heparitin-sulfate and Kallmann-Syndrome

Kallmann syndrome is characterised by congenital hypogonadotropic hypogonadism and anosmia, sometimes with other non-reproductive defects. Although multiple genetic pathways are now known to be involved in the development of this disorder, KAL1, the gene causing the X-linked form of Kallmann syndrome was the first to be identified. It has thus been extensively studied both in vitro and in vivo, though the absence of an identifiable murine ortholog has denied researchers the opportunity to create and study Kal-1 knock-out mice. This review looks at several studies in species with a kal-1 ortholog, revealing functional similarities with the human disorder. Further work has shown that the kal-1 domain structure is maintained across genera, that it controls similar morphological and cellular processes during development, and that data from the nematode Caenorhabditis elegans, in particular, may point to novel human candidate genes.

Topics: Animals; Caenorhabditis elegans; Cell Movement; Extracellular Matrix Proteins; Genes, X-Linked; Gonadotropin-Releasing Hormone; Heparitin Sulfate; Humans; Kallmann Syndrome; Mice; Nerve Tissue Proteins; Neurons; Phylogeny; Sequence Homology

Kallmann syndrome is a multigenic human developmental disorder where the molecular pathogenesis is still only partially understood and there is no single unifying animal model. The protein anosmin-1, encoded by the KAL1 gene, is associated with the X-linked form of the disease. The biology and molecular structure of anosmin-1 has been investigated systematically over the years by various cell culture experiments, biochemical analyses and animal models. Anosmin-1 is an extracellular matrix-associated protein which plays pleiotropic roles in neuronal development, migration and organogenesis.

Topics: Animals; Embryo, Mammalian; Embryonic Development; Extracellular Matrix Proteins; Genes, X-Linked; Heparitin Sulfate; Humans; Kallmann Syndrome; Nerve Tissue Proteins; Neurons; Olfactory Bulb; Protein Structure, Tertiary; Receptor, Fibroblast Growth Factor, Type 1; Signal Transduction

The unravelling of the genetic basis of the hypogonadotrophic hypogonadal disorders, including Kallmann syndrome (KS), has led to renewed interest into the developmental biology of gonadotrophin-releasing hormone (GnRH) neurones and, more generally, into the molecular mechanisms of reproduction. KS is characterised by the association of GnRH deficiency with diminished olfaction. Until recently, only two KS-associated genes were known: KAL1 and KAL2. KAL1 encodes the cell membrane and extracellular matrix-associated secreted protein anosmin-1 which is implicated in the X-linked form of KS. Anosmin-1 shows high affinity binding to heparan sulphate (HS) and its function remains the focus of ongoing investigation, although a role in axonal guidance and neuronal migration, which are processes essential for normal GnRH ontogeny and olfactory bulb histogenesis, has been suggested. KAL2, identified as the fibroblast growth factor receptor 1 (FGFR1) gene, has now been recognised to be the underlying genetic defect for an autosomal dominant form of KS. The diverse signalling pathways initiated upon FGFR activation can elicit pleiotropic cellular responses depending on the cellular context. Signalling through FGFR requires HS for receptor dimerisation and ligand binding. Current evidence supports a HS-dependent interaction between anosmin-1 and FGFR1, where anosmin-1 serves as a co-ligand activator enhancing the signal activity, the finer details of whose mechanism remain the subject of intense investigation. Recently, mutations in the genes encoding prokineticin 2 (PK2) and prokineticin receptor 2 (PKR2) were reported in a cohort of KS patients, further reinforcing the view of KS as a multigenic trait involving divergent pathways. Here, we review the historical and current understandings of KS and discuss the latest findings from the molecular and cellular studies of the KS-associated proteins, and describe the evidence that suggests convergence of several of these pathways during normal GnRH and olfactory neuronal ontogeny.

