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First published online 13 June 2006
doi: 10.1242/jcs.03006
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Research Article |
Misaki Marine Biological Station, University of Tokyo, 1024 Ko-Ajiro, Misaki, Miura, Kanagawa 238-0225, Japan
e-mail: togot{at}mmbs.s.u-tokyo.ac.jp
Accepted 4 April 2006
| Summary |
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-tubulin and end-binding protein 1 (EB1) revealed that membrane disruption initially induced disassembly of microtubules around the wound site, followed by elongation of microtubules toward the wound site. Recruitment of EB1 to microtubules required Ca2+ influx, but was independent of PKC. NBD C6-ceramide, a probe for the Golgi apparatus and Golgi-derived lipids, initially stained the perinuclear region, and a portion of the probe was translocated to the wound site 5 minutes after wounding. Translocation of the lipids required microtubules and PKC activity, and was suppressed by low temperature. On the other hand, constitutive traffic of the lipid was still normal in the presence of a PKC inhibitor. These findings suggest that membrane disruption stimulates regulated vesicle traffic from the region of the trans-Golgi network to the wound site along rearranged microtubules in a PKC-dependent manner.
Key words: Membrane resealing, Microtubule, EB1, NBD C6-ceramide
| Introduction |
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When cells are wounded twice, the second membrane disruption generally reseals more quickly than the initial wound (Togo et al., 1999
; Togo et al., 2003
). The faster membrane resealing is due to an increased amount of exocytosis after repeated wounds. Two different signaling responses, potentiated and facilitated, have been described, dependent on the site of the second wound relative to the first (Togo et al., 2003
). The potentiated response is characterized by a faster resealing response to a second wound at a different site. On the other hand, the facilitated response is characterized by a faster resealing response to a second wound at the same initial wound site, depends on both a threshold extracellular Ca2+ concentration and protein kinase C (PKC) activity, and is sensitive to brefeldin A (BFA) (Togo et al., 1999
; Togo et al., 2003
; Shen and Steinhardt, 2005
). Specifically, when the same site of a cell membrane is wounded twice within 5 minutes in the presence of Gö-6976, a specific inhibitor for PKC-
and ß1 (Martiny-Baron et al., 1993
), facilitation of membrane resealing at a second wound is inhibited (Togo et al., 1999
; Togo et al., 2003
). However, inhibition of PKC by Gö-6976 has no effect on the facilitation of second wound resealing at a different wound site (Togo et al., 2003
). BFA inhibition of vesicle traffic from the Golgi complex (Klausner et al., 1992
) produces a similar pattern of inhibition of facilitation for second wounds at the same or different sites as does Gö-6976 (Togo et al., 1999
; Togo et al., 2003
; Shen and Steinhardt, 2005
). BFA does not affect membrane resealing after an initial wound (Togo et al., 1999
), even though several studies have shown that BFA also induces membrane tubulation of endosomes and lysosomes (Klausner et al., 1992
). These results strongly suggest that membrane traffic from the region of the trans-Golgi network (TGN) is directed toward the site where the vesicle pool has been depleted by a previous membrane disruption.
One aim of the present study was to clarify the behavior of microtubules (MTs) upon cell membrane disruption, because the long-range transport from the Golgi/TGN occurs along MTs (Toomre et al., 1999
; Schmoranzer and Simon, 2003
; Schmoranzer et al., 2003
). To monitor the behavior of MTs, green fluorescent protein (GFP)-tagged
-tubulin and end-binding protein 1 (EB1), a MT plus-end-tracking protein, were expressed in PtK2 cells. This study provides the first evidence that Ca2+ influx upon cell membrane disruption regulates the subcellular recruitment of EB1 to the MTs, resulting in the rearrangement of MTs. Furthermore, by use of a fluorescent lipid probe, this work also shows that regulated vesicle traffic toward the plasma membrane from the region of the TGN is stimulated by membrane disruption.
