(Circulation. 2001;104:2762.)
© 2001 American Heart Association, Inc.
Brief Rapid Communication |
From the Department of Radiation Oncology, Duke University Medical Center, Durham, NC.
Correspondence to Chuan-Yuan Li, Box 3455, Dept of Radiation Oncology, Duke University Medical Center, Durham, NC 27710. E-mail cyli{at}radonc.duke.edu
| Abstract |
|---|
|
|
|---|
Methods and Results Transcriptional and translational levels of ILK were investigated with reverse-transcriptase polymerase chain reaction and Western analysis. oxLDL treatment induced both the transcription and the translation of the ILK gene in endothelial cells. A recombinant adenovirus vector encoding the ILK gene was constructed to investigate its potential role in oxLDL-induced apoptosis in human umbilical vein endothelial cells and mouse lymphoid vein endothelial cells transformed by simian virus 40. In both types of cells, overexpression of the ILK gene significantly prevented oxLDL-induced apoptosis or cell death, as evaluated by 2 independent assay methods. Furthermore, we showed that ILK could inhibit oxLDL-induced upregulation of the kinase activity of p38 mitogen-activated protein kinase, which is often associated with stress-induced pro-apoptotic signal transduction. Finally, examination of other factors, such as bcl-2, bcl-xl, caspase 3, and caspase 9, demonstrated significant changes that were correlated with oxLDL treatment and ILK overexpression.
Conclusion ILK may be an important factor involved in the regulation of oxLDL-induced apoptosis in vascular endothelial cells. Modifying its activity may be a useful approach for prevention of endothelial cell injury in oxLDL-induced atherosclerosis.
Key Words: oxygen lipoproteins endothelium apoptosis kinases
| Introduction |
|---|
|
|
|---|
In our efforts to identify novel signal-transduction pathways further upstream, we came across integrin-linked kinase (ILK) by virtue of its upregulation in oxLDL-exposed HUVECs. ILK is a novel, ankyrin repeatcontaining serine-threonine kinase that exhibits cell typedependent activation and inhibition.9 ILK is expressed in cardiac and skeletal muscles.10 It has been demonstrated that overexpression of ILK in epithelial cells results in the stimulation of anchorage-independent cell growth and cell-cycle progression. In addition, ILK has been shown to be overexpressed in a number of malignancies10 and is implicated in tumorigenesis.11 In epithelial and tumor cells, ILK expression suppresses apoptosis.12,13 The function of this gene in the cardiovascular system, however, is unknown.
In the present study, we show that ILK is induced transcriptionally and translationally in endothelial cells exposed to oxLDL. We also show that ILK can protect vascular endothelial cells from apoptosis induced by oxLDL. Furthermore, oxLDL-induced p38 MAPK activation and caspase activation were inhibited significantly by ILK expression. Finally, oxLDL-induced phosphorylation of bcl-2 and downregulation of bcl-xl also were inhibited by ILK overexpression.
| Methods |
|---|
|
|
|---|
Preparation of oxLDL
Native human LDLs were purchased from Calbiochem. oxLDL was prepared according to a published protocol.5 Obtained oxLDL was extensively oxidized and moved 2 to 3 times faster on agarose gel electrophoresis than did the native LDL.
Plasmid Construction and Adenovirus Production
The AdEasy adenovirus-packaging system, including plasmid pAdtrack-cytomegalovirus (CMV), pAdeasy-1, and E coli BJ5183 (a recombination-competent strain) cells, was kindly provided by Drs T.-C. He and B. Vogelstein14 (The Johns Hopkins Medical School, Baltimore, Md). The human ILK gene was amplified by reverse-transcriptase polymerase chain reaction (PCR) from total RNA extracted from the Fadu cells (a human squamous cell carcinoma cell line). The forward primer sequence was 5'-GCTCGAGACTATGGACGACATTTTCACTCAG-3', and the reverse primer was 5'-GGATATCCTAAGCATAATCTGGAACATCATATGGATACTTGTCCTGCATCTTCTC-3'. They were designed according to gene bank sequence HSU40282. XhoI and EcoRV sites (underlined) were engineered into the forward and reverse primers, respectively. A 9-amino acid influenza hemagglutinin (HA) epitope tag sequence was fused to the 3 termini of ILK sequence for Western blot detection. The PCR product was cloned by TA cloning (Invitrogen, Carlsbad, Calif) and sequence verified. The cloned human ILK gene was then subcloned into the XhoI/EcoRV sites of the pAdtrack-CMV vector to produce the pAdtrack-CMV/hILK plasmid. Packaging and production of a recombinant adenovirus carrying the human ILK gene was achieved using the AdEasy system according to published protocols.14
Northern and Western Blot Analysis
Northern and Western blot analyses were carried out according to established protocols.15 For Northern blots, the subcloned human ILK (hILK) fragment was used as the probe. An antibody to the HA tag (Roche Molecular Biology) was used to detect recombinant hILK expression in the Western blot analysis of some samples. Another anti-ILK antibody (Upstate Biotechnology) also was used to detect ILK protein expression. An antiß-actin antibody was used as a loading control (NeoMarkers Corp). Anti-caspase 3 and anti-caspase 9 antibodies were from New England BioLabs. Anti-bcl2 and antibcl-xl antibodies were purchased from Pharmingen.
