Type Ialpha phosphatidylinositol-4-phosphate 5-kinase mediates Rac-dependent actin assembly

Action polymerization is essential for a variety of cellular processes including movement, cell division and shape change. The induction of actin polymerization requires the generation of free actin filament barbed ends, which results from the severing or uncapping of pre-existing actin filaments [1] [2], or de novo nucleation, initiated by the Arp2/3 complex [3] [4] [5] [6] [7]. Although little is known about the signaling pathways that regulate actin assembly, small GTPases of the Rho family appear to be necessary [8] [9] [10] [11]. In thrombin-stimulated platelets, the Rho family GTPase Rac1 induces actin polymerization by stimulating the uncapping of actin filament barbed ends [2]. The mechanism by which Rac regulates uncapping is unclear, however. We previously demonstrated that Rac interacts with a type I phosphatidylinositol-4-phosphate 5-kinase (PIP 5-kinase) in a GTP-independent manner [12] [13]. Because PIP 5-kinases synthesize phosphatidylinositol-4,5-bisphosphate (PI(4,5)P(2)), a lipid that dissociates capping proteins from the barbed ends of actin filaments [14] [15] [16], they are good candidates for mediating the effects of Rac on actin assembly. Here, we have identified the Rac-associated PIP 5-kinase as the PIP 5-kinase isoforms alpha and beta. When added to permeabilized platelets, PIP 5-kinase alpha induced actin filament uncapping and assembly. In contrast, a kinase-inactive PIP 5-kinase alpha mutant failed to induce actin assembly and blocked assembly stimulated by thrombin or Rac. Furthermore, thrombin- or Rac-induced actin polymerization was inhibited by a point mutation in the carboxyl terminus of Rac that disrupts PIP 5-kinase binding. These results demonstrate that PIP 5-kinase alpha is a critical mediator of thrombin- and Rac-dependent actin assembly.     

Auxin-induced changes in cell wall extensibility of maize roots

The rheological properties of corn (Zea mays L. cv. Garant) root elongation zones were investigated by means of a computer-controlled extensiometer. Creep closely followed a logarithmic time function, which was used to quantify creep activity. Pretreatment with auxin, which inhibits extension growth in roots, lowered the creep activity and the apparent plastic extensibility. While the time course of the inhibition of apparent plastic extensibility lagged behind the cessation of elongation growth, the drop in creep activity matched the growth inhibition more closely. Creep activity and apparent plastic extensibility were not significantly affected by pH. These data support the view that the auxin-induced cell wall stiffening (e.g. by cross-linking processes), while causal for the growth inhibition, is not brought about by a cell wall alkalinization. Received: 10 December 1996 / Accepted: 19 August 1997     

Molecular Subtypes in Stage II-III Colon Cancer Defined by Genomic Instability: Early Recurrence-Risk Associated with a High Copy-Number Variation and Loss of RUNX3 and CDKN2A

Objective

We sought to investigate various molecular subtypes defined by genomic instability that may be related to early death and recurrence in colon cancer.

Methods

We sought to investigate various molecular subtypes defined by instability at microsatellites (MSI), changes in methylation patterns (CpG island methylator phenotype, CIMP) or copy number variation (CNV) in 8 genes. Stage II-III colon cancers (n = 64) were investigated by methylation-specific multiplex ligated probe amplification (MS-MLPA). Correlation of CNV, CIMP and MSI, with mutations in KRAS and BRAFV600E were assessed for overlap in molecular subtypes and early recurrence risk by uni- and multivariate regression.

Results

The CIMP phenotype occurred in 34% (22/64) and MSI in 27% (16/60) of the tumors, with noted CIMP/MSI overlap. Among the molecular subtypes, a high CNV phenotype had an associated odds ratio (OR) for recurrence of 3.2 (95% CI 1.1-9.3; P = 0.026). Losses of CACNA1G (OR of 2.9, 95% CI 1.4-6.0; P = 0.001), IGF2 (OR of 4.3, 95% CI 1.1-15.8; P = 0.007), CDKN2A (p16) (OR of 2.0, 95% CI 1.1-3.6; P = 0.024), and RUNX3 (OR of 3.4, 95% CI 1.3-8.7; P = 0.002) were associated with early recurrence, while MSI, CIMP, KRAS or BRAF V600E mutations were not. The CNV was significantly higher in deceased patients (CNV in 6 of 8) compared to survivors (CNV in 3 of 8). Only stage and loss of RUNX3 and CDKN2A were significant in the multivariable risk-model for early recurrence.

