Cell surface-expressed phosphatidylserine and annexin A5 open a novel portal of cell entry

Expression of phosphatidylserine (PtdSer) at the cell surface is part of the membrane dynamics of apoptosis. Expressed phosphatidylserine functions as an "eat me" flag toward phagocytes. Here, we report that the expressed phosphatidylserine forms part of a hitherto undescribed pinocytic pathway. Annexin A5, a phosphatidylserine-binding protein, binds to and polymerizes through protein-protein interactions on membrane patches expressing phosphatidylserine. The two-dimensional protein network of annexin A5 at the surface prevents apoptotic body formation without interfering with the progression of apoptosis as demonstrated by activation of caspase-3, PtdSer exposure, and DNA fragmentation. The annexin A5 protein network bends the membrane patch nanomechanically into the cell and elicits budding, endocytic vesicle formation, and cytoskeleton-dependent trafficking of the endocytic vesicle. Annexin A1, which binds to PtdSer without forming a two-dimensional protein network, does not induce the formation of endocytic vesicles. This novel pinocytic pathway differs from macropinocytosis, which is preceded by membrane ruffling and actin polymerization. We clearly showed that actin polymerization is not involved in budding and endocytic vesicle formation but is required for intracellular trafficking. The phosphatidylserine-annexin A5-mediated pinocytic pathway is not restricted to cells in apoptosis. We demonstrated that living tumor cells can take up substances through this novel portal of cell entry. This opens new avenues for targeted drug delivery and cell entry.     

Bone-targeted 2,6,9-trisubstituted purines: novel inhibitors of Src tyrosine kinase for the treatment of bone diseases

Novel bone-targeted 2,6,9-trisubstituted purine template-based inhibitors of Src tyrosine kinase are described. Drug design studies of known purine compounds revealed that both positions-2 and -6 were suitable for incorporating bone-seeking moieties. A variety of bone-targeting groups with different affinity to hydroxyapatite were utilized in the study. Compound 3d was determined to be a potent Src inhibitor and was quite selective against a panel of other protein kinases.     

α,β-Dehydro-amino acid residues in the design of peptide structures: Synthesis,crystal structure,and molecular conformation of two homologous peptides—N-Ac-Dehydro-Phe-L-Leu-OCH3 and N-Ac-Dehydro-Phe-NorVal-OCH3

The dehydro-residue containing peptides N-Ac-dehydro-Phe-L -Leu-OCH₃ ( I ) and N-Ac-dehydro-Phe-NorVal-OCH₃ ( II ) were synthesized by the usual workup procedures. The peptides crystallize from their solutions in methanol in space group P6₅: ( I ) a = b = 12.528(2) Å, c = 21.653(5) Å; ( II ) a = b = 12.532(2) Å, c = 21.695(4) Å. The structures were determined by direct methods. Both peptides adopt similar conformations with ?,ψ of dehydro-Phe as follows: ( I ) ?57.0(5)° and ?37.0(5)°; ( II ) ?56.0(5),° and ?37.5(5)°. The observed data on dehydro-Phe when placed at the (i + 1) position show that the ?,ψ values of dehydro-Phe are either ?60°, 140° or ?60°, ?30°. The conformation of ?60°, 140° can be accommodated only with a flexible residue at the (i + 2) position while the ?,ψ values of ?60°, ?30° are obtained with a bulky residue at the (i + 2) position as in the present structures. The molecules are packed in a helical way along the c axis. These are held by two strong intermolecular hydrogen bonds involving both NH as donors and acetyl group and dehydro-Phe oxygen atoms as acceptors. © 1994 John Wiley & Sons, Inc.     

Synthesis, crystal structure, and molecular conformation of N-Boc-L-Phe-dehydro-Leu-L-Val-OCH3

The peptide N-Boc-L-Phe-dehydro-Leu-L-Val-OCH3 was synthesized by the usual workup procedure and finally by coupling the N-Boc-L-Phe-dehydro-Leu-OH to valine methyl ester. It was crystallized from its solution in methanol-water mixture at 4 degrees C. The crystals belong to the triclinic space group P1 with a = 5.972(5) A, b = 9.455(6) A, c = 13.101(6) A, alpha = 103.00(4) degrees, beta = 97.14(5) degrees, gamma = 102.86(5) degrees, V = 690.8(8) A, Z = 1, dm = 1.179(5) Mg m-3 and dc = 1.177(5) Mg m-3. The structure was determined by direct methods using SHELXS86. It was refined by block-diagonal least-squares procedure to an R value of 0.060 for 1674 observed reflections. The C alpha 2-C beta 2 distance of 1.323(9) A in dehydro-Leu is an appropriate double bond length. The bond angle C alpha-C beta-C gamma in the dehydro-Leu residue is 129.4(8) degrees. The peptide backbone torsion angles are theta 1 = -168.6(6) degrees, omega 0 = 170.0(6) degrees, phi 1 = -44.5(9) degrees, psi 1 = 134.5(6) degrees, omega 1 = 177.3(6) degrees, phi 2 = 54.5(9) degrees, psi 2 = 31.1(10) degrees, omega 2 = 171.7(6) degrees, phi 3 = 51.9(8) degrees, psi T3 = 139.0(6) degrees, theta T = -175.7(6) degrees. These values show that the backbone adopts a beta-turn II conformation. As a result of beta-turn, an intramolecular hydrogen bond is formed between the oxygen of the ith residue and NH of the (i + 3)th residue at a distance of 3.134(6) A.(ABSTRACT TRUNCATED AT 250 WORDS)     

