Abstract
The death receptor CD95 promotes apoptosis through well-defined signalling pathways. In colorectal cancer cells, CD95 primarily stimulates migration and invasion through pathways that are incompletely understood. Here, we identify a new CD95-activated tyrosine kinase pathway that is essential for CD95-stimulated tumour cell invasion. We show that CD95 promotes Tyr 783 phosphorylation of phospholipase C-γ1 through the platelet-derived growth factor receptor-β, resulting in ligand-stimulated phosphatidylinositol (4,5)-bisphosphate (PIP2) hydrolysis. PIP2 hydrolysis liberates the actin-severing protein cofilin from the plasma membrane to initiate cortical actin remodelling. Cofilin activation is required for CD95-stimulated formation of membrane protrusions and increased tumour cell invasion.
Keywords: CD95, colorectal, cancer, invasion, platelet-derived growth factor receptor, phospholipase
Introduction
Death receptors on tumour cells can suppress metastasis formation by stimulating apoptosis (Smyth et al, 2001; Takeda et al, 2001; Koshkina et al, 2007; Yang et al, 2008). Although CD95 is best known for its ability to induce apoptosis, it can also function as a promoter of tumour and metastasis formation by stimulating tumour cell proliferation, survival and/or invasion (Barnhart et al, 2004; Peter et al, 2007; Kleber et al, 2008; Chen et al, 2010; Hoogwater et al, 2010; Nijkamp et al, 2010). We have recently shown that endogenous oncogenic Kirsten-RAS (KRAS)—one of the first genes to be mutated during colorectal cancer development—can transform death receptors into invasion-stimulating receptors (Hoogwater et al, 2010). The signal-transduction pathways that cause apoptosis downstream of activated CD95 have been well documented (Strasser et al, 2009). By contrast, less is known about the factors that promote tumour cell invasion following CD95 stimulation. In many tumour cell lines, invasion is dependent on the actin-driven formation of membrane protrusions (Wang et al, 2006, 2007). In this report, we provide evidence that activated CD95 promotes the formation of cell protrusions through a new signalling pathway.
Results And Discussion
To study invasion signalling pathways downstream of CD95, we used the Kras-mutant murine- colorectal-cancer cell line C26. CD95 primarily signals motility and invasion in these cells (Hoogwater et al, 2010; Nijkamp et al, 2010; Fig 1A). Checkerboard analysis further showed that the CD95 ligand (CD95L) promotes directed—chemotaxis—rather than non-directed—chemokinesis—tumour cell migration (Fig 1B; supplementary Table S1 online). Real-time imaging showed that non-stimulated C26 cells spontaneously formed cell protrusions in a random manner with, on average, 1–2 protrusions per cell. On stimulation with CD95L, several protrusions increased to 4–6 per cell, and this increased the total cell by area by 35% over a period of 30 min (Fig 1C). Knockdown of the endogenous mutant KrasD12 allele mostly prevented CD95-induced formation of cell protrusions and invasion and allowed CD95 to induce apoptosis (Fig 1A; supplementary Fig S1 online). Stimulation of another murine colorectal-cancer cell line (MC38) with CD95L also resulted in increased migration, formation of cell protrusions and tumour cell invasion (supplementary Fig S2 online).
Figure 1.
