Article |
Address correspondence to Dan P. Felsenfeld, Dept. of Pharmacology and Biological Chemistry, Box 1215, One Gustave L. Levy Pl., Mt. Sinai School of Medicine, New York, NY 10029. Tel.: (212) 659-1723. Fax: (212) 831-0114. email: dan.felsenfeld{at}mssm.edu
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Abstract |
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Key Words: cell migration; single particle tracking; traction force; cell adhesion; axon growth
J.A. Kuo's present address is Medical College of Georgia, Augusta, GA 30912.
Abbreviations used in this paper: ERM, ezrin, radixin, moesin; IgCAM, immunoglobulin superfamily cell adhesion molecule; L1CAM, L1 cell adhesion molecule.
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Introduction |
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A variety of adhesion receptor families have been shown to serve as receptors for permissive, substrate-bound molecules that promote axon outgrowth, including integrins, immunoglobulin superfamily cell adhesion molecules (IgCAMs), and cadherins (Kamiguchi and Yoshihara, 2001). In light of the demonstrated role of IgCAMs in the guided growth of neuronal processes during development (Kamiguchi and Lemmon, 2000; Rutishauser, 2000), understanding the biophysical properties of these of proteins may provide crucial insight into the mechanism underlying growth cone translocation.
In the vertebrate central nervous system, L1 cell adhesion molecule (L1CAM), a neuronal IgCAM, plays an essential role in the guidance of descending cortico-spinal tract neurons (Dahme et al., 1997; Cohen et al., 1998). L1CAM is the founding member of a subfamily of neuronal IgCAMs that include both vertebrate and invertebrate members (Hortsch, 2000). L1CAM mutations in humans lead to a variety of developmental defects, including corpus callosum hyperplasia, mental retardation, adducted thumbs, spastic paraplegia, and hydrocephalus (CRASH syndrome), suggesting that L1CAM plays a crucial role in the development of the central nervous system (Fransen et al., 1995). Moreover, the capacity of substrate-bound L1CAM ligands to promote neurite extension in vitro through homophilic binding (Lemmon et al., 1989; Kuhn et al., 1991; Felsenfeld et al., 1994) raises the possibility that L1CAM on the growth cone may mediate traction-force generation in a mechanism similar to that observed for integrins in other cell types.
The regulation of receptor distribution, movement, and function in adhesion and migration depends on the connection between these glycoproteins and the cytoskeleton. L1CAM and L1 family members interact with four known cytosolic binding partners through two discrete sites in the cytoplasmic tail, including ankyrin, components of the clathrin AP-2 complex, ezrin, radixin, moesin (ERM) proteins, and doublecortin (Zhang et al., 1998; Dickson et al., 2002; Kizhatil et al., 2002; Schaefer et al., 2002). The binding of L1 family members to members of the ankyrin family of cytoskeletal adaptor proteins is perhaps the best characterized of these interactions (Davis and Bennett, 1994; Garver et al., 1997; Hortsch et al., 1998). The L1 family member neurofascin binds to ankyrin through a motif that is highly conserved among L1 family members near the carboxy terminus of the cytoplasmic tail (Garver et al., 1997). The ankyrin-binding site, mapped based on the interaction between neurofascin and ankyrin G, is comprised of a core 12-aa motif that is essential for ankyrin binding, including a carboxy-terminal tyrosine (QFNEDGSFIGQY; identical in neurofascin and L1 from rat; Miura et al., 1991; Zhang et al., 1998). In neurofascin, ankyrin binds to this motif in its dephosphorylated state (Garver et al., 1997). Mutations at this site in human L1CAM lead to a similar disruption in ankyrin binding (Needham et al., 2001). However, the Drosophila L1 homologue neuroglian, although requiring the FIGQY motif for ankyrin recruitment, appears to be regulated primarily through oligomerization of the extracellular domain (Dubreuil et al., 1996). At a functional level, the binding of ankyrin to L1 family members like neurofascin plays a critical role in cell adhesion (Tuvia et al., 1997).
