CXCL8-induced FAK phosphorylation via CXCR1 and CXCR2: cytoskeleton- and integrin-related mechanisms converge with FAK regulatory pathways in a receptor-specific manner

CXCL8 is a potent chemokine, inducing focal adhesion kinase (FAK) phosphorylation, and migration via a FAK-mediated pathway. Since, unlike growth factors, chemokines directly control integrins and cytoskeleton rearrangements, we determined whether these elements regulate CXCL8-induced FAK phosphorylation. The analysis intentionally dissociated between the CXCL8 receptors CXCR1 and CXCR2. In both CXCR1- and CXCR2-expressing cells, actin and microtubules were required for CXCL8-induced FAK phosphorylation, and CXCL8-induced cell spreading was accompanied by concordant re-localization of FAK with actin and beta-tubulin. The phosphorylation of five FAK sites depended on intact actin filaments and microtubules. While in CXCR2-expressing cells FAK phosphorylation was adhesion-dependent and was stimulated by fibronectin, in CXCR1-expressing cells FAK phosphorylation was adhesion-independent. Of note, even in the absence of integrin stimulation, the CXCL8-induced phosphorylation of FAK in CXCR1-expressing cells required cytoskeletal elements. CXCL8-induced migration in both cell types was highly reliant on actin filaments, but only the migration of CXCR1-expressing cells was fully dependent on microtubules. Overall, several aspects of CXCL8-induced FAK phosphorylation and migration are regulated in a receptor-specific manner. These observations lay the basis for future investigation of the equilibrium between CXCR1 and CXCR2 in cells expressing both receptors together, such as neutrophils, endothelial cells and tumor cells.     

Importance of Protein-tyrosine Phosphatase-α Catalytic Domains for Interactions with SHP-2 and Interleukin-1-induced Matrix Metalloproteinase-3 Expression

Interleukin-1 (IL-1) induces extracellular matrix degradation as a result of increased expression of matrix metalloproteinases (MMPs). We examined adhesion-restricted signaling pathways that enable IL-1-induced MMP release in human gingival and murine fibroblasts. Of the seven MMPs and three tissue inhibitors of MMPs screened, IL-1 enhanced release only of MMP3 when cells formed focal adhesions. Inhibition of protein-tyrosine phosphatases (PTPs), which are enriched in focal adhesions, blocked IL-1-induced MMP3 release. Accordingly, in contrast to wild-type cells, fibroblasts null for PTPα did not exhibit IL-1-induced MMP3 release. IL-1 treatment enhanced the recruitment of SHP-2 and PTPα to focal adhesions and the association of PTPα with SHP-2. Pulldown assays confirmed a direct interaction between PTPα and SHP-2, which was dependent on the intact, membrane-proximal phosphatase domain of PTPα. Interactions between SHP-2 and PTPα, recruitment of SHP-2 to focal adhesions, IL-1-induced ERK activation, and MMP3 expression were all blocked by point mutations in the phosphatase domains of PTPα. These data indicate that IL-1-induced signaling through focal adhesions leading to MMP3 release and interactions between SHP-2 and PTPα are dependent on the integrity of the catalytic domains of PTPα.     

Expression of Serum Amyloid A in Human Ovarian Epithelial Tumors: Implication for a Role in Ovarian Tumorigenesis

Serum amyloid A (SAA) is an acute phase protein which is expressed primarily in the liver as a part of the systemic response to various injuries and inflammatory stimuli; its expression in ovarian tumors has not been described. Here, we investigated the expression of SAA in human benign and malignant ovarian epithelial tumors. Non-radioactive in situ hybridization applied on ovarian paraffin tissue sections revealed mostly negative SAA mRNA expression in normal surface epithelium. Expression was increased gradually as epithelial cells progressed through benign and borderline adenomas to primary and metastatic adenocarcinomas. Similar expression pattern of the SAA protein was observed by immunohistochemical staining. RT-PCR analysis confirmed the overexpression of the SAA1 and SAA4 genes in ovarian carcinomas compared with normal ovarian tissues. In addition, strong expression of SAA mRNA and protein was found in the ovarian carcinoma cell line OVCAR-3. Finally, patients with ovarian carcinoma had high SAA serum levels, which strongly correlated with high levels of CA-125 and C-reactive protein. Enhanced expression of SAA in ovarian carcinomas may play a role in ovarian tumorigenesis and may have therapeutic application. (J Histochem Cytochem 58:1015–1023, 2010)     

Post genome-wide association studies of novel genes associated with type 2 diabetes show gene-gene interaction and high predictive value

Background

Recently, several Genome Wide Association (GWA) studies in populations of European descent have identified and validated novel single nucleotide polymorphisms (SNPs), highly associated with type 2 diabetes (T2D). Our aims were to validate these markers in other European and non-European populations, then to assess their combined effect in a large French study comparing T2D and normal glucose tolerant (NGT) individuals.

