Nicole Nelson

An Essential Role for Ectodomain Shedding in Mammalian Development

The ectodomains of numerous proteins are released from cells by proteolysis to yield soluble intercellular regulators. The responsible protease, tumor necrosis factor-alpha converting enzyme (TACE), has been identified only in the case when tumor necrosis factor-alpha (TNFalpha) is released. Analyses of cells lacking this metalloproteinase-disintegrin revealed an expanded role for TACE in the processing of other cell surface proteins, including a TNF receptor, the L-selectin adhesion molecule, and transforming growth factor-alpha (TGFalpha). The phenotype of mice lacking TACE suggests an essential role for soluble TGFalpha in normal development and emphasizes the importance of protein ectodomain shedding in vivo.

Molecular characterization of receptors for human interleukin-8, GRO/melanoma growth-stimulatory activity and neutrophil activating peptide-2

Interleukin-8 (IL-8), neutrophil activating peptide-2 (NAP-2), and growth regulated gene (GRO, also known as melanoma growth stimulatory activity) are members of a family of peptides which are chemotactic agents for inflammatory cells such as neutrophils. Receptors have been identified for IL-8, GRO and NAP-2 on human neutrophils and granulocytic cell lines, and it has been observed that these cytokines can cross-compete for binding to a common receptor. Using the recently characterized rabbit IL-8 receptor as a probe, two classes of cDNAs, termed type 1 and type 2, were isolated from a human neutrophil library. The type 1 receptor binds only IL-8 while the type 2 receptor binds IL-8, GRO and NAP-2 at high affinity when respective cDNAs are expressed in COS-7 cells. The two cDNAs encode proteins that have an amino acid sequence identity of 77% while the type 1 and 2 receptors have an identity of 84 and 74% with the rabbit IL-8 receptor. These receptors also show significant homology with receptors for other chemotactic agents and with potential coding regions from the human cytomegalovirus genome.

Isolation of LERK-5: A ligand of the eph-related receptor tyrosine kinases

Hek and elk are members of the eph-related family of receptor tyrosine kinases. Recently we isolated four cDNAs encoding membrane-bound ligands to hek and elk [Beckman et al. (1994) EMBO J. 13, 3757-3762; Kozlosky et al. (1995) Oncogene 10, 299-306]. Because of the promiscuous nature of their binding, we have termed these proteins ligands of the eph-related kinases or LERKs. A search of GenBank revealed an expressed sequence tag (EST) with homology to the LERKs. Using this EST as a probe, we have isolated human and murine cDNAs that encode a protein which we call LERK-5. The human and murine cDNAs encode proteins of 333 and 336 amino acids, respectively, with a 97% amino acid identity; LERK-5 has an amino acid identity of 27-59% with the other reported LERKs. LERK-5 is a ligand for both elk and hek and induces receptor phosphorylation. It is expressed in adult lung and kidney and the fetal tissues heart, lung, kidney, and brain. In addition, Southern blot analysis of DNA from interspecific backcross mice indicated that LERK-5 (Eplg5) maps to the proximal region of mouse chromosome 8.

Assignment of the genes encoding human interleukin-8 receptor types 1 and 2 and an interleukin-8 receptor pseudogene to chromosome 2q35.

Two human cDNA clones that encode different interleukin-8 (IL8) receptors have recently been isolated. The interleukin-8 receptor type 1 (IL8R1) binds IL8 only, whereas the interleukin-8 receptor type 2 (IL8R2) (previously designated IL8RA) also binds growth regulated gene (GRO), and neutrophil activating protein-2 (NAP-2) with high affinity. In the process of screening a genomic library with these cDNAs to obtain large clones for use in chromosomal localization studies, we isolated an interleukin-8 receptor pseudogene (IL8RP) that bears greatest similarity to IL8R2. Using Southern hybridization analysis of human x rodent somatic cell hybrid DNAs with cDNA probes for IL8R1 and IL8R2 and probes from the IL8RP locus, we assigned the three loci to chromosome 2; fluorescence in situ hybridization (FISH) to metaphase chromosome preparations using genomic clones from each locus refined this localization to chromosome 2, band q35, for all three. By virtue of their chromosomal location, IL8R1 and IL8R2 may be considered candidate genes for several human disorders in which the involved locus has been mapped to distal 2q or that are associated with structural abnormalities of this segment, including van der Woude syndrome and the neoplastic diseases rhabdomyosarcoma and uterine leiomyomata. In addition, because this region of chromosome 2q is homologous to proximal mouse chromosome 1 in the segment containing the Lsh-Ity-Bcg locus involved in mediating host resistance to infection with intracellular pathogens, examination for abnormalities of the murine homologues of the IL8R genes should be considered in mice affected by mutations of this locus.

The identification of seven metalloproteinase-disintegrin (ADAM) genes from genomic libraries

Metalloproteinase-disintegrins (ADAMs) are membrane-spanning multi-domain proteins containing a zinc metalloproteinase domain and a disintegrin domain which may serve as an integrin ligand. Based on a conserved sequence within the disintegrin domain, GE(E/Q)CDCG, seven genes were isolated from a human genomic library. Two of these genes lack introns and show testis-specific expression (ADAM20 and ADAM21), while the other two genes contain introns (ADAM22 and ADAM23) and are expressed predominantly in the brain. In addition, three pseudogenes were isolated; one of which evolved from ADAM21. Human chromosomal mapping indicated that ADAM22 and ADAM23 mapped to chromosome 7q21 and 2q33, respectively, while the three pseudogenes 1-2, 3-3, and 1-32 mapped to chromosome 14q24.1, 8p23, and 14q24.1, respectively. An ancestral analysis of all known ADAMs indicates that the zinc-binding motif in the catalytic domain arose once in a common ancestor and was lost by those members lacking this motif.