CD95 ligand stimulates rapid cofilin-dependent formation of cell protrusions and an increase in cell area. (A) C26 and C26 KRAS KD cells treated with CD95L (10 ng/ml) for 24 h and stained with propidium iodide. The apoptotic sub-G1 fraction was determined by FACS analysis (left panel). C26 and C26 KRAS KD cells were plated on matrigel-coated membranes in transwell chambers and were allowed to invade for 8 h in the presence or absence of CD95L (10 ng/ml; right panel). The bar graph shows fold increase relative to non-stimulated controls (=1). Error bars represent s.e.m. on the basis of two independent experiments conducted in triplicate. (B) Checkerboard analysis in which CD95L (8 h) was added to the insert (top) or to the well (bottom) of the matrigel invasion chamber. All conditions were tested in three to five independent experiments. Numbers represent fold change of several invaded cells relative to control (no CD95L in either compartment), ±s.e.m. (P-value). Significance was tested using Student's t-test (unpaired; double sided). (C) C26 cells were transiently transfected with LIMK–GFP or GFP and were analysed by real-time imaging before and after stimulation with CD95L (10 ng/ml). Differential interference contrast images were used to determine several protrusions before and after stimulation. Inset shows C26 cells before (left panel) and after (middle panel) CD95L stimulation. The right image is a merge of binary threshold images at both time points. Yellow represents no change; red represents increased protrusion formation; and green represents membrane retraction. Numbers indicate new protrusions formed. Scale bar, 10 μm. The generated images were also used to measure the total cell areas before and after stimulation (arrow) by using ImageJ software (n=4). These values were plotted as the percentage of average cell area before stimulation (right panel). Asterisk indicates significance on the basis of P-values <0.05. (D) C26 and C26–LIMK1 cells were treated with CD95L (10 ng/ml) for 24 h and apoptosis and invasion were assessed as in A (n=3). Asterisk indicates significance on the basis of P-values <0.05. CD95L, CD95 ligand; FACS, fluorescence-activated cell sorting; GFP, green fluorescent protein; KD, knockdown; LIMK, LIM kinase.
The polymerization of actin monomers into filamentous actin (F-actin) at the leading edge of migrating cells generates the forces that drive the formation of cell protrusions. Actin polymerization mainly occurs at one end of the filament, named the ‘barbed end’, and assembly of F-actin is controlled by regulation of several barbed ends. One of the key proteins in this process is the actin-binding protein cofilin, which can increase the number of barbed ends by severing existing F-actin (Ichetovkin et al, 2002) and by its intrinsic actin-nucleation activity (Andrianantoandro & Pollard, 2006). Cofilin is inactivated by LIM kinase 1 (LIMK1)-mediated phosphorylation on Ser 3, which is located in the actin-binding domain. The phospho group on Ser 3 inhibits cofilin binding to F-actin and makes it inactive (Moriyama et al, 1996; Arber et al, 1998; Yang et al, 1998; Bamburg, 1999; Bernard, 2007). We next tested whether CD95-stimulated formation of cell protrusions was cofilin dependent by overexpressing LIMK1. As expected, LIMK1 transfection into C26 cells resulted in the phosphorylation (inactivation) of cofilin on Ser 3 (pS3-cofilin; supplementary Fig S3 online). Cofilin inhibition by LIMK1 mostly prevented the formation of cell protrusions and the increase in cell area (Fig 1C), and reduced the invasive capacity of control and CD95L-stimulated C26 cells (Fig 1D). Instead, prolonged stimulation of C26–LIMK1 cells caused apoptosis (Fig 1D). Together, these data indicate that CD95 promotes the formation of cell protrusions in a LIMK1-suppressible manner, suggesting that it is a cofilin-dependent phenomenon.
The activity of cofilin is negatively regulated by LIMK1-mediated Ser 3 phosphorylation (Arber et al, 1998; Yang et al, 1998) and by binding to plasma membrane phosphatidylinositol (4,5)-bisphosphate (PIP2; van Rheenen et al, 2007, 2009). If CD95 activates cofilin by Ser 3 dephosphorylation, one would expect cofilin phosphorylation to decrease in response to CD95L. However, pS3–cofilin levels in C26 cells are low due to KRAS/RAF1-mediated suppression of LIMK1 (Hoogwater et al, 2010) and were unaffected by stimulation with CD95L (Fig 2A). Therefore, it seems unlikely that CD95 activates cofilin by promoting its dephosphorylation.
Figure 2.
