Biomedical subjects
Publications and source records attributed to M M Rechler.
Mutants of Salmonella typhimurium containing 1 to 2% of wild-type ribonuclease I activity were isolated. The rns mutation had no effect on the polarity of mutations in the S. typhimurium histidine operon. Even in the presence of an rns mutation, it was not possible to obtain strong suppressors of the polarity of two polar mutations in the his operon.
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Insulin-like growth factor-I (IGF-I) and IGF-II are mitogenic polypeptides of relative molecular mass (Mr) approximately 7,500 isolated from human plasma each containing four peptide domains in a single chain and identical at more than 60% of their amino acid loci. The B- and A-domains of the IGFs are approximately 40% identical to the B- and A-chains of human insulin. IGF-I and IGF-II have similar in vitro biological activities and receptor reactivity, but are immunologically distinct. IGF-I appears to mediate the effects of growth hormone on cartilage to promote skeletal growth whereas IGF-II may have a special role in fetal development and in the central nervous system. To investigate the in vivo role of IGF-II, we have studied IGF-II biosynthesis in the BRL-3A rat liver cell line. BRL-3A cells synthesize and secrete a 7,484 Mr protein 93% identical to human IGF-II and representing rat IGF-II (rIGF-II). Rat IGF-II is synthesized as a approximately 22,000 Mr prepro-rIGF-II (ref. 12) from 12 S poly(A)+mRNA. In addition, approximately 20,000 Mr pro-rIGF-II has been identified in lysates of biosynthetically labelled intact BRL-3A cells. We report here the isolation of an almost complete cDNA clone for rIGF-II. Our results indicate that pro-rIGF-II is synthesized as a 156 amino acid peptide precursor (17,619 Mr) containing mature rIGF-II 1-67 at its amino-terminus and an 89-residue carboxy-terminal peptide extension.
Most of the insulin-like growth factors (IGFs) in adult rat or human plasma circulate in 150-kDa heterotrimeric complexes with IGF-binding protein-3 (IGFBP-3) and an acid-labile subunit (ALS). These 150-kDa complexes are not present, however, in rat serum at birth. As ALS is the critical determinant in the formation of the 150-kDa complexes in adult rat serum, the present study asks whether the absence of 150-kDa complexes in fetal rat serum results from a low abundance of ALS. We report that ALS mRNA is expressed in term fetal rat liver at 30% of the levels in adult liver, that radioiodinated rat ALS is not proteolyzed by incubation with fetal rat serum, and that sufficient functional ALS is present in fetal rat serum to form 150-kDa complexes with recombinant human IGFBP-3. These results indicate that the low levels of 150-kDa complexes in perinatal rat serum are not due to low circulating levels of ALS.
The insulin-like growth factors (IGFs) in adult mammalian plasma circulate predominantly in 150-kDa complexes that also contain IGF-binding protein-3 (IGFBP-3) and an acid-labile subunit. Proteolysis of IGFBP-3 within the 150-kDa complex decreases its affinity for IGFs, facilitating their release to the tissues. By contrast, 150-kDa complexes are not detected in serum from fetal or pregnant adult rats. Decreased complex formation results from insufficient availability of IGFBP-3 due to increased IGFBP-3 proteolysis. The present study characterizes IGFBP-3 protease activity in serum from fetal, pregnant and non-pregnant adult rats by comparing the effect of different protease inhibitors. Proteolysis of exogenous recombinant human IGFBP-3 (for fetal and pregnancy serum) or endogenous IGFBP-3 (for non-pregnant adult rat serum) following incubation at 37 degrees C was measured by ligand blotting. In all three sera, IGFBP-3 proteolysis was inhibited completely by: (i) EDTA, a chelator of divalent cations. Inhibition was reversed by zinc, but not by calcium ions; (ii) 4-(2-aminoethyl)-benzenesulfonyl fluoride (AEBSF), an inhibitor of serine proteases; and (iii) a specific tissue inhibitor of matrix metalloproteinases (TIMP-1). Recombinant human matrix metalloproteinase-3 (MMP-3) proteolyzed recombinant human IGFBP-3 or endogenous rat IGFBP-3 in non-pregnancy serum pretreated with AEBSF to inactivate endogenous serine proteases. These results suggest that serine proteases initiate the activation of latent MMP precursor, and that the activated MMP directly degrades IGFBP-3.