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Phorbol ester-induced upregulation of polymorphonuclear leukocyte P-selectin ligand expression
G Todderud1, J Alford, A Aruffo
1Bristol-Myers Squibb Pharmaceutical Research Institute, Buffalo, New York 14213-1091, USA.
Abstract:
Proinflammatory stimuli cause the vascular endothelium to express P-selectin that tethers leukocytes by binding surface glycoprotein carbohydrate. While the activation of polymorphonuclear leukocytes (PMN) is associated with upregulation of the beta 2-integrins, there is little known about the regulated expression of the ligand for the endothelial P-selectin. We have used a soluble chimeric P-selectin protein as a probe for the expression of ligand on the surface of the PMN. Treatment with phorbol ester for more than 20 min stimulated P-selectin ligand expression. The upregulation of beta 2-integrin expression was affected in a similar manner. The mechanism of selectin ligand upregulation did not involve de novo protein synthesis, and may involve translocation of membranes containing performed intracellular ligand. C5a, which is generated in response to complement activation in vivo, also stimulated selectin ligand upregulation. Degranulation induced by nigericin increased ligand expression, and TNF-alpha treatment resulted in a modest upregulation.
Insights
Stimuli like phorbol ester and C5a upregulate P-selectin ligand expression on polymorphonuclear leukocytes (PMN). This process, crucial for leukocyte adhesion, may involve intracellular membrane translocation rather than new protein synthesis.
Area of Science:
- Immunology
- Cell Biology
- Vascular Biology
Background:
- Proinflammatory stimuli induce P-selectin expression on endothelium, mediating leukocyte tethering via carbohydrate binding.
- Leukocyte activation involves beta 2-integrin upregulation, but regulation of the P-selectin ligand on leukocytes is less understood.
Purpose of the Study:
- To investigate the regulated expression of the P-selectin ligand on the surface of polymorphonuclear leukocytes (PMN).
- To identify stimuli and mechanisms involved in P-selectin ligand upregulation on PMN.
Main Methods:
- Utilized a soluble chimeric P-selectin protein as a probe to detect surface ligand expression on PMN.
- Treated PMN with phorbol ester, C5a, nigericin, and TNF-alpha to assess their effects on ligand expression.
Main Results:
- Phorbol ester treatment (>20 min) significantly stimulated P-selectin ligand expression on PMN, mirroring beta 2-integrin upregulation.
- Upregulation of P-selectin ligand expression did not require de novo protein synthesis, suggesting involvement of pre-formed intracellular components.
- Complement component C5a, nigericin-induced degranulation, and TNF-alpha also modulated P-selectin ligand expression on PMN.
Conclusions:
- PMN surface P-selectin ligand expression is regulated by inflammatory stimuli and involves mechanisms independent of new protein synthesis.
- The findings suggest a role for intracellular membrane trafficking in the rapid upregulation of selectin ligands during inflammation.