| Results |
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-tubulin was transfected into PtK2 cells. Cells expressing EGFP-
-tubulin were wounded with a glass needle and were observed by conventional inverted fluorescent microscopy. Since PtK2 cells are extremely flat, the behavior of MTs can be adequately monitored in a single focal plane (Toomre et al., 1999
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-tubulin were wounded in 0.4 mM Ca2+ Ringer's solution, disassembly of MTs around the wound site was induced (Fig. 3A). Propagation of the MT disassembled area continued for 46.00±1.87 seconds (six cells), which was about 2.8 times longer than in 1.8 mM Ca2+ Ringer's solution, and the rate was about four times slower than in 1.8 mM Ca2+ Ringer's solution (0.228±0.008 µm/second, six cells). These results indicate that Ca2+ influx through the wound site promotes MT disassembly. It has already been shown that Ca2+ stimulates MT disassembly by specifically promoting the catastrophe reaction (O'Brien et al., 1997
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Sustained movement of plus-end tips of disassembled MTs toward the wound site could not be detected in 0.4 mM Ca2+ Ringer's solution. A typical time-lapse sequence is shown in Fig. 3B. For instance, an MT end indicated by a green dot in Fig. 3B approached the wound site 60-140 seconds after membrane disruption, but left the wound site after that. There were also MTs that did not approach the wound site at all during observation. Measurements of the distance between the wound site and the MT ends also indicated that behavior of MTs was independent of the wound site (Fig. 3C). These observations were reproduced five times in independent experiments.
When cells expressing EB1-GFP were wounded in 0.4 mM Ca2+ Ringer's solution, a slight increase in the bright EB1 comets was observed throughout the cell (Fig. 4B). However, there was no obvious directional movement of EB1 comets toward the wound site (Fig. 4A and supplementary material, Movie 3). Similar results were obtained from five other cells. These observations indicate that EB1 recruitment to the MTs around the wound site is induced by massive Ca2+ influx through the wound site.
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-tubulin were wounded in 1.8 mM Ca2+ Ringer's solution containing 1 µM Gö-6976. Disassembly of MTs upon cell membrane disruption was induced as in control experiments. The disassembled area propagated from the wound site for 15.00±1.09 seconds at the rate of 0.958±0.167 µm/second (five cells). Within 30 seconds of membrane disruption, approach of MT plus-end tips toward the wound site could be detected in five out of six cells. As in the control experiment, disassembled MTs spent more time approaching (84.4%), resulting in continuous elongation toward the wound site. The average approach rate was 2.73±0.65 µm/minute. To observe growing MT plus ends, cells expressing EB1-GFP were wounded in the presence of 1 µM Gö-6976 in 1.8 mM Ca2+ Ringer's solution. A typical time-lapse sequence is shown in Fig. 5. Within 30 seconds of cell membrane disruption, numerous EB1-GFP comets appeared around the wound site (arrowheads in Fig. 5A), and some comets approached the wound site (arrows in Fig. 5A), as observed in control experiments (see also supplementary material, Movie 4). There was also an increase in the number of brighter EB1 comets throughout the cell as observed in the control experiments (Fig. 5B). These results indicate that rearrangement of MTs upon cell membrane disruption is not sensitive to Gö-6976, and suggest that PKCs that are inhibited by Gö-6976 may have other targets than the MTs during facilitated response.
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To examine the effect of MT disassembly on the appearance of the fluorescent spot around the wound site, cells were loaded with NBD C6-ceramide in the presence of 1 µg/ml nocodazole, and further incubated with 1 µg/ml nocodazole for 30 minutes at 37°C before wounding. As shown in Fig. 6C, appearance of a fluorescent spot around the wound site was inhibited by treatment with nocodazole, indicating that lipid traffic toward the wound site required MTs.
It has been known that incubation at low temperature blocks vesicle transport from the Golgi complex (Matlin and Simons, 1983
; Saraste and Kuismanen, 1984
). As shown previously, incubation at low temperature (20°C) does not inhibit membrane resealing at the initial wound, but the facilitated response of second membrane resealing is specifically suppressed (Togo et al., 1999
). When cells were wounded at 20°C, fluorescent lipids could not be detected around the wound site (Fig. 6D).
To determine the effect of nocodazole on membrane resealing, cells were loaded with 1 µM calcein-AM for 1 hour in the presence or absence of 1 µg/ml nocodazole, and wounded twice. Membrane disruption was indicated by the loss of calcein (Fig. 7A). When the cell membrane resealed, the fluorescent intensity stabilized (bars in Fig. 7A). To compare the timing of membrane resealing in each condition, the resealing rate was defined as the inverse of the resealing time in seconds. When cells were wounded in the absence of nocodazole, second membrane resealing was facilitated (Fig. 7) as shown in other cell types previously (Togo et al., 1999
; Shen and Steinhardt, 2005
). When cells treated with nocodazole were wounded, the initial resealing rate was not affected by this treatment. On the other hand, nocodazole prevented membrane resealing at the second wound. Eight out of 12 cells could not survive a second membrane disruption, whereas only two out of 13 cells could not survive a second membrane disruption in control experiments. These results support the idea that the vesicles required for the second membrane resealing are derived from the Golgi complex and/or the region of the TGN along MTs in a PKC-dependent manner.
