title: Structural and functional characterization of monomeric EphrinA1 binding site to EphA2 receptor.
abstract: The EphA2 receptor is overexpressed in glioblastoma multiforme and has been to shown to contribute to cell transformation, tumor initiation, progression, and maintenance. EphrinA1 (eA1) is a preferred ligand for the receptor. Treatment with monomeric eA1, the form of eA1 found in the extracellular environment, causes receptor phosphorylation, internalization, and down-regulation with subsequent anti-tumor effects. Here, we investigated the structure-function relationship of a monomeric eA1 focusing on its G-H loop ((108)FQRFTPFTLGKEFKE(123)G), a highly conserved region among eAs that mediates binding to their receptors. Alanine substitution mutants of the G-H loop amino acids were transfected into U-251 MG glioblastoma multiforme cells, and functional activity of each mutant in conditioned media was assessed by EphA2 down-regulation, ERK and AKT activation and cellular response assays. Alanine substitutions at positions Pro-113 Thr-115, Gly-117, Glu-122, and also Gln-109 enhanced the EphA2 receptor down-regulation and decreased p-ERK and p-AKT. Substitution mutants of eA1 at positions Phe-108, Arg-110, Phe-111, Thr-112, Phe-114, Leu-116, Lys-118, Glu-119, and Phe-120 had a deleterious effect on EphA2 down-regulation when compared with eA1-WT. Mutants at positions Phe-108, Lys-18, Lys-121, Gly-123 retained similar properties to eA1-WT. Recombinant eA1-R110A, -T115A, -G117A, and -F120A have been found to exhibit the same characteristics as the ligands contained in the conditioned media mainly due to the differences in their binding to the receptor. Thus, we have identified variants of eA1 that possess either superagonistic or antagonistic properties. These new findings will be important in the understanding of the receptor/ligand interactions and in further design of anti-cancer therapies targeting the eA/EphA system.
authors.affiliation: Brain Tumor Center of Excellence, Department of Neurosurgery, Wake Forest School of Medicine, Winston-Salem, North Carolina 27157, USA.
authors.forename: Carla M
authors.initials: CM
authors.lastname: Lema Tomé
authors.forename: Enzo
authors.initials: E
authors.lastname: Palma
authors.forename: Sara
authors.initials: S
authors.lastname: Ferluga
authors.forename: W Todd
authors.initials: WT
authors.lastname: Lowther
authors.forename: Roy
authors.initials: R
authors.lastname: Hantgan
authors.forename: Jill
authors.initials: J
authors.lastname: Wykosky
authors.forename: Waldemar
authors.initials: W
authors.lastname: Debinski
mesh_terms: D000409:Alanine / Q000737:chemistry; D000970:Antineoplastic Agents / Q000494:pharmacology; D001665:Binding Sites; D045744:Cell Line, Tumor; D002462:Cell Membrane / Q000378:metabolism; D036382:Ephrin-A1 / Q000737:chemistry*; D005786:Gene Expression Regulation; D006801:Humans; D008024:Ligands; D008969:Molecular Sequence Data; D016296:Mutagenesis; D011485:Protein Binding; D011487:Protein Conformation; D020033:Protein Isoforms; D017433:Protein Structure, Secondary; D036104:Receptor, EphA2 / Q000737:chemistry*; D017386:Sequence Homology, Amino Acid; D020349:Surface Plasmon Resonance
chemical_list: D000970:Antineoplastic Agents; D036382:Ephrin-A1; D008024:Ligands; D020033:Protein Isoforms; D036104:Receptor, EphA2; D000409:Alanine