Conclusions

A high copy number variation phenotype is a strong predictor of early recurrence and death, and may indicate a dose-dependent relationship between genetic instability and outcome. Loss of tumor suppressors RUNX3 and CDKN2A were related to recurrence-risk and warrants further investigation.     

Atherosclerotic Plaque Destabilization in Mice: A Comparative Study

Atherosclerosis-associated diseases are the main cause of mortality and morbidity in western societies. The progression of atherosclerosis is a dynamic process evolving from early to advanced lesions that may become rupture-prone vulnerable plaques. Acute coronary syndromes are the clinical manifestation of life-threatening thrombotic events associated with high-risk vulnerable plaques. Hyperlipidemic mouse models have been extensively used in studying the mechanisms controlling initiation and progression of atherosclerosis. However, the understanding of mechanisms leading to atherosclerotic plaque destabilization has been hampered by the lack of proper animal models mimicking this process. Although various mouse models generate atherosclerotic plaques with histological features of human advanced lesions, a consensus model to study atherosclerotic plaque destabilization is still lacking. Hence, we studied the degree and features of plaque vulnerability in different mouse models of atherosclerotic plaque destabilization and find that the model based on the placement of a shear stress modifier in combination with hypercholesterolemia represent with high incidence the most human like lesions compared to the other models.     

Lipidic phase membrane protein serial femtosecond crystallography

X-ray free electron laser (X-FEL)-based serial femtosecond crystallography is an emerging method with potential to rapidly advance the challenging field of membrane protein structural biology. Here we recorded interpretable diffraction data from micrometer-sized lipidic sponge phase crystals of the Blastochloris viridis photosynthetic reaction center delivered into an X-FEL beam using a sponge phase micro-jet.     

Tenascin-C and carcinoma cell invasion in oral and urinary bladder cancer

Carcinoma invasion is a complex process regulated by genetic and epigenetic factors as well. A relevant supportive condition for cancer cell migration is the reorganization of the extracellular matrix (ECM), which is realized in an orchestrated multicellular manner including carcinoma cells and stromal fibroblasts. An important key player in the process of ECM reorganization is Tenascin-C (Tn-C). The molecule occurs as different isoforms generated by alternative splicing and de novo glycosylation. Large variants of Tn-C are abundantly re-expressed in the invasive front of many carcinoma types. A special role for initiating migration and accompanied epithelial to mesenchymal transition has been suggested. Here, we review the current knowledge concerning the tumor biological importance of Tn-C, the synthesis and alternative splicing during the invasive process in general, and give an overview on the impact of Tn-C in urothelial carcinoma of the urinary bladder (UBC) and oral squamous cell carcinoma (OSCC).     

Mechanisms of actin rearrangements mediating platelet activation.