The work presented here is directed at understanding the regulation of L1CAM function as reflected in changes in its diffusion kinetics. Quantifying directly the movement of receptors on the upper surface of the cell provides an accurate reflection of receptor function on the lower surface, where cells exert traction forces during migration (Galbraith and Sheetz, 1999). Therefore, the detailed analysis of L1CAM kinetics in the plane of the membrane may provide crucial insight into the mechanism underlying L1CAM function in both axon growth during development and static adhesion between mature axons. Previous work has revealed that L1 family members display two discrete diffusion rates on the cell surface, consistent with protein that is either bound or unbound from the cytoskeleton (Pollerberg et al., 1990; Garver et al., 1997). However, as this work relies on photobleaching of populations of receptors, it provides no information about the directed movement of protein in the lower diffusion state. Here, we describe evidence for three distinct classes of L1CAM movement on the cell surface, including diffusing, nondiffusing with directed movement (retrograde), and nondiffusing without directed movement (stationary). Although the stationary state of L1CAM depends on ankyrin binding to the L1CAM tail, retrograde movement occurs under conditions that inhibit ankyrin binding and depends on interactions between the L1CAM cytoplasmic tail and dynamic actin in the cytosol. Ankyrin binding inhibits L1CAM retrograde movement, suggesting that ankyrin may play a crucial role in effecting the switch between the stationary and directed behavior of L1CAM on the cell surface. More significantly, peptides that inhibit ankyrin binding stimulate L1CAM-mediated neuronal extension, suggesting that the regulation of L1CAM-mediated traction-force generation is essential to the migration of neuronal growth cones on L1CAM ligands in vivo.
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Results |
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To determine whether the low diffusive states of L1CAM on the cell surface are mediated directly by the L1CAM cytoplasmic tail, we generated a truncation mutant of L1CAM that interrupts the cytoplasmic tail with a stop mutation 4 aa after the predicted transmembrane domain. Beads bound to truncated L1CAM on the cell surface diffused in 100% of trials (Fig. 4 B; n = 17, P < .01), suggesting that both retrograde movement and stationary behavior depend on interactions between the L1CAM cytoplasmic tail and the cytoskeleton.
Mutations that affect ankyrin binding modulate L1CAM movement in the plane of the membrane
To examine directly the role of L1CAMcytoskeleton interactions in L1CAM movement on the upper surface, we introduced a series of point mutations into the region of the L1CAM tail that has been implicated in ankyrin binding. Mutant constructs were generated encoding single aa substitutions for tyrosine1229 to either phenylalanine, a mutation that induces constitutive ankyrin binding in other vertebrate L1 family members (L1-YF; Garver et al., 1997; Tuvia et al., 1997), or to histidine to inhibit ankyrin binding (L1-YH; a naturally occurring MASA mutation in humans; Garver et al., 1997; Tuvia et al., 1997; Needham et al., 2001). Each of these constructs was expressed in ND-7 cells and displayed cell surface distribution comparable to that seen for wild-type L1CAM (Fig. 1, BD). In culture, 9E10 beads placed on the upper surface of the cell with a laser trap bound with a frequency similar to that seen in cells expressing wild-type mycL1CAM. Like wild-type L1CAM, L1-YF displayed a combination of diffusive, retrograde, and stationary behaviors. However, the ratio of these behaviors was different from that of the wild-type receptor, showing an increase in stationary behavior (62.5%) with a commensurate decrease in retrograde movement (37.5%; Fig. 4 B; n = 16, P < .01). In contrast, beads bound to the L1-YH mutant showed a large increase in the percentage of trials undergoing retrograde movement (92.9%) and a complete loss of stationary behavior (Fig. 4 B; n = 14, P < .011). These results suggest that L1CAM stationary behavior is mediated by ankyrin binding, whereas the retrograde movement of L1CAM on the cell surface is ankyrin independent.
Growth factor treatment inhibits ankyrin recruitment and L1CAM stationary behavior at the cell surface
To test further this hypothesis, we examined the behavior of wild-type L1CAM (including the myc-epitope tag) after growth factor treatment. It has been reported previously that tyrosine phosphorylation of L1 family members at the FIGQY motif is modulated by activation of a variety of membrane-linked tyrosine kinase receptors, including receptors for NGF, FGF, EGF (Garver et al., 1997), and by the Eph kinase Cek5 (Zisch et al., 1997). L1CAM-transfected 293 cells recruited ankyrin to the membrane in an L1CAM-dependent manner (Fig. 5, A, C, and E). Treatment of these cells with EGF (50 ng/ml; 1 h) inhibited ankyrin membrane localization (Fig. 5, B, D, and F), similar to the behavior of other L1 family members (Zhang et al., 1998) and consistent with a phosphorylation-dependent inhibition of L1CAMankyrin binding. Measurement of ankyrin immunolocalization along a line drawn across the junction of L1CAM-positive cells (Fig. 5 H; Oancea et al., 1998) demonstrates a quantifiable and significant change in ankyrinmembrane association (Fig. 5 G; P < .01). Similar results were obtained using ND-7 cells treated with NGF (unpublished data), suggesting that these cells, derived from primary sensory neurons, have maintained their sensitivity to NGF.
