Solution structure of the PWWP domain of the hepatoma-derived growth factor family

Among the many PWWP-containing proteins, the largest group of homologous proteins is related to hepatoma-derived growth factor (HDGF). Within a well-conserved region at the extreme N-terminus, HDGF and five HDGF-related proteins (HRPs) always have a PWWP domain, which is a module found in many chromatin-associated proteins. In this study, we determined the solution structure of the PWWP domain of HDGF-related protein-3 (HRP-3) by NMR spectroscopy. The structure consists of a five-stranded beta-barrel with a PWWP-specific long loop connecting beta2 and beta3 (PR-loop), followed by a helical region including two alpha-helices. Its structure was found to have a characteristic solvent-exposed hydrophobic cavity, which is composed of an abundance of aromatic residues in the beta1/beta2 loop (beta-beta arch) and the beta3/beta4 loop. A similar ligand binding cavity occurs at the corresponding position in the Tudor, chromo, and MBT domains, which have structural and probable evolutionary relationships with PWWP domains. These findings suggest that the PWWP domains of the HDGF family bind to some component of chromatin via the cavity.     

The Schizosaccharomyces pombe spqM gene is a new member of the Qm transcription factor family

The Qm family of proteins, which are found in a wide variety of species such as budding yeast, plants and humans, are believed to play a role in gene expression. Here, we report the isolation of a gene, spqM, from the fission yeast Schizosaccharomyces pombe whose deduced amino-acid sequence shared 71.6 to 61.36% identity with members of the Qm family. The high degree of conservation of the Qm members suggest that they were selectively conserved, because of an important biological role     

A human T cell-specific molecule is a member of a new gene family

We have used a cDNA library enriched for T cell-specific sequences to isolate genes expressed by T cells but not by other cell types. We report here one such gene, designated RANTES, which encodes a novel T cell-specific molecule. The RANTES gene product is predicted to be 10 kDa and, after cleavage of the signal peptide, approximately 8 kDa. Of the 68 residues, 4 are cysteines, and there are no sites for N-linked glycosylation. RANTES is expressed by cultured T cell lines that are Ag specific and growth factor dependent. RANTES expression is inducible in PBL by Ag or mitogen. In CTL, expression of RANTES decreases after stimulation with Ag and growth factors. Interestingly, RANTES was not expressed by any T cell tumor line tested. There is significant homology between the RANTES sequence and several other T cell genes, suggesting that they comprise a previously undescribed family of small T cell molecules.     

A new member of the plasma protease inhibitor gene family.

A 2.1-kb cDNA clone representing a new member of the protease inhibitor family was isolated from a human liver cDNA library. The inhibitor, named human Leuserpin 2 (hLS2), comprises 480 amino acids and contains a leucine residue at its putative reactive center. HLS2 is about 25-28% homologous to three human members of the plasma protease inhibitor family: antithrombin III, alpha 1-antitrypsin and alpha 1-antichymotrypsin. A comparison with published partial amino acid sequences shows that hLS2 is closely related to the thrombin inhibitor heparin cofactor II.     

Platelet-derived growth factor-inducible gene JE is a member of a family of small inducible genes related to platelet factor 4

The platelet-derived growth factor-inducible gene JE was found to encode a 148-residue basic (pI = 10.4) secretory protein which shows striking similarity to the gene products of a family of small inducible genes (SIG), LD78, TCA3, IP10, 3-10C, 9E3/pCEF4, and gro/MGSA, and to several of the proteins secreted from platelet alpha-granules. Members of the SIG family have spatially conserved cysteine residues that vary in distance by only one amino acid residue as well as conserved proline residues at analogous sites. Hydrophilicity plots show alternating hydrophobic and hydrophilic domains which are similar for all members of the SIG family except IP10 and platelet factor 4, which show similarities to each other. The genomic organization of SIG family members is similar in the location of the splice junctions and the number of introns and exons, suggesting that they were derived from a common ancestor. The collective evidence suggests that a family of inducible cytokines, which are mitogenic or chemotactic, may act as intercellular coordinators of diverse responses designed to combat infection and promote the healing and regeneration of injured tissue.     

