Downregulation of CIITA Function by Protein Kinase A (PKA)-Mediated Phosphorylation: Mechanism of Prostaglandin E, Cyclic AMP, and PKA Inhibition of Class II Major Histocompatibility Complex Expression in Monocytic Lines

Abstract

Prostaglandins, pleiotropic immune modulators that induce protein kinase A (PKA), inhibit gamma interferon induction of class II major histocompatibility complex (MHC) genes. We show that phosphorylation of CIITA by PKA accounts for this inhibition. Treatment with prostaglandin E or 8-bromo-cyclic AMP or transfection with PKA inhibits the activity of CIITA in both mouse and human monocytic cell lines. This inhibition is independent of other transcription factors for the class II MHC promoter. These same treatments also greatly reduced the induction of class II MHC mRNA by CIITA. PKA phosphorylation sites were identified using site-directed mutagenesis and phosphoamino acid analysis. Phosphorylation at CIITA serines 834 and 1050 accounts for the inhibitory effects of PKA on CIITA-driven class II MHC transcription. This is the first demonstration that the posttranslational modification of CIITA mediates inhibition of class II MHC transcription.Class II molecules of the major histocompatibility complex (MHC) play a critical role in T-cell-dependent immunity and the inflammatory response by presenting processed, exogenous antigens to T helper (Th) cells (reviewed in references 13, 42, and 50). These important molecules are commonly used as targets for immune therapies aimed at blocking graft rejection or promoting the recognition of cancer. Although expressed constitutively on "professional" antigen-presenting cells (monocytes/macrophages, B cells, and dendritic cells) class II MHC can be induced in most cell types and tissues in the presence of gamma interferon (IFN-␥) (1, 3, 9-11, 24, 28, 31, 38, 45, 57, 60, 62). Patients lacking class II MHC have reduced numbers of CD4 ϩ Th cells and succumb to repeated bacterial, viral, and protozoal infections, generally dying in early childhood (39). Class II MHC has been implicated as a contributing factor for numerous diseases including diabetes, rheumatoid arthritis, Alzheimer's disease, and multiple sclerosis (7,39,49).The constitutive and inducible expression of nearly all class II MHC and related genes is regulated globally at the level of transcription by the class II transactivator (CIITA) (8,27,60). Transient transfection of CIITA into cells which are class II MHC deficient or have low-level expression of class II MHC is sufficient to drive class II MHC transcription and expression (12,46,48). In normal tissues, CIITA expression patterns are controlled by as many as four promoters, which allow both constitutive and IFN-␥-inducible expression of CIITA (44, 52). Though not a DNA-binding protein, CIITA is required for the opening and subsequent activation of class II MHC promoters through interactions with the ubiquitously expressed transcription factors RFX and NF-Y, which recognize the X and Y DNA elements of class II and class I MHC promoters (41,54,64). CIITA contains an N-terminal acidic domain (residues 1 to 125) which can act as a transcription activation domain when fused to GAL4 DNA-binding sequences (34,54,63). A variety of proteins interact with the acidic do...

Regulation of Class II MHC Expression in APCs: Roles of Types I, III, and IV Class II Transactivator

“…CIITA transcription is highly regulated (6,(31)(32)(33)(34), and posttranslational mechanisms also affect CIITA activity (35,36). Transcriptional regulation of CIITA occurs through the actions of three independent promoters (pI, pIII, pIV) in mice.…”

Patterned variation in murine MHC promoters

“…An important facet of the present study is that the X2 box, now securely identified as the cAMP response element (CRE) octamer (15), receives signals from G protein-coupled seven-pass receptors (16) that bind modulators of MHC II expression. Well-characterized examples of such modulators include thyroid-stimulating hormone (17) and prostaglandin E2 (18), although in the latter case signaling via CIITA is also involved. The octamer varies, particularly in its 3Ј tetramer (19), and a major human disease-associated polymorphism occurs 10 bp upstream of CRE in the IL-6 promoter (20).…”

Different levels of control prevent interferon-γ-inducible HLA-class II expression in human neuroblastoma cells

“…Thus, the instability of CIITA mRNA or protein has been recently hypothesized to explain the defect in CIITA protein and the consequent lack of MHC-II expression in a murine tumor cell line (Naves et al, 2002). In addition, other observations indicate that post-translational modifications, such as phosphorylation (Li et al, 2001;Tosi et al, 2002) or acetylation (Spilianakis et al, 2000) play an important role in CIITA stability or nuclear shuttling. Our data indicate that SK-NB-E2(c) transfected with CIITA gene express low levels of cytoplasmic CIITA protein, suggesting that a reduced CIITA protein accumulation or a deficient CIITA Figure 7 Analysis of CIITA nuclear localization by confocal microscopy.…”