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Peptides derived from the L1CAM tail inhibit ankyrin binding and stationary behavior by L1CAM on the cell surface
To examine independently the role of ankyrin binding in the directed movement of L1, we designed peptides directed at inhibiting L1ankyrin interactions in live cells. The inhibitory peptide is a fusion between the ankyrin-binding region of the L1CAM tail and the membrane-permeable penetratin domain of antennapedia (Derossi et al., 1998). The inhibitory region of this peptide was derived from the 12-aa conserved ankyrin-binding domain of the L1CAM tail (Zhang et al., 1998) including a Y to F substitution (QFNEDGSFIGQF; AP-YF). Peptide activity was compared with that of a peptide in which the inhibitory sequence was reversed (AP-Scramble).
To test the function of the AP-YF in situ, we examined its capacity to inhibit L1CAM-mediated recruitment of ankyrin to the cell membrane. In the presence of peptide AP-YF, ankyrinB was almost entirely absent from sites of cellcell contact (Fig. 6 A). In contrast, in the absence of peptide or in the presence of the control, scrambled peptide, ankyrinB appeared at the cell membrane where L1CAM was expressed (Fig. 6 A; unpublished data). Quantification of ankyrin colocalization with L1CAM at the membrane revealed a significant reduction in the junctional distribution of ankyrin in AP-YFtreated cells (Fig. 6 A; P < 0.01). These results suggest that the AP-YF peptide is an effective inhibitor of L1CAMankyrin interactions in live cells.
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To address this question, we quantified the velocity of bead movement in trials undergoing translocation on the cell surface in the presence of AP-YF or control peptides. Cells cultured in the presence of inhibitory peptide showed, on average, a twofold increase in the velocity of L1CAM-directed movement on the cell surface as compared with cells treated with control peptide (Fig. 6 C; P < 0.01) or untreated cells (P < 0.01). The movement of L1CAM in the presence of control peptide was largely unaffected. Similarly, analysis of mutant L1-YH, which is also deficient in ankyrin binding, displays a significant increase in the rate of directed protein movement on the cell surface as compared with untreated cells expressing wild-type L1CAM (P < 0.01). The change in mean velocity does not merely reflect the decrease in the percentage of stationary beads, as beads with a mean velocity of 0 were not included in the calculated average velocity. Together, these results implicate L1CAMankyrin interactions in the regulation of L1CAM-directed movement on the cell surface.
Inhibitors of ankyrin binding stimulate L1CAM-mediated neurite outgrowth
The changes in bead kinetics on the upper surface of the cell raise the possibility that the role of ankyrin binding in vivo may be to differentially regulate the adhesion and migration of growing neurons. To address this question directly, we cultured mouse cerebellar granular neurons in the presence of either inhibitory AP-YF or control peptides (Fig. 7). These neurons use cell surface L1CAM as the primary receptor for substrate-bound L1CAM ligands (Dahme et al., 1997), permitting us to test directly L1CAM function in neurite extension. Neurons grown on NgCAM, a chick homologue of L1CAM, extend 21 µm (± 2) after 24 h in culture in the presence of control peptides. In contrast, neurons cultured in the presence of AP-YF extend 55% above control levels (32 ± 2 µm; P < 0.01). Axon extension on laminin, which promotes outgrowth through interactions with cell surface integrins (Felsenfeld et al., 1994), was not significantly affected by peptide treatment (P > 0.05). These results suggest that L1CAM-dependent neuronal growth is modulated by changes in L1CAMankyrin interactions. Additionally, these results support the idea that traction-force generation in the neuronal growth cone plays a role in neurite extension.
