Fibroblast growth factor-1 induction of delayed-early mRNA expression in NIH 3T3 cells is prolonged by heparin addition

Construction and characterization of a thrombin-resistant designer FGF-based collagen binding domain angiogen

Humans demonstrate limited spontaneous endothelialization of prosthetic bypass grafts. However the local application of growth factors to prosthetic grafts or to injured blood vessels can provide an immediate effect on endothelialization. Novel chimeric proteins combining potent angiogens with extracellular matrix binding domains may localize to exposed matrices and provide sustained activity to promote endothelial regeneration after vascular interventions. We have ligated a thrombin-resistant mutant of fibroblast growth factor (FGF)-1 (R136K) with a collagen binding domain (CBD) in order to direct this growth factor to sites of exposed vascular collagen or selected bioengineered scaffolds. While FGF-1 and R136K are readily attracted to a variety of matrix proteins, R136K-CBD demonstrated selective and avid binding to collagen approximately 4x that of FGF-1 or R136K alone (P<0.05). The molecular stability of R136K-CBD was superior to FGF-1 and R136K. Its chemotactic activity was superior to R136K and FGF-1 (11+/-1% vs. 6+/-2% and 4+/-1%; P<0.01). Its angiogenic activity was similar to R136K and significantly greater than control by day 2 (P<0.01). After day 3, FGF-1-treated endothelial cell's (EC) sprouts had regressed back to levels insignificant compared to the control group (P=0.17), while both R136K and R136K-CBD continued to demonstrate greater sprout lengthening as compared to control (P<0.0002). The mitogenic activity of all growth factors was greater than control groups (20% PBS); in all comparisons (P<0.0001). This dual functioning angiogen provides proof of concept for the application of designer angiogens to matrix binding proteins to intelligently promote endothelial regeneration of selected matrices.

Thrombospondins, their polymorphisms, and cardiovascular disease

The thrombospondins are a 5-member gene family that mediate cell-cell and cell-matrix interactions. The thrombospondins are either trimers or pentamers, and their functions depend on their abilities to interact with numerous extracellular ligands and cell surface receptors through the multiple domains that compose each subunit. Recent genetic studies have indicated associations of particular single nucleotide polymorphisms in 3 of the 5 thrombospondins with cardiovascular disease. This observation has stimulated efforts to understand how the thrombospondins influence cardiovascular pathology, to dissect how the individual polymorphisms alter the structure and function of the parent thrombospondin molecules, and to replicate the genetic data in different patient populations. This review seeks to summarize current information that has emerged on each of these fronts.

Coronary artery disease and the thrombospondin single nucleotide polymorphisms

GeneQuest was a high throughput, large-scale analysis of single nucleotide polymorphisms (SNPs) to identify gene associated with familial, premature coronary artery disease and myocardial infarction. The three SNPs showing the highest and most significant associations with disease were all members of the thrombospondin gene family, thrombospondin-1, thrombospondin-2 and thrombospondin-4. These unanticipated associations have kindled efforts to understand how the three SNPs influence the structures and functions of the thrombospondins. The SNP in thrombospondin-1 and thrombospondin-4 reside in their coding regions and result in single amino acid changes: in thrombospondin-1, the predominant asparagine at position 700 is changed to a serine while, in thrombospondin-4, it is a change of an alanine to a proline at position 387. The SNP in thrombospondin-2 is a base change in the 3'-untranslated region of the mRNA. At this early stage of investigation, predictive analyses suggest that the substitutions in thrombospondin-2 and thrombospondin-4 should alter structure, and there is direct evidence to indicate that the thrombospondin-1 SNP alters conformational stability. In addition, profound differences in the function of the thrombospondin-4 SNP variants have been identified with respect to their capacity to support endothelial cell adhesion and proliferation. While substantial additional information is needed to understand if and how the polymorphic forms of the thrombospondins affect coronary artery disease, the data assembled to date suggest marked effects of these SNPs on the structures and functions of the thrombospondins, which are consistent with induction of a proatherogenic and prothrombotic phenotype.

The mitogen-inducible Fn14 gene encodes a type I transmembrane protein that modulates fibroblast adhesion and migration

The binding of polypeptide growth factors to their appropriate cell surface transmembrane receptors triggers numerous biochemical responses, including the transcriptional activation of specific genes. We have used a differential display approach to identify fibroblast growth factor-1-inducible genes in murine NIH 3T3 cells. Here, we report that the fibroblast growth factor-inducible-14 (Fn14) gene is a growth factor-regulated, immediate-early response gene expressed in a developmental stage- and adult tissue-specific manner in vivo. This gene, located on mouse chromosome 17, is predicted to encode an 129-amino acid type Ia membrane protein with no significant sequence similarity to any known protein. We have used two experimental approaches, direct fluorescence microscopy and immunoprecipitation analysis of biotinylated cell surface proteins, to demonstrate that Fn14 is located on the plasma membrane. To examine the biological consequences of constitutive Fn14 expression, we isolated NIH 3T3 cell lines expressing variable levels of epitope-tagged Fn14 and analyzed their phenotypic properties in vitro. These experiments revealed that Fn14 expression decreased cellular adhesion to the extracellular matrix proteins fibronectin and vitronectin and also reduced serum-stimulated cell growth and migration. These results indicate that Fn14 is a novel plasma membrane-spanning molecule that may play a role in cell-matrix interactions.

Fibroblast growth factors as multifunctional signaling factors

The fibroblast growth factor (FGF) family consists of at least 15 structurally related polypeptide growth factors. Their expression is controlled at the levels of transcription, mRNA stability, and translation. The bioavailability of FGFs is further modulated by posttranslational processing and regulated protein trafficking. FGFs bind to receptor tyrosine kinases (FGFRs), heparan sulfate proteoglycans (HSPG), and a cysteine-rich FGF receptor (CFR). FGFRs are required for most biological activities of FGFs. HSPGs alter FGF-FGFR interactions and CFR participates in FGF intracellular transport. FGF signaling pathways are intricate and are intertwined with insulin-like growth factor, transforming growth factor-beta, bone morphogenetic protein, and vertebrate homologs of Drosophila wingless activated pathways. FGFs are major regulators of embryonic development: They influence the formation of the primary body axis, neural axis, limbs, and other structures. The activities of FGFs depend on their coordination of fundamental cellular functions, such as survival, replication, differentiation, adhesion, and motility, through effects on gene expression and the cytoskeleton.