MARCH1 protects the lipid raft and tetraspanin web from MHCII proteotoxicity in dendritic cells

Dendritic cells (DCs) produce major histocompatibility complex II (MHCII) in large amounts to function as professional antigen presenting cells. Paradoxically, DCs also ubiquitinate and degrade MHCII in a constitutive manner. Mice deficient in the MHCII-ubiquitinating enzyme membrane-anchored RING-CH1, or the ubiquitin-acceptor lysine of MHCII, exhibit a substantial reduction in the number of regulatory T (Treg) cells, but the underlying mechanism was unclear. Here we report that ubiquitin-dependent MHCII turnover is critical to maintain homeostasis of lipid rafts and the tetraspanin web in DCs. Lack of MHCII ubiquitination results in the accumulation of excessive quantities of MHCII in the plasma membrane, and the resulting disruption to lipid rafts and the tetraspanin web leads to significant impairment in the ability of DCs to engage and activate thymocytes for Treg cell differentiation. Thus, ubiquitin-dependent MHCII turnover represents a novel quality-control mechanism by which DCs maintain homeostasis of membrane domains that support DC's Treg cell-selecting function

Expression of SRG3, a core component of mouse SWI/SNF chromatin-remodeling complex, is regulated by cooperative interactions between Sp1/Sp3 and Ets transcription factors

SRG3, a mouse homolog of yeast SW13 and human BAF155, is known to be a core component of SWI/SNF chromatin-remodeling complex. We have previously shown that SRG3 plays essential roles in early mouse embryogenesis, brain development, and T-cell development. SRG3 gene expression was differentially regulated depending on the developmental stages and exhibited tissue-specific pattern. In this study, we showed that the functional interactions between Sp and Ets family transcription factors are crucial for the SRG3 expression. Sp I and Sp3 specifically bound to the two canonical Sp-binding sites (GC boxes) at -152 and -114, and a non-canonical Sp-binding site (CCTCCT inotif) at -108 in the SRG3 promoter. Using Drosophila SL2 cells, we found that Various Sp or Ets family members activate the SRG3 promoter through these Sp- or Ets-binding sites, respectively, in a dose-dependent manner. Intriguingly, different combinatorial expression of Ets and Sp factors in SL2 cells resulted in either strong synergistic activation or repression of the SRG3 promoter activity. Moreover, the Sp-mediated activation of SRG3 promoter required the intact Ets-binding element. Taken together, these results Suggest that diverse interactions between Sp1/Sp3 and Ets factors are crucial for the SRG3 gene expression. (c) 2005 Elsevier Inc. All rights reserved.close5

CD40 Mediates Maturation of Thymic Dendritic Cells Driven by Self-Reactive CD4+ Thymocytes and Supports Development of Natural Regulatory T Cells

Thymic dendritic cells (tDCs) play an important role in central tolerance by eliminating self-reactive thymocytes or differentiating them to regulatory T (Treg) cells. However, the molecular and cellular mechanisms underlying these functions are not completely understood. We found that mouse tDCs undergo maturation following cognate interaction with self-reactive CD4+ thymocytes and that this maturation is dependent on CD40 signaling. Ablation of CD40 expression in tDCs resulted in a significant reduction in the number of Treg cells in association with a significant reduction in the number of mature tDCs. In addition, CD40-deficient DCs failed to fully mature upon cognate interaction with CD4+ thymocytes in vitro and failed to differentiate them into Treg cells to a sufficient number. These findings suggest that tDCs mature and potentiate Treg cell development in feedback response to self-reactive CD4+ thymocytes

The anti-diabetic effects of NAG-1/GDF15 on HFD/STZ-induced mice

Nonsteroidal anti-inflammatory drug-activated gene-1 (NAG-1) plays a role in various diseases. Here, the anti-diabetic effects of NAG-1 were evaluated using a high-fat diet/streptozotocin-induced diabetic mouse model. NAG-1-overexpressing transgenic (NAG-1 Tg) mice exhibited lower body weight, fasting blood glucose levels, and serum insulin levels than wild-type (WT) mice. The homeostatic model assessment of insulin resistance scores of NAG-1 Tg mice were lower than those of WT mice. Hematoxylin and eosin staining revealed a smaller lipid droplet size in the adipose tissues, lower lipid accumulation in the hepatocytes, and larger beta cell area in the pancreas of NAG-1 Tg mice than in those of WT mice. Immunohistochemical analysis revealed downregulated expression of cleaved caspase-3, an apoptosis marker, in the beta cells of NAG-1 Tg mice. Adiponectin and leptin mRNA levels were upregulated and downregulated in NAG-1 Tg mice, respectively. Additionally, the expression of IRS1/PI3K/AKT signaling pathway components, especially Foxo1, which regulates gluconeogenesis in the muscle and white adipose tissue, was downregulated in NAG-1 Tg mice. Furthermore, NAG-1 overexpression promoted the expression of As160 in both muscles and adipocytes, and the mRNA levels of the NLRP3 pathway members were downregulated in NAG-1 Tg mice. Our findings suggest that NAG-1 expression alleviates diabetes in mice.Y

MARCH1 protects the lipid raft and tetraspanin web from MHCII proteotoxicity in dendritic cells.

Dendritic cells (DCs) produce major histocompatibility complex II (MHCII) in large amounts to function as professional antigen presenting cells. Paradoxically, DCs also ubiquitinate and degrade MHCII in a constitutive manner. Mice deficient in the MHCII-ubiquitinating enzyme membrane-anchored RING-CH1, or the ubiquitin-acceptor lysine of MHCII, exhibit a substantial reduction in the number of regulatory T (Treg) cells, but the underlying mechanism was unclear. Here we report that ubiquitin-dependent MHCII turnover is critical to maintain homeostasis of lipid rafts and the tetraspanin web in DCs. Lack of MHCII ubiquitination results in the accumulation of excessive quantities of MHCII in the plasma membrane, and the resulting disruption to lipid rafts and the tetraspanin web leads to significant impairment in the ability of DCs to engage and activate thymocytes for Treg cell differentiation. Thus, ubiquitin-dependent MHCII turnover represents a novel quality-control mechanism by which DCs maintain homeostasis of membrane domains that support DC's Treg cell-selecting function