Receptor specificity of the fibroblast growth factor family.

Gene targeting—homologous recombination of DNA sequences residing in the chromosome with newly introduced DNA sequences—in mouse embryo-derived stem cells promises to provide a means to generate mice of any desired genotype. We describe a positive and negative selection procedure that enriches 2,000-fold for those cells that contain a targeted mutation. The procedure was applied to the isolation of hprt− and int-2− mutants, but it should be applicable to any gene

Disruption of the proto-oncogene int-2 in mouse embryo-derived stem cells: a general strategy for targeting mutations to non-selectable genes

Fibroblast growth factors (FGFs) are small polypeptide growth factors, all of whom share in common certain structural characteristics, and most of whom bind heparin avidly. Many FGFs contain signal peptides for secretion and are secreted into the extracellular environment, where theycan bind to the heparan-like glycosaminoglycans (HLGAGs) of the extracellular matrix (ECM). From this reservoir, FGFs mayact directlyon target cells, or theycan be released through digestion of the ECM or the activityof a carrier protein, a secreted FGF binding protein. FGFs bind specific receptor tyrosine kinases in the context of HLGAGs and this binding induces receptor dimerization and activation, ultimatelyresulting in the activation of various signal transduction cascades. Some FGFs are potent angiogenic factors and most playimportant roles in embry onic development and wound healing. FGF signaling also appears to playa role in tumor growth and angiogenesis, and autocrine FGF signaling maybe particularlyimportant in the progression of steroid hormone-dependent cancers to a hormone-independent state.

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Fibroblast growth factors, their receptors and signaling.

Publisher Summary The fibroblast growth factors (FGFs) constitute a family of closely related polypeptide mitogens There are seven members of this family, identified on the basis of amino acid sequence homologies The FGF family has distinguished itself from other growth factor families by virtue of the pleiotropic actions of its members This chapter discusses the structural and functional diversity in the FGF receptor multigene family The effects of FGFs are known to be mediated by high-affinity receptor tyrosine kinases The structurally diverse receptor molecules are also functionally different The characterization of structural and functional diversity within the FGF receptor shows the differences in the mechanisms of action among members of the FGF family The first members of the FGF family to be purified and characterized were acidic FGF (aFGF) and basic FGF (bFGF), which are purified on the basis of their mitogenicity toward fibroblasts by using bovine pituitary Functional differences among the different receptor forms are observed in the chapter at two levels The long-range goal of designing the effective agonist and antagonists of FGF action has considerable therapeutic value

Structural and Functional Diversity in the FGf Receptor Multigene Family

Publisher Summary The family of fibroblast growth factors (FGF) is the largest family of growth factors involved in soft–tissue growth and regeneration. The FGF family includes seven members that share a varying degree of homology at the protein level and appear to have a similar broad mitogenic spectrum. They are angiogenic and promote the proliferation of a variety of cells of mesodermal and neuroectodermal origin . Three members of the family–namely, K–FGF/HST, FGF–5, INT–2 are identified originally as oncogenes, while two additions, FGF–6 and keratinocyte growth factor (KGF), are isolated by sequence homology or factor purification and cloning. FGF was identified as an activity in pituitary extracts that stimulated the proliferation of 3T3 cells in mice. The two prototypes of basic and acidic protein structure, the FGF genes, and the expressions of FGF are also discussed. FGF consist of three exons, separated by two introns of variable length and FGF genes map on several chromosomes. The molecular regulation of FGF expression, FGF receptors, and their interaction with extracellular matrix is described. The oncogenic potential of FGF members and their involvement in tumors is also discussed. All possible mechanisms operating on the expression of FGFs and their receptors: transcriptional controls, posttranscriptional regulation involving alternative splicing, alternative translation starts resulting in proteins with different properties, and control affecting the secretion of these proteins are discussed.

The FGF family of growth factors and oncogenes.

Tumorigenesis by mouse mammary tumor virus: Proviral activation of a cellular gene in the common integration region int-2

We report the genomic organization and DNA sequence of the human homologue of int-2, a proto-oncogene implicated in virally induced mammary tumours in the mouse, and expressed at specific sites and times during embryogenesis. Direct comparisons with the coding domains of mouse int-2 allowed us to delineate the intron-exon boundaries of the human gene. These boundaries were subsequently confirmed by ribonuclease protection analyses of the single 1.7 kilobase (kb) int-2 transcript detectable in the human teratocarcinoma cell line, Tera-2. The data suggest that human int-2 may also function in embryonic lineages but that its transcription may be less complex than in the mouse. The predicted human protein comprises 239 amino acids and is 89% homologous to its murine counterpart, except at the carboxy terminus. This divergence occurs distal to the region of int-2 that shows homology to other members of the FGF family of growth modulators and oncogenes.

Sequence organization of the human int-2 gene and its expression in teratocarcinoma cells.

The provirus of mouse mammary tumour virus (MMTV) is reputed to contain sequences within the viral gag gene that prevent or inhibit its propagation as a recombinant DNA clone in Escherichia coli. Here we report the successful isolation of several lambda and plasmid clones comprising the 5' virus-host DNA junction fragments from integrated MMTV proviruses in BR6 mice. Although the lambda clones appeared intact, almost all of the plasmids were found to contain the bacterial insertion sequences IS1 or IS2 within a small region of the gag gene. One nondisrupted clone was recovered which had undergone multiple G to A transitions, some of which created stop codons in gag. These results have provided more precise information as to the location of the poison sequences and are discussed in relation to possible explanations for the phenomenon.

S. Brookes

Papers

Tumorigenesis by mouse mammary tumor virus: Proviral activation of a cellular gene in the common integration region int-2

Sequence organization of the human int-2 gene and its expression in teratocarcinoma cells.

Insertion elements and transitions in cloned mouse mammary tumour virus DNA: further delineation of the poison sequences.