Early SIV and HIV infection promotes the LILRB2/MHC-I inhibitory axis in cDCs

Classical dendritic cells (cDCs) play a pivotal role in the early events that tip the immune response toward persistence or viral control. In vitro studies indicate that HIV infection induces the dysregulation of cDCs through binding of the LILRB2 inhibitory receptor to its MHC-I ligands and the strength of this interaction was proposed to drive disease progression. However, the dynamics of the LILRB2/MHC-I inhibitory axis in cDCs during early immune responses against HIV are yet unknown. Here, we show that early HIV-1 infection induces a strong and simultaneous increase of LILRB2 and MHC-I expression on the surface of blood cDCs. We further characterized the early dynamics of LILRB2 and MHC-I expression by showing that SIVmac251 infection of macaques promotes coordinated up-regulation of LILRB2 and MHC-I on cDCs and monocytes/macrophages, from blood and lymph nodes. Orientation towards the LILRB2/MHC-I inhibitory axis starts from the first days of infection and is transiently induced in the entire cDC population in acute phase. Analysis of the factors involved indicates that HIV-1 replication, TLR7/8 triggering, and treatment by IL-10 or type I IFNs increase LILRB2 expression. Finally, enhancement of the LILRB2/MHC-I inhibitory axis is specific to HIV-1 and SIVmac251 infections, as expression of LILRB2 on cDCs decreased in naturally controlled chikungunya virus infection of macaques. Altogether, our data reveal a unique up-regulation of LILRB2 and its MHC-I ligands on cDCs in the early phase of SIV/HIV infection, which may account for immune dysregulation at a critical stage of the anti-viral response.     

Role of the ubiquitin–proteasome system in the regulation of P2Y13 receptor expression: impact on hepatic HDL uptake

The protective effect of high density lipoproteins (HDL) against atherosclerosis is mainly attributed to their capacity to transport excess cholesterol from peripheral tissues back to the liver for further elimination into the bile, a process called reverse cholesterol transport (RCT). Recently, the importance of the P2Y₁₃ receptor (P2Y₁₃-R) was highlighted in HDL metabolism since HDL uptake by the liver was decreased in P2Y₁₃-R deficient mice, which translated into impaired RCT. Here, we investigated for the first time the molecular mechanisms regulating cell surface expression of P2Y₁₃-R. When transiently expressed, P2Y₁₃-R was mainly detected in the endoplasmic reticulum (ER) and strongly subjected to proteasome degradation while its homologous P2Y₁₂ receptor (P2Y₁₂-R) was efficiently targeted to the plasma membrane. We observed an inverse correlation between cell surface expression and ubiquitination level of P2Y₁₃-R in the ER, suggesting a close link between ubiquitination of P2Y₁₃-R and its efficient targeting to the plasma membrane. The C-terminus tail exchange between P2Y₁₃-R and P2Y₁₂-R strongly restored plasma membrane expression of P2Y₁₃-R, suggesting the involvement of the intra-cytoplasmic tail of P2Y₁₃-R in expression defect. Accordingly, proteasomal inhibition increased plasma membrane expression of functionally active P2Y₁₃-R in hepatocytes, and consequently stimulated P2Y₁₃-R-mediated HDL endocytosis. Importantly, proteasomal inhibition strongly potentiated HDL hepatic uptake (>200 %) in wild-type but not in P2Y₁₃-R-deficient mice, thus reinforcing the role of P2Y₁₃-R expression in regulating HDL metabolism. Therefore, specific inhibition of the ubiquitin–proteasome system might be a novel powerful HDL therapy to enhance P2Y₁₃-R expression and consequently promote the overall RCT.     

Pyk2 cytonuclear localization: mechanisms and regulation by serine dephosphorylation

Cytonuclear signaling is essential for long-term alterations of cellular properties. Several pathways involving regulated nuclear accumulation of Ser/Thr kinases have been described but little is known about cytonuclear trafficking of tyrosine kinases. Proline-rich tyrosine kinase 2 (Pyk2) is a cytoplasmic non-receptor tyrosine kinase enriched in neurons and involved in functions ranging from synaptic plasticity to bone resorption, as well as in cancer. We previously showed the Ca²⁺-induced, calcineurin-dependent, nuclear localization of Pyk2. Here, we characterize the molecular mechanisms of Pyk2 cytonuclear localization in transfected PC12 cells. The 700–841 linker region of Pyk2 recapitulates its depolarization-induced nuclear accumulation. This region includes a nuclear export motif regulated by phosphorylation at residue S778, a substrate of cAMP-dependent protein kinase and calcineurin. Nuclear import is controlled by a previously identified sequence in the N-terminal domain and by a novel nuclear targeting signal in the linker region. Regulation of cytonuclear trafficking is independent of Pyk2 activity. The region regulating nuclear localization is absent from the non-neuronal shorter splice isoform of Pyk2. Our results elucidate the mechanisms of Ca²⁺-induced nuclear accumulation of Pyk2. They also suggest that Pyk2 nuclear accumulation is a novel type of signaling response that may contribute to specific long-term adaptations in neurons.     

