Insulin‐like growth factors bind with high affinity to specific binding proteins in extracellular fluids. To identify structural characteristics of IGF‐binding proteins that might define their physiological roles, we determined the complete primary structure of a novel human IGF‐binding protein (IGFBP‐2) from a cloned cDNA. The cDNA encodes a 328 amino acid IGF‐binding protein precursor which contains a 39‐residue signal peptide. The mature 289 amino acid IGFBP‐2 has a predicted Mr of 31,325. Chinese hamster ovary (CHO) cells stably transformed with the IGFBP‐2 cDNA secreted a 36 kd protein which bound, with different affinities, IGFII and IGFI, but did not bind insulin. The predicted protein sequence of this IGF‐binding protein shares extensive amino acid homology (greater than 85%) with the IGF‐binding protein secreted by rat BRL‐3A cells, but less than 40% homology with human IGFBP‐1. Therefore IGFBP‐2, and not IGFBP‐1 as previously suggested, represents the human homologue of the rat BRL‐BP (alpha IGFBP‐2). Moreover, from alignment of the predicted protein sequences of IGFBP‐1 and IGFBP‐2, extensive conservation of the distribution of cysteine residues is observed. Although the overall amino acid homology shared by these proteins is not high, we suggest that they represent a family of structurally related human IGFBPs. Southern blot analysis of human DNA demonstrates that IGFBP‐2 is encoded by a single‐copy gene, different from that of IGFBP‐1.

Rat serum contains two major forms of insulin-like growth factor (IGF) binding proteins (BPs) that have apparent mol wts of about 35,000 and 150,000. We have isolated a cDNA clone encoding an IGF-BP whose N-terminal sequence is completely homologous to the NH2-terminal of the Buffalo rat liver cells-3A BP. The 270 amino acid mature protein has a predicted mol wt of 29,500. It contains a cysteine rich domain at each end of the molecule and an Arg-Gly-Asp (RGD) tripeptide motif near its C-terminus which suggests that this BP might associate with integrin cell surface receptors. The mature protein shares only partial homology with two published human IGF-BPs. Northern blot analysis shows that its mRNA is abundant in several fetal tissues, in adult brain, testes, ovaries, and kidney. Expression in the liver is high in fetal life but decreases to a barely detectable level in adulthood. However, upon hypophysectomy, the mRNA level increases at least 20-fold which suggests a hormonal regulation for the hepatic production of this small IGF-BP.

Excessive intake of retinol or of retinoic acid causes a syndrome of characteristic toxic effects known as hypervitaminosis A. To test the role of the nuclear retinoic acid receptor (RAR gamma) in this process we produced mice with a targeted disruption of the RAR gamma gene and examined toxic effects of repeated doses of retinoic acid and two other synthetic retinoids, Ro 15-1570 and Ro 40-6055. Surprisingly, homozygous mutant mice were resistant to fourfold higher doses of retinoic acid than wild-type mice as well as to elevated doses of the synthetic retinoids, indicating that RAR gamma may have a major role in mediating retinoid toxicity, a finding that possibly has practical implications for reducing the toxicity of synthetic retinoids in clinical use.

Compounds that inhibit 5-lipoxygenase (5-LO), the key enzyme in the biosynthesis of leukotrienes (LTs), possess potential for the treatment of inflammatory and allergic diseases as well as of atherosclerosis and cancer. Here we present the design and the synthesis of a series of novel 2-amino-5-hydroxyindoles that potently inhibit isolated human recombinant 5-LO as well as 5-LO in polymorphonuclear leukocytes, exemplified by ethyl 2-[(3-chlorophenyl)amino]-5-hydroxy-1H-indole-3-carboxylate (3n, IC(50) value congruent with 300 nM). Introduction of an aryl/arylethylamino group or 4-arylpiperazin-1-yl residues into position 2 of the 5-hydroxyindoles was essential for biological activity. Whereas the 4-arylpiperazin-1-yl derivatives were more potent in cell-free assays as compared to intact cell test systems, aryl/arylethylamino derivatives inhibited 5-LO activity in intact cells and cell-free assays almost equally well. On the basis of their 5-LO inhibitory properties, these novel 2-amino-5-hydroxyindoles represent potential candidates for the pharmacological intervention with LT-associated diseases.