagen type IV, as measured by electric cell-substrate impedance sensing. Fatty acid-treated cells displayed short cortical actin filaments associated with an increased number of β1 integrin-containing pseudopodia, whereas untreated cells displayed elongated stress fibers and fewer clusters of β1 integrins. Confocal microscopy of arachidonic acid-treated cells showed that vinculin and phospho-p38 both appeared enriched in pseudopodia and at the tips of actin filaments, and fluorescence ratio imaging indicated the increase was specific for the phospho-(active) form of p38. Immunoprecipitates of phospho-p38 from extracts of arachidonic acid-treated cells contained vinculin, and GST-vinculin fusion proteins carrying the central region of vinculin bound phospho-p38, whereas fusion proteins expressing the terminal portions of vinculin did not. These data suggest that phospho-p38 associates with particular domains on critical focal adhesion proteins that are involved in tumor cell adhesion and spreading, and that this association can be regulated by factors in the tumor microenvironment.

Oxidative stress and sarcomeric proteins

Oxidative stress accompanies a wide spectrum of clinically important cardiac disorders, including ischemia/reperfusion, diabetes mellitus, and hypertensive heart disease. Although reactive oxygen species (ROS) can activate signaling pathways that contribute to ischemic preconditioning and cardioprotection, high levels of ROS induce structural modifications of the sarcomere that impact on pump function and the pathogenesis of heart failure. However, the precise nature of the redox-dependent change in contractility is determined by the source/identity of the oxidant species, the level of oxidative stress, and the chemistry/position of oxidant-induced posttranslational modifications on individual proteins within the sarcomere. This review focuses on various ROS-induced posttranslational modifications of myofilament proteins (including direct oxidative modifications of myofilament proteins, myofilament protein phosphorylation by ROS-activated signaling enzymes, and myofilament protein cleavage by ROS-activated proteases) that have been implicated in the control of cardiac contractility.

Over-expression of calpastatin aggravates cardiotoxicity induced by doxorubicin

AIMS

Doxorubicin causes damage to the heart, which may present as cardiomyopathy. However, the mechanisms by which doxorubicin induces cardiotoxicity remain not fully understood and no effective prevention for doxorubicin cardiomyopathy is available. Calpains, a family of calcium-dependent thiol-proteases, have been implicated in cardiovascular diseases. Their activities are tightly controlled by calpastatin. This study employed transgenic mice over-expressing calpastatin to investigate the role of calpain in doxorubicin-induced cardiotoxicity.

METHODS AND RESULTS

Doxorubicin treatment decreased calpain activities in cultured neonatal mouse cardiomyocytes and in vivo mouse hearts, which correlated with down-regulation of calpain-1 and calpain-2 proteins. Over-expression of calpastatin or incubation with pharmacological calpain inhibitors enhanced apoptosis in neonatal and adult cardiomyocytes induced by doxorubicin. In contrast, over-expression of calpain-2 but not calpain-1 attenuated doxorubicin-induced apoptosis in cardiomyocytes. The pro-apoptotic effects of calpain inhibition were associated with down-regulation of protein kinase B (AKT) protein and mRNA expression, and a concomitant reduction in glycogen synthase kinase-3beta (GSK-3β) phosphorylation (Ser9) in doxorubicin-treated cardiomyocytes. Blocking AKT further increased doxorubicin-induced cardiac injuries, suggesting the effects of calpain inhibition may be mediated by inactivating the AKT signalling. In an in vivo model of doxorubicin-induced cardiotoxicity, over-expression of calpastatin exacerbated myocardial dysfunction as assessed by echocardiography and haemodynamic measurement in transgenic mice 5 days after doxorubicin injection. The 5-day mortality was higher in transgenic mice (29.16%) compared with their wild-type littermates (8%) after doxorubicin treatment.

CONCLUSION

Over-expression of calpastatin enhances doxorubicin-induced cardiac injuries through calpain inhibition and thus, calpains may protect cardiomyocytes against doxorubicin-induced cardiotoxicity.

