Tumour necrosis factor stimulates stress-activated protein kinases and the inhibition of DNA synthesis in cultures of bovine aortic endothelial cells

Distinctive role of integrin-mediated adhesion in TNF-induced PKB/Akt and NF-κB activation and endothelial cell survival

Tumor necrosis factor (TNF) is a pro-inflammatory cytokine exerting pleiotropic effects on endothelial cells. Depending on the vascular context it can induce endothelial cell activation and survival or death. The microenvironmental cues determining whether endothelial cells will survive or die, however, have remained elusive. Here we report that integrin ligation acts permissive for TNF-induced protein kinase B (PKB/Akt) but not nuclear factor (NF)-kappaB activation. Concomitant activation of PKB/Akt and NF-kappaB is essential for the survival of endothelial cells exposed to TNF. Active PKB/Akt strengthens integrin-dependent endothelial cell adhesion, whereas disruption of actin stress fibers abolishes the protective effect of PKB/Akt. Integrin-mediated adhesion also represses TNF-induced JNK activation, but JNK activity is not required for cell death. The alphaVbeta3/alphaVbeta5 integrin inhibitor EMD121974 sensitizes endothelial cells to TNF-dependent cytotoxicity and active PKB/Akt attenuates this effect. Interferon gamma synergistically enhanced TNF-induced endothelial cell death in all conditions tested. Taken together, these observations reveal a novel permissive role for integrins in TNF-induced PKB/Akt activation and prevention of TNF-induced death distinct of NF-kappaB, and implicate the actin cytoskeleton in PKB/Akt-mediated cell survival. The sensitizing effect of EMD121974 on TNF cytotoxicity may open new perspectives to the therapeutic use of TNF as anticancer agent.

Active stress kinases in proliferating endothelial cells associated with cytoskeletal structures

It has become increasingly clear that stress-activated protein kinases have cytoplasmic substrates in addition to well-established transcription factor substrates in cell nuclei. The present study documented specific cytoplasmic locations of these enzymes in proliferating vascular cells. Immunofluorescent staining for active c-jun NH2-terminal kinase (JNK), the precipitation of JNK with microfilaments, and the loss of fiber-associated active JNK after cytochalasin treatment, but not nocodazole treatment, together indicate that active JNK is associated with stress fibers. The lack of complete scaffold colocalization and the total lack of immediate upsteam kinase colocalization along with the inability of JNK inhibitors to alter JNK-microfilament associations suggest that the microfilament association is not simply involved in enzyme activation. In addition, active p38 was found along with vinculin in focal adhesions. Although the p38 in focal adhesions could also be disrupted by cytochalasin treatment, it remained stable after nocodazole treatment. These results support the hypothesis that vascular cell stress kinase enzymes are important for signal transduction in the cytoplasm. The localization of active stress-activated protein kinases to specific cytoskeletal structures in proliferating cells suggests that subsets of these enzymes are involved in signal transduction to and/or from the cytoskeleton under conditions that include vascular cell proliferation.

p38 MAPK regulates phosphorylation of Bad via PP2A-dependent suppression of the MEK1/2-ERK1/2 survival pathway in TNF-alpha induced endothelial apoptosis

We recently reported that p38 MAPK regulates TNF-induced endothelial apoptosis via phosphorylation and downregulation of Bcl-xL. Here, we describe that such apoptosis includes p38 MAPK-mediated, protein phosphatase 2A (PP2A)-dependent, downregulation of the MEK-ERK pathway. Inhibition of PP2A with fostriecin or calyculin A significantly increased MEK phosphorylation, as did exposure to the p38 MAPK inhibitor SB203580. Inhibition of MEK potentiated TNF-induced caspase-3 activity and cell death, and both those events were suppressed by treatment with fostriecin or calyculin A. Immunoprecipitation experiments revealed an association between p38 MAPK, PP2A and MEK, and the results of a phosphatase assay suggested that PP2A is a downstream target of p38 MAPK. Importantly, phosphorylation of Bad at Ser-112 was found to be regulated by p38 MAPK and PP2A. In summary, the present findings indicate a novel p38 MAPK-mediated apoptosis pathway, involving activation of Bad via PP2A-dependent inhibition of the MEK-ERK pathway.

