Gwen G. Krivi

Vascular permeability factor (VPF) is a 40-kilodalton disulfide-linked dimeric glycoprotein that is active in increasing blood vessel permeability, endothelial cell growth, and angiogenesis. These properties suggest that the expression of VPF by tumor cells could contribute to the increased neovascularization and vessel permeability that are associated with tumor vasculature. The cDNA sequence of VPF from human U937 cells was shown to code for a 189-amino acid polypeptide that is similar in structure to the B chain of platelet-derived growth factor (PDGF-B) and other PDGF-B-related proteins. The overall identity with PDGF-B is 18%. However, all eight of the cysteines in PDGF-B were found to be conserved in human VPF, an indication that the folding of the two proteins is probably similar. Clusters of basic amino acids in the COOH-terminal halves of human VPF and PDGF-B are also prevalent. Thus, VPF appears to be related to the PDGF/v-sis family of proteins.

Insulin-like growth factor I (IGF-I), a 70-amino acid basic polypeptide, plays a fundamental role in postnatal mammalian growth as a major mediator through which growth hormone exerts its biological effects. We have recently identified two human IGF-I cDNAs which predict distinct peptide precursors of 153 and 195 amino acids. In the present study, both cDNAs were used to isolate and characterize the human IGF-I gene from genomic libraries. The IGF-I gene extends over at least 45 kilobase pairs and contains five exons interrupted by four introns. The DNA sequence of exons 1 through 4 encodes the 195-amino acid precursor, while exons 1, 2, 3, and 5 code for the 153-residue peptide, confirming the hypothesis that at least two IGF-I mRNAs are generated by alternative RNA processing of the primary gene transcript. The structure of the IGF-I gene resembles that of its companion somatomedin, IGF-II, as judged by the analogous location of two introns and considerable nucleotide and amino acid sequence similarity, but appears more distantly related to other members of the insulin gene family. Restriction endonuclease polymorphisms in the IGF-I gene, which map near exon 5 as determined by Southern blot analysis, will be useful in defining the genetics of familial growth failure.

Bestatin, an inhibitor of aminopeptidases, was also a potent inhibitor of leukotriene (LT) A4 hydrolase. On isolated enzyme its effects were immediate and reversible with a Ki = 201 +/- 95 mM. With erythrocytes it inhibited LTB4 formation greater than 90% within 10 min; with neutrophils it inhibited LTB4 formation by only 10% during the same period, increasing to 40% in 2 h. Bestatin inhibited LTA4 hydrolase selectively; neither 5-lipoxygenase nor 15-lipoxygenase activity in neutrophil lysates was affected. Purified LTA4 hydrolase exhibited an intrinsic aminopeptidase activity, hydrolyzing L-lysine-p-nitroanilide and L-leucine-beta-naphthylamide with apparent Km = 156 microM and 70 microM and Vmax = 50 and 215 nmol/min/mg, respectively. Both LTA4 and bestatin suppressed the intrinsic aminopeptidase activity of LTA4 hydrolase with apparent Ki values of 5.3 microM and 172 nM, respectively. Other metallohydrolase inhibitors tested did not reduce LTA4 hydrolase/aminopeptidase activity, with one exception; captopril, an inhibitor of angiotensin-converting enzyme, was as effective as bestatin. The results demonstrate a functional resemblance between LTA4 hydrolase and certain metallohydrolases, consistent with a molecular resemblance at their putative Zn2(+)-binding sites. The availability of a reversible, chemically stable inhibitor of LTA4 hydrolase may facilitate investigations on the role of LTB4 in inflammation, particularly the process termed transcellular biosynthesis.