Cloning and characterization of a new member of the T-box gene family

The T-box is a strongly conserved protein domain, 174 to 186 amino acids in length, that binds DNA. Many genes from many species have been shown to encode T-box domain-containing proteins. Here we report the cloning and characterization of a novel T-box gene, TBX21. The human cDNA contains an open reading frame encoding a 535-amino-acid protein with a predicted molecular mass of 58.3 kDa. Except for the T-box sequence, database searches revealed no significant homology to any known sequences at the nucleotide or protein level. In addition to the human cDNA sequence, we report the cDNA sequence of the murine homologue, the structure and organization of the murine Tbx21 gene, and its localization to mouse chromosome 11. TBX21 expression was detected in peripheral blood lymphocytes, spleen, lung, and natural killer cells.     

Endothelial lipase: a new member of the triglyceride lipase gene family

The triglyceride lipase gene family plays a central role in intestinal lipid absorption, energy homeostasis, lipoprotein metabolism, and atherosclerosis. A new member of this gene family, termed endothelial lipase, was recently reported. The presence of key functional motifs, the endothelial synthesis, the enzymatic profile, and the in-vivo metabolic effects of endothelial lipase suggest that, like other members of this gene family, endothelial lipase may play a role in energy delivery to tissues and in modulating lipoprotein metabolism, and could impact on atherogenesis.     

Mitotic phosphorylation activates hepatoma-derived growth factor as a mitogen

Background  

Hepatoma-derived growth factor (HDGF) is a nuclear protein that is a mitogen for a wide variety of cells. Mass spectrometry based methods have identified HDGF as a phosphoprotein without validation or a functional consequence of this post-translational modification.     

A staphylococcal multidrug resistance gene product is a member of a new protein family.

The complete nucleotide sequence (321 bp) of smr (staphylococcal multidrug resistance), a gene coding for efflux-mediated multidrug resistance of Staphylococcus aureus, was determined by using two different plasmids as DNA templates. The smr gene product (identical to products of ebr and qacC/D genes) was shown to be homologous to a new family of small membrane proteins found in Escherichia coli, Pseudomonas aeruginosa, Agrobacterium tumefaciens, and Proteus vulgaris. The smr gene was subcloned and expressed in S. aureus and E. coli and its ability to confer the multidrug resistant phenotype was demonstrated for two different lipophilic cation classes: phosphonium derivatives and quarternary amines. Expression of smr gene leads to the efflux of tetraphenylphosphonium and to a net decrease in the uptake of lipophilic cations. The deduced polypeptide sequence (107 amino acid residues, 11,665 kDa) has 46% hydrophobic residues (Phe, Ile, Leu, and Val) and 20% hydroxylic residues (Ser and Thr). Four transmembrane segments are predicted for smr gene product. Of the charged amino acid residues, only Glu 13 is located in a transmembrane segment. This Glu 13 is conserved in all members of the family of small membrane proteins. We propose a mechanism whereby exchange of protons at the Glu 13 is a key in the efflux of the lipophilic cation. This mechanism includes the idea that protons are transported to the Glu 13 via an appropriate chain of hydroxylic residues in the transmembrane segments of Smr.     

SUMOylation of the hepatoma-derived growth factor negatively influences its binding to chromatin

Hepatoma-derived growth factor is a nuclear targeted mitogen containing a PWWP domain that mediates binding to DNA. To date, almost nothing is known about the molecular mechanisms of the functions of hepatoma-derived growth factor, its routes of secretion and internalization or post-translational modifications. In the present study, we show for the first time that hepatoma-derived growth factor is modified by the covalent attachment of small ubiquitin-related modifier 1 (SUMO-1), a post-translational modification with regulatory functions for an increasing number of proteins. Using a basal SUMOylation system in Escherichia coli followed by a MALDI-TOF-MS based peptide analysis, we identified the lysine residue SUMOylated located in the N-terminal part of the protein adjacent to the PWWP domain. Surprisingly, this lysine residue is not part of the consensus motif described for SUMOylation. With a series of hepatoma-derived growth factor mutants, we then confirmed that this unusual location is also used in mammalian cells and that SUMOylation of hepatoma-derived growth factor takes place in the nucleus. Finally, we demonstrate that SUMOylated hepatoma-derived growth factor is not binding to chromatin, in contrast to its unSUMOylated form. These observations potentially provide new perspectives for a better understanding of the functions of hepatoma-derived growth factor.     

Identification of a new, unorthodox member of the MAGE gene family.