LSP1 is an endothelial gatekeeper of leukocyte transendothelial migration

Leukocyte-specific protein 1 (LSP1), an F-actin binding protein and a major downstream substrate of p38 mitogen-activated protein kinase as well as protein kinase C, has been reported to be important in leukocyte chemotaxis. Although its distribution has been thought to be restricted to leukocytes, herein we report that LSP1 is expressed in endothelium and is essential to permit neutrophil emigration. Using intravital microscopy to directly visualize leukocyte rolling, adhesion, and emigration in postcapillary venules in LSP1-deficient (Lsp1^−/−) mice, we found that LSP1 deficiency inhibits neutrophil extravasation in response to various cytokines (tumor necrosis factor-α and interleukin-1β) and to neutrophil chemokine keratinocyte-derived chemokine in vivo. LSP1 deficiency did not affect leukocyte rolling or adhesion. Generation of Lsp1^−/− chimeric mice using bone marrow transplantation revealed that in mice with Lsp1^−/− endothelial cells and wild-type leukocytes, neutrophil transendothelial migration out of postcapillary venules is markedly restricted. In contrast, Lsp1^−/− neutrophils in wild-type mice were able to extravasate normally. Consistent with altered endothelial function was a reduction in vascular permeability to histamine in Lsp1^−/− animals. Western blot analysis and immunofluorescence microscopy examination confirmed the presence of LSP1 in wild-type but not in Lsp1^−/− mouse microvascular endothelial cells. Cultured human endothelial cells also stained positive for LSP1. Our results suggest that LSP1 expressed in endothelium regulates neutrophil transendothelial migration.

p38 MAPK mediates TNF-induced apoptosis in endothelial cells via phosphorylation and downregulation of Bcl-x(L)

The role of p38 mitogen-activated protein kinase (MAPK) in apoptosis is a matter of debate. Here, we investigated the involvement of p38 MAPK in endothelial apoptosis induced by tumor necrosis factor alpha (TNF). We found that activation of p38 MAPK preceded activation of caspase-3, and the early phase of p38 MAPK stimulation did not depend on caspase activity, as shown by pretreatment with the caspase inhibitors z-Val-Ala-Asp(OMe)-fluoromethylketone (zVAD-fmk) and Boc-Asp(OMe)-fluoromethylketone (BAF). The p38 MAPK inhibitor SB203580 significantly attenuated TNF-induced apoptosis in endothelial cells, suggesting that p38 MAPK is essential for apoptotic signaling. Furthermore, we observed a time-dependent increase in active p38 MAPK in the mitochondrial subfraction of cells exposed to TNF. Notably, the level of Bcl-x(L) protein was reduced in cells undergoing TNF-induced apoptosis, and this reduction was prevented by treatment with SB203580. Immunoprecipitation experiments revealed p38 MAPK-dependent serine-threonine phosphorylation of Bcl-x(L) in TNF-treated cells. Exposure to lactacystin prevented both the downregulation of Bcl-x(L) and activation of caspase-3. Taken together, our results suggest that TNF-induced p38 MAPK-mediated phosphorylation of Bcl-x(L) in endothelial cells leads to degradation of Bcl-x(L) in proteasomes and subsequent induction of apoptosis.

Inhibition of lipopolysaccharide-induced macrophage IL-12 production by Leishmania mexicana amastigotes: the role of cysteine peptidases and the NF-kappaB signaling pathway

Infection with lesion-derived Leishmania mexicana amastigotes inhibited LPS-induced IL-12 production by mouse bone marrow-derived macrophages. This effect was associated with expression of cysteine peptidase B (CPB) because amastigotes of CPB deletion mutants had limited ability to inhibit IL-12 production, whereas preincubation of cells with a CPB inhibitor, cathepsin inhibitor IV, was able to suppress the effect of wild-type amastigotes. Infection with wild-type amastigotes resulted in a time-dependent proteolytic degradation of IkappaBalpha and IkappaBbeta and the related protein NF-kappaB. This effect did not occur with amastigotes of CPB deletion mutants or wild-type promastigotes, which do not express detectable CPB. NF-kappaB DNA binding was also inhibited by amastigote infection, although nuclear translocation of cleaved fragments of p65 NF-kappaB was still observed. Cysteine peptidase inhibitors prevented IkappaBalpha, IkappaBbeta, and NF-kappaB degradation induced by amastigotes, and recombinant CPB2.8, an amastigote-specific isoenzyme of CPB, was shown to degrade GST-IkappaBalpha in vitro. LPS-mediated IkappaBalpha and IkappaBbeta degradation was not affected by these inhibitors, confirming that the site of degradation of IkappaBalpha, IkappaBbeta, and NF-kappaB by the amastigotes was not receptor-driven, proteosomal-mediated cleavage. Infection of bone marrow macrophages with amastigotes resulted in cleavage of JNK and ERK, but not p38 MAPK, whereas preincubation with a cysteine peptidase inhibitor prevented degradation of these proteins, but did not result in enhanced protein kinase activation. Collectively, our results suggest that the amastigote-specific cysteine peptidases of L. mexicana are central to the ability of the parasite to modulate signaling via NF-kappaB and consequently inhibit IL-12 production.

