Hematopoiesis occurs in close association with a complex network of cells loosely termed the hematopoietic microenvironment. Analysis of the mechanisms of microenvironmental regulation of hematopoiesis has been hindered by the complexity of the microenvironment as well as the heterogeneity of hematopoietic stem cells and early progenitor cells. We have established immortalized primate bone marrow-derived stromal cell lines to facilitate analysis of the interactions of hematopoietic cells with the microenvironment in a large animal species. One such line, PU-34, was found to produce a variety of growth factors, including an activity that stimulates the proliferation of an interleukin 6-dependent murine plasmacytoma cell line. A cDNA encoding the plasmacytoma stimulatory activity was isolated through functional expression cloning in mammalian cells. The nucleotide sequence contained a single long reading frame of 597 nucleotides encoding a predicted 199-amino acid polypeptide. The amino acid sequence of this cytokine, designated interleukin 11 (IL-11), did not display significant similarity with any other sequence in the GenBank data base. Preliminary biological characterization indicates that in addition to stimulating plasmacytoma proliferation, IL-11 stimulates the T-cell-dependent development of immunoglobulin-producing B cells and synergizes with IL-3 in supporting murine megakaryocyte colony formation. These properties implicate IL-11 as an additional multifunctional regulator in the hematopoietic microenvironment.

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Background: IB kinase ␤ is a key regulator in the NB signaling pathway. Results: Crystal structure of a human IKK␤ asymmetric dimer shows one kinase active site phosphorylated and in the active conformation and the other unphosphorylated and inactive. Conclusion: Depending on the phosphorylation state, IKK␤ can adopt distinct dimeric geometry. Significance: High resolution structure of hIKK␤ provides structural basis for its activation and potential use of inhibitor design.

Nogo receptor (NgR)-mediated control of axon growth relies on the central nervous system-specific type I transmembrane protein Lingo-1. Interactions between Lingo-1 and NgR, along with a complementary co-receptor, result in neurite and axonal collapse. In addition, the inhibitory role of Lingo-1 is particularly important in regulation of oligodendrocyte differentiation and myelination, suggesting that pharmacological modulation of Lingo-1 function could be a novel approach for nerve repair and remyelination therapies. Here we report on the crystal structure of the ligand-binding ectodomain of human Lingo-1 and show it has a bimodular, kinked structure composed of leucine-rich repeat (LRR) and immunoglobulin (Ig)-like modules. The structure, together with biophysical analysis of its solution properties, reveals that in the crystals and in solution Lingo-1 persistently associates with itself to form a stable tetramer and that it is its LRR-Ig-composite fold that drives such assembly. Specifically, in the crystal structure protomers of Lingo-1 associate in a ring-shaped tetramer, with each LRR domain filling an open cleft in an adjacent protomer. The tetramer buries a large surface area (9,200 Å 2 ) and may serve as an efficient scaffold to simultaneously bind and assemble the NgR complex components during activation on a membrane. Potential functional binding sites that can be identified on the ectodomain surface, including the site of self-recognition, suggest a model for protein assembly on the membrane.Injured neurons in mature organisms are unable to effectively regrow their axons after central nervous system damage. One of the many factors restricting axonal regeneration after injury is the growth-inhibiting components associated with damaged myelin. At least three of these components, Nogo-66, myelin-associated glycoprotein (MAG), 3 and oligodendrocyte myelin glycoprotein, either individually or collectively, have been shown to be potent inhibitors of neurite outgrowth (1, 2). All three signal inhibition through the Nogo receptor complex, composed of the ligand-binding Nogo-66 receptor (NgR) and two complementary co-receptors p75 and Lingo-1 that act as a signal-transducing pair on an axon's cell membrane (3, 4). Although both NgR and the p75 nerve growth factor receptor have well documented roles in the context of myelin inhibition, reports exploring the role of Lingo-1 are more recent.Human Lingo-1 is a central nervous system-specific transmembrane glycoprotein (Fig. 1) also known as LERN-1, which belongs to a larger family of LRR-Ig-containing proteins involved in central nervous system development and axonal growth (5). Its large extracellular or ectodomain is thought to be of functional importance in protein-protein recognition and is characterized by a tandem array of multiple LRRs and one Iglike domain. The first studies examining the role of Lingo-1 demonstrated that in cultured neurons Lingo-1 directly associates with NgR and p75 and that whenever myelin-NgR/p75-mediated growth inhibition is observe...

Eukaryotic protein synthesis initiation factor 4B (eIF‐4B) is an 80,000 dalton polypeptide which is essential for the binding of mRNA to ribosomes. A highly purified preparation of eIF‐4B from HeLa cells was subjected to enzymatic cleavage and amino‐terminal amino acid sequence analysis. Degenerate oligonucleotide probes were used to isolate a 3851 bp cDNA encoding eIF‐4B from a human cDNA library. The DNA encodes a protein comprising 611 residues with a mass of 69,843 daltons. The amino‐terminal domain of eIF‐4B contains a consensus RNA binding domain present in a number of other RNA binding proteins. Expression of eIF‐4B in transfected COS‐1 cells yielded a polypeptide which reacted with anti‐eIF‐4B antiserum and comigrated with purified eIF‐4B. Expression of eIF‐4B in COS‐1 cells resulted in a general inhibition of translation, possibly due to a 50‐fold eIF‐4B overproduction.