Hypertonicity-enhanced TNF-α release from activated human monocytic THP-1 cells requires ERK activation.
BACKGROUND
Hypertonic stress enhances tumor necrosis factor (TNF)-α expression in activated monocytes. However, the underlying mechanism is unknown. The produced TNF-α is primarily cleaved and released by TNF-α-converting enzyme (TACE), and the surface expression of TACE is down-regulated by endocytosis. As hypertonicity inhibits endocytosis, we evaluated the mechanism of hypertonicity-induced TNF-α release from activated human monocytic THP-1 cells.


METHODS
THP-1 cells were stimulated with lipopolysaccharide (LPS) or phorbol 12-myristate 13-acetate (PMA) in the presence or absence of hypertonic agents (150 mM sucrose or 150-300 mM NaCl). The amount of TNF-α mRNA and protein, surface expression of TACE and activation of signaling pathways (mitogen-activated protein kinase, Akt and NF-κB) were assayed.


RESULTS
Hypertonic sucrose and NaCl significantly enhanced TNF-α release from THP-1 cells upon LPS or PMA stimulation. Hypertonic sucrose and other endocytosis inhibitors increased surface expression of TACE, but their effects on TNF-α release were inconsistent. This enhancement effect by hypertonicity was not attenuated by inhibition of TACE or IκB kinase, but it was blocked by cycloheximide and a MAP/ERK kinase inhibitor. The LPS- or PMA-induced TNF-α mRNA expression was not increased; rather, it was inhibited by hypertonicity. ERK1/2 was re-activated after sucrose treatment in LPS-stimulated THP-1 cells.


CONCLUSIONS
Hypertonicity-enhanced TNF-α protein synthesis from LPS- or PMA-activated THP-1 cells requires ERK activation and may proceed without TACE.


CONCLUSIONS
A vast amount of TNF-α production was regulated by a crucial post-transcriptional manner in activated human monocytic leukemia cells, and it may possibly be contributed to the cachexia condition.
Graduate Institute of Medical Sciences, Taipei Medical University, Taipei, Taiwan. [corrected].
Yung-Chen
YC
Chou
Joen-Rong
JR
Sheu
Chi-Li
CL
Chung
Che-Jen
CJ
Hsiao
Po-Jen
PJ
Hsueh
George
G
Hsiao
D051722:ADAM Proteins / Q000037:antagonists & inhibitors / Q000235:genetics; D000072198:ADAM17 Protein; D002460:Cell Line; D004705:Endocytosis / Q000187:drug effects; D048049:Extracellular Signal-Regulated MAP Kinases / Q000276:immunology*; D015870:Gene Expression / Q000187:drug effects; D006801:Humans; D008070:Lipopolysaccharides / Q000276:immunology*; D009000:Monocytes / Q000166:cytology / Q000276:immunology* / Q000378:metabolism; D009994:Osmolar Concentration; D012333:RNA, Messenger / Q000235:genetics; D012965:Sodium Chloride / Q000378:metabolism; D013395:Sucrose / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000276:immunology*; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000276:immunology*
D008070:Lipopolysaccharides; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha; D012965:Sodium Chloride; D013395:Sucrose; D048049:Extracellular Signal-Regulated MAP Kinases; D051722:ADAM Proteins; D000072198:ADAM17 Protein; C000606462:ADAM17 protein, human; D013755:Tetradecanoylphorbol Acetate