Verotoxin activates mitogen-activated protein kinase in human peripheral blood monocytes: role in apoptosis and proinflammatory cytokine release

. In this study, we examined the role of mitogen-activated protein (MAP) kinases in the effects of verotoxins (VTs), from Escherichia coli O157:H7, upon both apoptosis and the release of tumour necrosis factor alpha (TNF-alpha) and granulocyte-macrophage colony-stimulated factor (GM-CSF) from human monocytes. 2. Both VT1 and VT2 stimulated a weak, transient increase in c-Jun-N-terminal kinase (JNK) activity and a strong activation of both p38 mitogen-activated protein kinase (MAP kinase) and extracellular-regulated kinase (ERK) activity in human monocytes, which was sustained in the case of p38 MAP kinase. 3. Stimulation of human monocytes with VT2 (100 ng ml-1) did not result in an increase in apoptosis; however, the toxin stimulated the release of both TNF-alpha and GM-CSF. 4. Pretreatment of human monocytes with the p38 MAP kinase inhibitor SB203580, at concentrations from 100 nM to 10 microM, significantly decreased the VT1- and VT2-induced TNF-alpha and GM-CSF release from monocytes. In contrast, inhibition of MEK1 with PD98059 only significantly decreased GM-CSF release. 5. Pretreatment of monocytes with SP600125 inhibited both GM-CSF and TNF-alpha production; however, significant effects upon p38 MAP kinase and ERK activation were observed. 6. Taken together, these results suggest a role for p38 MAP kinase and ERK in cytokine generation in response to the verotoxins. A role for JNK remains undetermined.

Tumor necrosis factor-alpha and troglitazone regulate plasminogen activator inhibitor type 1 production through extracellular signal-regulated kinase- and nuclear factor-kappaB-dependent pathways in cultured human umbilical vein endothelial cells

Plasminogen activator inhibitor type 1 (PAI-1) plays a role in the development of atherosclerosis in diabetic patients. PAI-1 is produced by endothelial cells stimulated with various inflammatory cytokines, such as tumor necrosis factor (TNF)-alpha, which induces insulin resistance. In diabetic patients, troglitazone, a thiazolidinedione, can lower the concentration of PAI-1. We investigated the TNF-alpha-induced signaling pathway that leads to PAI-1 synthesis and the target step of troglitazone in this pathway. TNF-alpha induced PAI-1 mRNA expression and protein production in human umbilical vein endothelial cells (HUVECs). A specific inhibitor for p38 mitogen-activated protein kinase, 4-(4-fluorophenyl)-2-(4-methylsulfinylphenyl)-5-(4-pyridyl)1H-imidazole (SB 203580), and a protein kinase C inhibitor, calphostin C, had no inhibitory effects on TNF-alpha-induced PAI-1 secretion. A protein tyrosine kinase inhibitor, genistein, completely inhibited TNF-alpha-induced PAI-1 secretion, whereas an inhibitor of extracellular signal-regulated kinase (ERK) kinase, 2'-amino-3'-methoxyflavone (PD98059), and a nuclear factor-kappaB (NF-kappaB) inhibitor, emodin, partly inhibited TNF-alpha-induced PAI-1 secretion. Together, PD98059 and emodin completely inhibited TNF-alpha-induced PAI-1 secretion, suggesting that both NF-kappaB-dependent and NF-kappaB-independent pathways are involved in TNF-alpha-induced signal pathway to PAI-1 production and that the latter pathway is mediated by activation of ERK. Furthermore, we have shown that troglitazone inhibited both TNF-alpha-induced PAI-1 protein secretion and mRNA in HUVECs. Genistein, but neither PD98059 nor emodin, was additive to the inhibitory effect of troglitazone on TNF-alpha-induced PAI-1 secretion. These results indicate That ERK and NF-kappaB are possible targets of TNF-alpha and troglitazone in the regulation of PAI-1 production.

