RECEPTOR-INDUCED TRANSLOCATION OF ACTIVATED GUANINE-NUCLEOTIDE-BINDING PROTEIN ALPHA(I) SUBUNITS TO THE CYTOSKELETON IN MYELOID DIFFERENTIATED HUMAN LEUKEMIA (HL-60) CELLS

The regulation of the cytoskeletal localization of guanine-nucleotide- binding protein alpha(i) subunits by formyl peptide receptors was stud ied in myeloid differentiated human leukemia (HL-60) cells. Stimulatio n of formyl peptide receptors with N-formyl-Met-Leu-Phe (fMet-Leu-Phe) transiently increased the amount of alpha(1) subunits in the Triton X -100-insoluble cytoskeleton, Similar to tire biphasic regulation of th e actin content, fMet-Leu-Phe (greater than or equal to 10 nM) rapidly increased the cytoskeletal alpha(i) content (about threefold at 30 s) , which was followed by a rapid reversal to control levels. The formyl peptide receptor increased the cytoskeletal content of both alpha(i) subtypes, alpha(i2) and alpha(i3), present in HL-60 cells. In cells pe rmeabilized with Staphylococcus aureus alpha-toxin, fMet-Leu-Phe incre ased binding of the stable GTP analogue, guanosine 5'-[gamma-thio]trip hosphate (GTP[S]), to cytoskeletal proteins in a pertussis-toxin-sensi tive manner, which was completely abolished by the F-actin-disrupting agent, cytochalasin B. Using the photoreactive CTP analogue, m-acetyla nilido-GTP, the formyl peptide receptor-regulated GTP binding sires at the cytoskeleton were identified as 40-kDa proteins, the molecular si ze of alpha(i) subunits. Cytoskeleton prepared from stimulated cells d id not exhibit increased GTP[S] binding, which suggests that activated alpha(i) subunits are translocated to the cytoskeleton. Finally in al pha-toxin-permeabilized HL-60 cells, fMet-Leu-Phe and GTP[S] cooperati vely stimulated actin polymerization. In conclusion, evidence is provi ded that chemoattractant receptors cause translocation of activated al pha(i) subunits to the cytoskeleton coincidentally with F-actin format ion. The data therefore argue for a potential role of translocated alp ha(i) subunits in the process of receptor-induced actin polymerization .