C/EBPbeta phosphorylation by RSK creates a functional XEXD caspase inhibitory box critical for cell survival.
Upon activation by liver injury, hepatic stellate cells produce excessive fibrous tissue leading to cirrhosis. The hepatotoxin CCl(4) induced activation of RSK, phosphorylation of C/EBPbeta on Thr(217), and proliferation of stellate cells in normal mice, but caused apoptosis of these cells in C/EBPbeta-/- or C/EBPbeta-Ala(217) (a dominant-negative nonphosphorylatable mutant) transgenic mice. Both C/EBPbeta-PThr(217) and the phosphorylation mimic C/EBPbeta-Glu(217), but not C/EBPbeta-Ala(217), were associated with procaspases 1 and 8 in vivo and in vitro and inhibited their activation. Our data suggest that C/EBPbeta phosphorylation on Thr(217) creates a functional XEXD caspase substrate/inhibitor box (K-Phospho-T(217)VD) that is mimicked by C/EBPbeta-Glu(217) (KE(217)VD). C/EBPbeta-/- and C/EBPbeta-Ala(217) stellate cells were rescued from apoptosis by the cell permeant KE(217)VD tetrapeptide or C/EBPbeta-Glu(217).
Buck
M
M
Molecular Biology and Virology Laboratory, The Salk Institute for Biological Studies, La Jolla, CA 92037, USA.
Poli
V
V
Hunter
T
T
Chojkier
M
M
D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology; D020816:Amino Acid Motifs; D000818:Animals; D017209:Apoptosis / Q000502:physiology; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000235:genetics / Q000378:metabolism*; D002251:Carbon Tetrachloride / Q000633:toxicity; D061945:Caspase Inhibitors; D020169:Caspases / Q000378:metabolism*; D002470:Cell Survival / Q000502:physiology*; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free; D004789:Enzyme Activation; D004792:Enzyme Precursors / Q000378:metabolism; D022781:Hepatocytes / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D008106:Liver Cirrhosis, Experimental / Q000139:chemically induced; D008297:Male; D051379:Mice; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D010766:Phosphorylation; D051381:Rats; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000235:genetics / Q000378:metabolism*
D022782:CCAAT-Enhancer-Binding Protein-beta; D061945:Caspase Inhibitors; D016895:Culture Media, Serum-Free; D004792:Enzyme Precursors; D011994:Recombinant Proteins; C067713:lactacystin; D002251:Carbon Tetrachloride; D019893:Ribosomal Protein S6 Kinases; D020169:Caspases; D000111:Acetylcysteine