H3K27 demethylation by JMJD3 at a poised enhancer of anti-apoptotic gene BCL2 determines ERα ligand dependency.

Chromatin represents a repressive barrier to the process of ligand-dependent transcriptional activity of nuclear receptors. Here, we show that H3K27 methylation imposes ligand-dependent regulation of the oestrogen receptor α (ERα)-dependent apoptotic response via Bcl-2 in breast cancer cells. The activation of BCL2 transcription is dependent on the simultaneous inactivation of the H3K27 methyltransferase, EZH2, and the demethylation of H3K27 at a poised enhancer by the ERα-dependent recruitment of JMJD3 in hormone-dependent breast cancer cells. We also provide evidence that this pathway is modified in cells resistant to anti-oestrogen (AE), which constitutively express BCL2. We show that the lack of H3K27 methylation at BCL2 regulatory elements due to the inactivation of EZH2 by the HER2 pathway leads to this constitutive activation of BCL2 in these AE-resistant cells. Our results describe a mechanism in which the epigenetic state of chromatin affects ligand dependency during ERα-regulated gene expression.

Interleukin-10-induced MARCH1 mediates intracellular sequestration of MHC class II in monocytes.

IL-10 is a potent anti-inflammatory cytokine interfering with antigen presentation by inducing the intracellular sequestration of MHC class II (MHC-II) molecules. Here we studied the contribution of membrane-associated RING-CH (MARCH) ubiquitin ligase family members to the IL-10-induced down-regulation of MHC-II molecules. We found that MARCH1 and MARCH8 proteins are the most potent family members for the down-regulation of MHC-II surface expression in transfected cells, but only MARCH1 mRNA expression is strongly induced by IL-10 in human primary monocytes. We detected mono- and poly-ubiquitinated forms of MHC-II molecules both in IL-10-treated monocytes and in cells transfected with MARCH1. We also show direct interaction between MHC-II and MARCH1 molecules in co-immunoprecipitation assays. Finally, we found that siRNA-mediated knockdown of MARCH1 reverses IL-10-induced MHC-II down-regulation in primary monocytes. Thus, the immunosuppressive effect of IL-10 on antigen presentation is mediated through induced expression of MARCH1.

The structure and location of SIMP/STT3B account for its prominent imprint on the MHC I immunopeptidome.

Proteins show drastic discrepancies in their contribution to the collection of self-peptides that shape the repertoire of CD8 T cells (MHC I self-immunopeptidome). To decipher why selected proteins are the foremost sources of MHC I-associated self-peptides, we chose to study SIMP/STT3B because this protein generates very high amounts of MHC I-associated peptides in mice and humans. We show that the endoplasmic reticulum (ER)-associated degradation pathway and MHC I processing intersect at SIMP/STT3B. Relevant key features of SIMP/STT3B are its lysine-rich region, its propensity to misfold and its location in the ER membrane in close proximity to the immunoproteasome. Moreover, we show that coupling to SIMP/STT3B can be used to foster MHC I presentation of a selected peptide, here the ovalbumin peptide SIINFEKL. These data yield novel insights into relations between the cell proteome and the MHC I immunopeptidome. They suggest that the contribution of a given protein to the MHC I immunopeptidome results from the interplay of at least three factors: the presence of degrons (degradation signals), the tendency of the protein to misfold and its subcellular localization. Furthermore, they indicate that substrates of the ER-associated degradation pathway may have a prominent imprint on the MHC I self-immunopeptidome.