Cloning and characterization of a specific receptor for mouse oncostatin M.

Oncostatin M (OSM) is a member of a family of cytokines that includes ciliary neurotrophic factor, interleukin-6, interleukin-11, cardiotrophin-1, and leukemia inhibitory factor (LIF). The receptors for these cytokines consist of a common signaling subunit, gp130, to which other subunits are added to modify ligand specificity. We report here the isolation and characterization of a cDNA encoding a subunit of the mouse OSM receptor. In NIH 3T3 cells (which endogenously express gp130, LIF receptor beta [LIFRbeta], and the protein product, c12, of the cDNA described here), mouse LIF, human LIF, and human OSM signaled through receptors containing the LIFRbeta and gp130 but not through the mouse OSM receptor. Mouse OSM, however, signaled only through a c12-gp130 complex; it did not use the LIF receptor. Binding studies demonstrated that mouse OSM associated directly with either the c12 protein or gp130. These data highlight the species-specific differences in receptor utilization and signal transduction between mouse and human OSM. In mouse cells, only mouse OSM is capable of activating the mouse OSM receptor; human OSM instead activates the LIF receptor. Therefore, these data suggest that all previous studies with human OSM in mouse systems did not elucidate the biology of OSM but, rather, reflected the biological actions of LIF.

Molecular characterization of ALK, a receptor tyrosine kinase expressed specifically in the nervous system.

The 2;5 chromosomal translocation is frequently associated with anaplastic large cell lymphomas (ALCLs). The translocation creates a fusion gene consisting of the alk (anaplastic lymphoma kinase) gene and the nucelophosmin (npm) gene: the 3' half of alk derived from chromosome 2 is fused to the 5' portion of npm from chromosome 5. A recent study shows that the product of the npm-alk fusion gene is oncogenic. To help understand how the npm-alk oncogene transform cells, it is important to investigate the normal biological function of the alk gene product, ALK. Here, we show molecular cloning of cDNAs for both the human and mouse ALK proteins. The deduced amino acid sequences reveal that ALK is a novel receptor protein-tyrosine kinase having a putative transmembrane domain and an extracellular domain. These sequences are absent in the product of the transforming npm-alk gene. ALK shows the greatest sequence similarity to LTK (leukocyte tyrosine kinase) whose biological function is presently unknown. RNA blot hybridization analysis of various tissues reveals that the alk mRNA is dominantly detected in the brain and spinal cord. Immunoblotting with anti-ALK antibody shows that ALK is highly expressed in the neonatal brain. Furthermore, RNA in situ hybridization analysis shows that the alk mRNA is dominantly expressed in neurons in specific regions of the nervous system such as the thalamus, mid-brain, olfactory bulb, and ganglia of embryonic and neonatal mice. These data suggest that ALK plays an important role(s) in the development of the brain and exerts its effects on specific neurons in the nervous system.

GDNF-induced activation of the ret protein tyrosine kinase is mediated by GDNFR-alpha, a novel receptor for GDNF.

We report the expression cloning and characterization of GDNFR-alpha, a novel glycosylphosphatidylinositol-linked cell surface receptor for glial cell line-derived neurotrophic factor (GDNF). GDNFR-alpha binds GDNF specifically and mediates activation of the Ret protein-tyrosine kinase (PTK). Treatment of Neuro-2a cells expressing GDNFR-alpha with GDNF rapidly stimulates Ret autophosphorylation. Ret is also activated by treatment with a combination of GDNF and soluble GDNFR-alpha in cells lacking GDNFR-alpha, and this effect is blocked by a soluble Ret-Fc fusion protein. Ret activation by GDNF was also observed in cultured embryonic rat spinal cord motor neurons, a cell type that responds to GDNF in vivo. A model for the stepwise formation of a GDNF signal-transducing complex including GDNF, GDNFR-alpha, and the Ret PTK is proposed.

Cloning of cDNAs encoding human TIMP-3, a novel member of the tissue inhibitor of metalloproteinase family.

Proteins of the tissue inhibitor of metalloproteinase (TIMP) family bind and inactivate matrix metalloproteinases such as collagenases and gelatinases. We report the cloning and sequencing of cDNAs encoding a novel human TIMP, which we designated TIMP-3, the third member of the human TIMP family. Degenerate PCR primers derived from highly conserved regions of TIMP family cDNAs amplified a 402-bp product from human fetal kidney cDNA. This product and a related 333-bp PCR product were used as probes to screen two cDNA libraries. Three TIMP-3 cDNA clones were isolated, including a 1240-bp fetal kidney clone that contained a complete TIMP-3 precursor coding region of 211 amino acids (aa). The deduced precursor protein includes twelve Cys and 27 other aa that are invariant in the TIMP family. The predicted aa sequence is 89, 39 and 46% identical to those of ChIMP-3, human TIMP-1 and human TIMP-2, respectively. Northern blot analyses detected three TIMP-3 mRNA bands of 2.2, 2.5 and 4.4 kb in several human cell lines.