Methodology/Principal Findings

In the same French population analyzed in our previous GWA study (3,295 T2D and 3,595 NGT), strong associations with T2D were found for CDKAL1 (OR_rs7756992 = 1.30[1.19–1.42], P = 2.3×10⁻⁹), CDKN2A/2B (OR_rs10811661 = 0.74[0.66–0.82], P = 3.5×10⁻⁸) and more modestly for IGFBP2 (OR_rs1470579 = 1.17[1.07–1.27], P = 0.0003) SNPs. These results were replicated in both Israeli Ashkenazi (577 T2D and 552 NGT) and Austrian (504 T2D and 753 NGT) populations (except for CDKAL1) but not in the Moroccan population (521 T2D and 423 NGT). In the overall group of French subjects (4,232 T2D and 4,595 NGT), IGFBP2 and CXCR4 synergistically interacted with (LOC38776, SLC30A8, HHEX) and (NGN3, CDKN2A/2B), respectively, encoding for proteins presumably regulating pancreatic endocrine cell development and function. The T2D risk increased strongly when risk alleles, including the previously discovered T2D-associated TCF7L2 rs7903146 SNP, were combined (8.68-fold for the 14% of French individuals carrying 18 to 30 risk alleles with an allelic OR of 1.24). With an area under the ROC curve of 0.86, only 15 novel loci were necessary to discriminate French individuals susceptible to develop T2D.

Conclusions/Significance

In addition to TCF7L2, SLC30A8 and HHEX, initially identified by the French GWA scan, CDKAL1, IGFBP2 and CDKN2A/2B strongly associate with T2D in French individuals, and mostly in populations of Central European descent but not in Moroccan subjects. Genes expressed in the pancreas interact together and their combined effect dramatically increases the risk for T2D, opening avenues for the development of genetic prediction tests.     

Symmetry at the active site of the ribosome: structural and functional implications

The sizable symmetrical region, comprising 180 ribosomal RNA nucleotides, which has been identified in and around the peptidyl transferase center (PTC) in crystal structures of eubacterial and archaeal large ribosomal subunits, indicates its universality, confirms that the ribosome is a ribozyme and evokes the suggestion that the PTC evolved by gene fusion. The symmetrical region can act as a center that coordinates amino acid polymerization by transferring intra-ribosomal signals between remote functional locations, as it connects, directly or through its extensions, the PTC, the three tRNA sites, the tunnel entrance, and the regions hosting elongation factors. Significant deviations from the overall symmetry stabilize the entire region and can be correlated with the shaping and guiding of the motion of the tRNA 3'-end from the A- into the P-site. The linkage between the elaborate PTC architecture and the spatial arrangements of the tRNA 3'-ends revealed the rotatory mechanism that integrates peptide bond formation, translocation within the PTC and nascent protein entrance into the exit tunnel. The positional catalysis exerted by the ribosome places the reactants in stereochemistry close to the intermediate state and facilitates the catalytic contribution of the P-site tRNA 2'-hydroxyl.     

MuA transposase separates DNA sequence recognition from catalysis

Confronted with thousands of potential DNA substrates, a site-specific enzyme must restrict itself to the correct DNA sequence. The MuA transposase protein performs site-specific DNA cleavage and joining reactions, resulting in DNA transposition-a specialized form of genetic recombination. To determine how sequence information is used to restrict transposition to the proper DNA sites, we performed kinetic analyses of transposition with DNA substrates containing either wild-type transposon sequences or sequences carrying mutations in specific DNA recognition modules. As expected, mutations near the DNA cleavage site reduce the rate of cleavage; the observed effect is about 10-fold. In contrast, mutations within the MuA recognition sequences do not directly affect the DNA cleavage or joining steps of transposition. It is well established that the recognition sequences are necessary for assembly of stable, multimeric MuA-DNA complexes, and we find that recognition site mutations severely reduce both the extent and the rate of this assembly process. Yet if the MuA-DNA complexes are preassembled, the first-order rate constants for both DNA cleavage and DNA strand transfer (the joining reaction) are unaffected by the mutations. Furthermore, most of the mutant DNA molecules that are cleaved also complete DNA strand transfer. We conclude that the sequence-specific contacts within the recognition sites contribute energetically to complex assembly, but not directly to catalysis. These results contrast with studies of more orthodox enzymes, such as EcoRI and some other type II restriction enzymes. We propose that the strategy employed by MuA may serve as an example for how recombinases and modular restriction enzymes solve the DNA specificity problem, in that they, too, may separate substrate recognition from catalysis.     