Protein kinase D-HDAC5 signaling regulates erythropoiesis and contributes to erythropoietin cross-talk with GATA1

In red cell development, the differentiation program directed by the transcriptional regulator GATA1 requires signaling by the cytokine erythropoietin, but the mechanistic basis for this signaling requirement has remained unknown. Here we show that erythropoietin regulates GATA1 through protein kinase D activation, promoting histone deacetylase 5 (HDAC5) dissociation from GATA1, and subsequent GATA1 acetylation. Mice deficient for HDAC5 show resistance to anemic challenge and altered marrow responsiveness to erythropoietin injections. In ex vivo studies, HDAC5(-/-) progenitors display enhanced entry into and passage through the erythroid lineage, as well as evidence of erythropoietin-independent differentiation. These results reveal a molecular pathway that contributes to cytokine regulation of hematopoietic differentiation and offer a potential mechanism for fine tuning of lineage-restricted transcription factors by lineage-specific cytokines.

Critical role of arachidonic acid-activated mTOR signaling in breast carcinogenesis and angiogenesis

The mammalian target of rapamycin (mTOR) signaling pathway is upregulated in the pathogenesis of many cancers. Arachidonic acid (AA) and its metabolites play critical role in the development of breast cancer, but the mechanisms through which AA promotes mammary tumorigenesis and progression are poorly understood. We found that the levels of AA and cytosolic phospholipase A2 (cPLA2) strongly correlated with the signaling activity of mTORC1 and mTORC2 as well as the expression levels of vascular epithelial growth factor (VEGF) in human breast tumor tissues. In cultured breast cancer cells, AA effectively activated both mTOR complex 1 (mTORC1) and mTORC2. Interestingly, AA-stimulated mTORC1 activation was independent of amino acids, phosphatidylinositol 3-kinase (PI3-K) and tuberous sclerosis complex 2 (TSC2), which suggests a novel mechanism for mTORC1 activation. Further studies revealed that AA stimulated mTORC1 activity through destabilization of mTOR-raptor association in ras homolog enriched in brain (Rheb)-dependent mechanism. Moreover, we showed that AA-stimulated cell proliferation and angiogenesis required mTOR activity and that the effect of AA was mediated by lipoxygenase (LOX) but not cyclooxygenase-2 (COX-2). In animal models, AA-enhanced incidences of rat mammary tumorigenesis, tumor weights and angiogenesis were inhibited by rapamycin. Our findings suggest that AA is an effective intracellular stimulus of mTOR and that AA-activated mTOR plays critical roles in angiogenesis and tumorigenesis of breast cancer.

Neuroprotection against traumatic brain injury by a peptide derived from the collapsin response mediator protein 2 (CRMP2)

Neurological disabilities following traumatic brain injury (TBI) may be due to excitotoxic neuronal loss. The excitotoxic loss of neurons following TBI occurs largely due to hyperactivation of N-methyl-d-aspartate receptors (NMDARs), leading to toxic levels of intracellular Ca(2+). The axon guidance and outgrowth protein collapsin response mediator protein 2 (CRMP2) has been linked to NMDAR trafficking and may be involved in neuronal survival following excitotoxicity. Lentivirus-mediated CRMP2 knockdown or treatment with a CRMP2 peptide fused to HIV TAT protein (TAT-CBD3) blocked neuronal death following glutamate exposure probably via blunting toxicity from delayed calcium deregulation. Application of TAT-CBD3 attenuated postsynaptic NMDAR-mediated currents in cortical slices. In exploring modulation of NMDARs by TAT-CBD3, we found that TAT-CBD3 induced NR2B internalization in dendritic spines without altering somal NR2B surface expression. Furthermore, TAT-CBD3 reduced NMDA-mediated Ca(2+) influx and currents in cultured neurons. Systemic administration of TAT-CBD3 following a controlled cortical impact model of TBI decreased hippocampal neuronal death. These findings support TAT-CBD3 as a novel neuroprotective agent that may increase neuronal survival following injury by reducing surface expression of dendritic NR2B receptors.

