Lysophosphatidylcholine mediates melanocyte dendricity through PKCzeta activation

Genetic Basis of Pigment Dispersion Syndrome and Pigmentary Glaucoma: An Update and Functional Insights

Pigment Dispersion Syndrome (PDS) and Pigmentary Glaucoma (PG) comprise a spectrum of ocular disorders characterized by iris pigment dispersion and trabecular meshwork changes, resulting in increased intraocular pressure and potential glaucomatous optic neuropathy. This review summarizes recent progress in PDS/PG genetics including rare pathogenic protein coding alterations (PMEL) and susceptibility loci identified from genome-wide association studies (GSAP and GRM5/TYR). Areas for future research are also identified, especially the development of efficient model systems. While substantial strides have been made in understanding the genetics of PDS/PG, our review identifies key gaps and outlines the future directions necessary for further advancing this important field of ocular genetics.

Decreased MARCKS Protein Expression in Kidney Cortex Membrane Fractions of Cathepsin B Knockout Mice Is Associated with Reduced Lysophosphatidylcholine and Protein Kinase C Activity

Cathpesin B is a multi-functional protease that plays numerous roles in physiology and pathophysiology. We hypothesized that actin cytoskeleton proteins that are substrates of cathepsin B, various lipids, and kinases that are regulated by lipids would be down-regulated in the kidney of cathepsin B knockout mice. Here, we show by Western blot and densitometric analysis that the expression and proteolysis of the actin cytoskeleton proteins myristoylated alanine-rich C-kinase substrate (MARCKS) and spectrin are significantly reduced in kidney cortex membrane fractions of cathepsin B knockout mice compared to C57B6 wild-type control mice. Lipidomic results show that specific lipids are increased while other lipids, including lysophosphatidylcholine (LPC) species LPC (16:0), LPC (18:0), LPC (18:1), and LPC (18:2), are significantly decreased in membrane fractions of the kidney cortex from Cathepsin B null mice. Protein Kinase C (PKC) activity is significantly lower in the kidney cortex of cathepsin B knockout mice compared to wild-type mice, while calcium/calmodulin-dependent protein kinase II (CaMKII) activity and phospholipase D (PLD) activity are comparable between the two groups. Together, these results provide the first evidence of altered actin cytoskeleton organization, membrane lipid composition, and PKC activity in the kidneys of mice lacking cathepsin B.

Lysophosphatidylcholine exerts an anti-skin photoaging effect via heat shock protein 70 induction

OBJECTIVE

Skin-brightening agents prevent melanogenesis and reduce melanin production. However, a lower melanin content leads to weaker protection against sunlight. In this study, we evaluated the effect of lysophosphatidylcholine (LPC) and its commercial-grade product, Lysofix Dry™ (LD), on heat shock protein 70 (HSP70) expression in epidermal cells and their anti-skin photoaging effect against ultraviolet B (UVB) and blue light.

METHODS

The HSP70 induction was detected using ELISA. To confirm the inhibition of melanin synthesis by LPC or LD, the melanin content assay and gene expression were analyzed. Cell viability was assessed to verify whether LPC or LD prevents photo-induced skin damage. The split-face test was performed to confirm skin-brightening effect of LD. Cream formulation with 2% of LD and placebo were used for 8 weeks, and skin brightness (L) was measured with chromameter (CR-400, Konica Minolta).

RESULTS

LPC- and LD-induced HSP70 expression in epidermal cells. LPC and LD effectively suppressed melanogenesis provoked by α-MSH in B16 cells. They also inhibited the mRNA transcription of MITF and tyrosinase under blue light irradiation. LD increased the viability of B16 and HaCaT cells after UVB and blue light irradiation in vitro. The cream containing 2% LD increased ΔL by 1.7 after 8 weeks of use, whereas the placebo led to an increase of 0.7.

CONCLUSION

LPC and LD were effective in suppressing melanogenesis and enhancing cell viability under UVB and blue light via HSP70 expression. Thus, they can be considered as potent skin-brightening agents with protective effects against skin photoaging.