Cell Death Assays
Cell death in oxLDL-treated SVECs and HUVECs was evaluated by 2 independent methods: The first was the Hoechst33342 staining of nuclear DNA according to established protocols. The second was the 3-(4,5-dimethyl-2-thiazolyl)-2,5-diphenyl-2H-tetrazolium bromide (MTT) assay, which was carried out according to an established protocol.16
Phospho-p38 MAPK Assay
p38 MAPK activity was measured using a nonradioactive immobilized phospho-p38 MAPK assay kit purchased from Cell Signaling Technology, Inc. Manufacturers instructions were followed to carry out the assay.
| Results |
|---|
|
|
|---|
8 hours after oxLDL exposure.
|
In order to evaluate the function of ILK, an adenovirus encoding the human ILK gene under the control of a CMV promoter was engineered. The constructed virus, AdILK, mediated the efficient expression of ILK gene in both the HUVECs (Figure 1A) and the SVECs (Figure 1B and 1C). The artificially enforced expression of the human ILK gene affected neither the growth rate nor the morphology of AdILK-infected cells (data not shown).
Exposure of endothelial cells to oxLDL has been shown to induce apoptosis in a time- and concentration- dependent manner. Two assays were used to evaluate the effects of ILK expression on oxLDL-induced cell death. In the first method, Hoechst33342 was used to stain the nuclei of oxLDL-treated cells. Apoptotic cells typically are identified as those cells that possess significantly smaller, condensed, and fragmented nuclei under a fluorescence microscope. Exposure of SVECs to oxLDL (at 25 µg/mL for 24 hours) caused a significant amount of apoptosis. Adenovirus-mediated expression of a reporter gene, the green fluorescence protein (GFP), had no effect on oxLDL-mediated cell death (Figure 2A). Cell death was observed in
90.2±1.5% of cells. AdILK-infected SVECs, however, showed a significant reduction in oxLDL-mediated cell death (Figure 2A), with only 14.8±2.2% of the cells showing apparent apoptosis.
|
Similar observations were made in HUVECs, except for the fact that HUVECs were more resistant to the cell-killing effects of oxLDL (300 µg/mL for 36 hours caused significant apoptosis). Adenovirus-mediated ILK expression significantly protected HUVECs from oxLDL-induced apoptosis (Figure 2A), with only 20.5±2.8% of the cells demonstrating apoptosis in the AdILK-infected group versus 43.4±7.3% in the AdGFP-infected control group.
The protective effects of artificially expressed ILK gene also were confirmed by use of a second approach for evaluating cellular death: the MTT assay. Instead of measuring apoptotic cells, the MTT assay allows one to quantify the amount of live cells by detecting active enzymes in the mitochondria. It is based on the conversion of the yellow tetrazolium salt MTT to the blue formazan derivative by mitochondria enzymes in viable cells.16 We used an improved version of the assay.17 Our MTT assays confirmed the results of the Hoechst33342 staining. In both the HUVECs and the SVECs, AdILK infection significantly protected the cells from oxLDL-induced cytotoxicity (Figure 2B). In AdGFP-treated HUVECs, oxLDL treatment left 59.5% of the cells to survive, whereas AdILK treatment left 80.3% of the cells to survive (Figure 2B). In SVECs, AdGFP infection left 10.4% of the cells to survive after oxLDL treatment, whereas AdILK infection left 82.2% of the cells to survive (Figure 2B).
At the molecular level, oxLDL-induced apoptosis in endothelial cells has been associated with the activation of the p38 stress-activated protein kinase (MAPK).5,18 Indeed, this is confirmed in both the HUVECs and the SVECs exposed to apoptosis-causing doses of oxLDL (Figure 2C). When SVECs and HUVECs were treated with oxLDL, there was a significant upregulation of p38 MAPK activity. Adenovirus-mediated GFP expression had no effect on this upregulation, whereas adenovirus-mediated ILK expression suppressed it. These data indicate that the antiapoptotic effect of ILK functions upstream of the p38 MAPK gene.
