Bacterial lipopolysaccharide has structural similarity to ceramide and stimulates ceramide-activated protein kinase in myeloid cells.
Bacterial lipopolysaccharide (LPS), tumor necrosis factor (TNF)-alpha and interleukin-1 beta (IL-1 beta) stimulate similar cellular responses. TNF-alpha and IL-1 beta are known to initiate signaling through a pathway involving hydrolysis of sphingomyelin to ceramide (Kolesnick, R. N., and Golde, D. W. (1994) Cell 77, 325-328). In this system, ceramide acts as a second messenger stimulating a ceramide-activated serine/threonine protein kinase. The present studies demonstrate that LPS, like TNF and IL-1, stimulates ceramide-activated protein kinase activity in human leukemia (HL-60) cells and in freshly isolated human neutrophils. Lipid A, the biologically active core of LPS, enhanced kinase activity in a time- and concentration-dependent manner. As little as 10 nM lipid A was effective, and a maximal effect occurred with 500 nM lipid A, increasing kinase activity 5-fold. Native LPS similarly induced kinase activation. This effect of LPS was markedly enhanced by LPS binding protein and required the LPS receptor CD14. In contrast to TNF and IL-1, LPS did not cause sphingomyelin hydrolysis and thus stimulates ceramide-activated protein kinase without generating ceramide. Molecular modeling showed strong structural similarity between ceramide and a region of lipid A. Based on these observations, we propose that LPS stimulates cells by mimicking the second messenger function of ceramide.
Laboratory of Signal Transduction, Memorial Sloan-Kettering Cancer Center, New York, New York 10021.
C K
CK
Joseph
S D
SD
Wright
W G
WG
Bornmann
J T
JT
Randolph
E R
ER
Kumar
R
R
Bittman
J
J
Liu
R N
RN
Kolesnick
D000595:Amino Acid Sequence; D001665:Binding Sites; D002236:Carbohydrate Conformation; D002478:Cells, Cultured; D002518:Ceramides / Q000096:biosynthesis / Q000737:chemistry* / Q000378:metabolism; D004789:Enzyme Activation; D006801:Humans; D007375:Interleukin-1 / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000737:chemistry* / Q000494:pharmacology; D008958:Models, Molecular; D008969:Molecular Sequence Data; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf; D015290:Second Messenger Systems; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology
D002518:Ceramides; D007375:Interleukin-1; D008070:Lipopolysaccharides; D014409:Tumor Necrosis Factor-alpha; D017346:Protein Serine-Threonine Kinases; D019908:Proto-Oncogene Proteins c-raf