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Discussion |
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Both retrograde and stationary behaviors depend on the interactions of the L1CAM cytoplasmic tail. L1CAM truncation mutants (Stop) diffuse freely on the cell surface, demonstrating that the L1CAM cytoplasmic domain is crucial for these phenomena, and suggesting that cis interactions with other receptors in the bilayer contribute little to the restricted movement of L1CAM in our assay system. The effects of cytochalasin D treatment suggest that dynamic actin in the cytosol mediates L1CAM retrograde movement. In combination with the velocity and direction of retrograde movement, these results strongly suggest that L1CAM, like other cell surface glycoproteins, associates with treadmilling actin in the lamella of the cell (Fig. 8 B, I; Felsenfeld et al., 1996; Suter et al., 1998; Lambert et al., 2002). However, the observed decrease in retrograde movement after nocadazole treatment raises the possibility that microtubules may also play some part in this process. Conditions that inhibit ankyrin binding, including L1-YH mutants, consistently stimulate retrograde movement, suggesting that ankyrin is not the primary adaptor in this process. In contrast, stationary behavior is independent of dynamic actin and microtubules, suggesting that a distinct cytoskeletal pool, perhaps the membrane skeleton, serves as a transient attachment site for L1CAM in the cytosol (Fig. 8 B, III). Mutations and treatments that inhibit or block ankyrin binding including L1-YH, growth factors, and the AP-YF peptide all inhibit stationary behavior of L1CAM, indicating that ankyrin binding to the FIGQY motif in L1CAM plays a primary role in this process.
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The anti-coordinate regulation of retrograde and stationary behavior by ankyrin binding has important implications for the function of L1CAM in live cells. Although it is reasonable to assume that ankyrin binding modulates the activity of an independent cytoskeletal adaptor protein responsible for the interaction between L1CAM and treadmilling actin, the mechanism underlying this regulation has not been determined. First, ankyrin could serve as a competitive inhibitor for a distinct adaptor protein that binds at the same site on L1CAM. Although it is unlikely that doublecortin mediates L1CAM retrograde movement, we cannot preclude the existence of other proteins that bind at or near the FIGQY motif in the L1CAM tail. Second, ankyrin binding could induce a change in the conformation of the L1CAM tail that inhibits interactions with other adaptor proteins at a distance. Finally, the L1CAM tail may serve as a mechanical integrator of traction forces and as the restraining force provided by ankyrin binding (Fig. 8 B, II). According to this model, ankyrin binding would retard the movement of L1CAM being dragged backward through the membrane through an indirect interaction with treadmilling actin.
Previous work focusing on traction-force generation alone has shed little light on how cells regulate the transition between adhesion and migration (Felsenfeld et al., 1996; Choquet et al., 1997), a common occurrence in vivo. The experiments described here raise the possibility that the modulation of adhesion receptorcytoskeleton interactions plays an essential role in the regulation of cell migration and adhesion by effecting changes in the capacity of these proteins to transfer traction forces to the extracellular environment. Moreover, the observation of a single receptor with three discrete kinetic behaviors on the cell surface is, to the best of our knowledge, entirely novel. The versatility of L1CAM in this respect may reflect a critical feature of the biology of L1CAM; the repertoire of L1 family members is relatively limited compared with other families of adhesion receptors (e.g., integrins, cadherins). Therefore, modulation of L1CAM-mediated neuronal growth may require post-translational regulation rather than a change in receptor expression. This type of direct modulation would also provide a means for rapidly promoting or arresting cell movement, which may be required during axon guidance. The capacity of a single cytosolic interaction to modulate the function of a receptor between static adhesion and traction-force generation raises the possibility that ankyrin binding may serve as a master switch for L1 function in these two classes of cell behavior, an idea that is strongly supported by the nerve growthpromoting properties of the inhibitory peptide. This form of direct modulation has important implications for the regulation of the shift from nerve growth to static adhesion during neural development.
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Materials and methods |
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L1CAM-GFP was generated by linking GFP2 (PerkinElmer) in frame to the carboxy terminus of the full-length wild-type L1CAM construct by PCR.
