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Rainbow trout, Oncorhynchus mykiss, were used to evaluate the effects of carbohydrate loading on plasma levels of pancreatic hormones and associated changes in metabolic indexes in a carnivorous fish. Glucose (3,000 mg/dl, 10 microliters/g body wt) was injected intraperitoneally into fish (mean wt 54 +/- 5 g) that were killed 0.5-24 h after administration. Glucose injection resulted in hyperglycemia with maximum glucose levels of 306 +/- 13 mg/dl observed 60 min after injection. Glucose administration also resulted in hyperlipidemia. Plasma fatty acids increased twofold in glucose-injected animals. Alterations in plasma metabolites reflected changes in energy stores. Although total lipid concentration was unaffected by glucose injection, lipolytic enzyme activity in the liver was enhanced. Biosynthetic capacity, as indicated by NADPH production from glucose-6-phosphate dehydrogenase, was decreased by glucose injection. Liver glycogen content was reduced in glucose-injected animals 1 h after injection. Glucose injection was attended by increases in the plasma levels of gene II somatostatin-25 (predominant form of pancreatic somatostatin in salmonids) and of glucagon. Insulin levels were initially suppressed after glucose injection. These results indicate that metabolic adjustments caused by glucose administration can be related to the regulatory action of pancreatic hormones. Furthermore, these results suggest that the somatostatin-secreting cells of the trout are sensitive to glucose and that somatostatin-suppressed insulin secretion contributes to the glucose intolerance of trout.

The mouse tumor cell line alpha TC1-6 was used as a model system to examine the post-translational processing of proglucagon. Determination of the mouse preproglucagon cDNA sequence and comparison with the published sequences of rat and human preproglucagons revealed nucleic acid homologies of 89.1 and 84%, respectively, and amino acid homologies of 94 and 89.4%, respectively. Immunohistochemical analyses with antibodies directed against PC2 and glucagon colocalized both the enzyme and substrate within the same secretory granules. PC1 was also immunolocalized in secretory granules. Cells were metabolically labeled with [3H]tryptophan, and extracts were analyzed by reverse-phase high pressure liquid chromatography. Radioactive peptides with retention times identical to those of synthetic peptide standards were recovered and subjected to peptide mapping to verify their identities. To determine the potential role of PC1 and PC2 in proglucagon processing, 3H-labeled proglucagon was incubated in vitro with recombinant PC1 and/or immunopurified PC2. Both enzymes cleaved proglucagon to yield the major proglucagon fragment, glicentin, and oxyntomodulin, whereas only PC1 released glucagon-like peptide-I from the major proglucagon fragment. Neither PC1 nor PC2 processed glucagon from proglucagon in vitro. These results suggest a potential role for PC1 and/or PC2 in cleaving several of the normal products, excluding glucagon, from the mouse proglucagon precursor.

Glioblastoma (GBM) is a highly aggressive primary brain tumor with a poor prognosis. Despite aggressive therapy with surgery, radiotherapy, and chemotherapy, nearly all patients succumb to disease within 2 years. Several studies have supported the presence of stem-like cells in brain tumor cultures that are CD133-positive, are capable of self-renewal, and give rise to all cell types found within the tumor, potentially perpetuating growth. CD133 is a widely accepted marker for glioma-derived cancer stem cells; however, its reliability has been questioned, creating a need for other identifiers of this biologically important subpopulation. We used a panel of 20 lectins to identify differences in glycan expression found in the glycocalyx of undifferentiated gliomaderived stem cells and differentiated cells that arise from them. Fluorescently labeled lectins that specifically recognize a-N-acetylgalactosamine (GalNAc) and a-N-acetylglucosamine (GlcNAc) differentially bound to the cell surface based on the state of cellular differentiation. GalNAc and GlcNAc were highly expressed on the surface of undifferentiated cells and showed markedly reduced expression over a 12-day duration of differentiation. Additionally, the GalNAc-recognizing lectin Dolichos biflorus agglutinin was capable of specifically selecting and sorting glioma-derived stem cell populations from an unsorted tumor stock and this subpopulation had proliferative properties similar to CD133+ cells in vitro and also had tumor-forming capability in vivo. Our preliminary results on a single cerebellar GBM suggest that GalNAc and GlcNAc are novel biomarkers for identifying glioma-derived stem cells and can be used to isolate cancer stem cells from unsorted cell populations, thereby creating new cell lines for research or clinical testing.

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To further examine the physiological roles of the neuroendocrine prohormone convertases (PCs) in proglucagon processing, alpha TC1-6 cells were transiently transfected with PC1/3 and PC2 expression vectors containing either antisense or sense encoding cDNAs. PC1/3- and PC2-directed RIAs were used to determine that the PC1/3 antisense transfections lowered endogenous levels of PC1/3 by 40 +/- 7.9% but did not alter the levels of PC2. The PC2 antisense transfections decreased the endogenous levels of PC2 by 91 +/- 11.7% without affecting the levels of PC1/3. To quantitate the levels of proglucagon and proglucagon-derived products, transfected cells were metabolically labeled with [3H]tryptophan, and extracts were chromatographed by reversed-phase HPLC. Recovered peptides were then subjected to peptide mapping analyses, allowing precise quantification of 3H-radioactivity incorporated into proglucagon and its cleavage products. Product-precursor ratios were determined, and percent change in the proportion of products generated in antisense-transfected vs. sense-transfected cells was calculated. The decrease in PC1/3 after antisense treatment significantly reduced the amounts of glicentin produced and partially reduced the levels of all other proglucagon cleavage products. PC2 antisense treatment significantly reduced the levels of glicentin and 9K glucagon generated but had no significant effect on the remainder of the proglucagon-derived peptides. These results suggest the existence of redundant mechanisms that ensure the production of each of the intermediate and product peptides derived from proglucagon. PC1/3 is potentially an important enzyme in the processing of most proglucagon-derived peptides, whereas PC2-processing activity appears to predominate at only two of the four potential cleavage sites.

Previous work suggested that teleost fish possess two somatostatin (SS) genes. Regulation of differential secretion of SS gene I (SS-25) and SS gene II products (SS-14) by nutrients was studied using rainbow trout. Hemi-islets were cultured in medium containing different concentrations of glucose and arginine. SS-14 and insulin were determined by radioimmunoassay; SS-25 was determined by a novel enzyme-linked immunosorbent assay. Glucose stimulated SS-25 release in a concentration-related manner, with 10 mM being the most effective concentration; at higher (25 mM) glucose, release decreased. Insulin levels in the medium also were found to be more elevated from islets incubated in 10 mM glucose than those incubated in 25 mM glucose. Maximum SS-14 release was observed at lower (1-5 mM) glucose concentrations. Arginine stimulated SS release so that maximum release of both SS forms occurred at the lowest glucose concentrations (1 mM). A concentration-related effect of arginine was observed on SS-25 release. The results of this study indicate that glucose and arginine regulate secretion of both pancreatic SS gene I and gene II products from rainbow trout islets, suggesting that two different pancreatic SS interact in nutrient homeostasis in this species.

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