Mechanisms of melanocyte polarity and differentiation: What can we learn from other neuroectoderm-derived lineages?

Melanocytes are neuroectoderm-derived pigment-producing cells with highly polarized dendritic morphology. They protect the skin against ultraviolet radiation by providing melanin to neighbouring keratinocytes. However, the mechanisms underlying melanocyte polarization and its relevance for diseases remain mostly elusive. Numerous studies have instead revealed roles for polarity regulators in other neuroectoderm-derived lineages including different neuronal cell types. Considering the shared ontogeny and morphological similarities, these lineages may be used as reference models for the exploration of melanocyte polarity, for example, regarding dendrite formation, spine morphogenesis and polarized organelle transport. In this review, we summarize and compare the latest progress in understanding polarity regulation in neuronal cells and melanocytes and project key open questions for future work.

Melanocyte Precursors in the Hair Follicle Bulge of Repigmented Vitiligo Skin Are Controlled by RHO-GTPase, KCTD10, and CTNNB1 Signaling

In repigmentation of human vitiligo, the melanocyte (MC) precursors in the hair follicle bulge proliferate, migrate, and differentiate to repopulate the depigmented epidermis. Here, we present a comprehensive characterization of pathways and signals in the bulge that control the repigmentation process. Using biopsies from patients with vitiligo, we have selectively harvested, by laser capture microdissection, MC and keratinocyte precursors from the hair follicle bulge of untreated vitiligo skin and vitiligo skin treated with narrow-band UVB. The captured material was subjected to whole transcriptome RNA-sequencing. With this strategy, we found that repigmentation in the bulge MC precursors is driven by KCTD10, a signal with unknown roles in the skin, and CTNNB1 (encoding β-catenin) and RHO guanosine triphosphatase [RHO GTPase, RHO], two signaling pathways previously shown to be involved in pigmentation biology. Knockdown studies in cultured human MCs of RHOJ, the upmost differentially expressed RHO family component, corroborated with our findings in patients with vitiligo, identified RHOJ involvement in UV response and melanization, and confirmed previously identified roles in melanocytic cell migration and apoptosis. A better understanding of mechanisms that govern repigmentation in MC precursors will enable the discovery of molecules that induce robust repigmentation phenotypes in vitiligo.

Sodium tanshinone IIA silate increases melanin synthesis by activating the MAPK and PKA pathways and protects melanocytes from H2O2-induced oxidative stress

Vitiligo is an intriguing depigmentation disorder that affects about 0.5–2% of the world population. In the past decade, first-line treatments of vitiligo have involved the use of calcineurin inhibitors and corticosteroids. Sodium tanshinone IIA sulfonate (STS) has been widely applied in the treatment of cardiovascular and cerebrovascular diseases in China. In the present study, the effect of STS on melanogenesis was confirmed in the B16F10 cells and zebrafish by direct observation. The prevention of hydrogen peroxide (H₂O₂)-induced oxidative stress has been proven to be beneficial to vitiligo patients, and STS that can protect the B16F10 cells against oxidative stress has been investigated in the present reversed study. Moreover, we found that pre-treatment with STS led to a concentration-dependent mitochondrial impairment and decreased cell apoptosis of the B16F10 cells in response to H₂O₂. In addition, we demonstrated that STS increased melanin synthesis in the B16F10 cells by activating the mitogen-activated protein kinase (MAPK) and protein kinase A (PKA) pathways. STS also increased the Cdc42 and KIF5b expression to stimulate the translocation of melanin. These results suggest that STS protects the B16F10 cells against H₂O₂-induced oxidative stress and exerts melanin synthesis activity in the B16F10 cells by activating the MAPK and PKA pathways; thus, it shows therapeutic potential for vitiligo.

Vitiligo is an intriguing depigmentation disorder that affects about 0.5–2% of the world population.