CD95 ligand stimulates phospholipase C-γ1 Tyr 783 phosphorylation and PIP2 hydrolysis. (A) C26 cells were treated with CD95L (10 ng/ml) for the indicated time periods. Cell lysates were prepared and analysed for cofilin Ser 3 phosphorylation (pS3–Cofilin), total cofilin, Tyr 783 phosphorylation of PLC-γ1 (pY783–PLC-γ1) and total PLC-γ1 by western blotting. (B) Cells were transiently transfected with mRFP–PH and analysed by real-time confocal microscopy. Images represent mRFP–PH in C26 cells before stimulation (left) and 15 min after stimulation with CD95L (10 ng/ml; middle). Scale bar, 5 μm. Plotting of total cell area (measured by differential interference contrast images) and PIP2 hydrolysis (measured using mRFP–PH) over time shows that addition of CD95L (10 ng/ml; black bar) caused a simultaneous increase in cell area and PIP2 hydrolysis (lower left panel). The average of five independent experiments is plotted (n=5). The right lower panel shows a quantification of maximal CD95L-induced PIP2 hydrolysis, relative to ionomycin-induced maximum translocation of the mRFP–PH probe (100%). Significance was tested using Student's t-test (unpaired; double sided); asterisk indicates P<0.05. CD95L, CD95 ligand; mRFP–PH, PH domain fused to red fluorescent protein; PIP2, phosphatidylinositol (4,5)-bisphosphate; PLC-γ1, phospholipase C-γ1.
In breast cancer cells, epidermal growth factor (EGF) stimulation causes local phospholipase C-γ1 (PLC-γ1)-mediated PIP2 hydrolysis that liberates cofilin from inhibition by PIP2 (van Rheenen et al, 2007, 2009). PLC-γ1 is activated by growth factors through phosphorylation of Tyr 783, which increases its PIP2 hydrolysis activity (Kim et al, 2000). Stimulation of C26 or MC38 cells with CD95L caused an increase in Tyr 783–PLC-γ1 phosphorylation without altering cofilin Ser 3 phosphorylation (Fig 2A and 4C). PIP2 hydrolysis can be detected by using the PLC-δ1 PH domain fused to red fluorescent protein (RFP; mRFP–PH) as a PIP2 probe (Stauffer et al, 1998; Varnai & Balla, 1998; van Rheenen et al, 2005). In resting C26 cells, mRFP–PH is bound to PIP2 in the plasma membrane (Fig 2B, left panel). Stimulation with CD95L induced a rapid 40–50% translocation of mRFP–PH from the membrane to the cytosol (Fig 2B). Interestingly, PIP2 hydrolysis following CD95L stimulation occurred concomitantly with the formation of cell protrusions and the increase in cell area (Fig 2B, lower left panel).
Figure 4.
Platelet-derived growth factor receptor-β mediates CD95-stimulated phospholipase C-γ1 phosphorylation and tumour cell invasion. (A) C26 cells were stimulated with PDGF or EGF and pY783–PLC-γ1 was analysed by western blotting. (B) C26 cells were stimulated with CD95L and PDGFR-β phosphorylation on Tyr 1021 was assessed by western blotting. (C) C26 and MC38 cells were pretreated with sunitinib (2 μM) or AG1296 (20 μM) for 16 h and subsequently stimulated with CD95L for 5, 15 or 30 min. Cell lysates were prepared and analysed for pY783–PLC-γ1 by western blotting. (D) C26 cells were transfected with siRNAs against PDGFR-β and stimulated for the indicated times with CD95L. Y783–PLC-γ1 phosphorylation and PDGFR-β knockdown were analysed by western blotting. Cell area enlargement (right panel) was measured as shown in Fig 1A. (E) Transwell invasion assays of C26 and MC38 cells treated with sunitinib, AG1296 or vehicle (DMSO). Data are from two independent experiments (n=2) conducted in triplicate. (F) Transwell invasion assay of C26 and MC38 cells transfected with control or PDGFR-β-targeting siRNAs (n=2). Significance was tested using Student's t-test (unpaired; double sided), asterisk indicates P<0.05. EGF, epidermal growth factor; PDGF, platelet-derived growth factor; PDGFR-β, PDGF receptor-β; PLC-γ1, phospholipase C-γ1; siRNA, small-interfering RNA.
