Construction of transforming growth factor alpha (TGF-alpha) phage library and identification of high binders of epidermal growth factor receptor (EGFR) by phage display

Study of transforming growth factor alpha for the maintenance of human embryonic stem cells

Human embryonic stem cells (hESCs) have great potential for regenerative medicine as they have self-regenerative and pluripotent properties. Feeder cells or their conditioned medium are required for the maintenance of hESC in the undifferentiated state. Feeder cells have been postulated to produce growth factors and extracellular molecules for maintaining hESC in culture. The present study has aimed at identifying these molecules. The gene expression of supportive feeder cells, namely human foreskin fibroblast (hFF-1) and non-supportive human lung fibroblast (WI-38) was analyzed by microarray and 445 genes were found to be differentially expressed. Gene ontology analysis showed that 20.9% and 15.5% of the products of these genes belonged to the extracellular region and regulation of transcription activity, respectively. After validation of selected differentially expressed genes in both human and mouse feeder cells, transforming growth factor α (TGFα) was chosen for functional study. The results demonstrated that knockdown or protein neutralization of TGFα in hFF-1 led to increased expression of early differentiation markers and lower attachment rates of hESC. More importantly, TGFα maintained pluripotent gene expression levels, attachment rates and pluripotency by the in vitro differentiation of H9 under non-supportive conditions. TGFα treatment activated the p44/42 MAPK pathway but not the PI3K/Akt pathway. In addition, TGFα treatment increased the expression of pluripotent markers, NANOG and SSEA-3 but had no effects on the proliferation of hESCs. This study of the functional role of TGFα provides insights for the development of clinical grade hESCs for therapeutic applications.

The use of phage display in neurobiology

Phage display is a technique that involves the coupling of phenotype to genotype in a selectable format. It has been extensively used in molecular biology to study protein-protein interactions, receptor and antibody binding sites, and immune responses; to modify protein properties; and to select antibodies against a wide range of different antigens. In the format most often used, a polypeptide is displayed on the surface of a filamentous phage by genetic fusion to one of the coat proteins, creating a chimeric coat protein. As the gene encoding the chimeric coat protein is packaged within the phage, selection of the phage on the basis of the binding properties of the polypeptide displayed on the surface simultaneously results in the isolation of the gene encoding the polypeptide. This unit describes the background of the technique and illustrates how it has been applied to a number of different problems, each of which has its neurobiological counterparts.

Selection of rotavirus VP4 cell receptor binding domains for MA104 cells using a phage display library

Rotavirus infection of host cells, like other viruses, is a complex process that has not been fully elucidated, and much attention has been focused on the regions of the viral attachment protein, VP4, that are involved in binding to the cellular receptor. In this study, phage display technology was employed to generate a g3p VP4 gene-targeted phage display peptide library using the porcine rotavirus strain CRW8, and a method was optimised for panning this library on adherent MA104 cells to identify receptor binding domains. Recombinant phage that displayed expressed peptides from both the rotavirus VP4 trypsin cleavage products VP8* and VP5* were selected, and while some of the phage clones contained insert sequences from regions of VP4 implicated previously in cell binding and infection, new domains were also identified. In all, four regions within VP8* and six regions of VP5* were selected by panning. To our knowledge, this paper is the first description of using a gene-targeted phage display library to identify receptor binding domains on viral proteins.

Receptor-mediated gene transfer by phage-display vectors: applications in functional genomics and gene therapy

Recent studies have demonstrated targeted gene-delivery to mammalian cells using modified phage-display vectors. Specificity is determined by the choice of the genetically displayed targeting ligand. Without targeting, phage particles have virtually no tropism for mammalian cells. Thus, novel ligands can be selected from phage libraries by their ability to deliver a reporter gene to targeted cells. Together with advances in cDNA display technologies, these findings offer new opportunities for the use of phage-display technology in functional genomics. In addition, targeted phage particles have potential as alternative gene therapy vectors that can be further improved using directed evolution.

The EGF domain: requirements for binding to receptors of the ErbB family

Epidermal growth factor (EGF) has been the prototype growth-stimulating peptide for many years. It has a characteristic structure with three disulfide bridges, which is essential for its activity. However, many other proteins, including both growth factors and proteins with unrelated functions, have similar EGF-like domains. This indicates that besides a characteristic conformation provided by the EGF-like domain, specific amino acids are required to provide specificity in protein functioning. Currently, more than 10 different growth factors with an EGF-like domain have been characterized which all exert their action by binding to the four members of the erbB family of receptors. In this review, studies are described on the structure-function relationship of these EGF-like growth factor molecules in an attempt to analyze the individual amino acids that determine their binding specificity to the individual members of the erbB family.

Structure-based minimization of transforming growth factor-alpha (TGF-alpha) through NMR analysis of the receptor-bound ligand. Design, solution structure, and activity of TGF-alpha 8-50

The investigation of a N-terminally truncated human transforming growth factor-alpha (TGF-alpha; residues 8-50) has been completed to determine the contribution of the N terminus to receptor binding and activation. The deletion protein was proposed and designed through study of NMR relaxation and nuclear Overhauser enhancement data obtained from the TGF-alpha-epidermal growth factor (EGF) receptor complex, which indicated that the residues N-terminal to the A loop remain flexible in receptor-bound TGF-alpha and thus suggested their lack of involvement in receptor binding (Hoyt, D. W., Harkins, R. N., Debanne, M. T., O'Connor-McCourt, M., and Sykes, B. D. (1994) Biochemistry 33, 15283-15292; McInnes, C., Hoyt, D. W., Harkins, R. N., Pagila, R. N., Debanne, M. T., O'Connor-McCourt, M., and Sykes, B. D. (1996) J. Biol. Chem. 271, 32204-32211). TGF-alpha 8-50 was shown to have approximately 10-fold lower affinity for the receptor than the native molecule in an assay quantifying the ability to compete with EGF for binding and to have a similar reduction in activity as indicated by a cell proliferation assay. NMR solution structural calculations on this molecule demonstrate correct formation of the three disulfide bonds of TGF-alpha 8-50 and have established the presence of native secondary structure in the B and C loops of the protein. However, some perturbation of the global fold with respect to the orientation of the subdomains was observed. These results suggest that although the N-terminal residues do not contribute directly to binding, they make a significant contribution in defining the conformation of the growth factor, which is required for complete binding and activity and is therefore significant in terms of producing native folding of TGF-alpha. They also show that information obtained from the receptor-bound ligand can be used to guide the design and minimization of TGF-alpha analogues. The implications of the study of TGF-alpha 8-50 for the design and synthesis of reductants of this growth factor are therefore discussed.