Altered calcium handling following the recombinant overexpression of protein kinase C isoforms in HaCaT cells

Epoxytiglianes induce keratinocyte wound healing responses via classical protein kinase C activation to promote skin re-epithelialization

Epoxytiglianes are a novel class of diterpene esters. The prototype epoxytigliane, EBC-46 (tigilanol tiglate), is a potent anti-cancer agent in clinical development for local treatment of a range of human and animal tumors. EBC-46 also consistently promotes wound re-epithelialization at the treatment sites, mediated via activation of classical protein kinase C (PKC) isoforms. We have previously shown that epoxytiglianes stimulate proliferative and wound repopulation responses in immortalized human skin keratinocytes (HaCaTs) in vitro, abrogated by pan-PKC inhibitor, bisindolylmaleimide-1. In this study, we further investigate the specific PKC isoforms responsible for inducing such wound healing responses, following HaCaT treatment with 1.51 nM-15.1 µM EBC-46 or analogue, EBC-211. Classical PKC inhibition by GӦ6976 (1 μM), significantly attenuated epoxytigliane induced, HaCaT proliferation and wound repopulation at all epoxytigliane concentrations. PKC-βI/-βII isoform inhibition by enzastaurin (1 μM), significantly inhibited HaCaT proliferation and wound repopulation responses induced by both epoxytiglianes, especially at 1.51-151 nM. PKC-α inhibitor, Ro 31-8220 mesylate (10 nM), exerted lesser inhibitory effects on HaCaT responses. Epoxytigliane changes in key keratin (KRT17) and cell cycle (cyclin B1, CDKN1A) protein levels were partly attenuated by GӦ6976 and enzastaurin. GӦ6976 also inhibited increases in matrix metalloproteinase (MMP-1, MMP-7, MMP-10) activities. Phospho-PKC (p-PKC) studies confirmed that epoxytiglianes transiently activated classical PKC isoforms (p-PKCα, p-PKC-βI/-βII, p-PKCγ) in a dose- and time-dependent manner. By identifying how epoxytiglianes stimulate classical PKCs to facilitate keratinocyte healing responses and re-epithelialization, these findings support further epoxytigliane development as topical therapeutics for clinical situations involving impaired re-epithelialization, such as non-healing wounds in skin.

Pregnant Women and Endocrine Disruptors: Role of P2X7 Receptor and Mitochondrial Alterations in Placental Cell Disorders

In pregnant women, the lungs, skin and placenta are exposed daily to endocrine-disrupting chemicals (EDCs). EDCs induce multiple adverse effects, not only on endocrine organs, but also on non-endocrine organs, with the P2X7 cell death receptor being potentially the common key element. Our objective was first to investigate mechanisms of EDCs toxicity in both endocrine and non-endocrine cells through P2X7 receptor activation, and second, to compare the level of activation in lung, skin and placental cells. In addition, apoptosis in placental cells was studied because the placenta is the most exposed organ to EDCs and has essential endocrine functions. A total of nine EDCs were evaluated on three human cell models. We observed that the P2X7 receptor was not activated by EDCs in lung non-endocrine cells but was activated in skin and placenta cells, with the highest activation in placenta cells. P2X7 receptor activation and apoptosis are pathways shared by all tested EDCs in endocrine placental cells. P2X7 receptor activation along with apoptosis induction could be key elements in understanding endocrine placental and skin disorders induced by EDCs.

P2X7 receptor in skin biology and diseases

The P2X7 receptor is a trimeric ligand-gated cation channel present on immune and other cells. Activation of this receptor by its natural ligand extracellular adenosine triphosphate results in a variety of downstream responses, including the release of pro-inflammatory mediators and cell death. In normal skin, P2X7 is present on keratinocytes, Langerhans cells and fibroblasts, while the presence of this receptor on other cutaneous cells is mainly inferred from studies of equivalent cell types present in other tissues. Mast cells in normal skin however express negligible amounts of P2X7, which can be upregulated in cutaneous disease. This review discusses the potential significance of P2X7 in skin biology, and the role of this receptor in inflammatory skin disorders such as irritant and chronic dermatitis, psoriasis, graft-versus-host disease, as well is in wound healing, transplantation and skin cancer.