The results so far indicate that CD95L promotes cofilin activation to induce cell protrusions, possibly through PLC-γ1-mediated PIP2 hydrolysis. To test the requirement for PLC in CD95L-stimulated formation of cell protrusions and invasion, C26 cells were treated with the PLC inhibitor U73122. As expected, U73122 inhibited CD95L-stimulated PIP2 hydrolysis (Fig 3A). Strikingly, in U73122-treated cells, CD95L caused an increase in plasma membrane PIP2 levels. This could indicate that PIP-5 kinase is activated following CD95L stimulation. Importantly, U73122 not only prevented PIP2 hydrolysis, but also blocked CD95L-stimulated formation of cell protrusions and the increase in total cell area (Fig 3B). In addition, RNA interference-mediated suppression of PLC-γ1 significantly reduced the CD95L-stimulated increase in cell area (Fig 3B). Transwell assays further showed that U73122 treatment or PLC-γ1 knockdown reduced CD95L-stimulated invasion of C26 and MC38 cells (Fig 3C,D).
Figure 3.
CD95 ligand-induced tumour cell invasion requires phospholipase C-γ1 activation. (A) C26 cells were transiently transfected with mRFP–PH. After 24 h, cells were either pretreated with U73122 (5 μM) or with vehicle (DMSO) for 1 h before stimulation with CD95L (10 ng/ml). PIP2 hydrolysis was measured over time, as shown in Fig 2B. (B) C26 cells were either pretreated with U73122 (5 μM) or with vehicle (DMSO) for 1 h before stimulation with CD95L (10 ng/ml). Knockdown of PLC-γ1 was established by transfection of siRNAs 2 days before stimulation. Cells were analysed by real-time imaging. Several cell protrusions and the increase in cell area were measured as shown in Fig 1B. (C) Transwell invasion assays of C26 and MC38 cells treated with U73343 or U73122 were performed as in Fig 1A. Data are from two independent experiments conducted in triplicate. (D) Transwell invasion assays of C26 and MC38 cells transfected with control or PLC-γ1 siRNAs (n=2). Significance was tested using Student's t-test (unpaired; double-sided); asterisk indicates P<0.05. CD95L, CD95 ligand; DMSO, dimethyl sulphoxide; mRFP–PH, PH domain fused to red fluorescent protein; PIP2, phosphatidylinositol (4,5)-bisphosphate; PLC-γ1, phospholipase C-γ1; siRNA, small-interfering RNA.
PLC-γ1 is a growth factor-responsive PLC that is activated by receptor and non-receptor tyrosine kinases, including Src family kinases (SFKs) and the platelet-derived growth factor receptor-β (PDGFR-β; Ronnstrand et al, 1992; Kim et al, 2000). Interestingly, SFKs are activated by CD95 and might have a role in both apoptosis and invasion signalling (Schlottmann et al, 1996; Kleber et al, 2008). However, the small molecule SFK inhibitor SU6656 (Blake et al, 2000) had no effect on CD95L-stimulated Y783–PLC-γ1 phosphorylation in C26 cells (data not shown). To search for candidate PLC-γ1 kinases, C26 cells were stimulated with EGF and PDGF. PDGF, but not EGF, effectively stimulated PLC-γ1 phosphorylation in C26 cells (Fig 4A). Interestingly, PLC-γ1 activation is required for PDGFR-induced cell migration (Kundra et al, 1994). CD95L caused a marked increase in phosphorylation of Tyr 1021 of the PDGFR-β, which mediates binding to and activation of PLC-γ1 (Fig 4B; Ronnstrand et al, 1992). To assess whether PDGFR-β activity might have a role in CD95L-stimulated PLC-γ1 phosphorylation and tumour cell invasion, cells were treated with AG1296, a specific PDGFR inhibitor, or sunitinib, a PDGFR/vascular endothelial growth factor receptor inhibitor. Both AG1296 and sunitinib blocked CD95-stimulated phosphorylation of PLC-γ1 (Fig 4C). In addition, RNA interference-mediated suppression of PDGFR-β expression reduced CD95L-stimulated PLC-γ1 phosphorylation and cell-area enlargement (Fig 4D). Moreover, sunitinib, AG1296 and PDGFR-β-targeted small-interfering RNAs all prevented basal and CD95L-stimulated tumour cell invasion (Fig 4E,F). These results indicate that CD95L promotes PLC-γ1 Tyr 783-phosphorylation through the PDGFR-β.
