TY - JOUR AB - Most migrating cells extrude their front by the force of actin polymerization. Polymerization requires an initial nucleation step, which is mediated by factors establishing either parallel filaments in the case of filopodia or branched filaments that form the branched lamellipodial network. Branches are considered essential for regular cell motility and are initiated by the Arp2/3 complex, which in turn is activated by nucleation-promoting factors of the WASP and WAVE families. Here we employed rapid amoeboid crawling leukocytes and found that deletion of the WAVE complex eliminated actin branching and thus lamellipodia formation. The cells were left with parallel filaments at the leading edge, which translated, depending on the differentiation status of the cell, into a unipolar pointed cell shape or cells with multiple filopodia. Remarkably, unipolar cells migrated with increased speed and enormous directional persistence, while they were unable to turn towards chemotactic gradients. Cells with multiple filopodia retained chemotactic activity but their migration was progressively impaired with increasing geometrical complexity of the extracellular environment. These findings establish that diversified leading edge protrusions serve as explorative structures while they slow down actual locomotion. AU - Leithner, Alexander F AU - Eichner, Alexander AU - Müller, Jan AU - Reversat, Anne AU - Brown, Markus AU - Schwarz, Jan AU - Merrin, Jack AU - De Gorter, David AU - Schur, Florian AU - Bayerl, Jonathan AU - De Vries, Ingrid AU - Wieser, Stefan AU - Hauschild, Robert AU - Lai, Frank AU - Moser, Markus AU - Kerjaschki, Dontscho AU - Rottner, Klemens AU - Small, Victor AU - Stradal, Theresia AU - Sixt, Michael K ID - 1321 JF - Nature Cell Biology TI - Diversified actin protrusions promote environmental exploration but are dispensable for locomotion of leukocytes VL - 18 ER - TY - JOUR AB - MicroRNAs (miRNAs) are small RNAs that play important regulatory roles in many cellular pathways. MiRNAs associate with members of the Argonaute protein family and bind to partially complementary sequences on mRNAs and induce translational repression or mRNA decay. Using deep sequencing and Northern blotting, we characterized miRNA expression in wild type and miR-155-deficient dendritic cells (DCs) and macrophages. Analysis of different stimuli (LPS, LDL, eLDL, oxLDL) reveals a direct influence of miR-155 on the expression levels of other miRNAs. For example, miR-455 is negatively regulated in miR-155-deficient cells possibly due to inhibition of the transcription factor C/EBPbeta by miR-155. Based on our comprehensive data sets, we propose a model of hierarchical miRNA expression dominated by miR-155 in DCs and macrophages. AU - Dueck, Anne AU - Eichner, Alexander AU - Sixt, Michael K AU - Meister, Gunter ID - 2242 IS - 4 JF - FEBS Letters SN - 00145793 TI - A miR-155-dependent microRNA hierarchy in dendritic cell maturation and macrophage activation VL - 588 ER - TY - JOUR AB - MicroRNAs (miRNAs) are small noncoding RNAs that function in literally all cellular processes. miRNAs interact with Argonaute (Ago) proteins and guide them to specific target sites located in the 3′-untranslated region (3′-UTR) of target mRNAs leading to translational repression and deadenylation-induced mRNA degradation. Most miRNAs are processed from hairpin-structured precursors by the consecutive action of the RNase III enzymes Drosha and Dicer. However, processing of miR-451 is Dicer independent and cleavage is mediated by the endonuclease Ago2. Here we have characterized miR-451 sequence and structure requirements for processing as well as sorting of miRNAs into different Ago proteins. Pre-miR-451 appears to be optimized for Ago2 cleavage and changes result in reduced processing. In addition, we show that the mature miR-451 only associates with Ago2 suggesting that mature miRNAs are not exchanged between different members of the Ago protein family. Based on cloning and deep sequencing of endogenous miRNAs associated with Ago1-3, we do not find evidence for miRNA sorting in human cells. However, Ago identity appears to influence the length of some miRNAs, while others remain unaffected. AU - Dueck, Anne AU - Ziegler, Christian AU - Eichner, Alexander AU - Berezikov, Eugène AU - Meister, Gunter ID - 2946 IS - 19 JF - Nucleic Acids Research TI - MicroRNAs associated with the different human Argonaute proteins VL - 40 ER - TY - JOUR AB - In their search for antigens, lymphocytes continuously shuttle among blood vessels, lymph vessels, and lymphatic tissues. Chemokines mediate entry of lymphocytes into lymphatic tissues, and sphingosine 1-phosphate (S1P) promotes localization of lymphocytes to the vasculature. Both signals are sensed through G protein-coupled receptors (GPCRs). Most GPCRs undergo ligand-dependent homologous receptor desensitization, a process that decreases their signaling output after previous exposure to high ligand concentration. Such desensitization can explain why lymphocytes do not take an intermediate position between two signals but rather oscillate between them. The desensitization of S1P receptor 1 (S1PR1) is mediated by GPCR kinase 2 (GRK2). Deletion of GRK2 in lymphocytes compromises desensitization by high vascular S1P concentrations, thereby reducing responsiveness to the chemokine signal and trapping the cells in the vascular compartment. The desensitization kinetics of S1PR1 allows lymphocytes to dynamically shuttle between vasculature and lymphatic tissue, although the positional information in both compartments is static. AU - Eichner, Alexander AU - Sixt, Michael K ID - 491 IS - 198 JF - Science Signaling TI - Setting the clock for recirculating lymphocytes VL - 4 ER - TY - JOUR AB - Cancer stem cells or cancer initiating cells are believed to contribute to cancer recurrence after therapy. MicroRNAs (miRNAs) are short RNA molecules with fundamental roles in gene regulation. The role of miRNAs in cancer stem cells is only poorly understood. Here, we report miRNA expression profiles of glioblastoma stem cell-containing CD133 + cell populations. We find that miR-9, miR-9 * (referred to as miR-9/9 *), miR-17 and miR-106b are highly abundant in CD133 + cells. Furthermore, inhibition of miR-9/9 * or miR-17 leads to reduced neurosphere formation and stimulates cell differentiation. Calmodulin-binding transcription activator 1 (CAMTA1) is a putative transcription factor, which induces the expression of the anti-proliferative cardiac hormone natriuretic peptide A (NPPA). We identify CAMTA1 as an miR-9/9 * and miR-17 target. CAMTA1 expression leads to reduced neurosphere formation and tumour growth in nude mice, suggesting that CAMTA1 can function as tumour suppressor. Consistently, CAMTA1 and NPPA expression correlate with patient survival. Our findings could provide a basis for novel strategies of glioblastoma therapy. AU - Schraivogel, Daniel AU - Weinmann, Lasse AU - Beier, Dagmar AU - Tabatabai, Ghazaleh AU - Eichner, Alexander AU - Zhu, Jia AU - Anton, Martina AU - Sixt, Michael K AU - Weller, Michael AU - Beier, Christoph AU - Meister, Gunter ID - 518 IS - 20 JF - EMBO Journal TI - CAMTA1 is a novel tumour suppressor regulated by miR-9/9 * in glioblastoma stem cells VL - 30 ER -