Several tumor-associated antigen families, such as MAGE, GAGE/PAGE, PRAME, BAGE, and LAGE/NY-ESO-1, exist. These antigens are of particular interest in tumor immunology, because their expression, with exception of testis and fetal tissues, seems to be restricted to tumor cells only. We have identified a novel member of the MAGE gene family, MAGED1. Northern hybridization and RT-PCR demonstrated that the expression level of MAGED1 in different normal adult tissues is comparable to that in testis and fetal liver. Thus, MAGED1 does not possess an expression pattern characteristic of previously identified MAGE family genes, suggesting that the biology of the MAGE-family genes is more complex than previously thought. Chromosome mapping linked MAGED1 to marker AFM119xd6 (DXS1039) on chromosome Xp11.23.     

c-Met must translocate to the nucleus to initiate calcium signals

Hepatocyte growth factor (HGF) is important for cell proliferation, differentiation, and related activities. HGF acts through its receptor c-Met, which activates downstream signaling pathways. HGF binds to c-Met at the plasma membrane, where it is generally believed that c-Met signaling is initiated. Here we report that c-Met rapidly translocates to the nucleus upon stimulation with HGF. Ca(2+) signals that are induced by HGF result from phosphatidylinositol 4,5-bisphosphate hydrolysis and inositol 1,4,5-trisphosphate formation within the nucleus rather than within the cytoplasm. Translocation of c-Met to the nucleus depends upon the adaptor protein Gab1 and importin beta1, and formation of Ca(2+) signals in turn depends upon this translocation. HGF may exert its particular effects on cells because it bypasses signaling pathways in the cytoplasm to directly activate signaling pathways in the nucleus.     

A new member of a secretory protein gene family in the dipteranChironomus tentans has a variant repeat structure

Summary We describe the structure of a gene expressed in the salivary gland cells of the dipteranChironomus tentans and show that it encodes 1 of the approximately 15 secretory proteins exported by the gland cells. This sp115,140 gene consists of approximately 65 copies of a 42-bp sequence in a central uninterrupted core block, surrounded by short nonrepetitive regions. The repeats within the gene are highly similar to each other, but divergent repeats are present in a pattern which suggests that the repeat structure has been remodeled during evolution. The 42-bp repeat in the gene is a simple variant of the more complex repeat unit present in the Balbiani ring genes, encoding four of the other secretory proteins. The structure of the sp115,140 gene suggests that related repeat structures have evolved from a common origin and resulted in the set of genes whose secretory proteins interact in the assembly of the secreted protein fibers.     

The T cell activation antigen CD27 is a member of the nerve growth factor/tumor necrosis factor receptor gene family.

CD27 is a dimeric membrane glycoprotein found on the surface of most human T lymphocytes. Activation of T cells by engagement of the Ag receptor increases CD27 surface expression, and anti-CD27 antibodies augment Ag receptor-mediated T cell proliferation. In this study a cDNA-encoding CD27 was isolated by expression and immunoselection in COS cells. The predicted polypeptide was found to belong to a recently characterized family of cysteine-rich receptors whose known ligands include nerve growth factor and TNF-alpha and -beta. Structural similarities suggest that CD27 belongs to a lymphocyte-specific subgroup of the family, comprised of the B cell Ag CD40, the rat T cell subset Ag OX40, and the mouse T cell activation Ag 4-1BB. Recent studies suggest some of these molecules may play a role in the survival of activated cells.     

A new member of the prolactin-growth hormone gene family expressed in mouse placenta.

Mouse placenta has been found to contain an mRNA that encodes a previously unidentified member of the prolactin-growth hormone family. This 1.1-kb mRNA (designated PRP mRNA) was detected as a cDNA clone that hydridized to a cDNA clone of mouse proliferin, a recently described growth-associated placental protein related to prolactin. PRP mRNA levels are highest in the fetal part of the placenta and peak at day 12 of gestation, decreasing gradually until term. The 972-bp sequence of PRP mRNA, determined from two cDNA clones, encodes a protein of 244 amino acid residues that has a hydrophobic leader sequence. The protein encoded by PRP mRNA has significant homology to all of the members of the prolactin family, yet is different from each of them; it also differs from mouse placental lactogen. Nucleotide sequence homology is most extensive between PRP and proliferin mRNAs, particularly at their 5' ends, where they share 92 of the first 97 nucleotides.