Topics: Cell Movement; Extracellular Matrix Proteins; Gastrointestinal Hormones; Genotype; Gonadotropin-Releasing Hormone; Heparitin Sulfate; History, 19th Century; History, 20th Century; Humans; Kallmann Syndrome; Nerve Tissue Proteins; Neurons; Neuropeptides; Phenotype; Receptor, Fibroblast Growth Factor, Type 1; Receptors, G-Protein-Coupled; Receptors, Peptide; Signal Transduction

The anosmin-1 protein family regulates cell migration, axon guidance, and branching, by mechanisms that are not well understood. We show that the C. elegans anosmin-1 ortholog KAL-1 promotes migrations of ventral neuroblasts prior to epidermal enclosure. KAL-1 does not modulate FGF signaling in neuroblast migration and acts in parallel to other neuroblast migration pathways. Defects in heparan sulfate (HS) synthesis or in specific HS modifications disrupt neuroblast migrations and affect the KAL-1 pathway. KAL-1 binds the cell surface HS proteoglycans syndecan/SDN-1 and glypican/GPN-1. This interaction is mediated via HS side chains and requires specific HS modifications. SDN-1 and GPN-1 are expressed in ventral neuroblasts and have redundant roles in KAL-1-dependent neuroblast migrations. Our findings suggest that KAL-1 interacts with multiple HSPGs to promote cell migration.

Topics: Animals; Caenorhabditis elegans; Caenorhabditis elegans Proteins; Carbohydrate Sequence; Cell Movement; Extracellular Matrix Proteins; Heparan Sulfate Proteoglycans; Heparitin Sulfate; Humans; Kallmann Syndrome; Membrane Glycoproteins; Molecular Sequence Data; Nerve Tissue Proteins; Neurons; Phenotype; Proteoglycans; Recombinant Fusion Proteins; Syndecans

Defective function of anosmin-1, the protein encoded by KAL-1, underlies X-linked Kallmann's syndrome (X-KS), a human hereditary developmental disorder. Anosmin-1 appears to play a role in neurite outgrowth and axon branching, although molecular mechanisms of its action are still unknown. Anosmin-1 contains a WAP (whey acidic protein-like) domain and four contiguous FnIII (fibronectin-like type III) repeats; its WAP domain shows similarity to known serine protease inhibitors, whereas the FnIII domains contain HS (heparan sulphate)-binding sequences. To investigate the functional role of these domains, we have generated both wild-type and mutant recombinant anosmin-1 proteins using a Drosophila S2 cell expression system. Here we present the first biochemical evidence demonstrating the high-binding affinity between HS and anosmin-1, as measured by SPR (surface plasmon resonance) (K(d)=2 nM). The FnIII domains, particularly the first, are essential for dose-dependent HS binding and HS-mediated cell surface association. Furthermore, we have identified uPA (urokinase-type plasminogen activator) as an anosmin-1 interactant. Anosmin-1 significantly enhances the amidolytic activity of uPA in vitro; and anosmin-1-HS-uPA co-operation induces cell proliferation in the PC-3 prostate carcinoma cell line. Both the HS interaction and an intact WAP domain are required for the mitogenic activity of anosmin-1. These effects appear to be mediated by a direct protein interaction between anosmin-1 and uPA, since anosmin-1-uPA could be co-immunoprecipitated from PC-3 cell lysates, and their direct binding with high affinity (K(d)=6.91 nM) was demonstrated by SPR. We thus propose that anosmin-1 may modulate the catalytic activity of uPA and its signalling pathway, whereas HS determines cell surface localization of the anosmin-1-uPA complex.

Topics: Animals; Cattle; Cell Line; Cell Proliferation; Chromosomes, Human, X; Drosophila melanogaster; Extracellular Matrix Proteins; Genetic Vectors; Heparin; Heparitin Sulfate; Humans; Kallmann Syndrome; Kinetics; Multiprotein Complexes; Nerve Tissue Proteins; Protein Binding; Protein Structure, Tertiary; Surface Plasmon Resonance; Thrombin; Urokinase-Type Plasminogen Activator