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| Discussion |
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The present study shows that membrane disruption triggers recruitment of EB1 to the MTs especially around the wound site and stimulates elongation of MTs toward the wound site. This rearrangement of MTs seems to be required for the facilitated response of membrane resealing, because post-Golgi secretory traffic requires MTs (Toomre et al., 1999
; Schmoranzer and Simon, 2003
; Schmoranzer et al., 2003
). In fact, membrane disruption stimulates the delivery of the fluorescent probe for Golgi-derived lipids, NBD C6-ceramide, toward the wound site along MTs, as shown here by nocodazole inhibition. Furthermore, treatment of cells with nocodazole inhibited membrane resealing at the second wound, but not at the initial wound.
The present study suggests that Ca2+ influx upon cell membrane disruption locally regulates the affinity of EB1 for the MTs. PKCs have been associated with MTs in many cell types (Kiley and Parker, 1995
; Garcia-Rocha et al., 1997
; Hosotani et al., 2001
; Kabir et al., 2001
; Szalay et al., 2001
; Nakhost et al., 2002
), and, in yeast, PKC1 regulates the function of MTs through BIM1, the yeast EB1 homologue (Hosotani et al., 2001
). As shown in this study, however, PKC inhibition by Gö-6976 had no effect on the recruitment of EB1 upon cell membrane disruption. Further studies are required to clarify how Ca2+ influx upon cell membrane disruption stimulates EB1 recruitment to the MTs.
In contrast to the rearrangement of MTs, lipid traffic toward the wound site was PKC dependent. Gö-6976 does inhibit the facilitated response of membrane resealing for a second wound at the same site (Togo et al., 1999
). Also, PKC activation by phorbol ester facilitates membrane resealing at the initial wound, but phorbol ester does not facilitate membrane resealing if cells are pretreated with BFA (Togo et al., 1999
). These results support the hypothesis that PKC stimulates the regulated secretory pathway from the region of the TGN to the wound site, although the PKC subtypes involved in this process and substrates for PKC remain to be elucidated. These are currently under investigation. It should be noted that the delivery of fluorescent lipids toward the wound site was inhibited when cells were wounded at 20°C. This result further suggests that membrane traffic to the wound site from the region of the TGN was by a vesicle-mediated process, because incubation at low temperature blocks vesicle transport from the Golgi complex (Matlin and Simons, 1983
; Saraste and Kuismanen, 1984
). However, BFA and lower temperatures may have pleiotropic effects disrupting most endosomes and trafficking in addition to their dispersal and the ablation of Golgi function. An alternative mechanism would be mobilization of a store of vesicles that was previously stable and inactive and that therefore had not been labeled by the pretreatment with FM1-43 (Togo et al., 1999
).
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| Materials and Methods |
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Transfection
The expression vector for enhanced GFP (EGFP)-
-tubulin was purchased from Clontech Laboratories (Mountain View, CA). EB1-GFP plasmid DNA was kindly provided by Y. Mimori-Kiyosue (KAN Research Institute, Kyoto, Japan) (Mimori-Kiyosue et al., 2000
). Vectors were transfected into cells using the CalPhos transfection kit (Clontech) in accordance with the manufacturer's protocol. Cells were observed 48 hours after the transfection.
Fluorescent lipid-labeling of cells
A complex of NBD C6-ceramide with defatted BSA was purchased from Molecular Probes (Eugene, OR). Cultures were incubated with 5 µM NBD C6-ceramide/BSA in Hanks' balanced salt solution (HBSS, Invitrogen) for 30 minutes at 4°C, washed several times with ice-cold HBSS, and further incubated in fresh HBSS for 30 minutes at 37°C.
Wounding and image analysis
During wounding experiments, the cells were maintained either in 1.8 mM or in 0.4 mM Ca2+ Ringer's solution. Ca2+-free Ringer's solution contained 138 mM NaCl, 2.7 mM KCl, 1.06 mM MgCl2, 5.6 mM D-glucose and 12.4 mM HEPES, pH 7.25. A stock solution of 100 mM CaCl2 was used to adjust the concentration of Ca2+.