Protein kinase D1 (PKD1) activation mediates a compensatory protective response during early stages of oxidative stress-induced neuronal degeneration

Background

Oxidative stress is a key pathophysiological mechanism contributing to degenerative processes in many neurodegenerative diseases and therefore, unraveling molecular mechanisms underlying various stages of oxidative neuronal damage is critical to better understanding the diseases and developing new treatment modalities. We previously showed that protein kinase C delta (PKCδ) proteolytic activation during the late stages of oxidative stress is a key proapoptotic signaling mechanism that contributes to oxidative damage in Parkinson's disease (PD) models. The time course studies revealed that PKCδ activation precedes apoptotic cell death and that cells resisted early insults of oxidative damage, suggesting that some intrinsic compensatory response protects neurons from early oxidative insult. Therefore, the purpose of the present study was to characterize protective signaling pathways in dopaminergic neurons during early stages of oxidative stress.

Results

Herein, we identify that protein kinase D1 (PKD1) functions as a key anti-apoptotic kinase to protect neuronal cells against early stages of oxidative stress. Exposure of dopaminergic neuronal cells to H₂O₂ or 6-OHDA induced PKD1 activation loop (PKD1S744/748) phosphorylation long before induction of neuronal cell death. Blockade of PKCδ cleavage, PKCδ knockdown or overexpression of a cleavage-resistant PKCδ mutant effectively attenuated PKD1 activation, indicating that PKCδ proteolytic activation regulates PKD1 phosphorylation. Furthermore, the PKCδ catalytic fragment, but not the regulatory fragment, increased PKD1 activation, confirming PKCδ activity modulates PKD1 activation. We also identified that phosphorylation of S916 at the C-terminal is a preceding event required for PKD1 activation loop phosphorylation. Importantly, negative modulation of PKD1 by the RNAi knockdown or overexpression of PKD1^S916A phospho-defective mutants augmented oxidative stress-induced apoptosis, while positive modulation of PKD1 by the overexpression of full length PKD1 or constitutively active PKD1 plasmids attenuated oxidative stress-induced apoptosis, suggesting an anti-apoptotic role for PKD1 during oxidative neuronal injury.

Conclusion

Collectively, our results demonstrate that PKCδ-dependent activation of PKD1 represents a novel intrinsic protective response in counteracting early stage oxidative damage in neuronal cells. Our results suggest that positive modulation of the PKD1-mediated compensatory protective mechanism against oxidative damage in dopaminergic neurons may provide novel neuroprotective strategies for treatment of PD.

Arachidonic acid stimulates formation of a novel complex containing nucleolin and RhoA

Arachidonic acid (AA) stimulates cell adhesion through a p38 mitogen activated protein kinase-mediated RhoA signaling pathway. Here we report that a proteomic screen following AA-treatment identified nucleolin, a multifunctional nucleolar protein, in a complex with the GTPase, RhoA, that also included the Rho kinase, ROCK. AA-stimulated cell adhesion was inhibited by expression of nucleolin-targeted shRNA and formation of the multiprotein complex was blocked by expression of dominant-negative RhoA. AA-treatment also induced ROCK-dependent serine phosphorylation of nucleolin and translocation of nucleolin from the nucleus to the cytoplasm, where it appeared to co-localize with RhoA. These data suggest the existence of a new signaling pathway through which the location and post-translational state of nucleolin are modulated.

Disruption of Rac1 signaling reduces ischemia-reperfusion injury in the diabetic heart by inhibiting calpain

Diabetes increases myocardial ischemia/reperfusion (I/R) injury. However, the underlying mechanisms remain incompletely understood. This study investigated the role of Rac1 signaling and calpain in exacerbated I/R injury in diabetic hearts. Mice with cardiac-specific deletion of Rac1 (Rac1-ko) and transgenic mice with cardiac-specific superoxide dismutase-2 (SOD2) or calpastatin overexpression were rendered diabetic with streptozotocin. Isolated perfused hearts were subjected to global I/R. After I/R, Rac1 activity was significantly enhanced in diabetic compared with nondiabetic hearts. Diabetic hearts displayed more severe I/R injury than nondiabetic hearts, as evidenced by more lactate dehydrogenase release and apoptosis and decreased cardiac function. These adverse impacts of diabetes were abrogated in Rac1-ko hearts or by perfusion with the Rac1 inhibitor NSC23766. In an in vivo I/R mouse model, infarct size was much smaller in diabetic Rac1-ko compared with wild-type mice. Inhibition of Rac1 signaling prevented NADPH oxidase activation, reactive oxygen species production, and protein carbonyl accumulation, leading to inhibition of calpain activation. Furthermore, SOD2 or calpastatin overexpression significantly reduced I/R injury in diabetic hearts and improved cardiac function after I/R. In summary, Rac1 activation increases I/R injury in diabetic hearts and the role of Rac1 signaling is mediated, at least in part, through calpain activation.

