蛋白磷酸酶2A的结构、功能和活性调节

蛋白磷酸酶 2A(proteinphosphatase 2A ,PP2A)是主要的丝 /苏氨酸蛋白磷酸酶 ,拥有众多不同基因编码的亚基 ,分别组成多种不同的PP2A全酶 ,参与细胞周期、DNA复制、信号转导、细胞分化和细胞恶性转化等多种细胞生物学事件 ,并和神经退行性疾病、肿瘤等多种疾病的发生、发展有关。PP2A调节亚基的组织特异性表达和细胞内定位 ,催化亚基羧基末端的磷酸化和甲基化 ,第二信使神经酰胺 (ceramide)、天然小分子抑制剂等都能够调节PP2A的活性。     

Indatraline inhibits Rho- and calcium-mediated glioblastoma cell motility and angiogenesis

Glioblastoma multiforme (GBM) is the most common and lethal primary brain tumor of the central nervous system (CNS). As an attempt to identify drugs for GBM therapeutics, phenotypic assays were used to screen 1000 chemicals from a clinical compound library. GBM subtypes exhibited different capabilities to induce angiogenesis when cultured on Matrigel; proneural cells migrated and formed a tube-like structure without endothelial cells. Among the compounds screened, indatraline, a nonselective monoamine transporter inhibitor, suppressed these morphological changes; it dose dependently inhibited cell spreading, migration, and in vitro/in vivo tube formation. In addition to intracellular calcium concentration, indatraline increased the level of Rho GTPase and its activity. Moreover, indatraline downregulated angiogenesis-related genes such as IGFBP2, PTN, VEGFA, PDGFRA, and VEGFR as well as nestin, a stem cell marker. These findings collectively suggest that the activation of Rho GTPase and the suppression of angiogenesis-related factors mediate the antiangiogenic activity of indatraline in proneural GBM culture.     

Protein kinase A‐mediated phosphorylation of naked cuticle homolog 2 stimulates cell‐surface delivery of transforming growth factor‐α for epidermal growth factor receptor transactivation

The classic mode of G protein‐coupled receptor (GPCR)‐mediated transactivation of the receptor tyrosine kinase epidermal growth factor receptor (EGFR) transactivation occurs via matrix metalloprotease (MMP)‐mediated cleavage of plasma membrane‐anchored EGFR ligands. Herein, we show that the Gαs‐activating GPCR ligands vasoactive intestinal peptide (VIP) and prostaglandin E₂ (PGE₂) transactivate EGFR through increased cell‐surface delivery of the EGFR ligand transforming growth factor‐α (TGFα) in polarizing madin‐darby canine kidney (MDCK) and Caco‐2 cells. This is achieved by PKA‐mediated phosphorylation of naked cuticle homolog 2 (NKD2), previously shown to bind TGFα and direct delivery of TGFα‐containing vesicles to the basolateral surface of polarized epithelial cells. VIP and PGE₂ rapidly activate protein kinase A (PKA) that then phosphorylates NKD2 at Ser‐223, a process that is facilitated by the molecular scaffold A‐kinase anchoring protein 12 (AKAP12). This phosphorylation stabilized NKD2, ensuring efficient cell‐surface delivery of TGFα and increased EGFR activation. Thus, GPCR‐triggered, PKA/AKAP12/NKD2‐regulated targeting of TGFα to the cell surface represents a new mode of EGFR transactivation that occurs proximal to ligand cleavage by MMPs.      

Rapid Activation of Bone Morphogenic Protein 9 by Receptor-mediated Displacement of Pro-domains

By non-covalent association after proteolytic cleavage, the pro-domains modulate the activities of the mature growth factor domains across the transforming growth factor-β family. In the case of bone morphogenic protein 9 (BMP9), however, the pro-domains do not inhibit the bioactivity of the growth factor, and the BMP9·pro-domain complexes have equivalent biological activities as the BMP9 mature ligand dimers. By using real-time surface plasmon resonance, we could demonstrate that either binding of pro-domain-complexed BMP9 to type I receptor activin receptor-like kinase 1 (ALK1), type II receptors, co-receptor endoglin, or to mature BMP9 domain targeting antibodies leads to immediate and complete displacement of the pro-domains from the complex. Vice versa, pro-domain binding by an anti-pro-domain antibody results in release of the mature BMP9 growth factor. Based on these findings, we adjusted ELISA assays to measure the protein levels of different BMP9 variants. Although mature BMP9 and inactive precursor BMP9 protein were directly detectable by ELISA, BMP9·pro-domain complex could only be measured indirectly as dissociated fragments due to displacement of mature growth factor and pro-domains after antibody binding. Our studies provide a model in which BMP9 can be readily activated upon getting into contact with its receptors. This increases the understanding of the underlying biology of BMP9 activation and also provides guidance for ELISA development for the detection of circulating BMP9 variants.     