The cells were observed on an IX-71 inverted microscope (Olympus, Tokyo, Japan) equipped with a PlanApo 60x/1.40 NA oil-immersion objective. Cells were kept at 37°C during observation unless otherwise stated, and were wounded with a glass needle using an Injectman 5179 and Transjector 5246 (Eppendorf, Hamburg, Germany). The time setting for wounding was 0.3 seconds. Images were collected with Retiga EXi Fast 1394 camera (QImaging, Burnaby, Canada) driven by SlideBook imaging software (Intelligent Imaging Innovations, Denver, CO). Exposure was controlled by a Lambda 10-2 optical filter changer (Sutter Instrument, Novato, CA) that was also driven by SlideBook. After collecting images, the cell was visually inspected and MTs were also observed for viability. If the cell membrane failed to reseal, MTs were completely disassembled throughout the cell owing to a continuous influx of Ca2+. The data from these cells were discarded. If the cell survived the membrane disruption, then the cell was wounded again using bright field illumination, and the site of membrane disruption was recorded for later analysis. Images of EGFP-
-tubulin and EB1-GFP were then processed using the `No Neighbors' deconvolution menu with SlideBook software to reduce out-of-focus haze and to enhance contrast. The stored frames were subsequently exported into TIFF format. The TIFF series was then converted into a QuickTime movie.
Estimation of the resealing rate
Calcein-AM (Molecular Probes) was loaded into the cells in the presence or absence of 1 µg/ml nocodazole for 1 hour at 37°C. Then the cells were wounded with a glass needle in 1.8 mM Ca2+ Ringer's solution as described above, and the fluorescence of calcein was monitored. A persistent decrease of fluorescent intensity (as an indicator of dye loss) indicates resealing failure. A transient decrease of fluorescent intensity indicates successful resealing. The resealing rate was defined as the inverse of resealing time in seconds. For cells that failed to reseal, the rate was defined as zero.
| Acknowledgments |
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| Footnotes |
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| References |
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Bi, G.-Q., Alderton, J. M. and Steinhardt, R. A. (1995). Calcium-regulated exocytosis is required for cell membrane resealing. J. Cell Biol. 131, 1747-1758.
Busch, K. E. and Brunner, D. (2004). The microtubule plus end-tracking proteins mal3p and tip1p cooperate for cell-end targeting of interphase microtubules. Curr. Biol. 14, 548-559.[CrossRef][Medline]
Garcia-Rocha, M., Avila, J. and Lozano, J. (1997). The
isozyme of protein kinase C binds to tubulin through the pseudosubstrate domain. Exp. Cell Res. 230, 1-8.[CrossRef][Medline]
Hosotani, T., Koyama, H., Uchino, M., Miyakawa, T. and Tsuchiya, E. (2001). PKC1, a protein kinase C homologue of Saccharomyces cerevisiae, participates in microtubule function through the yeast EB1 homologue, BIM1. Genes Cells 6, 775-788.[Abstract]
Kabir, N., Schaefer, A. W., Nakhost, A., Sossin, W. S. and Forscher, P. (2001). Protein kinase C activation promotes microtubule advance in neuronal growth cones by increasing average microtubule growth lifetimes. J. Cell Biol. 152, 1033-1043.
Kiley, S. C. and Parker, P. J. (1995). Differential localization of protein kinase C isozymes in U937 cells: evidence for distinct isozyme functions during monocyte differentiation. J. Cell Sci. 108, 1003-1016.[Abstract]
Klausner, R. D., Donaldson, J. G. and Lippincott-Schwartz, J. (1992). Brefeldin A: insights into the control of membrane traffic and organelle structure. J. Cell Biol. 116, 1071-1080.
Lipsky, N. G. and Pagano, R. E. (1985a). A vital stain for the Golgi apparatus. Science 228, 745-747.
Lipsky, N. G. and Pagano, R. E. (1985b). Intracellular translocation of fluorescent sphingolipids in cultured fibroblasts: endogenously synthesized sphingomyelin and glucocerebroside analogues pass through the Golgi apparatus en route to the plasma membrane. J. Cell Biol. 100, 27-34.
Ma, Y., Shakiryanova, D., Vardya, I. and Povov, S. V. (2004). Quantitative analysis of microtubule transport in growing nerve processes. Curr. Biol. 14, 725-730.[CrossRef][Medline]
Martiny-Baron, G., Kazanietz, M. G., Mischak, H., Blumberg, P. M., Kochs, G., Hug, H., Marmé, D. and Schächtele, C. (1993). Selective inhibition of protein kinase C isozymes by the indolocarbazole Gö 6976. J. Biol. Chem. 268, 9194-9197.
