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Differential regulation of alpha 4 integrin-dependent binding to domains 1 and 4 of vascular cell adhesion molecule-1
G Kilger1, L A Needham, P J Nielsen
1Institute for Medical Microbiology and Hygiene, Technical University, Munich, Federal Republic of Germany.
Insights
Vascular cell adhesion molecule-1 (VCAM-1) interactions with alpha 4 beta 1 and alpha 4 beta 7 integrins differ in domain binding and activation. CD24 expression specifically impacts alpha 4 beta 1 binding to VCAM-1 domain 1.
Area of Science:
- Immunology
- Cell Biology
- Biochemistry
Background:
- Vascular cell adhesion molecule-1 (VCAM-1) is crucial in physiological and pathological processes.
- VCAM-1's immunoglobulin-like domains 1 and 4 bind alpha 4 beta 1 integrin.
Purpose of the Study:
- To investigate the binding interactions of alpha 4 beta 7 integrin with VCAM-1 domains 1 and 4.
- To compare the activation requirements and cation dependencies for alpha 4 beta 1 and alpha 4 beta 7 integrin binding to VCAM-1 domains.
- To determine the role of CD24 expression in VCAM-1-integrin interactions.
Main Methods:
- Utilized VCAM-1 domain deletion mutants to analyze integrin binding.
- Assessed integrin adhesion under varying cation (Mn2+, Ca2+, Mg2+) concentrations.
- Investigated the influence of CD24 expression on integrin-VCAM-1 interactions.
Main Results:
- Alpha 4 beta 7 integrin binds to both VCAM-1 domains 1 and 4.
- Alpha 4 beta 1 and alpha 4 beta 7 integrins exhibit distinct cation requirements for binding to VCAM-1 domain 4.
- CD24 expression regulates alpha 4 beta 1 binding to VCAM-1 domain 1, but not domain 4 or overall VCAM-1 binding.
Conclusions:
- Integrin heterodimer composition and CD24 expression differentially modulate VCAM-1 domain binding.
- These modulations can impact adhesion strength and signal transmission, influencing cellular responses to integrin occupancy.
Abstract:
The vascular cell adhesion molecule-1 (VCAM-1) plays an important role in diverse physiological and pathological processes. The homologous first and fourth immunoglobulin-like domains of the seven domain form of VCAM-1 present binding motifs for alpha 4 beta 1 integrin. Using a panel of VCAM-1 domain deletion mutants we show that alpha 4 beta 7 integrin interacts with both domains 1 and 4. In contrast to their identical domain usage, alpha 4 beta 1 and alpha 4 beta 7 integrins differ in the activation states required for binding to domains 1 and 4 of VCAM-1. We show that integrin alpha 4 beta 1 required significantly higher concentrations of Mn2+ than integrin alpha 4 beta 7 to support half-maximal adhesion to domain 4. Moreover, a clear difference in the capacity of integrins alpha 4 beta 1 and alpha 4 beta 7 to interact with domain 4 was detected in the presence of Ca2+ and Mg2+ cations. Adhesion to domain 1 of VCAM-1, however, was not affected by integrin heterodimer composition. Instead, the activity level of integrin alpha 4 beta 1 for domain 1 binding was regulated by CD24 expression. Binding to seven domain VCAM-1 was not altered significantly by beta 1 and beta 7 subunits or CD24. These data indicate that integrin heterodimer composition and CD24 expression differentially modulate integrin binding to domains 1 and 4 of VCAM-1. Mechanisms that alter integrin binding specificity or monovalent versus divalent interactions may affect the strength of adhesion as well as signal transmission in adherent cells and may therefore be critical to controlling the cellular response to integrin occupancy.