N-terminal destruction signals lead to rapid degradation of the major histocompatibility complex class II transactivator CIITA.
Major histocompatibility complex (MHC) class II molecules play an essential role for the cellular immune response by presenting peptide antigens to CD4(+) T cells. MHC class II molecules and genes show a highly complex expression pattern, which is orchestrated through a master regulatory factor, called CIITA (class II transactivator). CIITA controls MHC class II expression not only qualitatively, but also quantitatively, and has therefore a direct influence on the CD4 T cell-dependent immune response. CIITA is itself tightly regulated not only on the transcriptional level, but as we show here also on the protein level. CIITA is subjected to a very rapid protein turnover and shows a half-life of about 30 min. Inhibition of degradation by proteasome inhibitors and the identification of ubiquitylated CIITA intermediates indicate that the degradation of CIITA is mediated by the ubiquitin-proteasome system. We identified two regions mediating degradation within the N-terminal domain of CIITA. N-terminal fusions or deletions stabilized CIITA, indicating that the N termini contribute to degradation. Several non-functional CIITA mutants are partially stabilized, but we provide evidence that transcriptional activity of CIITA is not directly linked to degradation.
Schnappauf
Felix
F
Hans-Spemann-Laboratories, Max-Planck-Institut für Immunbiologie, Freiburg, Germany.
Hake
Sandra B
SB
Camacho Carvajal
Margarita M
MM
Bontron
Séverine
S
Lisowska-Grospierre
Barbara
B
Steimle
Viktor
V
D000595:Amino Acid Sequence; D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000378:metabolism; D004355:Drug Stability; D005802:Genes, MHC Class II; D006207:Half-Life; D006801:Humans; D008969:Molecular Sequence Data; D009097:Multienzyme Complexes / Q000378:metabolism; D009687:Nuclear Proteins; D046988:Proteasome Endopeptidase Complex; D021382:Protein Sorting Signals / Q000235:genetics; D017434:Protein Structure, Tertiary; D017384:Sequence Deletion; D015534:Trans-Activators / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D025801:Ubiquitin / Q000378:metabolism
C083728:MHC class II transactivator protein; D009097:Multienzyme Complexes; D009687:Nuclear Proteins; D021382:Protein Sorting Signals; D015534:Trans-Activators; D025801:Ubiquitin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex