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Mechanisms for actin reorganization in chemotactic factor-activated polymorphonuclear leukocytes
1Department of Pediatrics, University of Alabama, Birmingham 35233.
Blood
|May 15, 1993
Summary
Polymorphonuclear leukocytes (PMNs) actin dynamics involve three pools: globular (G)-actin, Triton-soluble (labile) F-actin, and Triton-insoluble (stable) F-actin. Upon activation, the stable F-actin pool grows while labile pools decrease, indicating complex polymerization mechanisms.
Area of Science:
- Cell Biology
- Biochemistry
- Immunology
Background:
- Polymorphonuclear leukocytes (PMNs) cytoskeletal structure was traditionally viewed as a simple equilibrium between globular (G)-actin and filamentous (F)-actin.
- Recent findings suggest two distinct F-actin pools in PMNs: Triton-insoluble (stable) and Triton-soluble (labile), implying a tripartite equilibrium involving G-actin and F-actin pools.
- This complexity suggests multiple potential mechanisms for actin polymerization within PMNs.
Purpose of the Study:
- To investigate the contribution of individual actin pools (G-actin, Triton-soluble F-actin, Triton-insoluble F-actin) to actin dynamics in chemotactic factor (CTF)-activated PMNs.
- To elucidate the polymerization mechanisms underlying changes in these actin pools during PMN activation.
Main Methods:
- Changes in G-actin, Triton-soluble F-actin, and Triton-insoluble F-actin content were quantified in CTF-activated PMNs.
- NBDphallacidin binding assays were employed to measure actin content.
- Gel scans of Triton-lysed PMNs provided further quantification of actin pools.
Main Results:
- Total F-actin content in PMNs rapidly increased within 30 seconds of CTF activation (1.7-fold basal).
- During this period, only the Triton-insoluble F-actin pool significantly grew (2.81-fold basal), while both Triton-soluble F-actin and G-actin pools decreased by 50%.
- The concurrent growth of the stable F-actin pool and reduction of the labile pools suggest F-actin polymerization involves new filament growth and cytoskeletal remodeling.
Conclusions:
- Actin dynamics in CTF-activated human PMNs are more complex than a simple G-actin/F-actin equilibrium.
- The distinct behaviors of Triton-soluble and Triton-insoluble F-actin pools highlight their functional differences.
- F-actin growth appears to result from simultaneous monomer addition to the Triton-insoluble pool and remodeling of the Triton-soluble pool, possibly through annealing or cross-linking.