Ankyrin cell membrane recruitment assay
Constructs encoding full-length wild-type L1CAM including the RSLE mini-exon and either by an amino-terminal myc-epitope tag or by a carboxy-terminal GFP tag (see cDNA constructs above) were introduced by LipofectAMINETM plus (Invitrogen) transfection into human kidney 293 cells. Cells were used 2448 h after transfection or as stable pooled lines of L1CAM-expressing cells. L1CAM expression was detected by indirect immunofluorescence using an antibody against either L1CAM (rabbit anti-L1CAM; gift of Carl Lagenaur, University of Pittsburgh, Pittsburgh, PA), by 9E10 (mouse anti-myc; Developmental Studies Hybridoma Bank, University of Iowa, Iowa City, IA), or by GFP distribution. In all cases, the results were indistinguishable. Ankyrin B was detected by indirect immunofluorescence using a mouse mAb (BD Biosciences). Confocal micrographs (Olympus) were collected at a plane intersecting cellcell junctions. Control images collected by exciting fluorophores with the inappropriate laser line revealed no detectable crosstalk between channels.
Images were analyzed using NIH ImageJ (National Institutes of Health (NIH), Bethesda, MD) under Macintosh OSX. Densitometry was performed using a 5 pixel-wide line scan normal to the interface between two L1CAM-positive cells. Signal maximum for ankyrin staining at junction between cells was determined at the position of the maximal L1CAM staining to ensure that we were quantifying membrane rather that juxtamembrane staining. Minima were determined from the regions of the line overlapping the cytoplasm of either of the two cells. Membrane localization index was determined using the equation index = max/(max-min) (Oancea et al., 1998).
Immunofluorescence
For immunolocalization, cells were fixed for 10 min using 1% PFA in 60 mM Pipes, 25 mM Hepes, 10 mM EGTA, and 2 mM MgCl2 (PHEM; Schliwa and van Blerkom, 1981). Staining was performed as described previously (Felsenfeld et al., 1999). Micrographs were collected on a microscope (Axiovert 100TV; Carl Zeiss MicroImaging, Inc.) using a 100x plan neofluor objective (NA 1.4). Antigens were detected by indirect immunofluorescence using primary antibodies described in figure legends and secondary antibodies (either donkey antirabbit or donkey antimouse) conjugated to indocarbocyanin Cy3 (Jackson ImmunoResearch Laboratories). Micrographs were collected using a cooled CCD camera (CoolSNAP HQTM; Roper Scientific) under the control of ISee imaging software (ISee Imaging Systems). Images were subsequently processed in Photoshop® (Adobe) to maximize contrast, and were subject to an unsharp mask.
Antennapedia peptides
Inhibitory peptides were generated as a fusion between the 16-aa penetratin domain of antennapedia at the amino end and the ankyrin-binding domain of L1CAM with the carboxy-terminal tyrosine modified to phenylalanine (inhibitory peptide sequence RQIKIWFQNRRMKWKKQFNEDGSFIGQF). Control peptides were identical with a reversed ankyrin-binding domain (control peptide sequence RQIKIWFQNRRMKWKKFQGIFSGDENFQ). Both peptides included an amino-terminal biotin. Peptides were synthesized by FastMoc chemistry (Tufts University Core Facility, Boston, MA) and purified by HPLC yielding >97% purity as determined by mass spectrometry. Peptides were dissolved in HBSS at 1 mg/ml and diluted into cell culture medium at a final concentration of 1.4 µg/ml.
Bead preparation
Beads were prepared as described previously (Choquet et al., 1997; Felsenfeld et al., 1999). 1-µm carboxylated latex microspheres (Polyscience) were covalently coupled to ovalbumin (fraction VII; Sigma-Aldrich) using a carbodiimide linkage to neutralize the bead surface. Ovalbumin-coated beads were derivatized with Sulpho-NHS-LC-biotin (Pierce Chemical Co.). Beads at this stage were used fresh or stored for up to 2 wk at 4°C. Biotinylated beads were subsequently incubated with an excess of neutravidin (Molecular Probes, Inc.) overnight at 4°C. Beads were washed extensively, and a 15-µl aliquot (based on starting concentration) was incubated with biotinylated 9E10 antibody for 1 h (at RT) or overnight (at 4°C). Unreacted sites were blocked with biotin-BSA (BSA-biotinamidocaproyl; Sigma-Aldrich). Beads were sonicated for 5 s in a 0°C bath sonicator before experiments.