ABCB6 is dispensable for erythropoiesis and specifies the new blood group system Langereis

The human ATP-binding cassette (ABC) transporter ABCB6 has been described as a mitochondrial porphyrin transporter essential for heme biosynthesis, but it is also suspected to contribute to anticancer drug resistance, as do other ABC transporters located at the plasma membrane. We identified ABCB6 as the genetic basis of the Lan blood group antigen expressed on red blood cells but also at the plasma membrane of hepatocellular carcinoma (HCC) cells, and we established that ABCB6 encodes a new blood group system (Langereis, Lan). Targeted sequencing of ABCB6 in 12 unrelated individuals of the Lan(-) blood type identified 10 different ABCB6 null mutations. This is the first report of deficient alleles of this human ABC transporter gene. Of note, Lan(-) (ABCB6(-/-)) individuals do not suffer any clinical consequences, although their deficiency in ABCB6 may place them at risk when determining drug dosage.     

The nucleotide receptor P2Y13 is a key regulator of hepatic High-Density Lipoprotein (HDL) endocytosis

Cell surface receptors for high-density lipoprotein (HDL) on hepatocytes are major partners in the regulation of cholesterol homeostasis. We recently identified a cell surface ATP synthase as a high-affinity receptor for HDL apolipoprotein A-I (apoA-I) on human hepatocytes. Stimulation of this ectopic ATP synthase by apoA-I triggered a low-affinity-receptor-dependent HDL endocytosis by a mechanism strictly related to the generation of ADP. This suggests that nucleotide G-protein- coupled receptors of the P2Y family are molecular components in this pathway. Only P2Y₁ and P2Y₁₃ are present on the membrane of hepatocytes. Using both a pharmacological approach and small interference RNA, we identified P2Y₁₃ as the main partner in hepatic HDL endocytosis, in cultured cells as well as in situ in perfused mouse livers. We also found a new important action of the antithrombotic agent AR-C69931MX as a strong activator of P2Y₁₃-mediated HDL endocytosis. Received 9 May 2005; received after revision 24 June 2005; accepted 1 September 2005     

A globally coherent fingerprint of climate change impacts across natural systems

Causal attribution of recent biological trends to climate change is complicated because non-climatic influences dominate local, short-term biological changes. Any underlying signal from climate change is likely to be revealed by analyses that seek systematic trends across diverse species and geographic regions; however, debates within the Intergovernmental Panel on Climate Change (IPCC) reveal several definitions of a 'systematic trend'. Here, we explore these differences, apply diverse analyses to more than 1,700 species, and show that recent biological trends match climate change predictions. Global meta-analyses documented significant range shifts averaging 6.1 km per decade towards the poles (or metres per decade upward), and significant mean advancement of spring events by 2.3 days per decade. We define a diagnostic fingerprint of temporal and spatial 'sign-switching' responses uniquely predicted by twentieth century climate trends. Among appropriate long-term/large-scale/multi-species data sets, this diagnostic fingerprint was found for 279 species. This suite of analyses generates 'very high confidence' (as laid down by the IPCC) that climate change is already affecting living systems.     

Towards a proteome-scale map of the human protein-protein interaction network

Systematic mapping of protein-protein interactions, or 'interactome' mapping, was initiated in model organisms, starting with defined biological processes and then expanding to the scale of the proteome. Although far from complete, such maps have revealed global topological and dynamic features of interactome networks that relate to known biological properties, suggesting that a human interactome map will provide insight into development and disease mechanisms at a systems level. Here we describe an initial version of a proteome-scale map of human binary protein-protein interactions. Using a stringent, high-throughput yeast two-hybrid system, we tested pairwise interactions among the products of approximately 8,100 currently available Gateway-cloned open reading frames and detected approximately 2,800 interactions. This data set, called CCSB-HI1, has a verification rate of approximately 78% as revealed by an independent co-affinity purification assay, and correlates significantly with other biological attributes. The CCSB-HI1 data set increases by approximately 70% the set of available binary interactions within the tested space and reveals more than 300 new connections to over 100 disease-associated proteins. This work represents an important step towards a systematic and comprehensive human interactome project.