勝沼 功吉

RNA-binding motif 10 (Rbm10) is an RNA-binding protein that regulates alternative splicing, but its role in inflammation is not well defined. Here, we show that Rbm10 controls appropriate splicing of DNA (cytosine-5)-methyltransferase 3b (Dnmt3b), a DNA methyltransferase, to regulate the activity of NF-κB-responsive promoters and consequently inflammation development. Rbm10 deficiency suppressed NF-κB-mediated responses in vivo and in vitro. Mechanistic analysis showed that Rbm10 deficiency decreased promoter recruitment of NF-κB, with increased DNA methylation of the promoter regions in NF-κB-responsive genes. Consistently, Rbm10 deficiency increased the expression level of Dnmt3b2, which has enzyme activity, while it decreased the splicing isoform Dnmt3b3, which does not. These two isoforms associated with NF-κB efficiently, and overexpression of enzymatically active Dnmt3b2 suppressed the expression of NF-κB targets, indicating that Rbm10-mediated Dnmt3b2 regulation is important for the induction of NF-κB-mediated transcription. Therefore, Rbm10-dependent Dnmt3b regulation is a possible therapeutic target for various inflammatory diseases.

KDEL receptors are responsible for retrotransporting endoplasmic reticulum (ER) chaperones from the Golgi complex to the ER. Here we describe a role for KDEL receptor 1 (KDELR1) that involves the regulation of integrated stress responses (ISR) in T cells. Designing and using an N-ethyl-N-nitrosourea (ENU)-mutant mouse line, T-Red (naïve T-cell reduced), we show that a point mutation in KDELR1 is responsible for the reduction in the number of naïve T cells in this model owing to an increase in ISR. Mechanistic analysis shows that KDELR1 directly regulates protein phosphatase 1 (PP1), a key phosphatase for ISR in naïve T cells. T-Red KDELR1 does not associate with PP1, resulting in reduced phosphatase activity against eIF2α and subsequent expression of stress responsive genes including the proapoptotic factor Bim. These results demonstrate that KDELR1 regulates naïve T-cell homeostasis by controlling ISR.

Macrophages are a major component of the innate immune system, and the cytokines they secrete are involved in antitumor responses. Z-100 is obtained from hot-water extract of human-type Mycobacterium tuberculosis strain Aoyama B and activates the innate immune response. However, while Z-100 is known to modulate macrophage activity, the mechanism behind this modulation is not fully understood. We evaluated the effects of Z-100 on the murine macrophage cell line RAW264.7. Tumor necrosis factor-alpha (TNF-α) production from RAW264.7 cells was strongly induced by Z-100 and interferon-gamma (IFN-γ) stimulation but only weakly induced by Z-100 alone. Quantitative gene expression analysis showed that nucleotide-binding oligomerization domain containing 2 (Nod2) expression was up-regulated by IFN-γ treatment in RAW264.7 cells while Z-100-induced TNF-α production was attenuated by Nod2 gene silencing. Further, componential analysis demonstrated that muramic acid and amino acids distinctive of muramyl dipeptide (MDP) were contained within Z-100 and Z-100Fr I, the low-molecular-weight fraction containing components <3 kDa in size. In addition, Z-100Fr I enhanced TNF-α production in RAW264.7 cells and promoted NOD2-dependent nuclear factor-kappa B (NF-κB) activation in murine NOD2-expressing SEAP reporter HEK293 (HEK-Blue-mNOD2) cells. Taken together, these results suggest that Z-100 contains MDP-like molecules and augments NF-κB signaling via the direct activation of Nod2 in macrophages, which might be one mechanism driving the innate immune responses induced by Z-100 in cancer immunotherapy.

The survival of naïve T cells is believed to require signals from TCR-pMHC interactions and cytokines such as IL-7. In contrast, signals that negatively impact naïve T cell survival are less understood. We conducted a forward genetic screening of mice and found a mutant mouse line with reduced number of naïve T cells (T-Red mice). T-Red mice have a point mutation in the Kdelr1 gene, and their naïve T cells show enhanced integrated stress response (ISR), which eventually induces their apoptosis. Therefore, naïve T cells require a KDEL receptor-mediated mechanism that efficiently relieves cellular stress for their survival in vivo. Interestingly, naïve T cells expressing TCR with higher affinity/avidity to self-antigens survive in T-Red mice, suggesting the possible link between TCR-mediated survival and ISR-induced apoptosis. In this article, we discuss the regulation of naïve T cell homeostasis, keeping special attention on the ISR and TCR signal.