MAP kinases bind endothelial nitric oxide synthase

AbstractEndothelial nitric oxide synthase (eNOS) contains a motif similar to recognition sequences in known MAPK binding partners. In optical biosensing experiments, eNOS bound p38 and ERK with ∼100nM affinity and complex kinetics. Binding is diffusion-limited (kon∼.15×106M−1s−1). Neuronal NOS also bound p38 but exhibited much slower and weaker binding. p38-eNOS binding was inhibited by calmodulin. Evidence for a ternary complex was found when eNOS bound p38 was exposed to CaM, increasing the apparent dissociation rate. These observations strongly suggest a direct role for MAPK in regulation of NOS with implications for signaling pathways including angiogenesis and control of vascular tone

Endothelial Nitric Oxide Synthase is Regulated by ERK Phosphorylation at Ser602

eNOS (endothelial nitric oxide synthase) contains a MAPK (mitogen-activated protein kinase)-binding site associated with a major eNOS control element. Purified ERK (extracellular-signal-regulated kinase) phosphorylates eNOS with a stoichiometry of 2–3 phosphates per eNOS monomer. Phosphorylation decreases NO synthesis and cytochrome c reductase activity. Three sites of phosphorylation were detected by MS. All sites matched the SP and TP MAPK (mitogen-activated protein kinase) phosphorylation motif. Ser602 lies at the N-terminal edge of the 42-residue eNOS AI (autoinhibitory) element. The pentabasic MAPK-binding site lies at the opposite end of the AI, and other critical regulatory features are between them. Thr46 and Ser58 are located in a flexible region associated with the N terminus of the oxygenase domain. In contrast with PKC (protein kinase C), phosphorylation by ERK did not significantly interfere with CaM (calmodulin) binding as analysed by optical biosensing. Instead, ERK phosphorylation favours a state in which FMN and FAD are in close association and prevents conformational changes that expose reduced FMN to acceptors. The close associations between control sites in a few regions of the molecule suggest that control of signal generation is modulated by multiple inputs interacting directly on the surface of eNOS via overlapping binding domains and tightly grouped targets

Novel Cell Penetrating Peptide-adaptors Effect Intracellular Delivery and Endosomal Escape of Protein Cargos

The use of cell penetrating peptides (CPPs) as biomolecular delivery vehicles holds great promise for therapeutic and other applications, but development has been stymied by poor delivery and lack of endosomal escape. We have developed a CPP-adaptor system capable of efficient intracellular delivery and endosomal escape of user-defined protein cargos. The cell penetrating sequence of HIV transactivator of transcription was fused to calmodulin, which binds with subnanomolar affinity to proteins containing a calmodulin binding site. Our strategy has tremendous advantage over prior CPP technologies because it utilizes high affinity noncovalent, but reversible coupling between CPP and cargo. Three different cargo proteins fused to a calmodulin binding sequence were delivered to the cytoplasm of eukaryotic cells and released, demonstrating the feasibility of numerous applications in living cells including alteration of signaling pathways and gene expression

Loss of MNK Function Sensitizes Fibroblasts to Serum-withdrawal Induced Apoptosis

Map kinase-interacting protein kinases 1 and 2 (MNK1, MNK2) function downstream of p38 and ERK MAP kinases, but there are large gaps in our knowledge of how MNKs are regulated and function. Mice deleted of both genes are apparently normal, suggesting that MNKs function in adaptive pathways during stress. Here, we show that mouse embryo fibroblasts (MEFs) obtained from mnk1 (–/–)/mnk2 (–/–) as well as mnk1 (–/–) and mnk2 (–/–) mice are sensitized to caspase-3 activation upon withdrawal of serum in comparison to wild-type cells. Caspase-3 cleavage occurs with all cells in the panel, but most rapidly and robustly in cells derived from mice lacking both MNK genes. Treatment of wild-type MEFs in the panel with a compound (CGP57380) that inhibits MNK1 and MNK2 sensitizes wild-type cells for serum-withdrawal induced apoptosis, suggesting that sensitization is due to loss of MNK function and not to a secondary event. Reintroduction of wild-type MNK1 in the double knockout MEFs results in decreased sensitivity to serum withdrawal that is not observed for wild-type MNK2, or the kinase dead variant. Our work identifies MNKs as kinases involved in anti-apoptotic signaling in response to serum withdrawal

A versatile cell-penetrating peptide-adaptor system for efficient delivery of molecular cargos to subcellular destinations.

