1,25-dihydroxyvitamin D3 induces responsiveness to the chemotactic peptide f-Met-Leu-Phe in the human monocytic line U937: dissociation between calcium and oxidative metabolic responses.
In the human premonocytic line U937, 1,25-dihydroxyvitamin D3 (1,25-(OH)2D3) induces a functional NADPH oxidase, that is responsive to both phorbol esters and opsonized zymosan. The chemotactic peptide f-Met-Leu-Phe (fMLP) did not, however, induce superoxide generation by these cells. This was not due to the absence of receptors for fMLP. Although there was no significant binding of [3H]-fMLP to undifferentiated U937 cells, preincubation with 1,25-(OH)2D3 induced expression of specific and saturable binding sites. Moreover, fMLP induced a rapid and reversible rise in cytosolic free Ca2+ concentration ([Ca2+]i) in 1,25-(OH)2D3-treated U937 cells, but not in control or 24,25-dihydroxyvitamin D3 (24,25-(OH)2D3)-treated cells. This [Ca2+]i response was dependent on concentrations of both fMLP and 1,25-(OH)2D3 and was observed at physiologic concentrations of the hormone (approximately 25 pM). The rise in [Ca2+]i induced by fMLP in 1,25-(OH)2D3-treated U937 cells was blocked by pertussis toxin and presumably mediated by inositol (1,4,5)-trisphosphate generation. These results indicate that in U937 cells differentiated with 1,25-(OH)2D3, inositol phosphate-mediated [Ca2+]i responses to fMLP are uncoupled from NADPH oxidase activation.
Polla
B S
BS
Respiratory Division, University Hospital Geneva, Switzerland.
Werlen
G
G
Clerget
M
M
Pittet
D
D
Rossier
M F
MF
Capponi
A M
AM
D002117:Calcitriol / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002454:Cell Differentiation / Q000187:drug effects; D002460:Cell Line; D006801:Humans; D015544:Inositol 1,4,5-Trisphosphate; D007295:Inositol Phosphates / Q000096:biosynthesis; D009000:Monocytes / Q000187:drug effects* / Q000378:metabolism; D009240:N-Formylmethionine Leucyl-Phenylalanine / Q000378:metabolism / Q000494:pharmacology*; D013481:Superoxides / Q000096:biosynthesis
D007295:Inositol Phosphates; D013481:Superoxides; D009240:N-Formylmethionine Leucyl-Phenylalanine; D015544:Inositol 1,4,5-Trisphosphate; D002117:Calcitriol; D002118:Calcium