Protein kinase D as a potential new target for cancer therapy

Protein kinase D is a novel family of serine/threonine kinases and diacylglycerol receptors that belongs to the calcium/calmodulin-dependent kinase superfamily. Evidence has established that specific PKD isoforms are dysregulated in several cancer types, and PKD involvement has been documented in a variety of cellular processes important to cancer development, including cell growth, apoptosis, motility, and angiogenesis. In light of this, there has been a recent surge in the development of novel chemical inhibitors of PKD. This review focuses on the potential of PKD as a chemotherapeutic target in cancer treatment and highlights important recent advances in the development of PKD inhibitors.

Oleic acid promotes migration on MDA-MB-231 breast cancer cells through an arachidonic acid-dependent pathway

An association between dietary fatty, obesity and an increased risk of developing breast cancer has been suggested. In breast cancer cells, free fatty acids (FFAs) mediate biological effects including cell proliferation and ERK1/2 activation. However, the contribution of FFAs to tumor progression and metastasis through the regulation of cell migration has not been studied. We demonstrated here that stimulation on MDA-MB-231 breast cancer cells with oleic acid (OA) promotes an increase in focal adhesion kinase (FAK) phosphorylation, as revealed by site-specific antibodies that recognize the phosphorylation state of FAK at tyrosine-397 (Tyr-397), Tyr-577 and in vitro kinase assays. OA also promotes the migration of MDA-MB-231 cells. Treatment with Gi/Go proteins, phospholipase C (PLC), lipoxygenases (LOXs) and Src inhibitor prevents FAK phosphorylation and cell migration. In summary, our findings delineate a new signal transduction pathway, where OA mediates the production of arachidonic acid (AA), and then AA metabolites mediate FAK phosphorylation and cell migration in MDA-MB-231 breast cancer cells.

Calpain-1 induces apoptosis in pulmonary microvascular endothelial cells under septic conditions

This study was to investigate the role of calpain in the apoptosis of pulmonary microvascular endothelial cells (PMEC) during septic plasma stimulation. Septic plasma was collected from endotoxemic mice. In cultured PMEC, incubation with septic plasma stimulated calpain activation, increased caspase-3 activity and induced apoptotic cell death. These effects of septic plasma were abrogated by knockdown of calpain-1 but not calpain-2 using specific siRNA. Consistently, treatment with calpain inhibitor-III, or over-expression of calpastatin, an endogenous calpain inhibitor significantly decreased apoptosis induced by septic plasma. Septic plasma also induced NADPH oxidase activation and reactive oxygen species (ROS) production. Inhibiting NADPH oxidase or scavenging ROS attenuated calpain activity and decreased apoptosis in PMEC during septic plasma stimulation. In summary, our study demonstrates that ROS produced from NADPH oxidase stimulates calpain-1 activation, which induces apoptosis under septic conditions. Thus, targeting calpain-1/calpastatin may represent a potential strategy to protect against endothelial injury in sepsis.

Osteopontin mediates dense culture-induced proliferation and adhesion of prostate tumour cells: role of protein kinase C, p38 mitogen-activated protein kinase and calcium

Cells growing in high density were observed to undergo a variety of responses due to cell-cell contact, pericellular hypoxia, etc. In order to investigate the influence of cell density on cell proliferation and adhesion and to elucidate possible mechanisms, we tested the growth ability of human prostate tumour (PC-3M) cells in dense culture and the influences of density on cell adhesion. Our results demonstrate that increasing cell density exerted stress on PC-3M cells, which decreased cell proliferation in dense cultures, but tended to facilitate tumour metastasis since cell adhesion ability was elevated and the cells showed an increased growth rate after being moved to a favourable growth environment. We conclude that higher cell density-mediated pericellular hypoxia was an important factor inducing expression of the intrinsic hypoxia marker osteopontin, another mechanism contributing to cell adhesion enhancement in PC-3M cells. In addition, cell density enhanced adhesion ability due to the activation of p38 mitogen-activated protein kinase (p38 MAPK) and protein kinase C. Intracellular calcium also played positive roles at least partially through activating p38 MAPK.

