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Signal regulatory protein alpha negatively regulates beta2 integrin-mediated monocyte adhesion, transendothelial migration and phagocytosis.

Liu DQ, Li LM, Guo YL, Bai R, Wang C, Bian Z, Zhang CY, Zen K - PLoS ONE (2008)

Bottom Line: In contrast, SIRPalpha overexpression in THP-1 cells showed a significant less monocyte chemotactic protein-1 (MCP-1)-triggered cell surface expression of beta(2) integrins, in particular CD11b/CD18.SIRPalpha overexpression also reduced MCP-1-initiated migration of THP-1 cells across TNFalpha-stimulated HMEC-1 monolayers.Furthermore, beta(2) integrin-mediated THP-1 cell spreading and actin polymerization in response to MCP-1, and phagocytosis of bacteria were both inhibited by SIRPalpha overexpression.

View Article: PubMed Central - PubMed

Affiliation: Jiangsu Diabetes Research Center, State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu, China.

ABSTRACT

Background: Signal regulate protein alpha (SIRPalpha) is involved in many functional aspects of monocytes. Here we investigate the role of SIRPalpha in regulating beta(2) integrin-mediated monocyte adhesion, transendothelial migration (TEM) and phagocytosis.

Methodology/principal findings: THP-1 monocytes/macropahges treated with advanced glycation end products (AGEs) resulted in a decrease of SIRPalpha expression but an increase of beta(2) integrin cell surface expression and beta(2) integrin-mediated adhesion to tumor necrosis factor-alpha (TNFalpha)-stimulated human microvascular endothelial cell (HMEC-1) monolayers. In contrast, SIRPalpha overexpression in THP-1 cells showed a significant less monocyte chemotactic protein-1 (MCP-1)-triggered cell surface expression of beta(2) integrins, in particular CD11b/CD18. SIRPalpha overexpression reduced beta(2) integrin-mediated firm adhesion of THP-1 cells to either TNFalpha-stimulated HMEC-1 monolayers or to immobilized intercellular adhesion molecule-1 (ICAM-1). SIRPalpha overexpression also reduced MCP-1-initiated migration of THP-1 cells across TNFalpha-stimulated HMEC-1 monolayers. Furthermore, beta(2) integrin-mediated THP-1 cell spreading and actin polymerization in response to MCP-1, and phagocytosis of bacteria were both inhibited by SIRPalpha overexpression.

Conclusions/significance: SIRPalpha negatively regulates beta(2) integrin-mediated monocyte adhesion, transendothelial migration and phagocytosis, thus may serve as a critical molecule in preventing excessive activation and accumulation of monocytes in the arterial wall during early stage of atherosclerosis.

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Related in: MedlinePlus

SIRPα overexpression in THP-1 cells decreases MCP-1–stimulated adhesion.A: Micrographs and histograms show THP-1 cells adhered to HMEC-1 monolayers. Bar = 20 µm. B: MCP-1–dependent adhesion of SIRPα– or mock–transfected THP1 monocytes to plates coated with ICAM-1 or VCAM-1. In separate experiments, monocytes were pretreated with 50 µM Bt2cAMP to determine background integrin-independent nonspecific adhesion. All data are mean±SD (n = 3) of three independent experiments.
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pone-0003291-g003: SIRPα overexpression in THP-1 cells decreases MCP-1–stimulated adhesion.A: Micrographs and histograms show THP-1 cells adhered to HMEC-1 monolayers. Bar = 20 µm. B: MCP-1–dependent adhesion of SIRPα– or mock–transfected THP1 monocytes to plates coated with ICAM-1 or VCAM-1. In separate experiments, monocytes were pretreated with 50 µM Bt2cAMP to determine background integrin-independent nonspecific adhesion. All data are mean±SD (n = 3) of three independent experiments.

Mentions: Chemokines such as MCP-1 has been reported to trigger integrin–mediated firm adhesion and subsequent transmigration of monocytes [8]. As shown in Figure 3A, MCP-1–stimulated THP-1 cells showed a significant integrin-mediated firm adhesion to TNFα–activated HMEC-1 monolayers. However, this firm adhesion was largely reduced in THP-1 cells with SIRPα overexpression. Since TNFα–stimulated HMEC-1 monolayers express both VCAM-1 and ICAM-1, the specific ligands for β1 and β2 integrins, respectively, additional adhesion assays were performed using plates coated with human recombinant ICAM-1 or VCAM-1, respectively. To estimate background adhesion, control adhesion assays were performed using THP-1 cells pretreated with Bt2cAMP, a permeable analogue of cAMP that blocks integrin-dependent firm adhesion triggered by MCP-1 [30]. SIRPα–transfected THP-1 cells did not show MCP-1–induced firm adhesion to plates coated with ICAM-1, while adhesion to plates coated with VCAM-1 was intact (Fig. 3B).