Regulation of leucine-stimulated insulin secretion and glutamine metabolism in isolated rat islets

Glutamate dehydrogenase (GDH) is regulated by both positive (leucine and ADP) and negative (GTP and ATP) allosteric factors. We hypothesized that the phosphate potential of beta-cells regulates the sensitivity of leucine stimulation. These predictions were tested by measuring leucine-stimulated insulin secretion in perifused rat islets following glucose depletion and by tracing the nitrogen flux of [2-(15)N]glutamine using stable isotope techniques. The sensitivity of leucine stimulation was enhanced by long time (120-min) energy depletion and inhibited by glucose pretreatment. After limited 50-min glucose depletion, leucine, not alpha-ketoisocaproate, failed to stimulate insulin release. beta-Cells sensitivity to leucine is therefore proposed to be a function of GDH activation. Leucine increased the flux through GDH 3-fold compared with controls while causing insulin release. High glucose inhibited flux through both glutaminase and GDH, and leucine was unable to override this inhibition. These results clearly show that leucine induced the secretion of insulin by augmenting glutaminolysis through activating glutaminase and GDH. Glucose regulates beta-cell sensitivity to leucine by elevating the ratio of ATP and GTP to ADP and P(i) and thereby decreasing the flux through GDH and glutaminase. These mechanisms provide an explanation for hypoglycemia caused by mutations of GDH in children.     

Infection of glioma cells with Sindbis virus induces selective activation and tyrosine phosphorylation of protein kinase C delta. Implications for Sindbis virus-induced apoptosis

Sindbis virus (SV) is an alpha virus used as a model for studying the role of apoptosis in virus infection. In this study, we examined the role of protein kinase C (PKC) in the apoptosis induced by SVNI, a virulent strain of SV. Infection of C6 cells with SVNI induced a selective translocation of PKCdelta to the endoplasmic reticulum and its tyrosine phosphorylation. The specific PKCdelta inhibitor rottlerin and a PKCdelta kinase-dead mutant increased the apoptosis induced by SVNI. To examine the role of the tyrosine phosphorylation of PKCdelta in the apoptosis induced by SVNI we used a PKCdelta mutant in which five tyrosine residues were mutated to phenylalanine (PKCdelta5). PKCdelta5-overexpressing cells exhibited increased apoptosis in response to SVNI as compared with control cells and to cells overexpressing PKCdelta. SVNI also increased the cleavage of caspase 3 in cells overexpressing PKCdelta5 but did not induce cleavage of PKCdelta or PKCdelta5. Using single tyrosine mutants, we identified tyrosines 52, 64, and 155 as the phosphorylation sites associated with the apoptosis induced by SVNI. We conclude that PKCdelta exerts an inhibitory effect on the apoptosis induced by SV and that phosphorylation of PKCdelta on specific tyrosines is required for this function.     

Process design for microbial plastic factories: metabolic engineering of polyhydroxyalkanoates

Implementing several metabolic engineering strategies, either individually or in combination, it is possible to construct microbial plastic factories to produce a variety of polyhydroxyalkanoate (PHA) biopolymers with desirable structures and material properties. Approaches include external substrate manipulation, inhibitor addition, recombinant gene expression, host cell genome manipulation and, most recently, protein engineering of PHA biosynthetic enzymes. In addition, mathematical models and molecular methods can be used to elucidate metabolically engineered systems and to identify targets for performance improvement.     

'Intervening is representing': medical campaigns that helped identify the prevalence of hookworm

This paper compares anti-hookworm campaigns conducted in the early twentieth century in France, Germany, Brazil and West India. The populations that suffer from hookworm are not identical in the North and in the South. In tropical and semi-tropical regions hookworm is mainly found among poor peasants and is related to lack of hygiene, while in temperate climates hookworm was a professional disease of miners, a highly organized professional segment. Nevertheless, major disparities in the pattern of hookworm control did not reflect the North-South divide, but a difference between campaigns. These aimed at the eradication of hookworm infection (Germany and West-India) and at alleviating the effects of this infection on populations (France and Brazil). Maps that represented the prevalence of hookworm mirrored the aims of the sanitary campaign in which they were used: eradication of parasitic worms versus the reduction of the handicap induced by these worms. In public health as well, representing is intervening. And vice versa: patterns of intervention shape representations.