Structural and functional aspects of the multiplicity of Neu differentiation factors.

We used molecular cloning and functional analyses to extend the family of Neu differentiation factors (NDFs) and to explore the biochemical activity of different NDF isoforms. Exhaustive cloning revealed the existence of six distinct fibroblastic pro-NDFs, whose basic transmembrane structure includes an immunoglobulin-like motif and an epidermal growth factor (EGF)-like domain. Structural variation is confined to three domains: the C-terminal portion of the EGF-like domain (isoforms alpha and beta), the adjacent juxtamembrane stretch (isoforms 1 to 4), and the variable-length cytoplasmic domain (isoforms a, b, and c). Only certain combinations of the variable domains exist, and they display partial tissue specificity in their expression: pro-NDF-alpha 2 is the predominant form in mesenchymal cells, whereas pro-NDF-beta 1 is the major neuronal isoform. Only the transmembrane isoforms were glycosylated and secreted as biologically active 44-kDa glycoproteins, implying that the transmembrane domain functions as an internal signal peptide. Extensive glycosylation precedes proteolytic cleavage of pro-NDF but has no effect on receptor binding. By contrast, the EGF-like domain fully retains receptor binding activity when expressed separately, but its beta-type C terminus displays higher affinity than alpha-type NDFs. Likewise, structural heterogeneity of the cytoplasmic tails may determine isoform-specific rate of pro-NDF processing. Taken together, these results suggest that different NDF isoforms are generated by alternative splicing and perform distinct tissue-specific functions.

Isolation, characterization, and expression of a cDNA encoding N-acetylglucosaminyltransferase V.

A cDNA clone for the complete coding sequence for alpha-1,3(6)-mannosylglycoprotein beta-1,6-N-acetylglucosaminyltransferase V (GlcNAc-T V, EC 2.4.1.155) was isolated and expressed in COS-7 cells. Degenerate oligonucleotide primers for polymerase chain reaction were synthesized based on the amino acid sequence of three tryptic peptides isolated from affinity-purified GlcNAc-T V. Polymerase chain reaction amplimers were isolated from rat and mouse mRNA. A cDNA-encoding full-length enzyme was isolated from a rat 1 cell (EJ-ras-transformed) library and sequenced. Transient expression of this clone in COS-7 cells, followed by enzymatic activity assays, demonstrated that this cDNA sequence encodes GlcNAc-T V. Northern analysis of rat kidney mRNA revealed a single band corresponding to a length of about 7 kilobases. Sequence analysis of the cDNA clone demonstrated an open reading frame that encoded a type II membrane protein of 740 amino acids.

Neu differentiation factor: a transmembrane glycoprotein containing an EGF domain and an immunoglobulin homology unit.

We recently reported that a 44 kd glycoprotein secreted by transformed fibroblasts stimulates tyrosine phosphorylation of the product of the neu proto-oncogene and induces differentiation of mammary tumor cells to milk-producing, growth-arrested cells. A partial amino acid sequence of the protein, termed Neu differentiation factor (NDF), enabled cloning of the corresponding complementary DNA. The deduced structure of the precursor of NDF indicated that it is a transmembrane protein whose extracellular portion contains an EGF-like domain that probably functions as a receptor recognition site. In addition, the ectodomain contains one immunoglobulin homology unit. Despite the lack of a recognizable hydrophobic signal peptide at the N-terminus, a recombinant NDF, like the natural molecule, is released into the medium of transfected COS-7 cells in a biologically active form. Northern blot analysis indicated the existence of several NDF transcripts, the major ones being 1.8, 2.6, and 6.7 kb in size. Transformation by the ras oncogene dramatically elevated the expression of NDF in fibroblasts.

Human alpha 2-HS-glycoprotein/bovine fetuin homologue in mice: identification and developmental regulation of the gene.