In conclusion, our results identify a new CD95-initiated signalling pathway involving PDGFR-β-mediated PLC-γ1 activation and PIP2 hydrolysis. Future work should address how CD95 stimulates PDGFR-β tyrosine phosphorylation and whether this requires PDGF binding to the receptor. Alternatively, a direct interaction between activated CD95 and the PDGFR-β could recruit the latter into the CD95 signalling complex, which contains tyrosine kinase activity (Sancho-Martinez & Martin-Villalba, 2009). In this hypothesis, CD95 stimulation could cause PDGFR-β activation in a PDGF-independent manner.
Earlier work has implicated caspase 8 and ERK in CD95-stimulated tumour cell invasion (Barnhart et al, 2004). More recently, it was shown that CD95 activates tyrosine kinases (Yes and Syk) to promote the expression of matrix-degrading metalloproteinases, thereby facilitating tissue invasion of tumour cells and myeloid cells (Kleber et al, 2008; Letellier et al, 2010). This study shows that tyrosine kinase activation by CD95 also results in the rapid actin-driven formation of cell protrusions, a process that is essential for tumour cell invasion. Thus, CD95 can promote tumour cell invasion through distinct pathways. The specific tyrosine kinases involved and the dominance of each of these pathways in determining invasive behaviour is probably cell-type dependent.
We propose a model in which CD95 stimulates PDGFR-β-mediated PLC activation and PIP2 hydrolysis. The consequent release of cofilin from the plasma membrane and the continued suppression of LIMK1 by KRAS/RAF1 together allow robust activation of the cofilin pathway. Cofilin-generated actin barbed-ends act as nucleation points for de novo actin polymerization. This process is driven by the small GTPases Rac and Cdc42, which are also activated following CD95 stimulation (Subauste et al, 2000; Ruan et al, 2008). Cofilin and Rac/Cdc42 cooperate to stimulate actin polymerization, which causes the formation of cell protrusions (van Rheenen et al, 2009). This process is essential for tumour cell invasion and, presumably, for metastasis formation.
Methods
Real-time imaging. Cells were seeded in a Lab-Tek Chambered #1.0 Borosilicate Coverglass System (Nalgene Nunc International, Rochester, NY, USA) and were mounted on a Zeiss Axiovert 200M microscope for live-cell imaging (5% CO2; 37°C) for 2–14 h. Phase-contrast images were captured every 2 min using a Photometics Coolsnap CCD camera (Scientific, Tuscon, AZ, USA). Images were processed using the Metamorph software (Universal imaging, Downington, PA, USA). Several protrusions was scored by off-line analysis of the generated videos and plotted as means±s.e.m. For real-time fluorescence imaging, cells were placed on a Leica SP5 inverted microscope equipped with a × 63 1.3NA glycerol objective. Cells were maintained in Leibovitz-15-buffered medium (Invitrogen, Breda, The Netherlands) at 37°C in a climate chamber.
