TPL2-mediated activation of ERK1 and ERK2 regulates the processing of pre-TNF alpha in LPS-stimulated macrophages.
Activation of the TPL2-MKK1/2-ERK1/2 signalling pathway is essential for lipopolysaccharide (LPS)-stimulated production of TNF alpha in macrophages. Here, we demonstrate that, unexpectedly, TPL2-deficient or MKK1-inhibited macrophages produce near normal levels of pre-TNF alpha when TLR2, TLR4 and TLR6 are activated by their respective agonists, but fail to secrete TNFalpha. We show that LPS stimulates the appearance of pre-TNFalpha at the cell surface and that this is prevented by inhibition of MAPK kinases 1 and 2 (MKK1/2) or in TPL2-deficient macrophages. However, the transport of pre-TNF alpha from the Golgi to the plasma membrane is unaffected by inhibition of the TPL2-MKK1/2-ERK1/2 pathway. Finally, we show that TACE, the protease that cleaves pre-TNF alpha to secreted TNFalpha, is phosphorylated by ERK1 and ERK2 (ERK1/2) at Thr735 in LPS-stimulated macrophages. Therefore, although TACE activity per se is not required for the LPS-stimulated cell surface expression of pre-TNF alpha, the phosphorylation of this protease might contribute to, or be required for, the cell surface expression of the pre-TNF alpha-TACE complex.
Rousseau
Simon
S
MRC Protein Phosphorylation Unit, College of Life Sciences, University of Dundee, Dow Street, Dundee, DD1 5EH, UK. s.rousseau@dundee.ac.uk
Papoutsopoulou
Matoula
M
Symons
Antony
A
Cook
Dorthe
D
Lucocq
John M
JM
Prescott
Alan R
AR
O'Garra
Anne
A
Ley
Steven C
SC
Cohen
Philip
P
D000818:Animals; D002462:Cell Membrane / Q000378:metabolism*; D015971:Gene Expression Regulation, Enzymologic; D006056:Golgi Apparatus / Q000378:metabolism*; D006801:Humans; D008070:Lipopolysaccharides / Q000378:metabolism*; D020930:MAP Kinase Kinase Kinases / Q000378:metabolism*; D020935:MAP Kinase Signaling System; D008264:Macrophages / Q000378:metabolism*; D051379:Mice; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism*; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism*; D008954:Models, Biological; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D014409:Tumor Necrosis Factor-alpha / Q000378:metabolism*
D008070:Lipopolysaccharides; D011518:Proto-Oncogene Proteins; D014409:Tumor Necrosis Factor-alpha; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020930:MAP Kinase Kinase Kinases; C069937:MAP3K8 protein, human; C489843:Map3k8 protein, mouse