Lawrence Weissbach

The Ras GTPase-activating-protein-related human protein IQGAP2 harbors a potential actin binding domain and interacts with calmodulin and Rho family GTPases.

We previously described IQGAP1 as a human protein related to a putative Ras GTPase-activating protein (RasGAP) from the fission yeast Schizosaccharomyces pombe. Here we report the identification of a liver-specific human protein that is 62% identical to IQGAP1. Like IQGAP1, the novel IQGAP2 protein harbors an N-terminal calponin homology motif which functions as an F-actin binding domain in members of the spectrin, filamin, and fimbrin families. Both IQGAPs also harbor several copies of a novel 50- to 55-amino-acid repeat, a single WW domain, and four IQ motifs and have 25% sequence identity with almost the entire S. pombe sar1 RasGAP homolog. As predicted by the presence of IQ motifs, IQGAP2 binds calmodulin. However, neither full-length nor truncated IQGAP2 stimulated the GTPase activity of Ras or its close relatives. Instead, IQGAP2 binds Cdc42 and Racl but not RhoA. This interaction involves the C-terminal half of IQGAP2 and appears to be independent of the nucleotide binding status of the GTPases. Although IQGAP2 shows no GAP activity towards Cdc42 and Rac1, the protein did inhibit both the intrinsic and RhoGAP-stimulated GTP hydrolysis rates of Cdc42 and Rac1, suggesting an alternative mechanism via which IQGAPs might modulate signaling by these GTPases. Since IQGAPs harbor a potential actin binding domain, they could play roles in the Cdc42 and Rac1 controlled generation of specific actin structures.

A plasminogen-related gene is expressed in cancer cells

The breakdown of blood clots requires the fibrinolytic action of the serine proteinase plasmin, a two-chain polypeptide derived posttranslationally from its precursor zymogen, plasminogen. While investigating plasminogen gene expression in human extrahepatic tissues, a cDNA sequence was obtained which closely resembled the plasminogen cDNA, yet appeared to represent a distinct gene product. This sequence, which represents the transcript of the recently characterized plasminogen-related gene B, encodes a putative polypeptide of Mr 8800 and is expressed most prominently in malignant cancer cells.

Alternatively spliced annexin XI transcripts encode proteins that differ near the amino-terminus☆

Annexins are a family of structurally related calcium-dependent phospholipid binding proteins. We recently described a new member of this family, bovine annexin XI [1]. Two kinds of cDNAs were identified corresponding to annexin XI mRNA variants A and B, which are generated by alternative splicing of identical primary transcripts. Annexin XI isoforms are predicted to differ at the amino-terminus, suggesting that they may have distinct biological roles.

Interaction of plasminogen-related protein B with endothelial and smooth muscle cells in vitro

Plasminogen-related protein B (PRP-B) closely resembles the N-terminal plasminogen activation peptide, which is released from plasminogen during conversion to plasmin. We have previously demonstrated that the steady-state level of mRNA encoding PRP-B is increased within tumor tissues, and that recombinant PRP-B antagonizes neoplastic growth when administered systemically to mice harboring tumors, but no insights into the cell targets of PRP-B have been presented. Employing serum-free medium optimized for culturing human endothelial or smooth muscle cells, we show that recombinant PRP-B inhibits basic fibroblast growth factor-dependent cell migration for both cell types, as well as tube formation of endothelial cells. Comparison with the angiogenesis inhibitors angiostatin and endostatin revealed similar results. Recombinant PRP-B is effective in promoting cell attachment of endothelial and smooth muscle cells, and antibody interference experiments reveal that the interaction of recombinant PRP-B with endothelial cells is mediated at least in part by alpha(v)-containing integrins. Inhibition of angiogenesis in vivo by PRP-B was demonstrated in the chicken chorioallantoic membrane assay. PRP-B and other antiangiogenic molecules may elicit metabolic perturbations in endothelial cells as well as perivascular mesenchymal cells such as smooth muscle cells and pericytes.

Treatment of collagen-induced arthritis with recombinant plasminogen-related protein B: a novel inhibitor of angiogenesis

BackgroundWe have previously reported that recombinant human plasminogen-related protein B (rPRP-B), a putative 9-kDa protein that closely resembles the activation peptide of plasminogen, has shown significant inhibition of tumor growth through inhibition of angiogenesis. Based on recent reports suggesting a close relationship between rheumatoid arthritis (RA) and angiogenesis, we hypothesized that this compound would regulate inflammatory conditions in RA. The present study therefore tested the effects of rPRP-B in the treatment of collagen-induced arthritis (CIA) to elucidate the mechanisms underlying these effects.MethodsDBA/1J mice immunized with type II collagen to induce CIA were monitored to assess the effects of rPRP-B on clinical severity of the disease. Pathological changes in joints, including vessel formation and vascular endothelial growth factor (VEGF) production, were examined histologically. Bone destruction was radiologically evaluated. In vitro studies on the effects of rPRP-B on cell proliferation and production of VEGF in interleukin (IL)-1β or basic fibroblast growth factor (bFGF)-stimulated human synoviocytes were also performed.ResultsDevelopment of CIA was effectively inhibited by rPRP-B. Radiological examinations revealed that the protein reduced bone destruction in CIA. CIA-induced vessel formation and VEGF expression in vivo were also reduced. In vitro mechanistic studies demonstrated that rPRP-B affected human synoviocyte proliferation and VEGF production stimulated by IL-1β and bFGF.ConclusionsGiven the ability to effectively promote multistep anti-angiogenic activities, including cell growth inhibition and cytokine regulation, rPRP-B represents a promising candidate for a novel therapeutic agent against RA.