Because the protein kinase B (PKB/Akt) signal-transduction pathway has been implicated as a downstream molecule of the ILK gene, the total protein levels of PKB/akt as well as the phosphorylated forms of the protein were analyzed by Western blot in both HUVECs and SVECs. Results indicate that both HUVECs and SVECs expressed low but detectable amounts of PKB/akt, but no phosphorylated forms of the protein could be detected either before or after oxLDL treatment (data not shown). This may reflect a cell-type variation in the functions of PKB/akt.
Additional experiments were also conducted to examine the status of several effector genes involved in the apoptotic signal-transduction pathway. The expression of bcl2 was examined in the HUVECs. The level of the bcl2 protein showed no obvious changes. However, the phosphorylation patterns of bcl2 were different between the control GFP expression and ILK expression groups. In the AdGFP-infected group, oxLDL treatment caused a clear increase in the level of phosphorylated bcl2 (top light band, Figure 2D). On the other hand, in the AdILK-infected group, oxLDL treatment caused no changes in the levels of the phosphorylated bcl2. Examination of bcl-xl in both SVECs and HUVECs demonstrated differences in the overall levels of the protein. In the control AdGFP group, oxLDL caused a clear reduction in bcl-xl levels, whereas no changes were observed in the AdILK group. These results demonstrate the involvement of bcl2 family of proteins in oxLDL-induced endothelial cell death and a role for ILK in regulating their functions.
When caspase 9 was analyzed, cleavage of the full-length protein was clear in the oxLDL-treated, AdGFP-infected cells and was significantly reduced (HUVECs) or nearly absent (SVECs) in the oxLDL-treated, AdILK-infected cells (Figure 2D). A similar pattern was observed for caspase 3 in SVECs: Clear cleavage was induced in oxLDL-treated, AdGFP-infected cells but was significantly reduced in oxLDL-treated, AdILK-infected cells.
Conclusions
Our studies indicate that oxLDL exposure induced the expression of the ILK gene. We further show that the preexpression of the ILK gene can substantially prevent oxLDL-induced apoptosis. Inasmuch as the ILK gene is expressed abundantly in cardiac and skeletal muscles and has been shown to be an important regulator of cellextracellular matrix interactions that lead to cell survival, our results strongly suggest that ILK is an important player in oxLDL-induced endothelial cell apoptosis. It is also notable that the manner in which ILK is induced by stress induction resembles that of the heat shock proteins. This suggests that ILK is part of the signal-transduction feedback loop in endothelial cells that is activated in the event of cellular stress. The suppression of p38 MAPK activity and other effectors by ILK in cellular apoptotic machinery further points to potential molecular pathways through which ILK may participate in regulating apoptosis in endothelial cells and in oxLDL-induced atherosclerogenesis.
| Acknowledgments |
|---|
Received August 27, 2001; revision received October 15, 2001; accepted October 16, 2001.
| References |
|---|
|
|
|---|
2.
Steinberg D. Lewis A. Conner Memorial Lecture: oxidative modification of LDL and atherogenesis. Circulation. 1997; 95: 10621071.
3.
Okura Y, Brink M, Itabe H, et al. Oxidized low-density lipoprotein is associated with apoptosis of vascular smooth muscle cells in human atherosclerotic plaques. Circulation. 2000; 102: 26802686.
4. Thomas MJ. Physiological aspects of low-density lipoprotein oxidation. Curr Opin Lipidol. 2000; 11: 297301.[Medline] [Order article via Infotrieve]
5.
Jing Q, Xin SM, Cheng ZJ, et al. Activation of p38 mitogen-activated protein kinase by oxidized LDL in vascular smooth muscle cells: mediation via pertussis toxin-sensitive G proteins and association with oxidized LDL-induced cytotoxicity. Circ Res. 1999; 84: 831839.
6.
Napoli C, Quehenberger O, De Nigris F, et al. Mildly oxidized low density lipoprotein activates multiple apoptotic signaling pathways in human coronary cells. Faseb J. 2000; 14: 19962007.
7.
Walter DH, Haendeler J, Galle J, et al. Cyclosporin A inhibits apoptosis of human endothelial cells by preventing release of cytochrome C from mitochondria. Circulation. 1998; 98: 11531157.
8. Claise C, Edeas M, Chaouchi N, et al. Oxidized-LDL induce apoptosis in HUVEC but not in the endothelial cell line EA.hy 926. Atherosclerosis. 1999; 147: 95104.[Medline] [Order article via Infotrieve]
9.