Cell culture and transfection
Neuroblastoma/DRG hybrid cells (ND-7) were transfected with constructs encoding either wild-type or mutant forms of L1CAM expressed in a bicistronic vector encoding EGFP after an internal ribosomal entry site (pIRES2-EGFP; CLONTECH Laboratories, Inc.). ND-7 cells were plated in L15 buffered for CO2 (supplemented with 1:1:2 glucose/glutamine/Pen-Strep and with dimethlytetrahydropterine, glutathione, and ascorbic acid; Cell and Molecular Technologies) containing 10% bovine calf serum (Hyclone) on coverslips 24 h before transfection. For video microscopy, medium was replaced before moving cells to the microscope with phenol redfree, serum-free L15 (air buffered) with 20 mM Hepes, 0.1% BSA, and 0.5% ovalbumin. Coverslips were silanized and laminin-coated for video microscopy as described previously (Felsenfeld et al., 1996). Alternatively, cells were plated on coverslips coated with poly-D-lysine and laminin sealed to the bottom of 35-mm culture dishes (MatTek Corporation). Transfections were performed using LipofectAMINETM plus (Invitrogen), and cells were used 2436 h later either live for video microscopy or fixed for immunohistochemistry.
Video microscopy, laser tweezers, and data analysis
Video microscopy was performed largely as described previously (Felsenfeld et al., 1999). All experiments were performed on a microscope (Axiovert 100 TV; Carl Zeiss MicroImaging, Inc.). Cells on laminin-coated coverslips were cultured in sealed chambers permitting illumination with a high resolution, oil immersion condenser. Images were collected and laser trap formed through a 100x plan neofluor NA 1.4 objective. The laser trap consisted of a Titanium Sapphire laser (model 890; Coherent) pumped by a 5-W Neodymium Vanadate laser (Coherent; Verdi) and tuned to 800 nm. Laser power at the output of the Ti:Sapp was 40 mW, and beads were placed and held on the cell surface for <3 s to further reduce the possibility of heating artifacts. Video images were collected using a Newvicon camera (VE-1000N; Dage MTI), and were subsequently digitized onto an Intel processor-based computer running the ISee software (ISee Imaging) for quantification. Diffusion analysis was performed using a custom spreadsheet in Excel (Microsoft). Individual traces were scored blind for classes of behavior. Statistical analysis of percentages of trials was performed using chi-squared analysis or a Fisher's exact probability test (Fig. 6 B). For cytoskeleton attachment assays (Fig. 2), beads were retested with a second pulse from the laser trap applied 0.5 µm from the bead center. Lateral movement of beads <0.2 µm was scored as rigidly attached.
Neurite outgrowth assays
For neurite outgrowth assays, 50 µg/ml purified chick NgCAM or 100 µg/ml mouse laminin (Invitrogen) was spotted on a 35-mm plastic culture dish at RT for 1 h. After washing with PBS, the plastic surface was blocked with 1% BSA/PBS at RT. Cerebellar cells were prepared from postnatal day 4 (P4) mouse by trypsinization followed by trituration. Cells were resuspended in BME/B27 with Pen/Strep (GIBCO BRL) at 5 x 105 cells/ml, and 250 µl was plated on the dishes. Cultures were incubated at 37°C for 24 h in 5% CO2. Antennapedia peptides dissolved in HBSS (GIBCO BRL) were added to the cultures at final concentration of 30 µg/ml when cells were plated. Cultures were fixed with 4% PFA, and images were captured as described earlier in Materials and methods. Neurite outgrowth measurements were performed by NIH image software and processed with Microsoft Excel. P values were determined using t test analysis.
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Acknowledgments |
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This work was supported by NIH grant GM63192-01 and by a grant from the Speaker's Fund of the New York Academy of Medicine. D.P. Felsenfeld is the Dale F. and Betty Ann Frey Scholar of the Damon Runyon Cancer Research Foundation.
Submitted: 4 November 2002
Accepted: 27 June 2003
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References |
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Bretscher, A., K. Edwards, and R.G. Fehon. 2002. ERM proteins and merlin: integrators at the cell cortex. Nat. Rev. Mol. Cell Biol. 3:586599.[CrossRef][Medline]
Choquet, D., D.P. Felsenfeld, and M.P. Sheetz. 1997. Extracellular matrix rigidity causes strengthening of integrin-cytoskeleton linkages. Cell. 88:3948.[Medline]
Cohen, N.R., J.S. Taylor, L.B. Scott, R.W. Guillery, P. Soriano, and A.J. Furley. 1998. Errors in corticospinal axon guidance in mice lacking the neural cell adhesion molecule L1. Curr. Biol. 8:2633.[Medline]
Dahme, M., U. Bartsch, R. Martini, B. Anliker, M. Schachner, and N. Mantei. 1997. Disruption of the mouse L1 gene leads to malformations of the nervous system. Nat. Genet. 17:346349.[Medline]
Davis, J.Q., and V. Bennett. 1994. Ankyrin binding activity shared by the neurofascin/L1/NrCAM family of nervous system cell adhesion molecules. J. Biol. Chem. 269:2716327166.