Signal regulatory protein alpha negatively regulates beta2 integrin-mediated monocyte adhesion, transendothelial migration and phagocytosis.

Liu DQ, Li LM, Guo YL, Bai R, Wang C, Bian Z, Zhang CY, Zen K - PLoS ONE (2008)

SIRPα overexpression in THP-1 cells decreases MCP-1–stimulated adhesion.A: Micrographs and histograms show THP-1 cells adhered to HMEC-1 monolayers. Bar = 20 µm. B: MCP-1–dependent adhesion of SIRPα– or mock–transfected THP1 monocytes to plates coated with ICAM-1 or VCAM-1. In separate experiments, monocytes were pretreated with 50 µM Bt2cAMP to determine background integrin-independent nonspecific adhesion. All data are mean±SD (n = 3) of three independent experiments.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2553263&req=5

pone-0003291-g003: SIRPα overexpression in THP-1 cells decreases MCP-1–stimulated adhesion.A: Micrographs and histograms show THP-1 cells adhered to HMEC-1 monolayers. Bar = 20 µm. B: MCP-1–dependent adhesion of SIRPα– or mock–transfected THP1 monocytes to plates coated with ICAM-1 or VCAM-1. In separate experiments, monocytes were pretreated with 50 µM Bt2cAMP to determine background integrin-independent nonspecific adhesion. All data are mean±SD (n = 3) of three independent experiments.
Mentions: Chemokines such as MCP-1 has been reported to trigger integrin–mediated firm adhesion and subsequent transmigration of monocytes [8]. As shown in Figure 3A, MCP-1–stimulated THP-1 cells showed a significant integrin-mediated firm adhesion to TNFα–activated HMEC-1 monolayers. However, this firm adhesion was largely reduced in THP-1 cells with SIRPα overexpression. Since TNFα–stimulated HMEC-1 monolayers express both VCAM-1 and ICAM-1, the specific ligands for β1 and β2 integrins, respectively, additional adhesion assays were performed using plates coated with human recombinant ICAM-1 or VCAM-1, respectively. To estimate background adhesion, control adhesion assays were performed using THP-1 cells pretreated with Bt2cAMP, a permeable analogue of cAMP that blocks integrin-dependent firm adhesion triggered by MCP-1 [30]. SIRPα–transfected THP-1 cells did not show MCP-1–induced firm adhesion to plates coated with ICAM-1, while adhesion to plates coated with VCAM-1 was intact (Fig. 3B).

Bottom Line: In contrast, SIRPalpha overexpression in THP-1 cells showed a significant less monocyte chemotactic protein-1 (MCP-1)-triggered cell surface expression of beta(2) integrins, in particular CD11b/CD18.SIRPalpha overexpression also reduced MCP-1-initiated migration of THP-1 cells across TNFalpha-stimulated HMEC-1 monolayers.Furthermore, beta(2) integrin-mediated THP-1 cell spreading and actin polymerization in response to MCP-1, and phagocytosis of bacteria were both inhibited by SIRPalpha overexpression.

View Article: PubMed Central - PubMed

Affiliation: Jiangsu Diabetes Research Center, State Key Laboratory of Pharmaceutical Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu, China.

ABSTRACT

Background: Signal regulate protein alpha (SIRPalpha) is involved in many functional aspects of monocytes. Here we investigate the role of SIRPalpha in regulating beta(2) integrin-mediated monocyte adhesion, transendothelial migration (TEM) and phagocytosis.

Methodology/principal findings: THP-1 monocytes/macropahges treated with advanced glycation end products (AGEs) resulted in a decrease of SIRPalpha expression but an increase of beta(2) integrin cell surface expression and beta(2) integrin-mediated adhesion to tumor necrosis factor-alpha (TNFalpha)-stimulated human microvascular endothelial cell (HMEC-1) monolayers. In contrast, SIRPalpha overexpression in THP-1 cells showed a significant less monocyte chemotactic protein-1 (MCP-1)-triggered cell surface expression of beta(2) integrins, in particular CD11b/CD18. SIRPalpha overexpression reduced beta(2) integrin-mediated firm adhesion of THP-1 cells to either TNFalpha-stimulated HMEC-1 monolayers or to immobilized intercellular adhesion molecule-1 (ICAM-1). SIRPalpha overexpression also reduced MCP-1-initiated migration of THP-1 cells across TNFalpha-stimulated HMEC-1 monolayers. Furthermore, beta(2) integrin-mediated THP-1 cell spreading and actin polymerization in response to MCP-1, and phagocytosis of bacteria were both inhibited by SIRPalpha overexpression.

Conclusions/significance: SIRPalpha negatively regulates beta(2) integrin-mediated monocyte adhesion, transendothelial migration and phagocytosis, thus may serve as a critical molecule in preventing excessive activation and accumulation of monocytes in the arterial wall during early stage of atherosclerosis.

Show MeSH
Related in: MedlinePlus