Matlin, K. S. and Simons, K. (1983). Reduced temperature prevents transfer of a membrane glycoprotein to the cell surface but does not prevent terminal glycosylation. Cell 34, 233-243.[CrossRef][Medline]
McNeil, P. L. and Steinhardt, R. A. (2003). Plasma membrane disruption: repair, prevention, adaptation. Annu. Rev. Cell Dev. Biol. 19, 697-731.[CrossRef][Medline]
Mimori-Kiyosue, Y., Shiina, N. and Tsukita, S. (2000). The dynamic behavior of the APC-binding protein EB1 on the distal ends of microtubules. Curr. Biol. 10, 865-868.[CrossRef][Medline]
Nakhost, A., Kabir, N., Forscher, P. and Sossin, W. S. (2002). Protein kinase C isoforms are translocated to microtubules in neurons. J. Biol. Chem. 277, 40633-40639.
O'Brien, E. T., Salmon, E. D. and Erickson, H. P. (1997). How calcium causes microtubule depolymerization. Cell Motil. Cytoskeleton 36, 125-135.[CrossRef][Medline]
Salaycik, K. J., Fagerstrom, C. J., Murthy, K., Tulu, U. S. and Wadsworth, P. (2005). Quantification of microtubule nucleation, growth and dynamics in wound-edge cells. J. Cell Sci. 118, 4113-4122.
Saraste, J. and Kuismanen, E. (1984). Pre- and post-Golgi vacuoles operate in the transport of Semliki Forest virus membrane glycoproteins to the cell surface. Cell 38, 535-549.[CrossRef][Medline]
Schmoranzer, J. and Simon, S. M. (2003). Role of microtubules in fusion of post-Golgi vesicles to the plasma membrane. Mol. Biol. Cell 14, 1558-1569.
Schmoranzer, J., Kreitzer, G. and Simon, S. M. (2003). Migrating fibroblasts perform polarized, microtubule-dependent exocytosis towards the leading edge. J. Cell Sci. 116, 4513-4519.
Schuyler, S. C. and Pellman, D. (2001). Microtubule "plus-end-tracking proteins": the end is just the beginning. Cell 105, 421-424.[CrossRef][Medline]
Shen, S. S. and Steinhardt, R. A. (2005). The mechanisms of cell membrane resealing in rabbit corneal epithelial cells. Curr. Eye Res. 30, 543-554.[CrossRef][Medline]
Steinhardt, R. A., Bi, G.-Q. and Alderton, J. M. (1994). Cell membrane resealing by a vesicular mechanism similar to neurotransmitter release. Science 263, 390-393.
Szalay, J., Bruno, P., Bhati, R., Adjodha, J., Schueler, D., Summerville, V. and Vazeos, R. (2001). Associations of PKC isoforms with the cytoskeleton of B16F10 melanoma cells. J. Histochem. Cytochem. 49, 49-66.
Tirnauer, J. S. and Bierer, B. E. (2000). EB1 proteins regulate microtubule dynamics, cell polarity, and chromosome stability. J. Cell Biol. 149, 761-766.
Tirnauer, J. S., Grego, S., Salmon, E. D. and Mitchison, T. J. (2002). EB1-microtubule interactions in Xenopus egg extracts: role of EB1 in microtubule stabilization and mechamisms of targeting to microtubules. Mol. Biol. Cell 13, 3614-3626.
Togo, T., Alderton, J. M., Bi, G.-Q. and Steinhardt, R. A. (1999). The mechanism of facilitated cell membrane resealing. J. Cell Sci. 112, 719-731.[Abstract]
Togo, T., Krasieva, T. B. and Steinhardt, R. A. (2000). A decrease in membrane tension precedes successful cell membrane repair. Mol. Biol. Cell 11, 4339-4346.
Togo, T., Alderton, J. M. and Steinhardt, R. A. (2003). Long-term potentiation of exocytosis and cell membrane repair in fibroblasts. Mol. Biol. Cell 14, 93-106.
Toomre, D., Keller, P., White, J., Olivo, J.-C. and Simons, K. (1999). Dual-color visualization of trans-Golgi network to plasma membrane traffic along microtubules in living cells. J. Cell Sci. 112, 21-33.[Abstract]
Trump, B. F. and Berezesky, I. K. (1995). Calcium-mediated cell injury and cell death. FASEB J. 9, 219-228.[Abstract]
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