Phylogeny of insulin. Some evolutionary aspects of insulin production with particular regard to the biosynthesis of insulin in Myxine glutinosa

Small is beautiful: insulin-like growth factors and their role in growth, development, and cancer

Insulin-like growth factors were discovered more than 50 years ago as mediators of growth hormone that effect growth and differentiation of bone and skeletal muscle. Interest of the role of insulin-like growth factors in cancer reached a peak in the 1990s, and then waned until the availability in the past 5 years of monoclonal antibodies and small molecules that block the insulin-like growth factor 1 receptor. In this article, we review the history of insulin-like growth factors and their role in growth, development, organism survival, and in cancer, both epithelial cancers and sarcomas. Recent developments regarding phase I to II clinical trials of such agents are discussed, as well as potential studies to consider in the future, given the lack of efficacy of one such monoclonal antibody in combination with cytotoxic chemotherapy in a first-line study in metastatic non-small-cell lung adenocarcinoma. Greater success with these agents clinically is expected when combining the agents with inhibitors of other cell signaling pathways in which cross-resistance has been observed.

Characterization of proinsulin- and proglucagon-converting activities in isolated islet secretory granules

The conversion of proglucagon and proinsulin by secretory granules isolated from both prelabeled and unlabeled anglerfish islets was investigated. Either granules isolated from tissue labeled with [3H]tryptophan and [14C]isoleucine or [35S]cysteine, or lysed granules from unlabeled tissue to which exogenously labeled prohormones had been added were incubated under various conditions. Acetic acid extracts of these granule preparations were analyzed for prohormone and hormone content by gel filtration. Both prelabeled and lysed, unlabeled secretory granules converted radiolabeled precursor peptides (Mr 8,000-15,000) to labeled insulin and glucagon. The accuracy of the cleavage process was established by demonstrating comigration of products obtained from in vitro cleavage with insulin and glucagon extracted from intact islets using electrophoresis and high-pressure liquid chromatography (HPLC). The pH optimum for granule-mediated conversion was found to be in the range of pH 4.5-5.5. Conversion of both proglucagon and proinsulin by secretory granules was significantly inhibited in the presence of antipain, leupeptin, p-chloromercuribenzoate (PCMB) or dithiodipyridine (DDP) but not chloroquine, diisopropyl fluorophosphate, EDTA, p-nitrophenyl guanidinobenzoate, soybean trypsin inhibitor, or N-p-tosyl-L-lysine chloromethyl ketone HCl. The inhibitory action of PCMB and DDP was reversed in the presence of dithiothreitol. Both membranous and soluble components of the secretory granules possessed significant converting activity. HPLC and electrophoretic analysis of cleavage products demonstrated that the converting activities of the membranous and soluble components were indistinguishable. The amount of inhibition of proinsulin and proglucagon conversion caused by 600 micrograms/ml porcine proinsulin was significantly lower than that caused by the same concentration of unlabeled anglerfish precursor peptides. These results indicate that the proinsulin and proglucagon converting enzyme(s) in the anglerfish pancreatic islet is a unique intracellular thiol proteinase(s) that may be granule membrane-associated and may require the presence of prohormone sequences in addition to the dibasic residues at cleavage sites for substrate recognition and/or binding.

Evolutionary origins of vertebrate hormones: substances similar to mammalian insulins are native to unicellular eukaryotes

Tetrahymena pyriformis, Neurospora crassa, and Aspergillus fumigatus that had been grown in simple defined media were extracted with acid ethanol by a classic method for recovering insulin from pancreas. After filtration of the extracts on Sephadex G-50, distinct peaks of insulin immunoreactivity were recovered in the region typical of insulin. The gel-filtered material from the Tetrahymena had reactivity in the pork insulin radioimmunoassay about equal to its reactivity in the insulin bioassay (stimulation of lipogenesis in isolated rat adipocytes), and the gel-filtered material from neurospora had an immunoreactivity-to-bioactivity ratio of about 1:3. The material that stimulated lipogenesis could be neturalized by anti-insulin sera (i.e., 75-95% of the Tetrahymena material and 60% of the Neurospora material). Bioactive and immunoactive insulin was found in the conditioned medium equal in amount to that in the cells. The findings suggest that insulin did not arise evolutionarily in the intestinal or neural tissues of primitive vertebrates or complex invertebrates but rather has its molecular origins at least as far back as the simplest unicellular eukaryotes.

Role of zinc in insulin biosynthesis. Some possible zinc-insulin interactions in the pancreatic B-cell

The behaviour of proinsulin and insulin in the presence of zinc suggests it plays an important role in insulin's production in the B-cell for the vast majority of animal species. The postulate that proinsulin forms a zinc containing hexamer soon after its synthesis and that this organization of the molecule is maintained through all the subsequent processes is supported by our observation that the proinsulin hexamer is converted readily into the insulin hexamer. In addition the zinc ions enhance proinsulin's solubility and render insulin insoluble. Zinc ions also appear to play an important role in the microcrystalline character of the precipitated insulin granule. There may be advantages in condensing the stored material in this way; it will reduce contact with the surrounding membrane where the converting, and possibly other enzymes, are thought to be located, and it will tend to exclude incompletely converted hexamers.