Invasion assay. For in vitro invasion assays, 24-well BioCoat matrigel invasion chambers (#354480, BD Biosciences, Alphen aan den Rijn, The Netherlands) were used according to the manufacturer's protocol. Cells were maintained under serum-free conditions overnight. In the upper compartment, 5 × 104 cells per well were plated in 0.5 ml serum-free medium. The lower compartment contained 0.75 ml medium with 5% FCS. CD95L (10 ng/ml) was added to the lower compartment. Cells were pretreated overnight in both compartments with 1 μM U73122 and U73343 or with 2 μM sunitinib for 1 h before plating. Invasion chambers were incubated for 8 h. Cells in the upper compartment were removed with a cotton swab. Transmigrated cells were fixed in 3.7% formaldehyde, stained with 4,6-diamidino-2-phenylindole and counted by analysing microscopic images (5–6 fields per membrane). Data are expressed relative to control. All assays were performed in triplicate and were repeated twice.
Checkerboard analysis. Checkerboard analysis was performed by adding 0, 2 and 10 ng/ml to the wells (bottom) and/or to the inserts (top) of the matrigel invasion chambers. Invasion assays were carried out as described above.
PIP2 hydrolysis assay. Cells grown on coverslips were transiently transfected with mRFP–PH. The coverslips were mounted on a SP5 Leica confocal microscope. Images of RFP–PH were collected every 20 s and stored on the computer. The images were imported and analysed using a custom-made visual basics program. Following a threshold step, background regions were determined and the background was measured and subtracted from the images. Cells were traced with a fixed threshold resulting in a binary image. Regions of the plasma membrane were determined by eroding the binary image with six pixels. The cytosol region was determined by eroding the binary image by another four pixels. Mean fluorescence level of the plasma membrane and cytosol region was measured and plotted over time. To calibrate the plasma membrane to cytosol translocation, 5 μM ionomycin +2 mM calcium was added to induce a full membrane-to-cytosol translocation. PIP2 hydrolysis was expressed as the ratio of fluorescent intensity of the plasma membrane to the cytosol, as induced by CD95 compared with ionomycin and calcium.
Statistical analysis. Statistical differences between groups were analysed by an unpaired two-sided t-test. Data are expressed as mean±s.e.m. A P-value of <0.05 was considered statistically significant.
Supplementary information is available at EMBO reports online (http://www.emboreports.org).
Supplementary Material
Acknowledgments
We thank A. de Graaff and the Hubrecht Imaging Center for imaging support. E.J.A.S., L.R., D.A.E.R., K.M.G., B.L.E. and J.L. were supported by grants from the Dutch Cancer Society (2009-4367, -4621, -4417, -4367, -4608). F.J.H.H. was supported by a grant from the PON foundation. J.v.R. was supported by the Dutch Organization for Scientific Research (ZON-Mw VIDI 91710330 and equipment grant NWO 175.010.2007.00).
Author contributions: E.J.A.S., L.R., D.A.E.R., J.L., K.M.G., F.J.H.H. and B.L.E. conducted the experiments. O.K. designed the study. O.K., J.v.R. and I.H.M.B.R. were involved in the experimental design and supervision. E.J.A.S., J.v.R. and O.K. wrote the manuscript.
Footnotes
The authors declare that they have no conflict of interest.