Arachidonic acid promotes FAK activation and migration in MDA-MB-231 breast cancer cells

Arachidonic acid (AA) is a common dietary n-6 polyunsaturated fatty acid that is present in an esterified form in cell membrane phospholipids, and it might be present in the extracellular microenvironment. In particular, AA promotes MAPK activation and mediates the adhesion of MDA-MB-435 breast cancer cells to type IV collagen. However, the signal transduction pathways mediated by AA have not been studied in detail. Our results demonstrate that stimulation of MDA-MB-231 breast cancer cells with AA promotes an increase in the phoshorylation of Src and FAK, as revealed by site-specific antibodies that recognized the phosphorylation state of Src at Tyr-418, and of FAK at tyrosine-397 and in vitro kinase assays. In addition, AA also induces an increase in the migration of MDA-MB-231 cells. In contrast, AA does not induce phosphorylation of FAK and an increase in cell migration of non-tumorigenic epithelial cells MCF10A. Inhibition of Gi/Go proteins, LOX and Src activity prevent FAK activation and cell migration. In conclusion, our results demonstrate, for the first time, that Gi/Go proteins, LOX and Src play an important role in FAK activation and cell migration induced by AA in MDA-MB-231 breast cancer cells.

Protein kinase D1: a new component in TLR9 signaling

Protein kinase D1 (PKD1) is expressed ubiquitously and regulates diverse cellular processes such as oxidative stress, gene expression, cell survival, and vesicle trafficking. However, the presence and function of PKD1 in monocytic cells are currently unknown. In this study, we provide evidence that PKD1 is involved in TLR9 signaling in macrophages. Class B-type CpG DNA (CpG-B DNA) induced activation of PKD1 via a pathway that is dependent on endosomal pH, TLR9, MyD88, and IL-1R-associated kinase 1 in macrophages. Upon CpG-B DNA stimulation, PKD1 interacted with the TLR9/MyD88/IL-1R-associated kinase/TNFR-associated factor 6 complex. Knockdown of PKD1 revealed that PKD1 is required for activation of NF-kappaB and MAPKs, and subsequent expression of cytokines in response to CpG-B DNA. Our findings identify PKD1 as a key signaling modulator in TLR9-mediated macrophage activation.

Angiotensin II directly triggers endothelial exocytosis via protein kinase C-dependent protein kinase D2 activation

Angiotensin II (AII) has been reported to induce leukocyte adhesion to endothelium through up-regulation of P-selectin surface expression. However, the underlying molecular and cellular mechanisms remain unknown. P-selectin is stored in Weibel-Palade bodies (WPBs), large secretory granules, in endothelial cells. In this study, we examined the role of protein kinase D (PKD), a newly identified regulator of protein transport, in AII-induced WPB exocytosis and the resultant P-selectin surface expression. We demonstrated that PKD2 was rapidly activated by AII in endothelial cells through phosphorylation of the activation loop at Ser744/748. AII-induced PKD2 activation correlated with increased P-selectin surface expression. Furthermore, AII-regulated PKD2 activation is protein kinase C (PKC) alpha-dependent. Importantly, knock-down of either PKD2 or PKCalpha expression inhibited AII-mediated P-selectin surface expression and monocyte adhesion. Our findings provide the first evidence that stimulation of P-selectin surface expression via PKCalpha-dependent PKD2 activation could be an important mechanism in the early onset of AII-initiated endothelial adhesiveness.