The pyrimidinergic P2Y6 receptor mediates a novel release of proinflammatory cytokines and chemokines in monocytic cells stimulated with UDP

The human P2Y6 receptor (hP2Y6) is a member of the G protein-coupled pyrimidinergic P2 receptor family that responds specifically to the extracellular nucleotide uridine diphosphate (UDP). Recently, the hP2Y6 receptor has been reported to mediate monocyte IL-8 production in response to UDP or lipopolysaccharide (LPS), but the role of hP2Y6 in regulating other pro-inflammatory cytokines or mediators is largely unknown. We demonstrate here that UDP specifically induces soluble TNF-alpha and IL-8 production in a promonocytic U937 cell line stably transfected with hP2Y6. However, we did not detect IL-1alpha, IL-1beta, IL-6, IL-10, IL-18, and PGE2 in the conditioned media from the same cell line. These results distinguish UDP/P2Y6 signaling from LPS signaling. Interestingly, UDP induces the production of IL-8, but not TNF-alpha, in human astrocytoma 1321N1 cell lines stably transfected with hP2Y6. Therefore, the immune effect of UDP/P2Y6 signaling on the production of proinflammatory cytokines is selective and dependent on cell types. We further identify that UDP can also induce the production of proinflammatory chemokines MCP-1 and IP-10 in hP2Y6 transfected promonocytic U937 cell lines, but not astrocytoma 1321N1 cell lines stably transfected with hP2Y6. From the Taqman analysis, UDP stimulation significantly upregulates the mRNA levels of IL-8, IP-10, and IL-1beta, but not TNF-alpha. Taken together, these new findings expand the pro-inflammatory biology of UDP mediated by the P2Y6 receptor.     

Visceral adipose inflammation in obesity is associated with critical alterations in tregulatory cell numbers

Background

The development of insulin resistance (IR) in mouse models of obesity and type 2 diabetes mellitus (DM) is characterized by progressive accumulation of inflammatory macrophages and subpopulations of T cells in the visceral adipose. Regulatory T cells (Tregs) may play a critical role in modulating tissue inflammation via their interactions with both adaptive and innate immune mechanisms. We hypothesized that an imbalance in Tregs is a critical determinant of adipose inflammation and investigated the role of Tregs in IR/obesity through coordinated studies in mice and humans.

Methods and Findings

Foxp3-green fluorescent protein (GFP) “knock-in” mice were randomized to a high-fat diet intervention for a duration of 12 weeks to induce DIO/IR. Morbidly obese humans without overt type 2 DM (n = 13) and lean controls (n = 7) were recruited prospectively for assessment of visceral adipose inflammation. DIO resulted in increased CD3⁺CD4⁺, and CD3⁺CD8⁺ cells in visceral adipose with a striking decrease in visceral adipose Tregs. Treg numbers in visceral adipose inversely correlated with CD11b⁺CD11c⁺ adipose tissue macrophages (ATMs). Splenic Treg numbers were increased with up-regulation of homing receptors CXCR3 and CCR7 and marker of activation CD44. In-vitro differentiation assays showed an inhibition of Treg differentiation in response to conditioned media from inflammatory macrophages. Human visceral adipose in morbid obesity was characterized by an increase in CD11c⁺ ATMs and a decrease in foxp3 expression.

Conclusions

Our experiments indicate that obesity in mice and humans results in adipose Treg depletion. These changes appear to occur via reduced local differentiation rather than impaired homing. Our findings implicate a role for Tregs as determinants of adipose inflammation.     

Intramolecular Conformation of Puromycin in Solution As Studied by Proton Magnetic Resonance

Abstract

The intramolecular conformation of puromycin, a broad spectrum antiobiotic, in solution has been investigated by proton magnetic resonance (PMR) spectroscopy. A comparison of the proton chemical shift and proton-proton coupling constant data of puromycin with puromycin aminonucleoside suggests that puromycin in solution exists as an equilibrium blend of extended and folded conformers. These folded conformers are the result of flexibility around the C^α-C^β bond of the aminoacyl segment of puromycin. One of the folded conformers predicted by PMR is in excellent agreement with the x-ray data.     

Guanidinium chloride-induced spectral perturbations of 4,4'-dianilino-1,1'-binaphthyl-5,5'-disulfonic acid confound interpretation of data on molten globule states

We describe limitations in the use of 4,4′-dianilino-1,1′-binaphthyl-5,5′-disulfonic acid (bis-ANS) to examine unfolding intermediates associated with guanidinium chloride (GuHCl)-induced protein denaturation. Several studies have used alterations in fluorescence emission of bis-ANS to quantify the population of “molten globule” states. Our findings indicate that the observed changes in bis-ANS spectroscopic properties could originate from the interactions of bis-ANS and GuHCl and the aggregation of the dye at higher GuHCl concentrations. We posit that in the absence of additional complementary structural or spectroscopic measurements, the use of bis-ANS emission alone to monitor protein conformations can be misleading.