title: PMA induces the ligand-independent internalization of CR1 on human neutrophils.
abstract: Phorbol myristate acetate (PMA) has been reported to confer on the C3b receptor (CR1) of neutrophils a capacity for phagocytosis of particles bearing C3b without the involvement of other membrane receptors. In the present study, we employed a monoclonal antibody, YZ-1, that is specific for CR1 to assess the effect of PMA on plasma membrane expression of CR1, total cellular CR1, and internalization of CR1 by neutrophils. PMA had a biphasic effect on the membrane expression of CR1 by purified neutrophils, with 4 ng/ml inducing a 60% increment in receptor expression, and higher concentrations causing up to a 70% decrement. PMA-dependent increases in CR1 expression were not accompanied by corresponding changes in total cellular CR1 and were preempted by treatment of cells with formyl-methionyl-leucyl-phenylalanine (FMLP). PMA-induced decreases in CR1 expression by neutrophils, as measured by binding of indirectly fluoresceinated or radiolabeled YZ-1, or of 125I-labeled dimeric C3b, were maximal with 20 to 30 ng/ml PMA, and occurred within 30 min of incubation at 37 degrees C. The PMA-dependent down-regulation of CR1 by neutrophils was not associated with a comparable decrease in total cellular CR1, and this response was observed to occur also with monocytes but not with peripheral blood lymphocytes. By tagging neutrophil CR1 with 125I-YZ-1 Fab and monitoring accessibility to Protease, intracellular CR1 (inaccessible) was discriminated from receptor on plasma membrane (accessible). Internalization of CR1 occurred within 5 min after addition of PMA to neutrophils, was dose dependent, and involved up to two-thirds of the tagged receptors. Therefore, PMA caused internalization of CR1 by neutrophils in the absence of ligand, indicating that this response was independent of a transmembrane signal generated by a C3b-CR1 interaction.
authors.forename: P S
authors.initials: PS
authors.lastname: Changelian
authors.forename: R M
authors.initials: RM
authors.lastname: Jack
authors.forename: L A
authors.initials: LA
authors.lastname: Collins
authors.forename: D T
authors.initials: DT
authors.lastname: Fearon
mesh_terms: D000818:Animals; D000911:Antibodies, Monoclonal / Q000032:analysis; D000918:Antibody Specificity; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D006801:Humans; D051379:Mice; D008807:Mice, Inbred BALB C; D009000:Monocytes / Q000378:metabolism; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology; D009504:Neutrophils / Q000378:metabolism*; D010587:Phagocytosis / Q000187:drug effects*; D010704:Phorbols / Q000494:pharmacology*; D011817:Rabbits; D011951:Receptors, Complement / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D017463:Receptors, Complement 3b; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*
chemical_list: D000911:Antibodies, Monoclonal; D010704:Phorbols; D011951:Receptors, Complement; D017463:Receptors, Complement 3b; D009240:N-Formylmethionine Leucyl-Phenylalanine; D013755:Tetradecanoylphorbol Acetate