The detergent-insoluble cytoskeleton of the resting human blood platelet contains approximately 2,000 actin filaments approximately 1 micron in length crosslinked at high angles by actin-binding protein and which bind to a spectrin-rich submembrane lamina (Fox, J., J. Boyles, M. Berndt, P. Steffen, and L. Anderson. 1988. J. Cell Biol. 106:1525-1538; Hartwig, J., and M. DeSisto. 1991. J. Cell Biol. 112:407-425). Activation of the platelets by contact with glass results within 30 s in a doubling of the polymerized actin content of the cytoskeleton and the appearance of two distinct new actin structures: bundles of long filaments within filopodia that end at the filopodial tips (filopodial bundles) and a circumferential zone of orthogonally arrayed short filaments within lamellipodia (lamellipodial network). Neither of these structures appears in cells exposed to glass with cytochalasin B present; instead the cytoskeletons have numerous 0.1-0.3-microns-long actin filament fragments attached to the membrane lamina. With the same time course as the glass-induced morphological changes, cytochalasin-sensitive actin nucleating activity, initially low in cytoskeletons of resting platelets, increases 10-fold in cytoskeletons of thrombin-activated platelets. This activity decays with a time course consistent with depolymerization of 0.1-0.3-microns-long actin filaments, and phalloidin inhibits this decay. Cytochalasin-insensitive and calcium-dependent nucleation activity also increases markedly in platelet extracts after thrombin activation of the cells. Prevention of the rise in cytosolic Ca2+ normally associated with platelet activation with the permeant Ca2+ chelator, Quin-2, inhibits formation of lamellipodial networks but not filopodial bundles after glass contact and reduces the cytochalasin B-sensitive nucleation activity by 60% after thrombin treatment. The filopodial bundles, however, are abnormal in that they do not end at the filopodial tips but form loops and return to the cell body. Addition of calcium to chelated cells restores lamellipodial networks, and calcium plus A23187 results in cytoskeletons with highly fragmented actin filaments within seconds. Immunogold labeling with antibodies against gelsolin reveals gelsolin molecules at the ends of filaments attached to the submembrane lamina of resting cytoskeletons and at the ends of some filaments in the lamellipodial networks and filopodial bundles of activated cytoskeletons. Addition of monomeric actin to myosin subfragment 1-labeled activated cytoskeletons leads to new (undecorated) filament growth off the ends of filaments in the filopodial bundles and the lamellipodial network. The simplest explanation for these findings is that gelsolin caps the barbed ends of the filaments in the resting platelet. Uncapping some of these filaments after activation leads to filopodial bundles.(ABSTRACT TRUNCATED AT 400 WORDS)     

Tissue-specific accumulation of carotenoids in carrot roots

Raman spectroscopy can be used for sensitive detection of carotenoids in living tissue and Raman mapping provides further information about their spatial distribution in the measured plant sample. In this work, the relative content and distribution of the main carrot (Daucus carota L.) root carotenoids, α-, β-carotene, lutein and lycopene were assessed using near-infrared Fourier transform Raman spectroscopy. The pigments were measured simultaneously in situ in root sections without any preliminary sample preparation. The Raman spectra obtained from carrots of different origin and root colour had intensive bands of carotenoids that could be assigned to β-carotene (1,520 cm⁻¹), lycopene (1,510 cm⁻¹) and α-carotene/lutein (1,527 cm⁻¹). The Raman mapping technique revealed detailed information regarding the relative content and distribution of these carotenoids. The level of β-carotene was heterogeneous across root sections of orange, yellow, red and purple roots, and in the secondary phloem increased gradually from periderm towards the core, but declined fast in cells close to the vascular cambium. α-carotene/lutein were deposited in younger cells with a higher rate than β-carotene while lycopene in red carrots accumulated throughout the whole secondary phloem at the same level. The results indicate developmental regulation of carotenoid genes in carrot root and that Raman spectroscopy can supply essential information on carotenogenesis useful for molecular investigations on gene expression and regulation.     

Antibody-mediated delivery of IL-10 inhibits the progression of established collagen-induced arthritis

The antibody-mediated targeted delivery of cytokines to sites of disease is a promising avenue for cancer therapy, but it is largely unexplored for the treatment of chronic inflammatory conditions. Using both radioactive and fluorescent techniques, the human monoclonal antibodies L19 and G11 (specific to two markers of angiogenesis that are virtually undetectable in normal adult tissues) were found to selectively localize at arthritic sites in the murine collagen-induced model of rheumatoid arthritis following intravenous (i.v.) administration. The same animal model was used to study the therapeutic action of the L19 antibody fused to the cytokines IL-2, tumour necrosis factor (TNF) and IL-10. Whereas L19–IL-2 and L19–TNF treatment led to increased arthritic scores and paw swellings, the fusion protein L19–IL-10 displayed a therapeutic activity, which was superior to the activity of IL-10 fused to an antibody of irrelevant specificity in the mouse. The anti-inflammatory cytokine IL-10 has been investigated for the treatment of patients with rheumatoid arthritis, but clinical development plans have been discontinued because of a lack of efficacy. Because the antigen recognised by L19 is strongly expressed at sites of arthritis in humans and identical in both mice and humans, it suggests that the fusion protein L19–IL-10 might help overcome some of the clinical limitations of IL-10 and provide a therapeutic benefit to patients with chronic inflammatory disorders, including arthritis.