Molecular Genetics of Pigment Dispersion Syndrome and Pigmentary Glaucoma: New Insights into Mechanisms

We explore the ideas and advances surrounding the genetic basis of pigment dispersion syndrome (PDS) and pigmentary glaucoma (PG). As PG is the leading cause of nontraumatic blindness in young adults and current tailored interventions have proven ineffective, a better understanding of the underlying causes of PDS, PG, and their relationship is essential. Despite PDS being a subclinical disease, a large proportion of patients progress to PG with associated vision loss. Decades of research have supported a genetic component both for PDS and conversion to PG. We review the body of evidence supporting a genetic basis in humans and animal models and reevaluate classical mechanisms of PDS/PG considering this new evidence.

Novel pleiotropic effects of bioactive phospholipids in human lung cancer metastasis

We previously proposed that one of the unwanted side effects of chemotherapy and radiotherapy is the increase in several peptide- and non-peptide based chemoattractants in damaged tissues, leading to induction of a prometastatic microenvironment for remaining cancer cells. Herein, we turned out our attention to a potential role of bioactive phospholipids (BphsLs), such as sphingosine-1-phosphate (S1P), ceramide-1-phosphate (C1P), lysophosphatidylcholine (LPC), and lysophosphatidic acid (LPA) in lung cancer (LC) metastasis. We report that LC cells express several functional BphL receptors (for S1P, LPC, and LPA) as well as several enzymes involved in their metabolism and that BphsLs are potent chemokinetic and adhesion factors for these cells. We also demonstrate for the first time the novel role of C1P as a prometastatic factor in LC cells. In addition to their chemokinetic activities, BphsLs also sensitize or prime the chemotactic responsiveness of LC cells to known prometastatic factors such as hepatocyte growth factor/scatter factor (HGF/SF). Thus, for the first time we demonstrate a prometastatic effect that is based on the priming of a cell's responsiveness to chemotactic factors by chemokinetic factors. To our surprise, none of the bioactive lipids induced proliferation of LC cells or ameliorated toxic effects of vincristine treatment. Interestingly, BphsLs increase adhesion of LC cells to bone marrow-derived stromal cells and stimulate these cells to release ExNs, which additionally increase LC cell motility. In conclusion, our results show that BphsLs are important modulators of prometastatic environment. Therefore, their inhibitors could be considered as potential anti-metastatic drug candidates to be included as a part of post radio- and/or chemo- therapy treatment.

PKCζ phosphorylates TRAF2 to protect against intestinal ischemia-reperfusion-induced injury

Intestinal ischemia-reperfusion (I/R) is a common clinical problem that occurs during various clinical pathological processes. Excessive apoptosis has an indispensable role in intestinal I/R injury. Tumor necrosis factor receptor-associated factor 2 (TRAF2) and PKCζ have an essential role in apoptosis. Here, we aimed to investigate the effects of PKCζ and TRAF2 and to explore the correlation between PKCζ and TRAF2 in intestinal I/R injury. Mice were subjected to intestinal I/R injury in vivo. In vitro experiments were conducted by treating Caco-2 cells with hypoxia/reoxygenation (H/R) stimulation to simulate intestinal I/R. Intestinal tissue samples and Caco-2 cells were examined using various approaches. Intestinal I/R induced the membrane translocation and phosphorylation of PKCζ. Pretreatment with the PKCζ activator phosphatidylcholine remarkably attenuated gut injury by suppressing apoptosis. H/R induced PKCζ to combine with TRAF2, which was phosphorylated by PKCζ at Ser⁵⁵, but not at Ser¹¹, under intestinal I/R or H/R conditions. In addition, TRAF2 Ser⁵⁵ phosphorylation increased cell survival by inhibiting cell apoptosis in the H/R model. Mechanistically, TRAF2 Ser⁵⁵ phosphorylation promoted NF-κB activation but suppressed c-Jun activation in Caco-2 cells under H/R conditions. The results of this study demonstrate that the PKCζ/TRAF2 pathway represents a novel protective mechanism against intestinal I/R injury. Therefore, the PKCζ/TRAF2 pathway is a novel target for potential treatments of intestinal I/R injury-related diseases.