Down-regulation of cAMP-dependent protein kinase by over-activated calpain in Alzheimer disease brain

Impaired cognition and memory may be associated with down-regulation of cAMP-response element-binding protein (CREB) in the brain in patients with Alzheimer disease, but the molecular mechanism leading to the down-regulation is not understood. In this study, we found a selective reduction in the levels of the regulatory subunits (RIIalpha and RIIbeta) and the catalytic subunit (Cbeta) as well as the enzymatic activity of cAMP-dependent protein kinase (PKA), which is the major positive regulator of CREB. We also observed that PKA subunits were proteolyzed by calpain and the levels of PKA subunits correlated negatively with calpain activation in the human brain. These findings led us to propose that in the brain in patients with Alzheimer disease, over-activation of calpain because of calcium dysregulation causes increased degradation and thus decreased activity of PKA, which, in turn, contributes to down-regulation of CREB and impaired cognition and memory.

H2O2 activation of HSP25/27 protects desmin from calpain proteolysis in rat ventricular myocytes

Ischemia-reperfusion-induced Ca2+ overload results in activation of calpain-1 in the heart. Calpain-dependent proteolysis contributes to myocardial dysfunction and cell death. Previously, preischemic treatment with low doses of H2O2 was shown to improve postischemic function and reduce myocardial infarct size. Our aim was to determine the mechanism by which H2O2 protects the heart. We hypothesized that H2O2 causes the activation of p38 MAPK which initiates translocation of heat shock protein 25/27 (HSP25/27) to the myofilament Z disk. We further hypothesized that HSP25/27 shields structural proteins, particularly desmin, from calpain-induced proteolysis. To address this hypothesis, we first determined that an ischemia-reperfusion-induced decrease in desmin content could be blocked by H2O2 pretreatment of hearts from rats. We next determined that ventricular myocytes that underwent Ca2+ overload also demonstrated a calpain-dependent disruption of desmin that could be reduced by H2O2/p38 MAPK activation. Furthermore, myocytes acutely treated with H2O2 exhibited a decrease in cleavage of desmin upon exposure to exogenous calpain-1 compared with myocytes not pretreated with H2O2. The H2O2-induced attenuation of desmin degradation by calpain-1 was blocked by inhibition of p38 MAPK. In a final series of experiments, we demonstrated that cardiac myofilaments exposed to recombinant phosphorylated HSP27, but not nonphosphorylated HSP27, had a significant reduction in the calpain-induced degradation of desmin compared with non-HSP27-treated myofilaments. These findings are consistent with the hypothesis that H2O2-induced activation of p38 MAPK and subsequent HSP25/27 translocation attenuates desmin degradation brought about by calpain-1 activation in ischemia-reperfused hearts.

Calpain involvement in the remodeling of cytoskeletal anchorage complexes

Cells offer different types of cytoskeletal anchorages: transitory structures such as focal contacts and perennial ones such as the sarcomeric cytoskeleton of muscle cells. The turnover of these structures is controlled with different timing by a family of cysteine proteases activated by calcium, the calpains. The large number of potential substrates present in each of these structures imposes fine tuning of the activity of the proteases to avoid excessive action. This phenomenon is thus guaranteed by various types of regulation, ranging from a relatively high calcium concentration necessary for activation, phosphorylation of substrates or the proteases themselves with either a favorable or inhibitory effect, possible intervention of phospholipids, and the presence of a specific inhibitor and its possible degradation before activation. Finally, formation of multiprotein complexes containing calpains offers a new method of regulation.

Transforming growth factor-beta1 induces epithelial-to-mesenchymal transition and apoptosis via a cell cycle-dependent mechanism

Apoptosis and epithelial-to-mesenchymal transition (EMT) have been implicated in a variety of biological processes, such as embryonic development, fibrosis and tumor progression. Transforming growth factor-beta (TGF-beta) can induce simultaneously both EMT and apoptotic response of epithelial cells. However, the underlying mechanism of these biological events remains not well understood. In the present study, we show that TGF-beta1 induces apoptosis and EMT in AML-12 cells in a cell cycle-related manner, in which apoptosis and EMT took place at G2/M and G1/S phases, respectively. TGF-beta1-induced apoptosis was correlated with different extent of caspase activation at different cell cycle phases. Interestingly, increased phosphorylation of protein kinase D (PKD) can be observed in G1/S phase in response to TGF-beta1, and inhibition of PKD by inhibitor or by small interference RNA blocked EMT but not apoptosis. Our data suggest a previously unrecognized role of cell cycle state in the regulation of TGF-beta-induced EMT and apoptosis, and demonstrate that PKD is involved in the TGF-beta1-induced EMT.

