Epigenetic regulation of MHC-II and CIITA genes

Inhibitory effects of anti-CII TA M1-RNA on IFN-γ induced major histocompatibility complex class II antigens expression on cultured human chondrocytes

Major histocompatibility complex class II (MHC-II) trans-activator (CII TA) has been shown to be required for constitutive and IFN-gamma-induced MHC-II transcription. This study investigated the inhibitory effect of anti-CII TA M1-RNA on expression of MHC-II in chondrocytes in response to IFN-gamma. M1-RNAs with different guide sequence (GS) recognizing 452 or 3408 sites in CII TA (M1-452-GS and M1-3408-GS, respectively) were cloned into pUC19 vector. Target mRNA (3176-3560) in CII TA was obtained from Raji cell and inserted into pGEM-7zf(+) plasmid. The recombinant M1-RNAs and their target mRNA were incubated in a cell-free condition. It showed that only M1-3408-GS could cleave the target mRNA exclusively. M1-3408-GS was also cloned into psNAV vector (named pA3408). Chondrocytes was stably transfected with pA3408 and expressions of classical MHC-II (HLA-DR, -DP, -DQ) were analyzed by Flow Cytometry. The level of CII TA mRNA was measured by RT-PCR. Peripheral blood mono-nucleated cells (PBMNCs) were stimulated by pA3408-positive chondrocytes in mixed lymphocyte reaction, and proliferation of PBMNCs and IL-2 mRNA were detected. The expression of HLA-DR and HLA-DP on pA3408-positive chondrocytes in response to IFN-gamma decreased 73.00%+/-5.24%, 88.47%+/-2.02%, respectively (P<0.05); So did the content of CII TA mRNA (70.11%+/-5.79%, P<0.05). Proliferation of PBMNCs and production of IL-2 mRNA were both inhibited by pA3408 in mixed lymphocyte reaction. This is the first description that anti-CII TA M1-RNA could prevent IFN-gamma-induced CII TA transcription and results in a decreased MHC-II expression in chondrocytes.

Transcription-coupled deposition of histone modifications during MHC class II gene activation

Posttranslational histone modifications associated with actively expressed genes are generally believed to be introduced primarily by histone-modifying enzymes that are recruited by transcription factors or their associated co-activators. We have performed a comprehensive spatial and temporal analyses of the histone modifications that are deposited upon activation of the MHC class II gene HLA-DRA by the co-activator CIITA. We find that transcription-associated histone modifications are introduced during two sequential phases. The first phase precedes transcription initiation and is characterized exclusively by a rapid increase in histone H4 acetylation over a large upstream domain. All other modifications examined, including the acetylation and methylation of several residues in histone H3, are restricted to short regions situated at or within the 5' end of the gene and are established during a second phase that is concomitant with ongoing transcription. This second phase is completely abrogated when elongation by RNA polymerase II is blocked. These results provide strong evidence that transcription elongation can play a decisive role in the deposition of histone modification patterns associated with inducible gene activation.

Nod-like proteins in immunity, inflammation and disease

The intracellular Nod-like proteins or receptors are a family of sensors of intracellularly encountered microbial motifs and 'danger signals' that have emerged as being critical components of the innate immune responses and of inflammation in mammals. Several Nod-like receptors, including Nod1, Nod2, NALP3, Ipaf and Naip, are strongly associated with host responses to intracellular invasion by bacteria or the intracellular presence of specific bacterial products. An additional key function of Nod-like receptors is in inflammatory conditions, which has been emphasized by the identification of several different mutations in the genes encoding Nod1, Nod2 and NALP3 that are associated with susceptibility to inflammatory disorders. Those and other issues related to the Nod-like receptor family are discussed here.