Mechanisms for actin reorganization in chemotactic factor-activated polymorphonuclear leukocytes.
Cytoskeletal structure in polymorphonuclear leukocytes (PMNs) is thought to reflect a simple equilibrium between two actin pools (globular [G]- and filamentous [F] actin). Recent description of two distinct F-actin pools in PMNs (Triton-insoluble [stable] and Triton-soluble [labile] F-actin pools) (Watts and Howard, Cell Motil Cytoskeleton, 21:25, 1992) suggest a tripartite equilibrium between these F-actin pools and G-actin and multiple possible mechanisms for polymerization. To study the contribution of each actin pool to actin dynamics in PMNs, changes in actin content of the Triton-soluble and -insoluble F-actin pools and G-actin in chemotactic factor (CTF)-activated PMNs were measured by NBDphallacidin binding and by gel scans of Triton-lysed PMNs. From 0 to 30 seconds after CTF activation, PMNs rapidly increase total (Triton-soluble + Triton-insoluble) F-actin content (maximum = 1.7- +/- 0.10-fold basal at 30 seconds). Concurrent measures of the actin content of individual actin pools (Triton-soluble and -insoluble F-actin and G-actin) show that at all times (0 to 30 seconds) only the Triton-insoluble F-actin pool grows (maximum = 2.81- +/- 0.73-fold basal at 30 seconds), whereas both the Triton-soluble and G-actin pools simultaneously decrease (50% decrease at 30 seconds). Concurrent growth of one F-actin pool (Triton-insoluble) and loss of another F-actin pool (Triton-soluble) emphasize the functional uniqueness of the F-actin pools and can occur only if the Triton-soluble F-actin anneals or cross-links filament-to-filament with the Triton-insoluble fraction or if the Triton-insoluble F-actin pool first depolymerizes to monomer, which is then added to the Triton-insoluble pool. Because from 0 to 30 seconds after FMLP activation G-actin never increases, but, like the Triton-soluble F-actin progressively decreases, the results suggest that F-actin growth results from simultaneous new filament growth by monomer addition to the Triton-insoluble F-actin and cytoskeletal remodelling by Triton-soluble F-actin annealing or cross-linking to Triton-insoluble F-actin. These findings offer important new insights into the mechanism(s) of actin polymerization in CTF-activated human PMNs.
Watts
R G
RG
Department of Pediatrics, University of Alabama, Birmingham 35233.
Howard
T H
TH
D008841:Actin Cytoskeleton / Q000187:drug effects / Q000502:physiology; D000199:Actins / Q000032:analysis / Q000097:blood*; D002630:Chemotactic Factors / Q000494:pharmacology*; D005434:Flow Cytometry; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D046911:Macromolecular Substances; D008954:Models, Biological; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D009504:Neutrophils / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013997:Time Factors
D000199:Actins; D002630:Chemotactic Factors; D046911:Macromolecular Substances; D009240:N-Formylmethionine Leucyl-Phenylalanine