Novak A, Hsu SC, Leung-Hagesteijn C, et al. Cell adhesion and the integrin-linked kinase regulate the LEF-1 and beta-catenin signaling pathways. Proc Natl Acad Sci U S A. 1998; 95: 43744379.
10. Chung DH, Lee JI, Kook MC, et al. ILK (beta1-integrin-linked protein kinase): a novel immunohistochemical marker for Ewings sarcoma and primitive neuroectodermal tumour. Virchows Arch. 1998; 433: 113117.[Medline] [Order article via Infotrieve]
11.
Wu C, Keightley SY, Leung-Hagesteijn C, et al. Integrin-linked protein kinase regulates fibronectin matrix assembly, E-cadherin expression, and tumorigenicity. J Biol Chem. 1998; 273: 528536.
12. Attwell S, Roskelley C, Dedhar S. The integrin-linked kinase (ILK) suppresses anoikis. Oncogene. 2000; 19: 38113815.[Medline] [Order article via Infotrieve]
13.
Persad S, Attwell S, Gray V, et al. Inhibition of integrin-linked kinase (ILK) suppresses activation of protein kinase B/Akt and induces cell cycle arrest and apoptosis of PTEN-mutant prostate cancer cells. Proc Natl Acad Sci U S A. 2000; 97: 32073212.
14.
He TC, Zhou S, da Costa LT, et al. A simplified system for generating recombinant adenoviruses. Proc Natl Acad Sci U S A. 1998; 95: 25092514.
15. Ausubel F, Brent R, Kingston P, et al, eds. Current Protocols in Molecular Biology. 2nd ed. New York: Wiley; 1994: 4.5,10.9.
16. Garn H, Krause H, Enzmann V, et al. An improved MTT assay using the electron-coupling agent menadione. J Immunol Methods. 1994; 168: 253256.[Medline] [Order article via Infotrieve]
17. Mosmann T. Rapid colorimetric assay for cellular growth and survival: application to proliferation and cytotoxicity assays. J Immunol Methods. 1983; 65: 5563.[Medline] [Order article via Infotrieve]
18.
Kusuhara M, Chait A, Cader A, et al. Oxidized LDL stimulates mitogen-activated protein kinases in smooth muscle cells and macrophages. Arterioscler Thromb Vasc Biol. 1997; 17: 141148.
This article has been cited by other articles:
![]() |
M. Ohnishi, G. Hasegawa, M. Yamasaki, H. Obayashi, M. Fukui, T. Nakajima, Y. Ichida, H. Ohse, S.-i. Mogami, T. Yoshikawa, et al. Integrin-linked kinase acts as a pro-survival factor against high glucose-associated osmotic stress in human mesangial cells Nephrol. Dial. Transplant., July 1, 2006; 21(7): 1786 - 1793. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. S. Nho, H. Xia, J. Kahm, J. Kleidon, D. Diebold, and C. A. Henke Role of Integrin-linked Kinase in Regulating Phosphorylation of Akt and Fibroblast Survival in Type I Collagen Matrices through a {beta}1 Integrin Viability Signaling Pathway J. Biol. Chem., July 15, 2005; 280(28): 26630 - 26639. [Abstract] [Full Text] [PDF] |
||||
![]() |
H.-J. Cho, S.-W. Youn, S.-I. Cheon, T.-Y. Kim, J. Hur, S.-Y. Zhang, S. P. Lee, K.-W. Park, M.-M. Lee, Y.-S. Choi, et al. Regulation of Endothelial Cell and Endothelial Progenitor Cell Survival and Vasculogenesis by Integrin-Linked Kinase Arterioscler Thromb Vasc Biol, June 1, 2005; 25(6): 1154 - 1160. [Abstract] [Full Text] [PDF] |
||||
![]() |
R. S. Rosenson-Schloss, E. Chnari, T. A. Brieva, A. Dang, and P. V. Moghe Glutathione Preconditioning Attenuates Ac-LDL-Induced Macrophage Apoptosis via Protein Kinase C-Dependent Ac-LDL Trafficking Experimental Biology and Medicine, January 1, 2005; 230(1): 40 - 48. [Abstract] [Full Text] [PDF] |
||||
![]() |
X. Zhang, Y. Li, Q. Huang, H. Wang, B. Yan, M. W. Dewhirst, and C.-Y. Li Increased Resistance of Tumor Cells to Hyperthermia Mediated By Integrin-linked Kinase Clin. Cancer Res., March 1, 2003; 9(3): 1155 - 1160. [Abstract] [Full Text] [PDF] |
||||
| ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
|
Circulation Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search Copyright © 2001 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited. |