RESUMO
The apical inflammatory cytokine TNF regulates numerous important biological processes including inflammation and cell death, and drives inflammatory diseases. TNF secretion requires TACE (also called ADAM17), which cleaves TNF from its transmembrane tether. The trafficking of TACE to the cell surface, and stimulation of its proteolytic activity, depends on membrane proteins, called iRhoms. To delineate how the TNF/TACE/iRhom axis is regulated, we performed an immunoprecipitation/mass spectrometry screen to identify iRhom-binding proteins. This identified a novel protein, that we name iTAP (iRhom Tail-Associated Protein) that binds to iRhoms, enhancing the cell surface stability of iRhoms and TACE, preventing their degradation in lysosomes. Depleting iTAP in primary human macrophages profoundly impaired TNF production and tissues from iTAP KO mice exhibit a pronounced depletion in active TACE levels. Our work identifies iTAP as a physiological regulator of TNF signalling and a novel target for the control of inflammation.
Assuntos
Proteína ADAM17/metabolismo , Proteínas de Transporte/metabolismo , Proteínas do Citoesqueleto/metabolismo , Macrófagos/metabolismo , Proteínas de Membrana/metabolismo , Fator de Necrose Tumoral alfa/genética , Proteína ADAM17/genética , Sequência de Aminoácidos , Animais , Proteínas de Transporte/genética , Linhagem Celular , Proteínas do Citoesqueleto/genética , Endossomos/metabolismo , Fibroblastos/citologia , Fibroblastos/metabolismo , Regulação da Expressão Gênica , Células HEK293 , Células HeLa , Humanos , Peptídeos e Proteínas de Sinalização Intracelular , Macrófagos/citologia , Proteínas de Membrana/genética , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Cultura Primária de Células , Ligação Proteica , Proteólise , Células RAW 264.7 , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Transdução de Sinais , Fator de Necrose Tumoral alfa/metabolismoRESUMO
The extracellular signal-regulated kinase (ERK) pathway plays an important role during the development and activation of B lymphocytes. We have recently shown that B-Raf is a dominant ERK activator in B-cell antigen receptor signalling. We now show that B-Raf is hyperphosphorylated upon BCR engagement and undergoes a prominent electrophoretic mobility shift. This shift correlates with ERK activation and is prevented by the MEK inhibitor U0126. Syk-deficient DT40 B cells display neither dual ERK phosphorylation nor a mobility shift of B-Raf upon BCR engagement. The inducible expression of a constitutively active B-Raf in this mutant line restores dual ERK phosphorylation and the mobility shift of endogenous B-Raf, indicating that these two events are connected to each other. By site-directed mutagenesis studies, we demonstrate that the shift is due to an ERK2-mediated feedback phosphorylation of serine/threonine residues within an evolutionary conserved SPKTP motif at the C-terminus of B-Raf. Replacement of these residues by negatively charged amino acids causes a constitutive mobility shift and a reduction of PC12 cell differentiation. We discuss a model in which ERK-mediated phosphorylation of the SPKTP motif is involved in negative feedback regulation of B-Raf.