Cumulin,an Oocyte-secreted Heterodimer of the Transforming Growth Factor-β Family,Is a Potent Activator of Granulosa Cells and Improves Oocyte Quality

Growth differentiation factor 9 (GDF9) and bone morphogenetic protein 15 (BMP15) are oocyte-specific growth factors with central roles in mammalian reproduction, regulating species-specific fecundity, ovarian follicular somatic cell differentiation, and oocyte quality. In the human, GDF9 is produced in a latent form, the mechanism of activation being an open question. Here, we produced a range of recombinant GDF9 and BMP15 variants, examined their in silico and physical interactions and their effects on ovarian granulosa cells (GC) and oocytes. We found that the potent synergistic actions of GDF9 and BMP15 on GC can be attributed to the formation of a heterodimer, which we have termed cumulin. Structural modeling of cumulin revealed a dimerization interface identical to homodimeric GDF9 and BMP15, indicating likely formation of a stable complex. This was confirmed by generation of recombinant heterodimeric complexes of pro/mature domains (pro-cumulin) and covalent mature domains (cumulin). Both pro-cumulin and cumulin exhibited highly potent bioactivity on GC, activating both SMAD2/3 and SMAD1/5/8 signaling pathways and promoting proliferation and expression of a set of genes associated with oocyte-regulated GC differentiation. Cumulin was more potent than pro-cumulin, pro-GDF9, pro-BMP15, or the two combined on GC. However, on cumulus-oocyte complexes, pro-cumulin was more effective than all other growth factors at notably improving oocyte quality as assessed by subsequent day 7 embryo development. Our results support a model of activation for human GDF9 dependent on cumulin formation through heterodimerization with BMP15. Oocyte-secreted cumulin is likely to be a central regulator of fertility in mono-ovular mammals.     

Ixodid tick salivary gland products target host wound healing growth factors

For successful blood-feeding, ticks must confront the host immune system comprising many cells and signaling molecules, mainly cytokines and growth factors. These factors bind to specific receptors on the cell membranes, thereby initiating a signaling cascade that leads to distinct cellular activities. Ticks are able to manipulate host immune responses via molecules secreted from their salivary glands. Saliva of ixodid ticks contains factors binding important cytokines and their subgroup, chemokines. Here we demonstrate that constituents of tick salivary gland extract (SGE) also appear to bind growth factors: transforming growth factor beta (TGF-β1), platelet-derived growth factor (PDGF), fibroblast growth factor (FGF-2), and hepatocyte growth factor (HGF), depending on tick species. SGE derived from Amblyommavariegatum reacted with TGF-β1, PDGF, FGF-2 and HGF; Dermacentorreticulatus and Rhipicephalusappendiculatus with TGF-β1, FGF-2 and HGF; and Ixodes ricinus and Ixodesscapularis with PDGF. SGE from the species targeting PDGF (A. variegatum and I. ricinus) also inhibited cell proliferation in vitro and induced a change in morphology of different cell lines. These effects correlated with disruption of the actin cytoskeleton. Such effects were not observed with SGE of the two species that did not target PDGF. Targeting of wound healing growth factors appears to be yet another strategy ixodid ticks adopt for suppression of inflammation and successful haematophagy.     

