siRNA-mediated silencing of the 37/67-kDa high affinity laminin receptor in Hep3B cells induces apoptosis

The laminin-binding protein, variously called the 37/67-kDa high affinity laminin receptor or p40, mediates the attachment of normal cells to the laminin network, and also has a role as a ribosomal protein. Over-expression of this protein has been strongly correlated with the metastatic phenotype. However, few studies have investigated the cellular consequence of the ablation of this gene's expression. To address this issue, the expression of the 37/67-kDa high affinity laminin receptor was knocked out with several siRNA constructs via RNA interference in transformed liver (Hep3B) cells. In each case where the message was specifically ablated, apoptosis was induced, as determined by annexin V/propidium iodide staining, and by double staining with annexin V and an antibody directed against the 37/67-kDa high affinity laminin receptor. These results suggest that this protein plays a critical role in maintaining cell viability.     

RAC3 down-regulation sensitizes human chronic myeloid leukemia cells to TRAIL-induced apoptosis

The nuclear receptor coactivator RAC3 plays important roles in many biological processes and tumorigenesis. We found that RAC3 is over-expressed in human chronic myeloid leukemia cells K562, which are normally resistant to TRAIL-induced apoptosis. RAC3 down-regulation by siRNA rendered these cells sensitive to TRAIL-induced cell death. In addition to the up-regulation of TRAIL receptors, the process involves Bid, caspases and PARP activation, loss of mitochondrial membrane potential, and release of AIF, cytochrome c and Smac/DIABLO to the cytoplasm. We conclude that RAC3 is required for TRAIL resistance and that this anti-apoptotic function is independent of its role in hormone receptor signaling.     

Six1 is essential for early neurogenesis in the development of olfactory epithelium

The olfactory epithelium (OE) is derived from the olfactory placode (OP) during mouse development. At embryonic day (E) 10.0-E10.5, “early neurogenesis” occurs in the OE, which includes production of pioneer neurons that emigrate out of the OE and other early-differentiated neurons. Around E12.5, the OE becomes organized into mature pseudostratified epithelium and shows “established neurogenesis,” in which olfactory receptor neurons (ORNs) are differentiated from basal progenitors. Little is known about the molecular pathway of early neurogenesis. The homeodomain protein Six1 is expressed in all OP cells and neurogenic precursors in the OE. Here we show that early neurogenesis is severely disturbed despite the unaltered expression of Mash1 at E10.5 in the Six1-deficient mice (Six1^−/−). Expression levels of neurogenin1 (Ngn1) and NeuroD are reduced and those of Hes1 and Hes5 are augmented in the OE of Six1^−/− at E10.5. Pioneer neurons and cellular aggregates, which are derived from the OP/OE and situated in the mesenchyme between the OE and forebrain, are completely absent in Six1^−/−. Moreover, ORN axons and the gonadotropin-releasing hormone-positive neurons fail to extend and migrate to the forebrain, respectively. Our study indicates that Six1 plays critical roles in early neurogenesis by regulating Ngn1, NeuroD, Hes1, and Hes5.     

A novel approach to identify bovine sperm membrane proteins that interact with receptors on the vitelline membrane of bovine oocytes

At fertilization, the sperm triggers intracellular calcium oscillations, which are pivotal to oocyte activation and development. A working hypothesis for the interaction between the sperm and the oocyte is that disintegrin ligands on the inner acrosomal membrane of the sperm bind to integrin receptors on the oocyte vitelline membrane. The aim of these experiments was to find and identify the sperm protein ligands involved in bovine sperm-oocyte interactions. In situ fluorescent labeling of proteins and 2-D gel electrophoresis were used to identify specific sperm membrane proteins that interact with proteins in the oocyte vitelline membrane. Sperm were labeled with a fluorescent dye and used to fertilize zona-free oocytes. Sperm-oocyte complexes were either lysed immediately, or following covalent cross-linking of proteins with dibromobimane. The cross-linking reagent serves the critical function of covalently linking proteins together so that they will remain as a unit through lysis of the cells and 2-D gel analysis, and which can be subsequently identified by mass spectrometry. Lysates were electrophoretically run on the same 2-D gel. The comparison of uncross-linked and cross-linked protein spots revealed that some proteins shifted position based on binding. These spots were picked and proteins identified by mass spectrometry. These results provide a list of specific sperm proteins that interact with oocyte membrane proteins and establish a group of candidate ligands, one or more of which may be responsible for induction of outside-in signaling resulting in oocyte activation and fusion of the gametes.     