Human alpha 2-HS-glycoprotein (AHSG) is a plasma protein synthesized in liver and selectively concentrated in bone matrix. It has been reported to be involved in bone formation and resorption as well as immune responses. Recently, AHSG was found to be the species equivalent protein of fetuin, the major fetal serum protein in cattle and sheep. The function and regulation of AHSG/fetuin in different species are not understood. We have isolated a liver cDNA clone that encodes the human AHSG/bovine fetuin homologue in the mouse. The AHSG/fetuin gene may have a role in differentiation since it is expressed in mouse limb buds and brain only at certain stages during development. Mouse liver AHSG/fetuin mRNA was present at low level at 12 days gestation but its level increased during the late part of gestation and peaked between 1 to 3 months after birth. The regulation of mouse AHSG/fetuin synthesis during development was found to be significantly different from that of sheep and bovine fetuin. Compared to fetuin, which is reduced in adult to 1 to 2% of the fetal level, mouse AHSG synthesis subsides only 50% 4 months after birth.

Human ceruloplasmin. Tissue-specific expression of transcripts produced by alternative splicing.

Ceruloplasmin (CP) is a plasma glycoprotein that transports copper throughout the body. In previous studies (Yang, F., Naylor, S., Lum, J., Cutshaw, S., McCombs, J., Naberhaus, K., McGill, J., Adrian, G., Moore, C., Barnett, D., and Bowman, B. (1986) Proc. Natl. Acad. Sci. U. S. A. 83, 3277-3261), two CP cDNA clones, CP-1 and CP-2, from a human cDNA library, differed from each other by the presence or absence, respectively, of 12 nucleotide bases encoding a deduced sequence of Gly-Glu-Tyr-Pro near the carboxyl-terminal region of the ceruloplasmin molecule. Examination of genomic DNA demonstrates that the two CP mRNAs are produced from a single gene by alternative spliced patterns. The additional amino acids deduced in CP-1 are products of alternative splicing within an intron of the CP gene at a site 12 nucleotide bases 3' to the commonly used site of CP-2. The CP-1 mRNA transcript encoding four extra amino acids appeared as a minor species accompanying CP-2 mRNA in placenta and chondrocytes. CP-1 mRNA was the predominant CP transcript in a lymphoblastic leukemia cell line, CEM. The mRNA examined from other tissues contained only CP-2 mRNA transcripts. These findings predict that alternative RNA splicing may lead to the differential expression of CP genomic sequences and produce alternate isoforms from a single CP gene in specific tissues.

Human group-specific component (Gc) is a member of the albumin family.

The group-specific component (Gc) is the major vitamin D-binding protein in plasma. The gene encoding Gc is linked, on human chromosome 4, to the albumin and alpha-fetoprotein genes. These two genes previously were shown to have evolved from a smaller ancestral gene by intragenic triplication. Recombinant plasmids containing human cDNA encoding Gc have been isolated by screening an adult human liver library with a mixed oligonucleotide probe. Characterization of Gc cDNA has provided the complete amino acid sequence of the protein and revealed strong sequence homology with albumin and alpha-fetoprotein. Of particular interest is a conserved pattern of disulfide bridges that form the triple-domain structures in albumin, alpha-fetoprotein, and Gc. Gc cDNA was used as a probe in Southern blot analysis of somatic-cell hybrids to confirm that the Gc locus is on chromosome 4.

Evolutionary and structural relationships among the group-specific component, albumin and alpha-fetoprotein.

The group-specific component (Gc) is a plasma protein that binds vitamin D. Recent characterization of human Gc cDNA demonstrated homology with serum albumin and alpha-fetoprotein. This study compares the sequences of the three proteins and demonstrates a strong evolutionary relationship. Albumin, alpha-fetoprotein and Gc evolved from an ancestral gene containing an intragenic triplication. Comparison of the amino acid sequences and patterns of double disulfide bonds suggests that the Gc gene may have diverged from an ancestral gene earlier in evolution than the genes encoding albumin and alpha-fetoprotein. Analysis of the amino acid and nucleotide sequences of the three internal domains of Gc revealed 19-23% amino acid sequence identity and the localization of three homology blocks with 40-44% nucleotide sequence identity. The deduced amino sequence of Gc furnished data for comparing its molecular configuration based on the predicted secondary structure with those predicted for human albumin and alpha-fetoprotein. Utilization of Gc cDNA has also led to the identification of its genomic DNA and detection of a human DNA polymorphism.

Teaching decision making to medical undergraduates by computer-assisted learning.

Undergraduate medical students improve their ability to make patient management decisions through using computer-assisted learning. With this problem-solving approach an improvement in their factural knowledge also occurs and they retain a significant amount of the content.

Computer-assisted learning in undergraduate medical teaching.

A programme of computer-assisted learning has been introduced for fifth-year medical students at Glasgow University during the teaching course in general practice. The programme allows students to make decisions on all aspects of patient care, and has the potential for combining a learning situation with an objective evaluation of skills and attitudes. The programme is popular with students and could have considerable potential in medical education.