References
- Andrianantoandro E, Pollard TD (2006) Mechanism of actin filament turnover by severing and nucleation at different concentrations of ADF/cofilin. Mol Cell 24: 13–23 [DOI] [PubMed] [Google Scholar]
- Arber S, Barbayannis FA, Hanser H, Schneider C, Stanyon CA, Bernard O, Caroni P (1998) Regulation of actin dynamics through phosphorylation of cofilin by LIM-kinase. Nature 393: 805–809 [DOI] [PubMed] [Google Scholar]
- Bamburg JR (1999) Proteins of the ADF/cofilin family: essential regulators of actin dynamics. Annu Rev Cell Dev Biol 15: 185–230 [DOI] [PubMed] [Google Scholar]
- Barnhart BC, Legembre P, Pietras E, Bubici C, Franzoso G, Peter ME (2004) CD95 ligand induces motility and invasiveness of apoptosis-resistant tumor cells. EMBO J 23: 3175–3185 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Bernard O (2007) Lim kinases, regulators of actin dynamics. Int J Biochem Cell Biol 39: 1071–1076 [DOI] [PubMed] [Google Scholar]
- Blake RA, Broome MA, Liu X, Wu J, Gishizky M, Sun L, Courtneidge SA (2000) SU6656, a selective src family kinase inhibitor, used to probe growth factor signaling. Mol Cell Biol 20: 9018–9027 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Chen L et al. (2010) CD95 promotes tumour growth. Nature 465: 492–496 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Hoogwater FJ et al. (2010) Oncogenic K-Ras turns death receptors into metastasis-promoting receptors in human and mouse colorectal cancer cells. Gastroenterology 138: 2357–2367 [DOI] [PubMed] [Google Scholar]
- Ichetovkin I, Grant W, Condeelis J (2002) Cofilin produces newly polymerized actin filaments that are preferred for dendritic nucleation by the Arp2/3 complex. Curr Biol 12: 79–84 [DOI] [PubMed] [Google Scholar]
- Kim MJ, Kim E, Ryu SH, Suh PG (2000) The mechanism of phospholipase C-γ1 regulation. Exp Mol Med 32: 101–109 [DOI] [PubMed] [Google Scholar]
- Kleber S et al. (2008) Yes and PI3K bind CD95 to signal invasion of glioblastoma. Cancer Cell 13: 235–248 [DOI] [PubMed] [Google Scholar]
- Koshkina NV, Khanna C, Mendoza A, Guan H, DeLauter L, Kleinerman ES (2007) Fas-negative osteosarcoma tumor cells are selected during metastasis to the lungs: the role of the Fas pathway in the metastatic process of osteosarcoma. Mol Cancer Res 5: 991–999 [DOI] [PubMed] [Google Scholar]
- Kundra V, Escobedo JA, Kazlauskas A, Kim HK, Rhee SG, Williams LT, Zetter BR (1994) Regulation of chemotaxis by the platelet-derived growth factor receptor-β. Nature 367: 474–476 [DOI] [PubMed] [Google Scholar]
- Letellier E et al. (2010) CD95-ligand on peripheral myeloid cells activates Syk kinase to trigger their recruitment to the inflammatory site. Immunity 32: 240–252 [DOI] [PubMed] [Google Scholar]
- Moriyama K, Iida K, Yahara I (1996) Phosphorylation of Ser-3 of cofilin regulates its essential function on actin. Genes Cells 1: 73–86 [DOI] [PubMed] [Google Scholar]
- Nijkamp MW, Hoogwater FJ, Steller EJ, Westendorp BF, van der Meulen TA, Leenders MW, Borel RI, Kranenburg O (2010) CD95 is a key mediator of invasion and accelerated outgrowth of mouse colorectal liver metastases following radiofrequency ablation. J Hepatol 53: 1069–1077 [DOI] [PubMed] [Google Scholar]
- Peter ME et al. (2007) The CD95 receptor: apoptosis revisited. Cell 129: 447–450 [DOI] [PubMed] [Google Scholar]
- Ronnstrand L, Mori S, Arridsson AK, Eriksson A, Wernstedt C, Hellman U, Claesson-Welsh L, Heldin CH (1992) Identification of two C-terminal autophosphorylation sites in the PDGF β-receptor: involvement in the interaction with phospholipase C-γ. EMBO J 11: 3911–3919 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Ruan W, Lee CT, Desbarats J (2008) A novel juxtamembrane domain in tumor necrosis factor receptor superfamily molecules activates Rac1 and controls neurite growth. Mol Biol Cell 19: 3192–3202 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Sancho-Martinez I, Martin-Villalba A (2009) Tyrosine phosphorylation and CD95: a FAScinating switch. Cell Cycle 8: 838–842 [DOI] [PubMed] [Google Scholar]