Endocannabinoids regulate growth and survival of human eccrine sweat gland-derived epithelial cells

The functional existence of the emerging endocannabinoid system (ECS), one of the new neuroendocrine players in cutaneous biology, is recently described in the human skin. In this study, using human eccrine sweat gland-derived immortalized NCL-SG3 model cells and a wide array of cellular and molecular assays, we investigated the effects of prototypic endocannabinoids (anandamide, 2-arachidonoylglycerol) on cellular functions. We show here that both endocannabinoids dose-dependently suppressed proliferation, induced apoptosis, altered expressions of various cytoskeleton proteins (e.g., cytokeratins), and upregulated lipid synthesis. Interestingly, as revealed by specific agonists and antagonists as well as by RNA interference, neither the metabotropic cannabinoid receptors (CB) nor the "ionotropic" CB transient receptor potential ion channels, expressed by these cells, mediated the cellular actions of the endocannabinoids. However, the endocannabinoids selectively activated the mitogen-activated protein kinase signaling pathway. Finally, other elements of the ECS (i.e., enzymes involved in the synthesis and degradation of endocannabinoids) were also identified on NCL-SG3 cells. These results collectively suggest that cannabinoids exert a profound regulatory role in the biology of the appendage. Therefore, from a therapeutic point of view, upregulation of endocannabinoid levels might help to manage certain sweat gland-derived disorders (e.g., tumors) characterized by unwanted growth.

Protein kinase C isoforms have differential roles in the regulation of human sebocyte biology

Protein kinase C (PKC) isoforms have crucial roles in cutaneous signaling. Interestingly, we lack information about their involvement in human sebaceous gland biology. Therefore, in this current study, we investigated the functions of the PKC system in human immortalized SZ95 sebocytes. Using molecular biological approaches, imaging, and functional assays, we report that SZ95 sebocytes express the conventional cPKCα; the novel nPKCδ, ɛ, and η; and the atypical aPKCζ. Activation of the PKC system by phorbol 12-myristate 13-acetate (PMA) stimulated lipid synthesis (a hallmark of differentiation) and resulted in translocation and then downregulation of cPKCα and nPKCδ. In good accord with these findings, the effect of PMA was effectively abrogated by inhibitors and short interfering RNA-mediated "silencing" of cPKCα and nPKCδ. Of further importance, molecular or pharmacological inhibition of nPKCδ also prevented the lipogenic and apoptosis-promoting action of arachidonic acid. Finally, we also found that "knockdown" of the endogenous aPKCζ activity markedly increased basal lipid synthesis and apoptosis, suggesting its constitutive activity in suppressing these processes. Collectively, our findings strongly argue for the fact that certain PKCs have pivotal, isoform-specific, differential, and antagonistic roles in the regulation of human sebaceous gland-derived sebocyte biology.

UV-B induced alteration in purinergic receptors and signaling on HaCaT keratinocytes

Although there are a number of recognized risk factors resulting in cutaneous malignancies, very little is known about the exact mechanism. In keratinocytes different purinergic receptors have been implicated to play essential roles in deciding the fate of the cells through regulating proliferation and differentiation. While P2Y receptors seem to control the former, P2X receptors, among which the P2X(7) receptor is associated with the induction of apoptosis, are likely to be responsible for the latter. Forty mJ/cm(2) UV-B irradiation decreased the number of viable cells as assessed using MTT assay. This irradiation decreased the amount of both P2X(1) and P2Y(2) receptors and essentially destroyed the P2X(7) receptors in surviving cells. Morphology of ATP-induced Ca(2+) transients were altered in irradiated cells compared to control. The amplitude and the rate of rise of the transients were decreased and the return to resting [Ca(2+)](i) prolonged. This observation is consistent with the finding that in control cells mostly ionotropic, while in irradiated cells mostly metabotropic receptors were underlying the response to ATP. These alterations in the expression pattern of purinergic receptors and in the Ca(2+) transients could explain the observed decreased tendency for ATP-induced apoptosis and possibly contribute to the malignant transformation of keratinocytes.

ATP signalling is crucial for the response of human keratinocytes to mechanical stimulation by hypo-osmotic shock

Touch is detected through receptors located in the skin and the activation of channels in sensory nerve fibres. Epidermal keratinocytes themselves, however, may sense mechanical stimulus and contribute to skin sensation. Here, we showed that the mechanical stimulation of human keratinocytes by hypo-osmotic shock releases adenosine triphosphate (ATP) and increases intracellular calcium. We demonstrated that the release of ATP was found to be calcium independent because emptying the intracellular calcium stores did not cause ATP release; ATP release was still observed in the absence of external calcium and it persisted on chelating cytosolic calcium. On the other hand, the released ATP activated purinergic receptors and mobilized intracellular calcium stores. The resulting depletion of stored calcium led to the activation of capacitative calcium entry. Increase in cytosolic calcium concentration was blocked by the purinergic receptor blocker suramin, phospholipase C inhibitor and apyrase, which hydrolyses ATP. Collectively, our data demonstrate that human keratinocytes are mechanically activated by hypo-osmotic shock, leading first to the release of ATP, which in turn stimulates purinergic receptors, resulting in the mobilization of intracellular calcium and capacitative calcium entry. These results emphasize the crucial role of ATP signalling in the transduction of mechanical stimuli in human keratinocytes.

