Enhancement of pertussis-toxin-sensitive Na(+)-dependent uridine transporter activity in HL-60 granulocytes by N-formylmethionyl-leucyl-phenylalanine.
N-Formyl-Met-Leu-Phe (FMLP), at concentrations as low as 5 nM, caused an increase in intracellular uridine pools in dimethyl sulphoxide (Me2SO)-differentiated HL-60 cells. Intracellular uridine pools were elevated rapidly and reached a maximum within 10 min of exposure to 10 microM FMLP, followed by a gradual decline. This enhancement by FMLP was a consequence of a 3-fold increase in the Vmax of pertussis-toxin-sensitive Na(+)-dependent uridine transport system, with no change in the apparent Km. Km values of 2.67 +/- 0.45 and 3.85 +/- 0.52 microM and Vmax. values of 0.046 +/- 0.017 and 0.125 +/- 0.020 microM/s were obtained for untreated and FMLP-treated Me2SO-differentiated cells respectively. The effect of FMLP on the Na(+)-dependent transport of uridine in Me2SO-differentiated HL-60 cells was specific, as the facilitated transport of uridine was unaffected. Furthermore, this phenomenon was not observed in undifferentiated, phorbol 12-myristate 13-acetate (PMA)-differentiated or pertussis-toxin-treated Me2SO-differentiated HL-60 cells. Removal of extracellular Ca2+ with EGTA abolished the FMLP enhancement of uridine transport in a reversible manner, suggesting the involvement of Ca2+. However, the Ca2+ ionophore A23187 only partially mimicked the effect of FMLP. Similarly, with PMA the transport was sub-optimally enhanced, but a full activation was observed in cells treated with both A23187 and PMA. These findings suggest that activation of the Na(+)-dependent uridine transporter by FMLP in Me2SO-differentiated HL-60 cells involves a pertussis-toxin-sensitive G-protein with a bifurcating signal-transduction pathway.
Department of Physiology, National University of Singapore.
L B
LB
Goh
J A
JA
Sokoloski
A C
AC
Sartorelli
C W
CW
Lee
D000595:Amino Acid Sequence; D001692:Biological Transport / Q000187:drug effects; D000001:Calcimycin / Q000494:pharmacology; D002118:Calcium / Q000494:pharmacology; D005110:Extracellular Space / Q000378:metabolism; D006098:Granulocytes / Q000378:metabolism*; D006801:Humans; D066298:In Vitro Techniques; D008969:Molecular Sequence Data; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000494:pharmacology*; D037342:Pertussis Toxin; D012964:Sodium / Q000502:physiology; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D014529:Uridine / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology*
D010566:Virulence Factors, Bordetella; D000001:Calcimycin; D009240:N-Formylmethionine Leucyl-Phenylalanine; D012964:Sodium; D037342:Pertussis Toxin; D013755:Tetradecanoylphorbol Acetate; D002118:Calcium; D014529:Uridine