关于脑心肌炎病毒2A蛋白的研究进展

脑心肌炎病毒(Encephalomyocarditis virus,EMCV)是一种无囊膜的单股RNA病毒,属于小RNA病毒科,能够引起多种哺乳动物乃至人的感染。其非结构蛋白2A是重要的毒力因子,能够通过阻断翻译起始复合物的形成、结合翻译起始复合物因子及核糖体40s小亚基等方式竞争性地抑制宿主细胞蛋白的合成,还可通过抑制宿主细胞凋亡促进病毒扩散,并通过激活NF-κB引起宿主发生强烈的炎症反应[1]。此外,根据EMCV 2A蛋白的生物学特性,近年来,细胞生物学、病毒学领域均将其作为真核细胞与病毒互作的生物学工具展开了深入研究。     

Structure and stability effects of mutations designed to increase the primary sequence symmetry within the core region of a β-trefoil

Human acidic fibroblast growth factor (FGF-1) is a member of the beta-trefoil hyperfamily and exhibits a characteristic threefold symmetry of the tertiary structure. However, evidence of this symmetry is not readily apparent at the level of the primary sequence. This suggests that while selective pressures may exist to retain (or converge upon) a symmetric tertiary structure, other selective pressures have resulted in divergence of the primary sequence during evolution. Using intra-chain and homologue sequence comparisons for 19 members of this family of proteins, we have designed mutants of FGF-1 that constrain a subset of core-packing residues to threefold symmetry at the level of the primary sequence. The consequences of these mutations regarding structure and stability were evaluated using a combination of X-ray crystallography and differential scanning calorimetry. The mutational effects on structure and stability can be rationalized through the characterization of "microcavities" within the core detected using a 1.0A probe radius. The results show that the symmetric constraint within the primary sequence is compatible with a well-packed core and near wild-type stability. However, despite the general maintenance of overall thermal stability, a noticeable increase in non-two-state denaturation follows the increase in primary sequence symmetry. Therefore, properties of folding, rather than stability, may contribute to the selective pressure for asymmetric primary core sequences within symmetric protein architectures.     

Structural Model of the Human BTG2–PABPC1 Complex by Combining Mutagenesis,NMR Chemical Shift Perturbation Data and Molecular Docking

Degradation of cytoplasmic mRNA in eukaryotes involves the shortening and removal of the mRNA poly(A) tail by poly(A)-selective ribonuclease (deadenylase) enzymes. In human cells, BTG2 can stimulate deadenylation of poly(A) bound by cytoplasmic poly(A)-binding protein PABPC1. This involves the concurrent binding by BTG2 of PABPC1 and the Caf1/CNOT7 nuclease subunit of the Ccr4-Not deadenylase complex. To understand in molecular detail how PABPC1 and BTG2 interact, we set out to identify amino acid residues of PABPC1 and BTG2 contributing to the interaction. To this end, we first used algorithms to predict PABPC1 interaction surfaces. Comparison of the predicted interaction surface with known residues involved in the binding to poly(A) resulted in the identification of a putative interaction surface for BTG2. Subsequently, we used pulldown assays to confirm the requirement of PABPC1 residues for the interaction with BTG2. Analysis of RNA-binding by PABPC1 variants indicated that PABPC1 residues required for interaction with BTG2 do not interfere with poly(A) binding. After further defining residues of BTG2 that are required for the interaction with PABPC1, we used information from published NMR chemical shift perturbation experiments to guide docking and generate a structural model of the BTG2-PABPC1 complex. A quaternary poly(A)-PABPC1-BTG2-Caf1/CNOT7 model showed that the 3′ end of poly(A) RNA is directed towards the catalytic centre of Caf1/CNOT7, thereby providing a rationale for enhanced deadenylation by Caf1/CNOT7 in the presence of BTG2 and PABPC1.     

A novel adipokine GM2AP impairs insulin signaling

In an attempt to discover novel adipokines, we performed proteomics analyses using culture medium from differentiated 3T3-L1 adipocytes, and first identified GM2AP. The levels of GM2AP mRNA and protein were augmented by adipogenesis in cultured adipocytes and expression in adipose tissue and serum of obese mice or human subjects was found to be significantly higher than in lean counterparts. Exposure of 3T3-L1 adipocytes to GM2AP protein accelerated dissociation of insulin receptor-beta (IRβ) from caveolin-1, and interrupted insulin signal transduction. Abrogation of GM2AP function by specific antibodies augmented glucose uptake. Furthermore, treatment of rat pheochromocytoma PC12 NS1 cells with GM2AP impaired NGF signal transduction. Taken together, these results provide novel insights into the physiological functions of GM2AP in obesity.     