Phosphorylation of ezrin enhances microvillus length via a p38 MAP-kinase pathway in an immortalized mouse hepatic cell line

The apical microvilli are closely related with the development and the maintenance of cell polarization, and the length of microvilli varies in a regular way among cell types. Ezrin, a member of the ezrin/radixin/moesin (ERM) family, seems to be involved in the formation and stabilization of the apical microvilli. We found that phosphorylation of ezrin caused elongation of microvilli via a p38 MAP-kinase signaling pathway in an immortalized mouse hepatic cell line. When, in the oncogenic Raf-1-transfected mouse hepatic cell line, epithelial to mesenchymal transition (EMT) indicated as down-regulation of E-cadherin and up-regulation of Snail occurred, loss of microvilli and down-regulation of ezrin but not radixin and moesin were also observed. In the Raf-1 transfectants treated with the MAP-kinase inhibitor PD98059 and the p38 MAP-kinase inhibitor SB203580, the numbers of microvilli and the expression of ezrin, E-cadherin and Snail were recovered. More interestingly, treatment with SB203580 induced elongation of microvilli and increased phosphorylation of ezrin (at Thr-567 and Tyr-353). Phosphorylated ezrin-positive dots were colocalized with actin-positive dots on the surface of some Raf-1 transfectants treated with SB203580. These results suggested that phosphorylation of ezrin via the p38 MAP-kinase signaling pathway might be involved in the formation of microvilli during development of epithelial cell polarization.

15(S)-Lipoxygenase-2 Mediates Arachidonic Acid-stimulated Adhesion of Human Breast Carcinoma Cells through the Activation of TAK1, MKK6, and p38 MAPK

The dietary cis-polyunsaturated fatty acid, arachidonic acid, stimulates adhesion of metastatic human breast carcinoma cells (MDA-MB-435) to the extracellular matrix, but the molecular mechanisms by which fatty acids modify the behavior of these cells are unclear. Exposure to arachidonic acid activates multiple signaling pathways. Activation of p38 mitogen-activated protein kinase (p38 MAPK) is required for increased cell adhesion to type IV collagen, and this activation is sensitive to inhibitors of lipoxygenases, suggesting a requirement for arachidonic acid metabolism. The goals of the current study were to identify the one or more key metabolites of arachidonic acid that are responsible for activation of p38 MAPK and to elucidate the upstream kinases that lead to p38 MAPK activation. High performance liquid chromatographic analysis revealed that MDA-MB-435 cells metabolize exogenous arachidonic acid predominantly to 15(S)-hydroxyeicosatetraenoic acid (15(S)-HETE). Immunoblot analysis with antibodies specific to 15(S)-lipoxygenase-1 (LOX-1) and 15(S)-lipoxygenase-2 (LOX-2) demonstrated the expression of 15-LOX-2, but not 15-LOX-1, in these tumor cells. A LOX inhibitor, nordihydroguaiaretic acid, attenuated production of 15(S)-HETE and inhibited the phosphorylation of p38 MAPK following exposure to arachidonic acid. In contrast, overexpression of LOX-2 sensitized the cells to the addition of arachidonic acid, leading to increased activation of p38 MAPK. Addition of exogenous 15(S)-HETE to MDA-MB-435 cells stimulated cell adhesion to type IV collagen and activated the p38 MAPK pathway, including the upstream kinases transforming growth factor-beta1-activated protein kinase-1 (TAK1) and MAPK kinase 6. Transfection of these cells with a dominant negative form of TAK1 blocked arachidonic acid-stimulated p38 MAPK phosphorylation. These data demonstrate that 15(S)-LOX-2 generation of 15(S)-HETE activates specific growth factor receptor-related signaling pathways, thereby initiating signal transduction events leading to increased cell adhesion to the extracellular matrix.

