We describe a case of recurrent hypoglycemia apparently caused by secretion of insulin-like growth factor II (IGF-II) by a leiomyosarcoma. A 67-year-old woman presented with recurrent severe hypoglycemia and a large mass in the thorax. During hypoglycemia, plasma cortisol was elevated, but insulin and growth hormone levels were low. After resection of a large leiomyosarcoma, the hypoglycemia resolved. After an eight-year remission, both the tumor and symptomatic hypoglycemia recurred. During a second operation a second large tumor was removed, with relief of the patient's hypoglycemia. The tumor contained high concentrations of IGF-II mRNA and 2100 ng of IGF-II immunoreactive peptide per gram. Filtration through a BioGel P-60 gel column established that 77 percent of the IGF-II was present as a larger molecule, demonstrating incomplete processing of the pro-IGF-II peptides. A similar fraction of high-molecular-weight IGF-II was present in the serum, indicating that the tumor was the chief source of IGF-II. The high-molecular-weight IGF-II found in both the tumor and serum was fully reactive with the IGF-II receptor. Radioimmunoassay showed that the concentrations of insulin-like growth factor I (IGF-I) in tumor and serum were low, suggesting feedback inhibition of growth hormone secretion by IGF-II. Eight months after reoperation, plasma concentrations of IGF-I and IGF-II were normal, and high-molecular-weight IGF-II was virtually undetectable. We conclude that the most likely cause of this patient's recurrent hypoglycemia was IGF-II produced by the leiomyosarcoma.

Previous measurements of somatomedins (Sms) and insulin-like growth factors (IGFs) in maternal and fetal serum have yielded contradictory results. We have, therefore, measured maternal, fetal, and neonatal rat serum with two highly specific assays: 1) IGF-I/Sm-C RiA and 2) a highly specific IGF-II/rat placental membrane radioreceptor assay (RRA). In addition, we have made measurements with a less specific multiplication-stimulating activity (MSA)-rat placental membrane RRA. To avoid possible serious artifacts created by Sm-binding proteins, preliminary acid-ethanol extraction of serum was performed. Results are expressed in terms of a reference human serum with an assigned potency of 1 U/ml. Maternal RIA IGF-I fluctuated between 1.1-1.4 U/ml from the 17th day of pregnancy to the 25th day after delivery (nonpregnant rat serum pool, 1.25 +/- 0.22 U/ml). On day 21 of gestation, fetal serum radioimmunoassayable IGF-I was 1.03 +/- 0.03 U/ml. After birth, radioimmunoassayable IGF-I fell and reached .19 +/- 0.03 U/ml at 18 days of age, but rose to 0.71 +/- 0.04 U/ml at 25 days of age. At term, maternal radioreceptor assayable IGF-II was 2.18 +/- 0.27 U/ml (nonpregnant female pool, 1.4 +/- 0.12). By the 25th postpartum day, radioreceptor assayable IGF-II was 1.39 +/- 0.12 U/ml. Radioreceptor assayable IGF-II in fetal serum on day 19 was 3.26 +/- 0.48 U/ml and rose to 5.37 +/- 0.66 U/ml on the day of delivery. A further rise to 8.92 +/- 1.03 occurred on day 5. A subsequent fall to 2.41 +/- 0.05 U/ml was observed on day 25. The patterns of results of the MSA RRA in fetal and neonatal rat serum were similar to that obtained with the IGF-II RRA. We now conclude that radioimmunoassayable IGF-I is present in higher concentrations than previously reported in term fetal rat serum and that radioreceptor assayable IGF-II is selectively elevated in rat fetal and neonatal life and may have unique metabolic and growth-promoting significance.U

