Secretory phospholipase A2 elicits proinflammatory changes and upregulates the surface expression of fas ligand in monocytic cells: potential relevance for atherogenesis

Producción CientíficaType IIA secretory phospholipase A2 (sPLA2) is an acute-phase reactant that plays a role in atherogenesis and is expressed in atherosclerotic arterial walls displaying inflammatory features. This generates a relevant question addressing the biological effects of this enzyme on monocytic cells, in view of the role of these cells in the inflammatory process associated with atherosclerosis. sPLA2 produced a mild activation of the p42 mitogen-activated protein module of the mitogen-activated protein kinase (MAPK) cascade and a prominent activation of c-Jun N-terminal kinase in THP-1 monocytes. This activation showed both an early and a late peak, different from that elicited by tumor necrosis factor-α (TNF-α), which only showed the first peak. This was accompanied by activation of arachidonate metabolism, as judged from both the activation of the cytosolic phospholipase A2 (cPLA2) and the induction of cyclooxygenase-2 (COX-2) expression. sPLA2 also elicited the production of monocyte chemoattractant protein-1 (MCP-1) and showed a synergistic effect with TNF-α on both COX-2 induction and MCP-1 production. sPLA2 upregulated the expression of Fas ligand at the cell surface, but it did not influence Fas expression nor cell survival of monocytes. In summary, these data indicate that some of the atherogenic effects of sPLA2 can be exerted by engagement of an sPLA2-binding structure on monocytic cells, most probably the M-type receptor for sPLA2, which produces the activation of the MAPK cascade, induces a proinflammatory phenotype, and upregulates the cell surface expression of Fas ligand.Plan Nacional de Salud y Farmacia (grant SAF98/0176)Comisión Interministerial de Ciencia y Tecnología - Comisión Europea (grant 1FD97-0590)Fondo de Investigación Sanitaria (grant FIS00/0393

Secretory phospholipase A2 activates the cascade of mitogen-activated protein kinases and cytosolic phospholipase A2 in the human astrocytoma cell line

Producción CientíficaThe biological effects of type IIA 14-kDa phospholipase A2 (sPLA2) on 1321N1 astrocytoma cells were studied. sPLA2 induced a release of [3H]arachidonic acid ([3H]AA) similar to that elicited by lysophosphatidic acid (LPA), a messenger acting via a G-protein-coupled receptor and a product of sPLA2 on lipid microvesicles. In contrast, no release of [1-14C]oleate could be detected in cells labeled with this fatty acid. As these findings pointed to a selective mechanism of [3H]AA release, it was hypothesized that sPLA2 could act by a signaling mechanism involving the activation of cytosolic PLA2 (cPLA2), i.e. the type of PLA2 involved in the release of [3H]AA elicited by agonists. In keeping with this view, stimulation of 1321N1 cells with sPLA2 elicited the decrease in electrophoretic mobility that is characteristic of the phosphorylation of cPLA2, as well as activation of p42 mitogen-activated protein (MAP) kinase, c-Jun kinase, and p38 MAP kinase. Incubation with sPLA2 of quiescent 1321N1 cells elicited a mitogenic response as judged from an increased incorporation of [3H]thymidine. Attempts to correlate the effect of extracellular PLA2 with the generation of LPA were negative. Incubation with pertussis toxin prior to the addition of either sPLA2 or LPA only showed abrogation of the response to LPA, thus suggesting the involvement of pertussis-sensitive Gi-proteins in the case of LPA. Treatments with inhibitors of the catalytic effect of sPLA2 such asp-bromophenacyl bromide and dithiothreitol did not prevent the effect on cPLA2 activation. In contrast, preincubation of 1321N1 cells with the antagonist of the sPLA2 receptorp-aminophenyl-α-d-mannopyranoside-bovine serum albumin, blocked cPLA2 activation with a EC50 similar to that described for the inhibition of binding of sPLA2 to its receptor. Moreover, treatment of 1321N1 cells with the MAP kinase kinase inhibitor PD-98059 inhibited the activation of both cPLA2 and p42 MAP kinase produced by sPLA2. In summary, these data indicate the existence in astrocytoma cells of a signaling pathway triggered by engagement of a sPLA2-binding structure, that produces the release of [3H]AA by activating the MAP kinase cascade and cPLA2, and leads to a mitogenic response after longer periods of incubation.Comisión Interministerial de Ciencia y Tecnología (grant PB94-1114

