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  • Title: N-terminal destruction signals lead to rapid degradation of the major histocompatibility complex class II transactivator CIITA.
    Author: Schnappauf F, Hake SB, Camacho Carvajal MM, Bontron S, Lisowska-Grospierre B, Steimle V.
    Journal: Eur J Immunol; 2003 Aug; 33(8):2337-47. PubMed ID: 12884309.
    Abstract:
    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.
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