- Schlottmann KE, Gulbins E, Lau SM, Coggeshall KM (1996) Activation of Src-family tyrosine kinases during Fas-induced apoptosis. J Leukoc Biol 60: 546–554 [DOI] [PubMed] [Google Scholar]
- Smyth MJ, Cretney E, Takeda K, Wiltrout RH, Sedger LM, Kayagaki N, Yagita H, Okumura K (2001) Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) contributes to interferon gamma-dependent natural killer cell protection from tumor metastasis. J Exp Med 193: 661–670 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Stauffer TP, Ahn S, Meyer T (1998) Receptor-induced transient reduction in plasma membrane PtdIns(4,5)P2 concentration monitored in living cells. Curr Biol 8: 343–346 [DOI] [PubMed] [Google Scholar]
- Strasser A, Jost PJ, Nagata S (2009) The many roles of FAS receptor signaling in the immune system. Immunity 30: 180–192 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Subauste MC, Von HM, Benard V, Chamberlain CE, Chuang TH, Chu K, Bokoch GM, Hahn KM (2000) Rho family proteins modulate rapid apoptosis induced by cytotoxic T lymphocytes and Fas. J Biol Chem 275: 9725–9733 [DOI] [PubMed] [Google Scholar]
- Takeda K, Hayakawa Y, Smyth MJ, Kayagaki N, Yamaguchi N, Kakuta S, Iwakura Y, Yagita H, Okumura K (2001) Involvement of tumor necrosis factor-related apoptosis-inducing ligand in surveillance of tumor metastasis by liver natural killer cells. Nat Med 7: 94–100 [DOI] [PubMed] [Google Scholar]
- van Rheenen J, Achame EM, Janssen H, Calafat J, Jalink K (2005) PIP2 signaling in lipid domains: a critical re-evaluation. EMBO J 24: 1664–1673 [DOI] [PMC free article] [PubMed] [Google Scholar]
- van Rheenen J, Song X, van RW, Cammer M, Chen X, Desmarais V, Yip SC, Backer JM, Eddy RJ, Condeelis JS (2007) EGF-induced PIP2 hydrolysis releases and activates cofilin locally in carcinoma cells. J Cell Biol 179: 1247–1259 [DOI] [PMC free article] [PubMed] [Google Scholar]
- van Rheenen J, Condeelis J, Glogauer M (2009) A common cofilin activity cycle in invasive tumor cells and inflammatory cells. J Cell Sci 122: 305–311 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Varnai P, Balla T (1998) Visualization of phosphoinositides that bind pleckstrin homology domains: calcium- and agonist-induced dynamic changes and relationship to myo-[3H]inositol-labeled phosphoinositide pools. J Cell Biol 143: 501–510 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wang W, Mouneimne G, Sidani M, Wyckoff J, Chen X, Makris A, Goswami S, Bresnick AR, Condeelis JS (2006) The activity status of cofilin is directly related to invasion, intravasation, and metastasis of mammary tumors. J Cell Biol 173: 395–404 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Wang W, Eddy R, Condeelis J (2007) The cofilin pathway in breast cancer invasion and metastasis. Nat Rev Cancer 7: 429–440 [DOI] [PMC free article] [PubMed] [Google Scholar]
- Yang N, Higuchi O, Ohashi K, Nagata K, Wada A, Kangawa K, Nishida E, Mizuno K (1998) Cofilin phosphorylation by LIM-kinase 1 and its role in Rac-mediated actin reorganization. Nature 393: 809–812 [DOI] [PubMed] [Google Scholar]
- Yang D, Stewart TJ, Smith KK, Georgi D, Abrams SI, Liu K (2008) Downregulation of IFN-γR in association with loss of Fas function is linked to tumor progression. Int J Cancer 122: 350–362 [DOI] [PubMed] [Google Scholar]
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