Ubiquitin enzymes in the regulation of immune responses.

Ubiquitination plays a central role in the regulation of various biological functions including immune responses. Ubiquitination is induced by a cascade of enzymatic reactions by E1 ubiquitin activating enzyme, E2 ubiquitin conjugating enzyme, and E3 ubiquitin ligase, and reversed by deubiquitinases. Depending on the enzymes, specific linkage types of ubiquitin chains are generated or hydrolyzed. Because different linkage types of ubiquitin chains control the fate of the substrate, understanding the regulatory mechanisms of ubiquitin enzymes is central. In this review, we highlight the most recent knowledge of ubiquitination in the immune signaling cascades including the T cell and B cell signaling cascades as well as the TNF signaling cascade regulated by various ubiquitin enzymes. Furthermore, we highlight the TRIM ubiquitin ligase family as one of the examples of critical E3 ubiquitin ligases in the regulation of immune responses.

Accumulation of VEGFR-2+/CD133+ cells and decreased number and impaired functionality of CD34+/VEGFR-2+ cells in patients with SLE.

OBJECTIVE: Inflammation and atherosclerosis are the major causes of cardiovascular disease (CVD) in SLE. Both traditional and disease-specific risk factors contribute to the formation of endothelial dysfunction. Endothelial progenitor cells (EPCs) have the ability to restore endothelial integrity. The aim of this study was to determine whether the number and function of EPCs are altered in SLE. METHODS: Nineteen patients with SLE and 19 controls were analysed. VEGF receptor-2 (VEGFR-2)(+)/CD133(+) and CD34(+)/VEGFR-2(+) cells were quantified by flow cytometry. EPC differentiation was measured by DiI-acLDL/Lectin I staining. Furthermore, apoptosis, proliferation capacity, migration capacity and clonogenic ability of EPCs were determined. RESULTS: VEGFR-2(+)/CD133(+) cells were enhanced in SLE [215 (37) vs 122 (11) cells/1 x 10(6) lymphocytes; P = 0.029], whereas the number [106 (13) vs 215 (27) cells/1 x 10(6) lymphocytes; P = 0.002] and the proliferation rate [96% (6%) vs 143% (19%); P = 0.008] of CD34(+)/VEGFR-2(+) cells were decreased compared with controls. Additionally, EPCs in SLE showed an increased apoptosis [7% (1.4%) vs 3% (0.4%); P = 0.004], an impaired differentiation [36 (5) vs 121 (20) cells/mm(2); P < 0.001] and a reduced migratory capacity [116% (4%) vs 139% (4%); P = 0.001]. CONCLUSIONS: Our results suggest that the mobilization of progenitor cells is unaffected in SLE, but the diminished number and the altered functionality of circulating CD34(+)/VEGFR-2(+) cells reduce the ability to repair vascular damage and thus may trigger the development of atherosclerosis in SLE.

The IAP family member BRUCE regulates autophagosome-lysosome fusion.

Autophagy has an important role in cellular homeostasis by degrading and recycling cytotoxic components. Ubiquitination is known to target cargoes for autophagy; however, key components of this pathway remain elusive. Here we performed an RNAi screen to uncover ubiquitin modifiers that are required for starvation-induced macroautophagy in mammalian cells. Our screen uncovered BRUCE/Apollon/Birc6, an IAP protein, as a new autophagy regulator. Depletion of BRUCE leads to defective fusion of autophagosomes and lysosomes. Mechanistically, BRUCE selectively interacts with two ATG8 members GABARAP and GABARAPL1, as well as with Syntaxin 17, which are all critical regulators of autophagosome-lysosome fusion. In addition, BRUCE colocalizes with LAMP2. Interestingly, a non-catalytic N-terminal BRUCE fragment that is sufficient to bind GABARAP/GABARAPL1 and Syntaxin 17, and to colocalize with LAMP2, rescues autolysosome formation in Bruce -/- cells. Thus, BRUCE promotes autolysosome formation independently of its ubiquitin-conjugating activity and is a regulator of both macroautophagy and apoptosis.

Nitric oxide differentially regulates proliferation and mobilization of endothelial progenitor cells but not of hematopoietic stem cells.