TRAIL promotes the survival and proliferation of primary human vascular endothelial cells by activating the Akt and ERK pathways

BACKGROUND

TRAIL protein is expressed in the medial smooth cell layer of aorta and pulmonary artery, whereas endothelial cells express all TRAIL receptors (TRAIL-Rs).

METHODS AND RESULTS

The role of TRAIL/TRAIL-Rs in vascular biology was investigated in primary human umbilical vein endothelial cells (HUVECs) and aortic endothelial cells, which showed comparable surface expression of death (TRAIL-R1 and -R2) and decoy (TRAIL-R3 and -R4) TRAIL-Rs. TRAIL activated the protein kinase Akt in HUVECs, as assessed by Western blot for phospho-Akt. Moreover, experiments performed with a pharmacological inhibitor of the phosphatidylinositol 3-kinase/Akt pathway (LY294002) or a dominant-negative Akt (K179M) demonstrated that TRAIL significantly protected HUVECs from apoptosis induced by trophic withdrawal via Akt and that inhibition of Akt sensitized HUVECs to TRAIL-induced caspase-dependent apoptosis. TRAIL also stimulated the ERK1/2 but not the p38 or the JNK pathways and induced a significant increase in endothelial cell proliferation in an ERK-dependent manner. Conversely, TRAIL did not activate NF-kappaB or affect the surface expression of the inflammatory markers E-selectin, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1.

CONCLUSIONS

The ability of TRAIL to promote the survival/proliferation of endothelial cells without inducing NF-kappaB activation and inflammatory markers suggests that the TRAIL/TRAIL-R system plays an important role in endothelial cell physiology.

Survival pathways regulating the apoptosis induced by tumour necrosis factor-alpha in primary cultured bovine endothelial cells

The aim of the present study was to identify biochemical pathways driving the resistance of endothelial cells to apoptosis induced by tumour necrosis factor-alpha (TNF). (1) Although nuclear factor-kappa B (NF-kappaB) was activated by TNF, its inhibition by MG-132 failed to sensitize these cells. (2) The activation of protein kinase C (PKC) by phorbol ester completely abolished the TNF-induced cell death. (3) The phosphatidylinositol 3-kinase (PI3K) inhibitor wortmannin (Wo) triggered apoptosis and enhanced the TNF-induced cell death. (4) The MEK inhibitor PD98059 did not affect the TNF-induced apoptotic process. (5) The p38 is activated by TNF and its inhibition by SB203580 sensitized the cells to TNF. This is correlated with the inhibition of phosphorylation of heat-shock protein of 27 kDa (HSP27). These results indicate that TNF activates NF-kappaB, which does not drive any anti-apoptotic response, and p38, which plays an anti-apoptotic function probably through HSP27 phosphorylation. Moreover, PKC and PI3K are involved in the control of survival pathways.

Essential role for verotoxin in sustained stress-activated protein kinase and nuclear factor kappa B signaling, stimulated by Escherichia coli O157:H7 in Vero cells

The effects of Escherichia coli O157:H7 (strains E30480 and PM601) and the associated verotoxins (VTs), VT1 and VT2, on stress-activated protein kinase and nuclear factor kappa B (NF-kappaB) signaling were investigated with Vero cells, which are extremely sensitive to the cytotoxic effects of E. coli O157:H7 in vitro. Cell-free supernatants prepared from E30480 and PM601 cultures and purified VT1 and VT2 stimulated a strong and prolonged (>4-h) activation of both c-Jun N-terminal kinase (JNK) and p38 mitogen-activated protein kinase. However, JNK activity stimulated in response to E30480 supernatants was substantially reduced following pretreatment with anti-VT1 and anti-VT2 antibodies, while a VT1 and VT2 gene knockout mutant of PM601 was unable to stimulate JNK activity. E30480 supernatants also caused a sustained activation of NF-kappaB DNA binding, degradation of inhibitory kappa B alpha (IkappaBalpha), and an increase in inhibitory kappa B kinase alpha activity, although PM601 supernatants and VT1 and VT2 had no effect. However, preincubation with VTs prolonged the transient activation of NF-kappaB and IkappaBalpha degradation stimulated by either tumor necrosis factor alpha or interleukin 1beta, while preincubation with anti-VT antibodies prevented the prolonged loss of IkappaBalpha and partially reduced DNA binding in response to E30480 supernatants. These results strongly suggest that in Vero cells, VT plays an essential role in sustained JNK and NF-kappaB signaling in response to E. coli O157:H7 and that this action may underpin their cell-selective cytotoxic effects. These studies also suggest that another component released by strain E30480 contributes to the early activation of JNK and NF-kappaB.

