Fibroblast growth factors (FGFs) are essential molecules for mammalian development. The nine known FGF ligands and the four signaling FGF receptors (and their alternatively spliced variants) are expressed in specific spatial and temporal patterns. The activity of this signaling pathway is regulated by ligand binding specificity, heparan sulfate proteoglycans, and the differential signaling capacity of individual FGF receptors. To determine potentially relevant ligand-receptor pairs we have engineered mitogenically responsive cell lines expressing the major splice variants of all the known FGF receptors. We have assayed the mitogenic activity of the nine known FGF ligands on these cell lines. These studies demonstrate that FGF 1 is the only FGF that can activate all FGF receptor splice variants. Using FGF 1 as an internal standard we have determined the relative activity of all the other members of the FGF family. These data should serve as a biochemical foundation for determining developmental, physiological, and pathophysiological processes that involve FGF signaling pathways. Fibroblast growth factor (FGF)1 was identified as an activity that stimulates the proliferation of NIH3T3 cells (1). Currently, FGFs comprise a family of nine structurally related proteins (FGF 1-9). FGFs are expressed in specific spatial and temporal patterns and are involved in developmental processes, angiogenesis, wound healing, and tumorigenesis (2-5).FGFs bind and activate high-affinity receptor tyrosine kinases. The cloning of FGF receptors (FGFRs) has identified four distinct genes (6 -13). These receptors bind members of the FGF family with varying affinity (13-16), and alternative mRNA splicing leads to isoforms of these receptors which have unique ligand binding properties (15,17,18). An additional mechanism regulating FGF activity involves heparin or heparan sulfate proteoglycans, molecules which facilitate ligandreceptor interactions (12,19,20). FGFRs contain an extracellular ligand binding domain, a single transmembrane domain, and an intracellular tyrosine kinase domain. The extracellular domain determines ligand binding specificity and mediates ligand-induced receptor dimerization. Dimerization in turn results in one or more trans-phosphorylation events and the subsequent activation of the receptor (21).The extracellular region of the FGFR contains three immunoglobulin-like (Ig-like) domains (6). Alternative mRNA splicing creates several forms of the FGF receptor which differ in their extracellular sequence and have unique ligand binding properties. One splicing event results in the skipping of exons encoding the amino-terminal Ig-like domain (domain I) resulting in a "short" two Ig-like domain form of the receptor (22). The ligand binding properties of the short (two Ig-like domain) and long (three Ig-like domain) FGFRs are similar.2 However, the short form of the receptor may have a higher affinity for some FGFs than the long form (23). Changes in this alternative splicing pattern may correlate with the progression of se...

The genus Coronavirus contains about 25 species of coronaviruses (CoVs), which are important pathogens causing highly prevalent diseases and often severe or fatal in humans and animals. No licensed specific drugs are available to prevent their infection. Different host receptors for cellular entry, poorly conserved structural proteins (antigens), and the high mutation and recombination rates of CoVs pose a significant problem in the development of wide-spectrum anti-CoV drugs and vaccines. CoV main proteases (Mpros), which are key enzymes in viral gene expression and replication, were revealed to share a highly conservative substrate-recognition pocket by comparison of four crystal structures and a homology model representing all three genetic clusters of the genus Coronavirus. This conclusion was further supported by enzyme activity assays. Mechanism-based irreversible inhibitors were designed, based on this conserved structural region, and a uniform inhibition mechanism was elucidated from the structures of Mpro-inhibitor complexes from severe acute respiratory syndrome-CoV and porcine transmissible gastroenteritis virus. A structure-assisted optimization program has yielded compounds with fast in vitro inactivation of multiple CoV Mpros, potent antiviral activity, and extremely low cellular toxicity in cell-based assays. Further modification could rapidly lead to the discovery of a single agent with clinical potential against existing and possible future emerging CoV-related diseases.

Cells have evolved multiple mechanisms to inhibit viral replication. To identify previously unknown antiviral activities, we screened mammalian complementary DNA (cDNA) libraries for genes that prevent infection by a genetically marked retrovirus. Virus-resistant cells were selected from pools of transduced clones, and an active antiviral cDNA was recovered. The gene encodes a CCCH-type zinc finger protein designated ZAP. Expression of the gene caused a profound and specific loss of viral messenger RNAs (mRNAs) from the cytoplasm without affecting the levels of nuclear mRNAs. The finding suggests the existence of a previously unknown machinery for the inhibition of virus replication, targeting a step in viral gene expression.