丁酸钠至少部分通过NF-Y 依赖的TXNIP 表达诱导人肺癌细胞A549死亡

组蛋白去乙酰化酶（HDACs）抑制剂丁酸钠调节细胞分化、增殖和抑制肿瘤发生。硫氧还蛋白相互作用蛋白( thioredoxin-interacting protein,TXNIP)通过负性调控硫氧还蛋白的活性,调控细胞内的氧化还原平衡,抑制细胞生长。本研究证明,丁酸钠可通过激活依赖于转录因子NF-Y的TXNIP 表达,诱导人非小细胞肺癌细胞A549死亡。MTT法显示,5 mmol/L丁酸钠处理A549 细胞72 h可显著诱导其死亡;流式细胞分析发现,其中大部分细胞以凋亡形式死亡。表达芯片分析表明,在丁酸钠处理的A549 细胞中,TXNIP 的mRNA 水平显著提高30～50倍;实时定量PCR、免疫细胞化学和蛋白质印迹结果进一步证明,丁酸钠可显著上调TXNIP 表达。荧光素酶报告基因分析证明,与对照细胞比较,丁酸钠刺激的细胞内报告酶活性可提高约10 倍,提示丁酸钠可激活TXNIP 启动子的转录活性。TXNIP 启动子删除突变分析显示,删除NF-Y 结合的DNA 序列显著降低丁酸钠对TXNIP 启动子的激活能力, 表明NF-Y转录因子参与丁酸钠介导的TXNIP基因转录激活。为分析TXNIP 在A549 细胞中的定位和部分功能,在A549细胞 中过表达GFP TXNIP 融合蛋白及其截短突变体融合蛋白;结果显示,野生型和保留N 端1-281aa的截短突变体定位在细胞核,而删除N 端1-200aa 时,其定位在细胞核和细胞质,提示N 端1 200aa 可调节该蛋白质的定位。然而,丁酸钠刺激未发现表达的GFP TXNIP在细胞内定位改变。以上结果表明,丁酸钠可通过激活转录因子NF YC 依赖的TXNIP激活,诱导A549 细胞死亡,但不能改变TXNIP蛋白在细胞内的定位。上述结果还提示,TXNIP 的N 端1-200aa 可能在调节TXNIP 的细胞定位中发挥作用。是否丁酸钠刺激TXNIP表达导致的细胞死亡系通过改变细胞氧化压力,以及TXNIP在细胞中定位的详尽调节机制尚待进一步研究证明。     

TGFβ induces proHB-EGF shedding and EGFR transactivation through ADAM activation in gastric cancer cells

Background and aims: Transforming growth factor-beta (TGFβ) is known to potently inhibit cell growth. Loss of responsiveness to TGFβ inhibition on cell growth is a hallmark of many types of cancer, yet its mechanism is not fully understood. Membrane-anchored heparin-binding EGF-like growth factor (proHB-EGF) ectodomain is cleaved by a disintegrin and metalloproteinase (ADAM) members and is implicated in epidermal growth factor receptor (EGFR) transactivation. Recently, nuclear translocation of the C-terminal fragment (CTF) of pro-HB-EGF was found to induce cell growth. We investigated the association between TGFβ and HB-EGF signal transduction via ADAM activation.Materials and methods: The CCK-8 assay in two gastric cancer cell lines was used to determine the effect for cell growth by TGFβ. The effect of two ADAM inhibitors was also evaluated. Induction of EGFR phosphorylation by TGFβ was analyzed and the effect of the ADAM inhibitors was also examined. Nuclear translocation of HB-EGF-CTF by shedding through ADAM activated by TGFβ was also analyzed. EGFR transactivation, HB-EGF-CTF nuclear translocation, and cell growth were examined under the condition of ADAM17 knockdown.Result: TGFβ-induced EGFR phosphorylation of which ADAM inhibitors were able to inhibit. TGFβ induced shedding of proHB-EGF allowing HB-EGF-CTF to translocate to the nucleus. ADAM inhibitors blocked this nuclear translocation. TGFβ enhanced gastric cancer cell growth and ADAM inhibitors suppressed this effect. EGFR phosphorylation, HB-EGF-CTF nuclear translocation, and cell growth were suppressed in ADAM17 knockdown cells.Conclusion: HB-EGF-CTF nuclear translocation and EGFR transactivation from proHB-EGF shedding mediated by ADAM17 activated by TGFβ might be an important pathway of gastric cancer cell proliferation by TGFβ.     