Apelin-13 induces ERK1/2 but not p38 MAPK activation through coupling of the human apelin receptor to the Gi2 pathway

Apelin signaling to the family of mitogen-activated protein kinases (MAPKs), such as extracellular-regulated kinases 1/2 (ERK1/2) and p38 MAPK, through the coupling of apelin receptor (APJ) to G-protein, mediates important pathophysiological responses. Although apelin fragments have been reported to induce ERK1/2 activation through G_i-protein, the intracellular pathways by which APJ activates these MAPKs are only partially understood. Here, using stably transfected human embryonic kidney 293 (HEK293) cells overexpressing human APJ (HEK293-apelinR), we showed that apelin-13 signaling leads to ERK1/2 and p38 MAPK pathways through APJ activation. It was found in HEK293-apelinR cells that ERK1/2 activation was initiated by apelin-13 at 5 min, with the peak of activation occurring at 15 min, and a return to the basal level within 60 min. The activation of ERK1/2 appeared to be dose-dependent with a significant activation being observed at 10 nM apelin-13 and maximal activation at 100 nM. However, phosphorylated-p38 MAPK was not detected in HEK293-apelinR cells treated with apelin-13. We also shown that the apelin-13-induced ERK1/2 activation requires a coupling with pertussis toxin-sensitive G-protein, and that overexpression of dominant-negative G_i2 completely inhibits the apelin-13-induced ERK1/2 activation. In addition, treatment with apelin-13 resulted in a concentration-dependent reduction of forskolin-stimulated cAMP production. It is therefore suggested that apelin-13 activates ERK1/2 but not p38 MAPK, which involves the coupling of APJ to the G_i2 cascade. In conclusion, the ERK1/ 2, but not p38 MAPKpathway is activated by apelin-13 through coupling of human APJ to G_i2-protein, which contributes to cellular responses.     

Activated T cells complicate the identification of regulatory T cells in rheumatoid arthritis

Most cell surface markers for CD4⁺CD25⁺ regulatory T cells (Tregs) are also expressed by activated non-regulatory T cells. Recently, CD127 down-regulation was found to identify functional Tregs in healthy individuals, but there are no data from patients with inflammatory conditions. We examined peripheral blood mononuclear cells (PBMC) from rheumatoid arthritis patients with active inflammation and from healthy controls, and found that CD4⁺ T cells contained an equal proportion of CD25⁺CD127⁻/low cells in both groups. In patients, not all these cells expressed intracellular FOXP3. Upon activation by anti-CD3/anti-CD28, PBMC rapidly down-regulated CD127, while FOXP3 up-regulation was transitory and occurred in fewer cells. The activated cells were not anergic to restimulation and had no suppressive effects. The distinct kinetics indicate that the FOXP3⁻CD127⁻/low cells in rheumatoid arthritis patients most likely represent activated non-regulatory T cells. This complicates the use of CD127 for identification of Tregs in inflammatory diseases.     

Genistein inhibits calcium release by platelet-derived growth factor but not bradykinin or cadmium in human fibroblasts

Cd²⁺ provokes inositol trisphosphateproduction and releases stored Ca²⁺, apparently by binding to a zinc site in the external domain of an orphan receptor. One pM Cd²⁺ evokes an immediate spike in cytosolic free Ca²⁺, which is similar to that evoked by bradykinin. Platelet-derived growth factor (PDGF) also increases free Ca²⁺ in human dermalfibroblasts, but there is a distinct lag before free Ca²⁺ rises in response to PDGF. Genistein, which selectively inhibits tyrosine kinases, markedly inhibited Ca²⁺ mobilization evoked by PDGF. Calcium mobilization triggered by cadmium or bradykinin was relatively insensitive to genistein. The PDGF receptor is known to be a tyrosine kinase, whichphosphorylates and thereby activatesphospholipase C, whereas a G protein couples the bradykinin receptor to anotherphospholipase C isoform. These findings support the hypothesis that the orphan receptor triggered by cadmium is coupled to phospholipase C via a G protein.Abbreviations BSA bovine serum albumin - BK bradykinin - [Ca²⁺]_i cytosolic free calcium - DME Dulbecco's modified Eagle's medium - FBS fetal bovine serum - HEPES 4-(2-hydroxyethyl)-1-piperazine-ethanesulfonic acid - IC₅₀ concentration that produces 50% inhibition - PDGF platelet-derived growth factor - PSS physiological salts solution - SE standard error of the mean     

Structural basis of importin-α-mediated nuclear transport for Ku70 and Ku80

Ku70 and Ku80 form a heterodimeric complex involved in multiple nuclear processes. This complex plays a key role in DNA repair due to its ability to bind DNA double-strand breaks and facilitate repair by the nonhomologous end-joining pathway. Ku70 and Ku80 have been proposed to contain bipartite and monopartite nuclear localization sequences (NLSs), respectively, that allow them to be translocated to the nucleus independently of each other via the classical importin-α (Impα)/importin-β-mediated nuclear import pathway. To determine the structural basis of the recognition of Ku70 and Ku80 proteins by Impα, we solved the crystal structures of the complexes of Impα with the peptides corresponding to the Ku70 and Ku80 NLSs. Our structural studies confirm the binding of the Ku80 NLS as a classical monopartite NLS but reveal an unexpected binding mode for Ku70 NLS with only one basic cluster bound to the receptor. Both Ku70 and Ku80 therefore contain monopartite NLSs, and sequences outside the basic cluster make favorable interactions with Impα, suggesting that this may be a general feature in monopartite NLSs. We show that the Ku70 NLS has a higher affinity for Impα than the Ku80 NLS, consistent with more extensive interactions in its N-terminal region. The prospect of nuclear import of Ku70 and Ku80 independently of each other provides a powerful regulatory mechanism for the function of the Ku70/Ku80 heterodimer and independent functions of the two proteins.