Role of phospholipases in adrenal steroidogenesis

Phospholipases are lipid-metabolizing enzymes that hydrolyze phospholipids. In some cases, their activity results in remodeling of lipids and/or allows the synthesis of other lipids. In other cases, however, and of interest to the topic of adrenal steroidogenesis, phospholipases produce second messengers that modify the function of a cell. In this review, the enzymatic reactions, products, and effectors of three phospholipases, phospholipase C, phospholipase D, and phospholipase A2, are discussed. Although much data have been obtained concerning the role of phospholipases C and D in regulating adrenal steroid hormone production, there are still many gaps in our knowledge. Furthermore, little is known about the involvement of phospholipase A2, perhaps, in part, because this enzyme comprises a large family of related enzymes that are differentially regulated and with different functions. This review presents the evidence supporting the role of each of these phospholipases in steroidogenesis in the adrenal cortex.

Dietary and biliary phosphatidylcholine activates PKCζ in rat intestine

Chylomicron output by the intestine is proportional to intestinal phosphatidylcholine (PC) delivery. Using five different variations of PC delivery to the intestine, we found that lyso-phosphatidylcholine (lyso-PC), the absorbed form of PC, concentrations in the cytosol (0 to 0.45 nM) were proportional to the input rate. The activity of protein kinase C (PKC)ζ, which controls prechylomicron output rate by the endoplasmic reticulum (ER), correlated with the lyso-PC concentration suggesting that it may be a PKCζ activator. Using recombinant PKCζ, the Km for lyso-PC activation was 1.49 nM and the Vmax 1.12 nM, more than the maximal lyso-PC concentration in cytosol, 0.45 nM. Among the phospholipids and their lyso derivatives, lyso-PC was the most potent activator of PKCζ and the only one whose cytosolic concentration suggested that it could be a physiological activator because other phospholipid concentrations were negligible. PKCζ was on the surface of the dietary fatty acid transport vesicle, the caveolin-1-containing endocytic vesicle. Once activated, PKCζ, eluted off the vesicle. A conformational change in PKCζ on activation was suggested by limited proteolysis. We conclude that PKCζ on activation changes its conformation resulting in elution from its vesicle. The downstream effect of dietary PC is to activate PKCζ, resulting in greater chylomicron output by the ER.

Synergy between enzastaurin doxorubicin in inducing melanoma apoptosis

Melanoma is resistant to most standard chemotherapeutics. We analysed the combined effect of doxorubicin and enzastaurin on cell death of four melanoma cell lines, namely G361, SK-MEL3, A375 and SAN. Enzastaurin IC50 was calculated by measure of growth inhibition with MTS assay and corresponded to 2 μM; the half maximal cytotoxicity of doxorubicin was obtained at 3 μM dose. Evaluation of combination index showed synergism (CI > 1) or additive effect (CI = 1) with all melanoma cell lines, with enzastaurin doses ≥0.6 μM and doxorubicin doses ≥1 μM. Combination of the two drugs resulted in increase in caspase 3 and 8 activation, in comparison with activation by single agents. Caspase 8 activation was impaired by TNFR-1 blocking. Our results show doxorubicin-stimulated production of TNFα, whereas enzastaurin-stimulated TNFR-1 expression on plasma membrane. The effect on TNFR-1 appeared to be mediated by PKCζ inhibition. Taken together, our findings suggest that enzastaurin increases doxorubicin-induced apoptosis of melanoma by a mechanism involving, at least in part, activation of the TNF-α signal.