Targeting SHP2 for EGFR inhibitor resistant non-small cell lung carcinoma

Targeted therapy with inhibitors of epidermal growth factor receptor (EGFR) has produced a noticeable benefit to non-small cell lung cancer (NSCLC) patients whose tumors carry activating mutations (e.g. L858R) in EGFR. Unfortunately, these patients develop drug resistance after treatment, due to acquired secondary gatekeeper mutations in EGFR (e.g. T790M). Given the critical role of SHP2 in growth factor receptor signaling, we sought to determine whether targeting SHP2 could have therapeutic value for EGFR inhibitor resistant NSCLC. We show that SHP2 is required for EGF-stimulated ERK1/2 phosphorylation and proliferation in EGFR inhibitor resistant NSCLC cell line H1975, which harbors the EGFR T790M/L858R double-mutant. We demonstrate that treatment of H1975 cells with II-B08, a specific SHP2 inhibitor, phenocopies the observed growth inhibition and reduced ERK1/2 activation seen in cells treated with SHP2 siRNA. Importantly, we also find that II-B08 exhibits marked anti-tumor activity in H1975 xenograft mice. Finally, we observe that combined inhibition of SHP2 and PI3K impairs both the ERK1/2 and PI3K/AKT signaling axes and produces significantly greater effects on repressing H1975 cell growth than inhibition of either protein individually. Collectively, these results suggest that targeting SHP2 may represent an effective strategy for treatment of EGFR inhibitor resistant NSCLCs.     

Improving clinical prediction rules in acute kidney injury with the use of biomarkers of cell cycle arrest: a pilot study

Introduction: Early recognition of patients developing acute kidney injury (AKI) is of considerable interest, we report the first use of a combination of a clinical prediction rule with a biomarker in emergent adult medical patients to improve AKI recognition.

Methods: Single-centre prospective pilot study of medical admissions without AKI identified as high risk by a clinical prediction rule. Urine samples were obtained and tissue inhibitor of metalloproteinases-2 (TIMP-2) and insulin-like growth factor binding protein 7 (IGFBP7) – biomarkers associated with cell cycle arrest, were measured.

Outcome: Creatinine-based KDIGO hospital-acquired AKI (HA-AKI).

Results: Of 69 patients recruited, HA-AKI developed in 13% (n?=?9), in whom biomarker values were higher (median 0.43 (interquartile range (IQR) 0.21–1.25) vs. 0.07 (0.03–0.16) in cases without (p?=?0.008). Peak rise in creatinine was higher in biomarker positive cases (median 30?μmol/L (7–72) vs. 1?μmol/L (0–16), p?=?0.002). AUROC was 0.78 (95% CI 0.57–0.98). At the suggested cut-off (0.3) sensitivity for predicting AKI was 78% (95% CI 40–97%), specificity 89% (78–95%), positive predictive value 50% (31–69%) and negative predictive value 96% (89–99%).

Discussion: Addition of a urinary biomarker allows exclusion of a significant number of patients identified to be at higher risk of AKI by a clinical prediction rule.     

Stepwise assembly of the eukaryotic translation initiation factor 2 complex

The eukaryotic translation initiation factor 2 (eIF2) has key functions in the initiation step of protein synthesis. eIF2 guides the initiator tRNA to the ribosome, participates in scanning of the mRNA molecule, supports selection of the start codon, and modulates the translation of mRNAs in response to stress. eIF2 comprises a heterotrimeric complex whose assembly depends on the ATP-grasp protein Cdc123. Mutations of the eIF2γ subunit that compromise eIF2 complex formation cause severe neurological disease in humans. To this date, however, details about the assembly mechanism, step order, and the individual functions of eIF2 subunits remain unclear. Here, we quantified assembly intermediates and studied the behavior of various binding site mutants in budding yeast. Based on these data, we present a model in which a Cdc123-mediated conformational change in eIF2γ exposes binding sites for eIF2α and eIF2β subunits. Contrary to an earlier hypothesis, we found that the associations of eIF2α and eIF2β with the γ-subunit are independent of each other, but the resulting heterodimers are nonfunctional and fail to bind the guanosine exchange factor eIF2B. In addition, levels of eIF2α influence the rate of eIF2 assembly. By binding to eIF2γ, eIF2α displaces Cdc123 and thereby completes the assembly process. Experiments in human cell culture indicate that the mechanism of eIF2 assembly is conserved between yeast and humans. This study sheds light on an essential step in eukaryotic translation initiation, the dysfunction of which is linked to human disease.     