De Angelis, E., T. Brummendorf, L. Cheng, V. Lemmon, and S. Kenwrick. 2001. Alternative use of a mini exon of the L1 gene affects L1 binding to neural ligands. J. Biol. Chem. 276:3273832742.
Derossi, D., G. Chassaing, and A. Prochiantz. 1998. Trojan peptides: the penetratin system for intracellular delivery. Trends Cell Biol. 8:8487.[CrossRef][Medline]
Dickson, T.C., C.D. Mintz, D.L. Benson, and S.R. Salton. 2002. Functional binding interaction identified between the axonal CAM L1 and members of the ERM family. J. Cell Biol. 157:11051112.
Dubreuil, R.R., G. MacVicar, S. Dissanayake, C. Liu, D. Homer, and M. Hortsch. 1996. Neuroglian-mediated cell adhesion induces assembly of the membrane skeleton at cell contact sites. J. Cell Biol. 133:647655.[Abstract]
Dunn, P.M., P.R. Coote, J.N. Wood, G.M. Burgess, and H.P. Rang. 1991. Bradykinin evoked depolarization of a novel neuroblastoma x DRG neurone hybrid cell line (ND7/23). Brain Res. 545:8086.[CrossRef][Medline]
Evan, G.I., G.K. Lewis, G. Ramsay, and J.M. Bishop. 1985. Isolation of monoclonal antibodies specific for human c-myc proto-oncogene product. Mol. Cell. Biol. 5:36103616.[Medline]
Felsenfeld, D.P., M.A. Hynes, K.M. Skoler, A.J. Furley, and T.M. Jessell. 1994. TAG-1 can mediate homophilic binding, but neurite outgrowth on TAG-1 requires an L1-like molecule and beta 1 integrins. Neuron. 12:675690.[Medline]
Felsenfeld, D.P., D. Choquet, and M.P. Sheetz. 1996. Ligand binding regulates the directed movement of beta1 integrins on fibroblasts. Nature. 383:438440.[CrossRef][Medline]
Felsenfeld, D.P., P.L. Schwartzberg, A. Venegas, R. Tse, and M.P. Sheetz. 1999. Selective regulation of integrincytoskeleton interactions by the tyrosine kinase Src. Nat. Cell Biol. 1:200206.[CrossRef][Medline]
Fransen, E., V. Lemmon, G. Van Camp, L. Vits, P. Coucke, and P.J. Willems. 1995. CRASH syndrome: clinical spectrum of corpus callosum hypoplasia, retardation, adducted thumbs, spastic paraparesis and hydrocephalus due to mutations in one single gene, L1. Eur. J. Hum. Genet. 3:273284.[Medline]
Galbraith, C.G., and M.P. Sheetz. 1999. Keratocytes pull with similar forces on their dorsal and ventral surfaces. J. Cell Biol. 147:13131324.
Garver, T.D., Q. Ren, S. Tuvia, and V. Bennett. 1997. Tyrosine phosphorylation at a site highly conserved in the L1 family of cell adhesion molecules abolishes ankyrin binding and increases lateral mobility of neurofascin. J. Cell Biol. 137:703714.
Harris, A.K., P. Wild, and D. Stopak. 1980. Silicone rubber substrata: a new wrinkle in the study of cell locomotion. Science. 208:177179.[Medline]
Hortsch, M. 2000. Structural and functional evolution of the L1 family: are four adhesion molecules better than one? Mol. Cell. Neurosci. 15:110.[CrossRef][Medline]
Hortsch, M., K.S. O'Shea, G. Zhao, F. Kim, Y. Vallejo, and R.R. Dubreuil. 1998. A conserved role for L1 as a transmembrane link between neuronal adhesion and membrane cytoskeleton assembly. Cell Adhes. Commun. 5:6173.[Medline]
Kamiguchi, H., and V. Lemmon. 2000. IgCAMs: bidirectional signals underlying neurite growth. Curr. Opin. Cell Biol. 12:598605.[CrossRef][Medline]
Kamiguchi, H., and F. Yoshihara. 2001. The role of endocytic L1 trafficking in polarized adhesion and migration of nerve growth cones. J. Neurosci. 21:91949203.