Endocannabinoids modulate human epidermal keratinocyte proliferation and survival via the sequential engagement of cannabinoid receptor-1 and transient receptor potential vanilloid-1

We have recently shown that lipid mediators of the emerging endocannabinoid system (ECS) are key players of growth control of the human pilosebaceous unit. In this study, we asked whether the prototypic endocannabinoid anandamide (N-arachidonoylethanolamine, AEA) has a role in growth and survival of epidermal keratinocytes (KCs). Using human cultured KCs and skin organ-culture models, and by employing combined pharmacological and molecular approaches, we provide early evidence that AEA markedly suppresses KC proliferation and induces cell death, both in vitro and in situ. Moreover, we present that these cellular actions are mediated by a most probably constitutively active signaling mechanism that involves the activation of the metabotropic cannabinoid receptor CB(1) and a sequential engagement of the "ionotropic cannabinoid receptor" transient receptor potential vanilloid-1 (TRPV1). Finally, we demonstrate that the cellular effects of AEA are most probably due to a Ca(2+) influx via the non-selective, highly Ca(2+)-permeable ion channel TRPV1, and the concomitant elevation of intracellular Ca(2+) concentration. The data reported here may encourage one to explore whether the targeted manipulation of the above signaling pathway of the cutaneous ECS could become a useful adjunct treatment strategy for hyperproliferative human dermatoses such as psoriasis or KC-derived skin tumors.

Murine epidermal Langerhans cells and keratinocytes express functional P2X7 receptors

Extracellular ATP via the activation of purinergic P2 receptors has an emerging role in cutaneous biology; however, the distribution of these receptors in mouse skin is poorly defined. This study investigated whether murine epidermal cell subpopulations express functional purinergic P2X(7) receptors. P2X(7) expression was examined by immunoblotting and immunofluorescence staining of epidermal cells from C57Bl/6 mice. P2X(7) function was evaluated by nucleotide-induced ethidium(+) uptake measurements in epidermal cells from C57Bl/6 mice, and from P2X(7) deficient mice and wild-type littermate controls. P2X(7) was detected in whole epidermal cell preparations, and specifically on Langerhans cells (LCs) and keratinocytes (KCs). ATP induced ethidium(+) uptake into LCs and KCs, with EC(50) values of 503 and 482 microm, respectively. BzATP, and to a lesser extent ATPgammaS and ADP, also induced ethidium(+) uptake; while UTP, alphabeta-meth-ATP and NAD were ineffective. ATP-induced ethidium(+) uptake was impaired by Na(+) and Mg(2+), and the P2X(7) antagonist, A-438079 and was absent in LCs and KCs from P2X(7) deficient mice. These results demonstrate that murine LCs and KCs express functional P2X(7), and support a role for this receptor in cutaneous biology.

Butyl benzyl phthalate suppresses the ATP-induced cell proliferation in human osteosarcoma HOS cells

Butyl benzyl phthalate (BBP), an endocrine disruptor present in the environment, exerts its genomic effects via intracellular steroid receptors and elicits non-genomic effects by interfering with membrane ion-channel receptors. We previously found that BBP blocks the calcium signaling coupled with P2X receptors in PC12 cells (Liu & Chen, 2006). Osteoblast P2X receptors were recently reported to play a role in cell proliferation and bone remodeling. In this present study, the effects of BBP on ATP-induced responses were investigated in human osteosarcoma HOS cells. These receptors mRNA had been detected, named P2X4, P2X7, P2Y2, P2Y4, P2Y5, P2Y9, and P2Y11, in human osteosarcoma HOS cells by RT-PCR. The enhancement of cell proliferation and the decrease of cytoviability had both been shown to be coupled to stimulation via different concentrations of ATP. BBP suppressed the ATP-induced calcium influx (mainly coupled with P2X) and cell proliferation but not the ATP-induced intracellular calcium release (mainly coupled with P2Y) and cytotoxicity in human osteosarcoma HOS cells. Suramin, a common P2 receptor's antagonist, blocked the ATP-induced calcium signaling, cell proliferation, and cytotoxicity. We suggest that P2X is mainly responsible for cell proliferation, and P2Y might be partially responsible for the observed cytotoxicity. BBP suppressed the calcium signaling coupled with P2X, suppressing cell proliferation. Since the importance of P2X receptors during bone metastasis has recently become apparent, the possible toxic risk of environmental BBP during bone remodeling is a public problem of concern.