To investigate the role of nitric oxide in controlling endothelial progenitor (EPC) and hematopoietic stem cell (HSC) mobilization, wild-type mice, L-NAME treated WT and eNOS-/- mice received either PBS or G-CSF for 5 days. Under unstimulated conditions bone marrow of either L-NAME treated WT and eNOS-/- mice, representing acute and chronic NO-deficiency, showed higher CD34(+)Flk-I+ EPC numbers compared to their WT littermates. Furthermore, CD34(+)Flk-I+ progenitors under NO-deficient conditions showed a higher cell turn over since the proliferation and apoptosis activity under in vivo as well as in vitro conditions were enhanced. In line with this finding bone marrow derived EPC differentiation towards endothelial cells was modulated in an NO-dependent manner. Administration of G-CSF resulted in an increase of EPC within the bone marrow of WT animals with a consecutive release of these cells into the peripheral circulation. Under NO-deficient conditions G-CSF failed to increase EPC numbers. In contrast, the HSC population c-kit(+)Lin- was not influenced by nitric oxide. Thus, NO differentially supports the mobilization of the endothelial committed progenitor subpopulation in bone marrow but does not have an effect on HSC in vivo.

Enhanced mobilization of CD34(+) progenitor cells expressing cell adhesion molecules in patients with STEMI.

BACKGROUND: Adult stem cells can contribute to myocardial regeneration after ischemic injury. The aim of the study was to determine (1) the amount of mobilized CD34(+)/CD117(+), CD34(+)/KDR(+) cells into peripheral blood (PB) in relation to inflammatory and haematopoietic cytokines, (2) the presence of circulating CD34(+) cells, expressing cell adhesion molecules (CAM), in patients with ST-segment elevation myocardial infarction (STEMI) in comparison to patients with coronary artery disease (CAD). MATERIALS AND METHODS: Twenty-three patients with STEMI (<12 h), 24 patients with CAD and 15 control subjects were enrolled in this study. The patients were matched in age, 2-CAD, ejection fraction (45%) and end-diastolic volume index (70 ml/m(2)). The number of stem cells and the expression of adhesion molecules were quantified by use of flow cytometry. Inflammatory cytokines [interleukin-6 (IL-6), granulocyte colony-stimulating factor (G-CSF), vascular endothelial growth factor] and chemotactic factors as stromal cell-derived factor-1 (SDF-1), hepatocyte growth factor (HGF) were determined by ELISA. RESULTS: The amount of circulating progenitor cells including CD34(+)/CD117(+) and CD34(+)/KDR(+) cells was significantly higher in patients with STEMI than in patients with CAD (CD34(+)/CD117(+) 433 +/- 128 vs. 100 +/- 17, P = 0.012; CD34(+)/KDR(+) 253 +/- 41 vs. 128 +/- 24, P = 0.02). The mobilization of CD34(+) progenitor cells expressing CXCR4-receptor, lymphocyte function-associated antigen-1 (LFA-1), very late antigen-4 (VLA-4) and ICAM-1 into PB was significantly higher in patients with STEMI compared to CAD (CD34(+)/CXCR4(+) 740 +/- 327 vs. 136 +/- 23, P = 0.006; CD34(+)/LFA-1 976 +/- 227 vs. 329 +/- 41, P = 0.025; CD34(+)/VLA4(+) 830 +/- 161 vs. 330 +/- 31, P = 0.007; CD34(+)/ICAM(+) 387 +/- 66 vs. 144 +/- 26, P < 0.001). Additionally, the cytokines G-CFS, IL-6 and HGF were upregulated and significantly increase in the STEMI group compared with controls and CAD (G-CSF 50.6 +/- 6.8 vs. 23 +/- 3 vs. 23.8 +/- 2, P (Co vs. STEMI) < 0.001, P (Co vs. CAD) = n.s., P (STEMI vs. CAD) < 0.001; IL-6 8.4 +/- 0.6 vs. 3.8 +/- 1.9 vs. 2.6 +/- 1, P (Co vs. STEMI) < 0.001, P (Co vs. CAD) = n.s., P (STEMI vs. CAD) < 0.001; HGF 4,502 +/- 461 vs. 686 +/- 195 vs. 1,746 +/- 461, P (Co vs. STEMI) < 0.001, P (Co vs. CAD) = n.s., P (STEMI vs. CAD) < 0.001), while the level of SDF-1 was increased in patients with CAD compared to controls and patients with STEMI (3,035 +/- 286 vs. 2,028 +/- 76 vs. 2,154 +/- 234, P (Co vs. STEMI) = n.s., P (Co vs. CAD) = n.s., P (STEMI vs. CAD) = 0.005). CONCLUSIONS: The study demonstrates in patients with STEMI an increased mobilization of progenitor cells like CD34(+)/CD117(+) and CD34(+)/KDR(+) compared to CAD. Furthermore, we could shown that in patients with STEMI the mobilization of CD34(+) progenitor cells with expressed CAM was increased. It is to speculate that an enhanced expression of adhesion molecules may increase the transmigration and implantation of progenitor cells into ischemic myocardium for myocardial repair.