Curcumin and its derivatives inhibit 2,3,7,8,-tetrachloro-dibenzo-p-dioxin-induced expression of drug metabolizing enzymes through aryl hydrocarbon receptor-mediated pathway

Abstract

Certain dioxins, including 2,3,7,8,-tetrachloro-dibenzo-p-dioxin (TCDD), are exogenous ligands for an aryl hydrocarbon receptor (AhR) and induces various drug-metabolizing enzymes. In this study, we examined the effect of curcumin on expression of drug-metabolizing enzymes through the AhR and NF-E2 related factor 2 (Nrf2) pathways. Curcumin dose-dependently inhibited TCDD-induced expression of phase I enzyme cytochrome P450 1A1 (CYP1A1) and phase II enzymes NAD(P)H:quinone oxidoreductase-1 (NQO1) and heme oxygenase 1 (HO-1) but not tert-butyl hydroquinone-induced NQO1 and HO-1, suggesting that curcumin inhibited only AhR pathway, but not Nrf2 one directly. Furthermore, we used 14 curcumin derivatives and obtained the correlation between hydrophobicity of the compounds and suppressive effect against AhR transformation. Results from the quantitative structure active correlative analysis indicated that methoxy groups and β-diketone structure possessing keto-enol tautomerism in curcumin were necessary to inhibit AhR transformation, and the addition of methyl and methoxy group(s) to the curcumin increased the inhibition effect.     

MAP2 IHC detection: a marker of antigenicity in CNS tissues

Immunohistochemistry (IHC) is used to detect antibody-specific antigens in tissues; the results depend on the ability of the primary antibodies to bind to their antigens. Therefore, results depend on the quality of preservation of the specimen. Many investigators have overcome the deleterious effects of over-fixation on the binding of primary antibodies to specimen antigens using IHC, but if the specimen is under-fixed or fixation is delayed, false negative results could be obtained despite certified laboratory practices. Microtubule-associated protein 2 (MAP2) is an abundant microtubule-associate protein that participates in the outgrowth of neuronal processes and synaptic plasticity; it is localized primarily in cell bodies and dendrites of neurons. MAP2 immunolabeling has been reported to be absent in areas of the entorhinal cortex and hippocampus of Alzheimer’s disease brains that were co-localized with the dense-core type of amyloid plaques. It was hypothesized that the lack of MAP2 immunolabeling in these structures was due to the degradation of the MAP2 antigen by the neuronal proteases that were released as the neurons lysed leading to the formation of these plaques. Because MAP2 is sensitive to proteolysis, we hypothesized that changes in MAP2 immunolabeling may be correlated with the degree of fixation of central nervous system (CNS) tissues. We detected normal MAP2 immunolabeling in fixed rat brain tissues, but MAP2 immunolabeling was decreased or lost in unfixed and delayed-fixed rat brain tissues. By contrast, two ubiquitous CNS-specific markers, myelin basic protein and glial fibrillary acidic protein, were unaffected by the degree of fixation in the same tissues. Our observations suggest that preservation of various CNS-specific antigens differs with the degree of fixation and that the lack of MAP2 immunolabeling in the rat brain may indicate inadequate tissue fixation. We recommend applying MAP2 IHC for all CNS tissues as a pre-screen to assess the quality of the tissue preservation and to avoid potentially false negative IHC results.     

Bimodal regulatory effect of melittin and phospholipase A2-activating protein on human type II secretory phospholipase A2

Melittin and phospholipase A2-activating protein (PLAP) are known as efficient activators of secretory phospholipase A2(sPLA2) types I, II, and III when phospholipid liposomes are used as substrate. The present study demonstrates that both peptides can either inhibit or activate sPLA2 depending on the peptide/phospholipid ratio when erythrocyte membranes serve as a biologically relevant substrate. Low concentrations of melittin and PLAP were observed to inhibit sPLA2-triggered release of fatty acids from erythrocyte membranes. The inhibition was reversed at melittin concentrations above 1 microM. PLAP-induced inhibition of sPLA2 persisted steadily throughout the used concentration range (0-150 nM). The two peptides induced a dose-dependent activation of sPLA2 at low concentrations, followed by inhibition when model membranes were used as substrate. This opposite modulatory effect on biological membranes and model membranes is discussed with respect to different mechanisms the interaction of the regulatory peptides with the enzyme molecules and the substrate vesicles.