Von Willebrand factor (VWF) dimerizes through C-terminal CK domains, and VWF dimers assemble into multimers in the Golgi by forming intersubunit disulfide bonds between D3 domains. This unusual oxidoreductase reaction requires the VWF propeptide (domains D1D2), which acts as an endogenous pH-dependent chaperone. The cysteines involved in multimer assembly were characterized by using a VWF construct that encodes the Nterminal D1D2DD3 domains. Modification with thiol-specific reagents demonstrated that secreted DD3 monomer contained reduced Cys, whereas DD3 dimer and propeptide did not. Reduced Cys in the DD3 monomer were alkylated with N-ethylmaleimide and analyzed by mass spectrometry. All 52 Cys within the DD3 region were observed, and only Cys 1099 and Cys 1142 were modified by N-ethylmaleimide. When introduced into the D1D2DD3 construct, the mutation C1099A or C1142A markedly impaired the formation of DD3 dimers, and the double mutation prevented dimerization. In full-length VWF, the mutations C1099A and C1099A/C1142A prevented multimer assembly; the mutation C1142A allowed the formation of almost exclusively dimers, with few tetramers and no multimers larger than hexamers. Therefore, Cys 1099 and Cys 1142 are essential for the oxidoreductase mechanism of VWF multimerization. Cys 1142 is reported to form a Cys 1142 -Cys 1142 intersubunit bond, suggesting that Cys 1099 also participates in a Cys 1099 -Cys 1099 disulfide bond between D3 domains. This arrangement of intersubunit disulfide bonds implies that the dimeric N-terminal DD3 domains of VWF subunits align in a parallel orientation within VWF multimers.disulfide bond ͉ mass spectrometry ͉ oxidoreductase

We reported that serum and tumor from a hypoglycemic patient with a fibrosarcoma contained insulinlike growth factor II (IGF-II), mostly in a large molecular form designated "big IGF-ll." We now describe two additional patients with non-islet-cell tumor with hypoglycemia (NICTH) whose sera contained big IGF-ll. Removal of the tumor eliminated most of the big IGF-ll from the sera of two patients. Because specific IGF-binding proteins modify the bioactivity of IGFs, the sizes of the endogenous IGF-binding protein complexes were determined after neutral gel ifitration through Sephadex G-200. Normally about 75% of IGFs are carried as a ternary complex of 150 kDa consisting of IGF, a growth hormone (GH)-dependent IGF-binding protein, and an acidlabile complexing component. The three patients with NICTH completely lacked the 150-kDa complex. IGF-U was present as a 60-kDa complex with variable contributions of smaller complexes. In the immediate postoperative period, a 110-kDa complex appeared rather than the expected 150-kDa complex.Abnormal IGF-ll binding may be important in NICTH because the 150-kDa complexes cross the capillary membrane poorly. The smaller complexes present in our patients' sera would be expected to enter interstitial fluid readily, and a 4-to 5-fold increase in the fraction of IGFs reaching the target cells would result.Many mesenchymal tumors express the insulin-like growth factor II (IGF-II) gene (1-7). Increased concentrations of IGF-II have been detected in some of these tumors (3, 6, 7), and explants of one tumor have released IGF-II into the medium (7). It has been suspected that secretion of IGF-II by certain large mesenchymal tumors might be related to the syndrome of non-islet-cell tumor hypoglycemia (NICTH), although attempts to detect such peptides in serum with relatively nonspecific insulin bioassays have given conflicting results (8, 9). Increased concentrations of serum IGF-II-like peptides were found by radioreceptor assay in some cases of NICTH (10, 11). Even when elevated, the increases in IGF-II concentrations were often small and could not be confirmed with a number of assay methods by Widmer et al. (12). Recently, Daughaday et al. (6) described a case of a woman with a fibrosarcoma (originally identified as a leiomyosarcoma) with hypoglycemia, whose tumor contained greatly increased IGF-II mRNA and IGF-II peptide. After acid gel filtration, most of the serum and tumor IGF-II was present as big IGF-II. Because the severity of the metabolic symptoms of these patients with NICTH is not easily explained by the modest degree of increase of IGF-II, we undertook studies of the association of endogenous IGF-II to serum binding proteins in three cases of mesenchymal tumors with clinically severe hypoglycemia. METHODS Source of Sera. Case 1. Sera from a 67-year-old woman with severe symptomatic hypoglycemia and a large recurrent sarcoma of her thorax were kindly provided by Mary Ann Emanuele of Loyola University School ofMedicine, Chicago. The tumor was originally considered t...

No abstract