Genetic modulation of the iris transillumination defect: a systems genetics analysis using the expanded family of BXD glaucoma strains

We investigated the contributions of Tyrp1 and Gpnmb to the iris transillumination defect (TID) in five age cohorts of BXD mice. Using systems genetics, we also evaluated the role of other known pigmentation genes (PGs). Mapping studies indicate that Tyrp1 contributes to the phenotype at all ages, yet the TID maps to Gpnmb only in the oldest cohort. Composite interval mapping reveals secondary loci viz. Oca2, Myo5a, Prkcz, and Zbtb20 that modulate the phenotype in the age groups up to 10–13 months. The contributions of Tyrp1 and Gpnmb were highly significant in all age cohorts. Moreover, in young mice, all six gene candidates had substantial interactions in our model. Our model accounted for 71–88% of the explained variance of the TID phenotype across the age bins. These results demonstrate that along with Tyrp1 and Gpnmb, Oca2, Myo5a, Prkcz, and Zbtb20 modulate the TID in an age-dependent manner.

Specifying protein kinase C functions in melanoma

The protein kinase C (PKC) family of serine/threonine protein kinases is a heterogeneous group of enzymes receiving and integrating signals involved in both normal melanocyte biology and melanoma pathology. Alterations in PKC enzyme expression and activation contribute to the malignant phenotype of melanoma in both oncogenic and tumor suppressive roles. Delineating the diverse and often context-dependent functions of PKC enzymes in melanocyte/melanoma biology is key to capitalize on these kinases as drug targets. This review summarizes several of the diverse functions of PKC in melanocyte and melanoma biology with a focus on PKC enzyme regulation and function.

Knowledge building insights on biomarkers of arsenic toxicity to keratinocytes and melanocytes

Exposure to inorganic arsenic induces skin cancer and abnormal pigmentation in susceptible humans. High-throughput gene transcription assays such as DNA microarrays allow for the identification of biological pathways affected by arsenic that lead to initiation and progression of skin cancer and abnormal pigmentation. The overall purpose of the reported research was to determine knowledge building insights on biomarker genes for arsenic toxicity to human epidermal cells by integrating a collection of gene lists annotated with biological information. The information sets included toxicogenomics gene-chemical interaction; enzymes encoded in the human genome; enriched biological information associated with genes; environmentally relevant gene sequence variation; and effects of non-synonymous single nucleotide polymorphisms (SNPs) on protein function. Molecular network construction for arsenic upregulated genes TNFSF18 (tumor necrosis factor [ligand] superfamily member 18) and IL1R2 (interleukin 1 Receptor, type 2) revealed subnetwork interconnections to E2F4, an oncogenic transcription factor, predominantly expressed at the onset of keratinocyte differentiation. Visual analytics integration of gene information sources helped identify RAC1, a GTP binding protein, and TFRC, an iron uptake protein as prioritized arsenic-perturbed protein targets for biological processes leading to skin hyperpigmentation. RAC1 regulates the formation of dendrites that transfer melanin from melanocytes to neighboring keratinocytes. Increased melanocyte dendricity is correlated with hyperpigmentation. TFRC is a key determinant of the amount and location of iron in the epidermis. Aberrant TFRC expression could impair cutaneous iron metabolism leading to abnormal pigmentation seen in some humans exposed to arsenicals. The reported findings contribute to insights on how arsenic could impair the function of genes and biological pathways in epidermal cells. Finally, we developed visual analytics resources to facilitate further exploration of the information and knowledge building insights on arsenic toxicity to human epidermal keratinocytes and melanocytes.

Aquaporin 9 phosphorylation mediates membrane localization and neutrophil polarization

Neutrophils are of prime importance in the host innate defense against invading microorganisms by using two primary mechanisms-locomotion toward and phagocytosis of the prey. Recent research points to pivotal roles for water channels known as AQPs in cell motility. Here, we focused on the role of AQP9 in chemoattractant-induced polarization and migration of primary mouse neutrophils and neutrophil-like HL60 cells. We found that AQP9 is phosphorylated downstream of fMLFR or PMA stimulation in primary human neutrophils. The dynamics of AQP9 were assessed using GFP-tagged AQP9 constructs and other fluorescent markers through various live-cell imaging techniques. Expression of WT or the phosphomimic S11D AQP9 changed cell volume regulation as a response to hyperosmotic changes and enhanced neutrophil polarization and chemotaxis. WT AQP9 and S11D AQP9 displayed a very dynamic distribution at the cell membrane, whereas the phosphorylation-deficient S11A AQP9 failed to localize to the plasma membrane. Furthermore, we found that Rac1 regulated the translocation of AQP9 to the plasma membrane. Our results show that AQP9 plays an active role in neutrophil volume regulation and migration. The display of AQP9 at the plasma membrane depends on AQP9 phosphorylation, which appeared to be regulated through a Rac1-dependent pathway.