TNF-alpha receptors simultaneously activate Ca2+ mobilisation and stress kinases in cultured sensory neurones

The cytokine tumour necrosis factor-alpha (TNF) has been implicated in autoimmune diseases and may play an indirect role in activation of pain pathways. In this study we have investigated the possibility that TNF directly activates cultured neonatal rat dorsal root ganglion (DRG) neurones and provides a signalling pathway from cells in the immune system such as macrophages to sensory neurones. Expression of TNF receptor subtypes (TNFR1 and TNFR2) on sensory neurones was identified using immunohistochemistry, fluorescence-activated cell sorting analysis and RT-PCR. Biochemical and immunocytochemical analysis showed that TNF activated p38 mitogen-activated protein kinase (p38MAPK) and c-Jun N-terminal kinase (JNK) but not p42/p44 MAPK. TNF treatment evoked transient Ca2+-dependent inward currents in 70% of DRG neurones. These TNF-evoked currents were significantly attenuated by ryanodine or thapsigargin or by inclusion of BAPTA in the patch pipette solution. Responses were also evoked in subpopulations of cultured DRG neurones by human mutant TNFs that cross-reacted with rat receptors and selectively activated TNFR1 or TNFR2 subtypes. TNF-evoked transient increases in [Ca2+]i were also detected in 34% of fura-2-loaded DRG neurones. The link between TNF receptor activation and Ca2+ release from stores remains to be elucidated. However, responses to TNF were mimicked by sphingolipids, including sphingosine-1-phosphate, which evoked a transient rises in [Ca2+]i in a pertussis toxin-insensitive manner in fura-2-loaded DRG neurones. We conclude that distinct receptors TNFR1 and TNFR2 are expressed on cultured DRG neurones and that they are functionally linked to intracellular Ca2+ mobilisation, a response that may involve sphingolipid signalling.

Nuclear factor kappa B is involved in lipopolysaccharide-stimulated induction of interferon regulatory factor-1 and GAS/GAF DNA-binding in human umbilical vein endothelial cells

1. In this study we examined the signalling events that regulate lipopolysaccharide (LPS)-stimulated induction of interferon regulatory factor (IRF)-1 in human umbilical vein endothelial cells (HUVECs). 2. LPS stimulated a time- and concentration-dependent increase in IRF-1 protein expression, an effect that was mimicked by the cytokine, tumour necrosis factor (TNF)-alpha. 3. LPS stimulated a rapid increase in nuclear factor kappa B (NFkappaB) DNA-binding activity. Pre-incubation with the NFkappaB pathway inhibitors, N-alpha-tosyl-L-lysine chloromethyl ketone (TLCK) or pyrrolidine dithiocarbamate (PDTC), or infection with adenovirus encoding IkappaBalpha, blocked both IRF-1 induction and NFkappaB DNA-binding activity. 4. LPS and TNFalpha also stimulated a rapid activation of gamma interferon activation site/gamma interferon activation factor (GAS/GAF) DNA-binding in HUVECs. Preincubation with the Janus kinase (JAK)-2 inhibitor, AG490 blocked LPS-stimulated IRF-1 induction but did not affect GAS/GAF DNA-binding. 5. Preincubation with TLCK, PDTC or infection with IkappaBalpha adenovirus abolished LPS-stimulated GAS/GAF DNA-binding. 6. Incubation of nuclear extracts with antibodies to RelA/p50 supershifted GAS/GAF DNA-binding demonstrating the involvement of NFkappaB isoforms in the formation of the GAS/GAF complex. 7. These studies show that NFkappaB plays an important role in the regulation of IRF-1 induction in HUVECs. This is in part due to the interaction of NFkappaB isoforms with the GAS/GAF complex either directly or via an intermediate protein.