Kizhatil, K., Y.X. Wu, A. Sen, and V. Bennett. 2002. A new activity of doublecortin in recognition of the phospho-FIGQY tyrosine in the cytoplasmic domain of neurofascin. J. Neurosci. 22:79487958.
Kuhn, T.B., E.T. Stoeckli, M.A. Condrau, F.G. Rathjen, and P. Sonderegger. 1991. Neurite outgrowth on immobilized axonin-1 is mediated by a heterophilic interaction with L1(G4). J. Cell Biol. 115:11131126.[Abstract]
Lambert, M., D. Choquet, and R.M. Mege. 2002. Dynamics of ligand-induced, Rac1-dependent anchoring of cadherins to the actin cytoskeleton. J. Cell Biol. 157:469479.
Lemmon, V., K.L. Farr, and C. Lagenaur. 1989. L1-mediated axon outgrowth occurs via a homophilic binding mechanism. Neuron. 2:15971603.[Medline]
Miura, M., M. Kobayashi, H. Asou, and K. Uyemura. 1991. Molecular cloning of cDNA encoding the rat neural cell adhesion molecule L1. Two L1 isoforms in the cytoplasmic region are produced by differential splicing. FEBS Lett. 289:9195.[CrossRef][Medline]
Needham, L.K., K. Thelen, and P.F. Maness. 2001. Cytoplasmic domain mutations of the L1 cell adhesion molecule reduce L1-ankyrin interactions. J. Neurosci. 21:14901500.
Oancea, E., M.N. Teruel, A.F. Quest, and T. Meyer. 1998. Green fluorescent protein (GFP)-tagged cysteine-rich domains from protein kinase C as fluorescent indicators for diacylglycerol signaling in living cells. J. Cell Biol. 140:485498.
Pollerberg, G.E., J. Davoust, and M. Schachner. 1990. Lateral mobility of the cell adhesion molecule L1 within the surface membrane of morphologically undifferentiated and differentiated neuroblastoma cells. Eur. J. Neurosci. 2:712717.[Medline]
Rutishauser, U. 2000. Defining a role and mechanism for IgCAM function in vertebrate axon guidance. J. Cell Biol. 149:757760.
Schaefer, A.W., Y. Kamei, H. Kamiguchi, E.V. Wong, I. Rapoport, T. Kirchhausen, C.M. Beach, G. Landreth, S.K. Lemmon, and V. Lemmon. 2002. L1 endocytosis is controlled by a phosphorylation-dephosphorylation cycle stimulated by outside-in signaling by L1. J. Cell Biol. 157:12231232.
Schliwa, M., and J. van Blerkom. 1981. Structural interaction of cytoskeletal components. J. Cell Biol. 90:222235.
Suter, D.M., L.D. Errante, V. Belotserkovsky, and P. Forscher. 1998. The Ig superfamily cell adhesion molecule, apCAM, mediates growth cone steering by substrate-cytoskeletal coupling. J. Cell Biol. 141:227240.
Tessier-Lavigne, M., and C.S. Goodman. 1996. The molecular biology of axon guidance. Science. 274:11231133.
Tuvia, S., T.D. Garver, and V. Bennett. 1997. The phosphorylation state of the FIGQY tyrosine of neurofascin determines ankyrin-binding activity and patterns of cell segregation. Proc. Natl. Acad. Sci. USA. 94:1295712962.
Zhang, X., J.Q. Davis, S. Carpenter, and V. Bennett. 1998. Structural requirements for association of neurofascin with ankyrin. J. Biol. Chem. 273:3078530794.
Zisch, A.H., W.B. Stallcup, L.D. Chong, K. Dahlin-Huppe, J. Voshol, M. Schachner, and E.B. Pasquale. 1997. Tyrosine phosphorylation of L1 family adhesion molecules: implication of the Eph kinase Cek5. J. Neurosci. Res. 47:655665.[CrossRef][Medline]
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