Acidification in the epidermis and the role of secretory phospholipases

The function of the epidermis is to form an effective barrier between the dry, external environment and the interior of the body. The barrier specifically resides in the extracellular lipid membranes of the stratum corneum (SC) and an acidic pH is necessary to maintain its competency against various insults. The purpose of this review is to explore the mechanisms which are postulated to contribute to the acidification of the stratum corneum, including both exogenous and endogenous sources. However, recent research as pointed to several endogenous mechanisms as the major source of acidification, including a sodium/proton pump (NHE1) and free fatty acid conversion from phospholipids by secretory phospholipase A₂ (sPLA₂). sPLA₂ has been shown to play a central role in the formation of the SC “acid mantle” in the early maturation of the epidermis postnatally. Many aspects of this enzyme family are complex and still being elucidated in research and the most recent findings on the localization and functions of sPL A₂-IB, -IIA, -IIC, -IID, -IIE, -IIF, -III, -V, -X and -XII in the epidermis are presented here. Given their role in inflammatory dermatoses, such as psoriasis and atopic dermatitis, understanding this complex enzyme family can lead to novel, life-changing therapies.

Functional alterations in protein kinase C beta II expression in melanoma

Protein kinase C (PKC) is a heterogeneous family of serine/threonine protein kinases that have different biological effects in normal and neoplastic melanocytes (MCs). To explore the mechanism behind their differential response to PKC activation, we analyzed the expression profile of all nine PKC isoforms in normal human MCs, HPV16 E6/E7 immortalized MCs, and a panel of melanoma cell lines. We found reduced PKCbeta and increased PKCzeta and PKCiota expression at both the protein and mRNA levels in immortalized MCs and melanoma lines. We focused on PKCbeta as it has been functionally linked to melanin production and oxidative stress response. Re-expression of PKCbeta in melanoma cells inhibited colony formation in soft agar, indicating that PKCbeta loss in melanoma is important for melanoma growth. PKCbetaII, but not PKCbetaI, was localized to the mitochondria, and inhibition of PKCbeta significantly reduced UV-induced reactive oxygen species (ROS) in MCs with high PKCbeta expression. Thus alterations in PKCbeta expression in melanoma contribute to their neoplastic phenotype, possibly by reducing oxidative stress, and may constitute a selective therapeutic target.

Peripheral delivery of a ROCK inhibitor improves learning and working memory

Previously, utilizing a series of genome-wide association, brain imaging, and gene expression studies we implicated the KIBRA gene and the RhoA/ROCK pathway in hippocampal-mediated human memory. Here we show that peripheral administration of the ROCK inhibitor hydroxyfasudil improves spatial learning and working memory in the rodent model. This study supports the action of ROCK on learning and memory, suggests the potential value of ROCK inhibition for the promotion of cognition in humans, and highlights the powerful potential of unbiased genome-wide association studies to inform potential novel uses for existing pharmaceuticals.