FK506 promotes adenosine release from endothelial cells via inhibition of adenosine kinase

The immunosuppressants, cyclosporin A and tacrolimus (FK506) induce an increase in plasma levels of adenosine and mimic ischemic preconditioning. However, the mechanism of action of the two drugs on adenosine metabolism is not clear. Since inhibition of adenosine kinase promotes an increase in endogenous adenosine release, we tested a hypothesis that FK506 induces adenosine release via inhibition of adenosine kinase activity. In cultured endothelial cells, FK506 enhanced release of tracer adenosine and inhibited uptake of tracer adenosine. It also reduced adenosine kinase activity of the cell membrane fraction. In addition, FK506 does not inhibit membrane transport of tracer adenosine. These observations indicate that FK506 inhibits in situ adenosine kinase activity in endothelial cells. Other cell signaling inhibitors were found to inhibit adenosine uptake via inhibition of adenosine transport. In conclusion, FK506 promotes adenosine release from endothelial cells by a novel mechanism involving inhibition of adenosine kinase activity associated with the membrane.

TNF-alpha increases entry of macromolecules into luminal endothelial cell glycocalyx

The endothelial luminal glycocalyx has been largely ignored as a target in vascular pathophysiology even though it occupies a key location. As a model of the inflammatory response, we tested the hypothesis that tumor necrosis factor-alpha (TNF-alpha) can alter the properties of the endothelial apical glycocalyx. In the intact hamster cremaster microcirculation, fluorescein isothiocyanate (FITC)-labeled Dextrans 70, 580, and 2,000 kDa are excluded from a region extending from the endothelial surface almost 0.5 micrometer into the lumen. This exclusion zone defines the boundaries of the glycocalyx. Red blood cells (RBC) under normal flow conditions are excluded from a region extending even farther into the lumen. The cremaster microcirculation was pretreated with topical or intrascrotal applications of TNF-alpha. After infusion of FITC-dextran, FITC-albumin, or FITC-immunoglubulin G (IgG) via a femoral cannula, microvessels were observed with bright-field and fluorescence microscopy to obtain estimates of the anatomic diameters and the widths of fluorescent tracer columns and of the RBC columns (means +/- SE). After 2 h of intrascrotal TNF-alpha exposure, there was a significant increase in access of FITC-Dextrans 70 and 580 to the space bounded by the apical glycocalyx in arterioles, capillaries, and venules, but no significant change in access of FITC-Dextran 2,000. The effects of TNF-alpha could be observed as early as 20 min after the onset of topical application. TNF-alpha treatment also significantly increased the penetration rate of FITC-Dextran 40, FITC-albumin, and FITC-IgG into the glycocalyx and caused a significant increase in the intraluminal volume occupied by flowing RBC. White blood cell adhesion increased during TNF-alpha application, and we used the selectin antagonist fucoidan to attenuate leukocyte adhesion during TNF-alpha stimulation. This did not inhibit the TNF-alpha-mediated increase in permeation of the glycocalyx. These results show that proinflammatory cytokines can cause disruption of the endothelial apical glycocalyx, leading to an increased macromolecular permeation in the absence of an increase in leukocyte recruitment.

Functional CB1 cannabinoid receptors in human vascular endothelial cells

Cannabinoid CB1 receptor mRNA was detected using reverse transcription-polymerase chain reaction (RT-PCR) in endothelial cells from human aorta and hepatic artery and in the ECV304 cell line derived from human umbilical vein endothelial cells. CB1 receptor-binding sites were detected by the high-affinity antagonist radioligand [(125)I]AM-251. In ECV304 cells, both the highly potent synthetic cannabinoid agonist HU-210 and the endogenous ligand anandamide induce activation of mitogen-activated protein (MAP) kinase, and the effect of HU-210 was completely blocked, whereas the effect of anandamide was partially inhibited by SR141716A, a selective CB1 receptor antagonist. Transfection of ECV304 cells with CB1 receptor antisense, but not sense, oligonucleotides caused the same pattern of inhibition as SR141716A. This provides more definitive evidence for the involvement of CB1 receptors in MAP kinase activation and suggests that anandamide may also activate MAP kinase via an additional, CB1 receptor-independent, SR141716A-resistant mechanism. The MAP kinase activation by anandamide in ECV304 cells requires genistein-sensitive tyrosine kinases and protein kinase C (PKC), and anandamide also activates p38 kinase and c-Jun kinase. These findings indicate that CB1 receptors located in human vascular endothelium are functionally coupled to the MAP kinase cascade. Activation of protein kinase cascades by anandamide may be involved in the modulation of endothelial cell growth and proliferation.