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Murine vascular cell adhesion molecule-1 (VCAM-1) proteins encoded by alternatively spliced mRNAs are differentially
G Pirozzi1, R W Terry, M A Labow
1Deprtment of Biotechnology, Roche Research Center, Hoffmann La Roche Inc., Nutley, NJ 07110, USA.
Abstract:
VCAM-1 is an immunoglobulin (Ig) superfamily member expressed in endothelial cells that mediates adhesion to a variety of leukocytes in a VLA-4 dependent manner. In the mouse, two distinct forms of VCAM are produced. One form, VCAMTM, contains seven Ig domains followed by a single transmembrane region and a short cytoplasmic domain. A second form, VCAMGPI, which is preferentially induced by cytokines and LPS, contains only the first three Ig domains and is attached to the cell surface via a glycosylphosphafidylinositol (GPI) anchor. Both vascular and nonvascular expression of VCAM have been reported in a variety of normal and pathological settings. One possible role for the two VCAM isoforms is to allow for the targeted localization of VCAM to specific cell surface domains of polarized cells. This may be particularly relevant since VCAM is known to be expressed by two different polarized cell types, namely endothelial cells and kidney epithelial cells. In this study, MDCK cells permanently expressing either VCAMTM or VCAMGPI were established and used to examine the targeting of VCAM proteins to different polarized surface domains. VCAMTM was primarily located on the basolateral surface while VCAMGPI was located on the apical surface of polarized MDCK cells. Data is also presented that demonstrates that polarized expression is reversed in endothelial cells where VCAMTM was observed primarily on the apical surface. The differential localization of VCAM isoforms on the cell surface has direct implications for the ability of VCAM to mediate cell adhesion and transmigration.
Insights
Vascular Cell Adhesion Molecule-1 (VCAM) has two forms, VCAM-transmembrane and VCAM-GPI anchor. Their distinct polarized cell surface localization impacts leukocyte adhesion and transmigration.
Area of Science:
- Cell Biology
- Immunology
- Biochemistry
Background:
- Vascular Cell Adhesion Molecule-1 (VCAM-1) is an immunoglobulin superfamily member mediating leukocyte adhesion.
- Two mouse VCAM-1 isoforms exist: VCAM-transmembrane (VCAMTM) and VCAM-glycosylphosphatidylinositol (VCAMGPI).
- VCAM-1 expression occurs in normal and pathological settings, suggesting roles in polarized cells like endothelial and kidney epithelial cells.
Purpose of the Study:
- To investigate the targeted localization of VCAMTM and VCAMGPI to specific cell surface domains in polarized cells.
- To determine if VCAM-1 isoforms exhibit differential localization in kidney epithelial cells (MDCK) and endothelial cells.
Main Methods:
- Established Madin-Darby Canine Kidney (MDCK) cells stably expressing VCAMTM or VCAMGPI.
- Analyzed the cell surface localization of VCAMTM and VCAMGPI in polarized MDCK cells.
- Examined VCAMTM localization in polarized endothelial cells.
Main Results:
- VCAMTM localized primarily to the basolateral surface of polarized MDCK cells.
- VCAMGPI localized primarily to the apical surface of polarized MDCK cells.
- Polarized expression was reversed in endothelial cells, with VCAMTM predominantly on the apical surface.
Conclusions:
- VCAM-1 isoforms display distinct, cell-type-specific polarized surface localization.
- Differential localization of VCAM-1 isoforms influences their function in cell adhesion and transmigration.
- Understanding VCAM-1 localization is crucial for its role in leukocyte trafficking and inflammatory processes.