Trypanosoma cruzi infection is enhanced by vector saliva through immunosuppressant mechanisms mediated by lysophosphatidylcholine

Trypanosoma cruzi, the etiological agent of Chagas disease, is transmitted by bug feces deposited on human skin during a blood meal. However, parasite infection occurs through the wound produced by insect mouthparts. Saliva of the Triatominae bug Rhodnius prolixus is a source of lysophosphatidylcholine (LPC). Here, we tested the role of both triatomine saliva and LPC on parasite transmission. We show that vector saliva is a powerful inducer of cell chemotaxis. A massive number of inflammatory cells were found at the sites where LPC or saliva was inoculated into the skin of mice. LPC is a known chemoattractant for monocytes, but neutrophil recruitment induced by saliva is LPC independent. The preincubation of peritoneal macrophages with saliva or LPC increased fivefold the association of T. cruzi with these cells. Moreover, saliva and LPC block nitric oxide production by T. cruzi-exposed macrophages. The injection of saliva or LPC into mouse skin in the presence of the parasite induces an up-to-sixfold increase in blood parasitemia. Together, our data suggest that saliva of the Triatominae enhances T. cruzi transmission and that some of its biological effects are attributed to LPC. This is a demonstration that a vector-derived lysophospholipid may act as an enhancing factor of Chagas disease.

Late sodium current in failing heart: friend or foe?

Most cardiac Na+ channels open transiently upon membrane depolarization and then are quickly inactivated. However, some channels remain active, carrying the so-called persistent or late Na+ current (INaL) throughout the action potential (AP) plateau. Experimental data and the results of numerical modeling accumulated over the past decade show the emerging importance of this late current component for the function of both normal and failing myocardium. INaL is produced by special gating modes of the cardiac-specific Na+ channel isoform. Heart failure (HF) slows channel gating and increases INaL, but HF-specific Na+ channel isoform underlying these changes has not been found. Na+ channels represent a multi-protein complex and its activity is determined not only by the pore-forming alpha subunit but also by its auxiliary beta subunits, cytoskeleton, calmodulin, regulatory kinases and phosphatases, and trafficking proteins. Disruption of the integrity of this protein complex may lead to alterations of INaL in pathological conditions. Increased INaL and the corresponding Na+ flux in failing myocardium contribute to abnormal repolarization and an increased cell Ca2+ load. Interventions designed to correct INaL rescue normal repolarization and improve Ca2+ handling and contractility of the failing cardiomyocytes. This review considers (1) quantitative integration of INaL into the established electrophysiological and Ca2+ regulatory mechanisms in normal and failing cardiomyocytes and (2) a new therapeutic strategy utilizing a selective inhibition of INaL to target both arrhythmias and impaired contractility in HF.

Prostaglandin E2 regulates melanocyte dendrite formation through activation of PKCzeta

Prostaglandins are lipid signaling intermediates released by keratinocytes in response to ultraviolet irradiation (UVR) in the skin. The main prostaglandin released following UVR is PGE(2), a ligand for 4 related G-protein-coupled receptors (EP(1), EP(2), EP(3) and EP(4)). Our previous work established that PGE(2) stimulates melanocyte dendrite formation through activation of the EP(1) and EP(3) receptors. The purpose of the present report is to define the signaling intermediates involved in EP(1)- and EP(3)-dependent dendrite formation in human melanocytes. We recently showed that activation of the atypical PKCzeta isoform stimulates melanocyte dendricity in response to treatment with lysophosphatidylcholine. We therefore examined the potential contribution of PKCzeta activation on EP(1)- and EP(3)-dependent dendrite formation in melanocytes. Stimulation of the EP(1) and EP(3) receptors by selective agonists activated PKCzeta, and inhibition of PKCzeta activation abrogated EP(1)- and EP(3)-receptor-mediated melanocyte dendricity. Because of the importance of Rho-GTP binding proteins in the regulation of melanocyte dendricity, we also examined the effect of EP(1) and EP(3) receptor activation on Rac and Rho activity. Neither Rac nor Rho was activated upon treatment with EP(1,3)-receptor agonists. We show that melanocytes express only the EP(3A1) isoform, but not the EP(3B) receptor isoform, previously associated with Rho activation, consistent with a lack of Rho stimulation by EP(3) agonists. Our data suggest that PKCzeta activation plays a predominant role in regulation of PGE(2)-dependent melanocyte dendricity.