Cooperation between secretory phospholipase A2 and TNF-receptor superfamily signaling: Implications for the inflammatory response in atherogenesis

Producción CientíficaAtherogenesis is the consequence of a variety of effector mechanisms rather than the result of a single functional molecule. In this connection, type IIA secretory phospholipase A2 (sPLA2) is an acute-phase reactant, which accumulates in atherosclerotic arterial walls, elicits several effects on monocytes, and has been related to the development of atherosclerosis. CD40/CD40 ligand pair is also a strong proatherogenic system. sPLA2 produced an increase of the surface expression of CD40 in THP-1 monocytes and enhanced the effect of CD40 ligation on the expression of both Fas and FasL, thus indicating the existence of a positive cooperation between sPLA2 and different elements of the TNF-receptor superfamily. Activation of the CD40/CD40L dyad with anti-CD40 antibody produced a small release of arachidonic acid and lacked any significant effect on the induction of cyclooxygenase-2, whereas the secretion of the chemokine MCP-1 and the surface display of CD11b, the α chain of the integrin Mac-1, were upregulated. Engagement of CD40 did not influence the survival of THP-1 monocytes, but coincubation of THP-1 monocytes pretreated with anti-CD40 antibody and Jurkat cells induced a significant increase of the number of Jurkat cells showing binding of annexin-V, and nuclear condensation and fragmentation, thus indicating that this treatment might trigger a juxtacrine/paracrine mechanism of apoptotic death in sensitive cell types. This data indicates the existence of overlapping routes for the response to CD40, TNF-α, and sPLA2, thus allowing the development of distinct patterns of response in monocytic cells.Plan Nacional de Salud y Farmacia (grant SAF2001-0506)Fondo de Investigación Sanitaria (grant FIS00/0393)Junta de Castilla y León (grant HUV 1/02

Natural triterpenic diols promote apoptosis in astrocytoma cells through ROS-mediated mitochondrial depolarization and JNK activation

Producción CientíficaBackground: Triterpene alcohols and acids are multifunctional compounds widely distributed throughout the plant kingdom that exhibit a variety of beneficial health properties, being synthetic analogs of oleanolic acid under clinical evaluation as anti-tumoral therapeutic agents. However, the antineoplastic activity of two natural occuring triterpenoid alcohols extracted from olive oil, erythrodiol (an intermediate from oleanolic acid), and its isomer, uvaol, has barely been reported, particularly on brain cancer cells. Astrocytomas are among the most common and aggressive type of primary malignant tumors in the neurological system lacking effective treatments, and in this study, we addressed the effect of these two triterpenic diols on the human 1321N1 astrocytoma cell line. Principal Findings: Erythrodiol and uvaol effectively affected cell proliferation, as well as cell cycle phases and induced 1321N1 cell death. Both triterpenes successfully modulated the apoptotic response, promoting nuclear condensation and fragmentation. They caused retraction and rounding of cultured cells, which lost adherence from their supports, while F-actin and vimentin filaments disappeared as an organized cytoplasmic network. At molecular level, changes in the expression of surface proteins associated with adhesion or death processes were also observed. Moreover, triterpene exposure resulted in the production of reactive oxygen species (ROS) with loss of mitochondrial transmembrane potential, and correlated with the activation of c-Jun N-terminal kinases (JNK). The presence of catalase reversed the triterpenic diols-induced mitochondrial depolarization, JNK activation, and apoptotic death, indicating the critical role of ROS in the action of these compounds. Conclusions: Overall, we provide a significant insight into the anticarcinogenic action of erythrodiol and uvaol that may have a potential in prevention and treatment of brain tumors and other cancers.Ministerio de Ciencia e Innovación (grants SAF2005-01242, SAF2008-00245 and AGL2008-022845)Junta de Castilla y León (grant CSI11A08