Oxidative Activation of Protein Kinase Cγ through the C1 Domain

The accumulation of reactive oxygen species (ROS, for example H2O2) is linked to several chronic pathologies, including cancer and cardiovascular and neurodegenerative diseases (Gate, L., Paul, J., Ba, G. N., Tew, K. D., and Tapiero, H. (1999) Biomed. Pharmacother. 53, 169-180). Protein kinase C (PKC) gamma is a unique isoform of PKC that is found in neuronal cells and eye tissues. This isoform is activated by ROS such as H2O2. Mutations (H101Y, G118D, S119P, and G128D) in the PKCgamma Cys-rich C1B domain caused a form of dominant non-episodic cerebellar ataxia in humans (Chen, D.-H., Brkanac, Z., Verlinde, C. L. M. J., Tan, X.-J., Bylenok, L., Nochli, D., Matsushita, M., Lipe, H., Wolff, J., Fernandez, M., Cimino, P. J., Bird, T. D., and Raskind, W. H. (2003) Am. J. Hum. Genet. 72, 839-849; van de Warrenburg, B. P. C., Verbeek, D. S., Piersma, S. J., Hennekam, F. A. M., Pearson, P. L., Knoers, N. V. A. M., Kremer, H. P. H., and Sinke, R. J. (2003) Neurology 61, 1760-1765). This could be due to a failure of the mutant PKCgamma proteins to be activated by ROS and to subsequently inhibit gap junctions. The purpose of this study was to demonstrate the cellular mechanism of activation of PKCgamma by H2O2 and the resultant effects on gap junction activity. H2O2 stimulated PKCgamma enzyme activity independently of elevations in cellular diacylglycerol, the natural PKC activator. Okadaic acid, a phosphatase inhibitor, did not affect H2O2-stimulated PKCgamma activity, indicating that dephosphorylation was not involved. The reductant, dithiothreitol, abolished the effects of H2O2, suggesting a direct oxidation of PKCgamma at the Cys-rich C1 domain. H2O2 induced the C1 domain of PKCgamma to translocate to plasma membranes, whereas the C2 domain did not. Direct effects of H2O2 on PKCgamma were demonstrated using two-dimensional SDS-PAGE. Results demonstrated that PKCgamma formed disulfide bonds in response to H2O2. H2O2-activated PKCgamma was targeted into caveolin-1- and connexin 43-containing lipid rafts, and the PKCgamma phosphorylated the connexin 43 gap junction proteins on Ser-368. This resulted in disassembly of connexin 43 gap junction plaques and decreased gap junction activity. Results suggested that H2O2 caused oxidation of the C1 domain, activation of the PKCgamma, and inhibition of gap junctions. This inhibition of gap junctions could provide a protection to cells against oxidative stress.

An overview of the effect of linoleic and conjugated-linoleic acids on the growth of several human tumor cell lines

Both n-6 and n-3 polyunsaturated fatty acids are dietary fats important for cell function, being involved in several physiologic and pathologic processes, such as tumorigenesis. Linoleic acid and conjugated linoleic acid, its geometrical and positional stereoisomer, were tested on several human tumor cell lines originating from different tissues and with different degrees of malignancy. This was to provide the widest possible view of the impact of dietary lipids on tumor development. While linoleic acid exerted different effects, ranging from inhibitory to neutral, even promoting growth, conjugated linoleic acid inhibited growth in all lines tested and was particularly effective against the more malignant cells, with the exception of mammary tumor cells, in which behavior was the opposite, the more malignant cell line being less affected. The inhibitory effect of conjugated linoleic acid on growth may be accompanied by different contributions from apoptosis and necrosis. The effects of conjugated linoleic acid on growth or death involved positive or negative variations in PPARs. The important observation is that a big increase of PPARalpha protein occurred in cells undergoing strong induction of apoptosis, whereas PPARbeta/delta protein decreased. Although PPARalpha and PPARbeta/delta seem to be correlated to execution of the apoptotic program, the modulation of PPARgamma appears to depend on the type of tumor cell, increasing as protein content, when inhibition of cell proliferation occurred. In conclusion, CLA may be regarded as a component of the diet that exerts antineoplastic activity and its effect may be antiproliferative or pro-apoptotic.