Cell penetrating peptides have long held great potential for delivery of biomolecular cargos for research, therapeutic and diagnostic purposes. They allow rapid, relatively nontoxic passage of a wide variety of biomolecules through the plasma membranes of living cells. However, CPP-based research tools and therapeutics have been stymied by poor efficiency in release from endosomes and a great deal of effort has been made to solve this 'endosomal escape problem.' Previously, we showed that use of a reversible, noncovalent coupling between CPP and cargo using calmodulin and a calmodulin binding motif allowed efficient delivery of cargo proteins to the cytoplasm in baby hamster kidney and other mammalian cell lines. The present report demonstrates the efficacy of our CPP-adaptor scheme for efficient delivery of model cargos to the cytoplasm using a variety of CPPs and adaptors. Effective overcoming of the endosomal escape problem is further demonstrated by the delivery of cargo to the nucleus, endoplasmic reticulum and peroxisomes by addition of appropriate subcellular localization signals to the cargos. CPP-adaptors were also used to deliver cargo to myotubes, demonstrating the feasibility of the system as an alternative to transfection for the manipulation of hard-to-transfect cells

Plasmids used in this study.

<p>Plasmids used in this study.</p

Biolayer interferometry analysis of CPP-adaptor-cargo binding.

<p>Association (0-300s) and dissociation (300-600s) phases are shown for A, TAT-CaM; B, TAT-CALL3; C, SAP-CaM; D, SAP(E)-CaM and E, TAT-Tropo binding to CBS-myoglobin (A-D) or TIP-myoglogbin. Analyte concentrations were 1000 nM (green), 500 nM (magenta), 250 nM (orange), 125 nM (red), and 63 nM (blue). Fits are shown to a single-state global model for which the constants are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0178648#pone.0178648.t001" target="_blank">Table 1</a>. F, EDTA dissociation phases for 1000 nM analyte samples moved into EDTA after dissociation phase. Binding normalized to % specific binding to eliminate differences in amplitude, allowing direct comparisons.</p

MAP kinases differentially bind and phosphorylate NOS3 via two unique NOS3 sites

Nitric oxide synthase 3 (NOS3) is a major vasoprotective enzyme that catalyzes the conversion of L-arginine to nitric oxide (NO) in response to a significant number of signaling pathways. Here, we provide evidence that NOS3 interactions with MAP kinases have physiological relevance. Binding interactions of NOS3 with c-Jun N-terminal kinase (JNK1 ), p38α, and ERK2 were characterized using optical biosensing with full length NOS3 and NOS3 specific peptides and phospho-peptides. Like p38α and ERK2, JNK1 exhibited high affinity binding to full length NOS3 (K 15 nM). Rate constants exhibited fast-on, slow-off binding (k = 4106 M s ; k = 6.2 x 10 s ). Further analysis using synthetic NOS3 peptides revealed two MAP kinase binding sites unique to NOS3. p38α evinced similar affinity with both NOS3 binding sites. For ERK2 and JNK1 the affinity at the two sites differed. However, NOS3 peptides with a phosphate at either S114 or S633 did not meaningfully interact with the kinases. Immunoblotting revealed that each kinase phosphorylated NOS3 with a unique pattern. JNK1 predominantly phosphorylated NOS3 at S114, ERK2 at S600, and p38α phosphorylated both residues. In vitro production of NO was unchanged by phosphorylation at these sites. In human microvascular endothelial cells, endogenous interactions of all the MAP kinases with NOS3 were captured using proximity ligation assay in resting cells. Our results underscore the importance of MAP kinase interactions, identifying two unique NOS3 interaction sites with potential for modulation by MAP kinase phosphorylation (S114) and other signaling inputs, like protein kinase A (S633)

Biolayer interferometry analysis of subcellular localization constructs.

<p>TAT-CaM was used as ligand and analytes were CBS-myoglobin-NLS (green), CBS-myoglobin-KDEL (blue), CBS-myoglobin-SKL (red). Phases, analyte concentrations and fits are the same as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0178648#pone.0178648.g001" target="_blank">Fig 1</a>.</p

Cell penetration assay for a variety of CPPs and adaptor proteins for delivery of myoglobin to BHK cells.

<p>Each panel are images from experiments with different CPP-adaptors: A, TAT-CaM 2.0; B, CALML3; C, SAP-CaM; D, SAP(E)-CaM. BHK cells were treated for 1 h with DyLight 550 fluorescently labeled CBS-myo (rendered as white in left panels, red in center and right panels), in either the absence or presence of CPP-adaptor, washed and imaged live. Center images are optical sections set at a similar depth of the nucleus (NucBlue staining, white, center and right panels), as determined by position within the Z-stack. Orthogonal projections are shown at the right (boxed in red) and top (boxed in green) sides of each panel. Cytoplasmic compartments in live cells were visualized using CellTracker Green CMFDA dye (green in right panels). Comparison of CPP-adaptor-treated versus untreated cells indicates that in all cases, myoglobin was delivered and localized primarily to the cytoplasm. Scale bars in all panels, 20 μm.</p