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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Recombinant human insulin-like growth factor-I (hIGF-I) and a biologically potent variant lacking the N-terminal tripeptide (des(1-3)IGF-I) were produced from transfected Chinese hamster ovary cells. The constructs encoding the signal peptide, sequence of the mature peptide and a C-terminal extension peptide were expressed under the control of a Rous sarcoma virus promoter. Successfully transfected clones secreting correctly processed recombinant hIGF-I or des(1-3)IGF-I were selected by their secretion of IGF-I-like activity into the culture medium. The recombinant peptides were purified to homogeneity as assessed by high-performance liquid chromatography and N-terminal sequence analysis. The purified recombinant peptides exhibited biological potencies equivalent to authentic IGF-I and des(1-3)IGF-I respectively.
J Mol Endocrinol 1991 Jun
PMID:Expression, purification and characterization of secreted recombinant human insulin-like growth factor-I (IGF-I) and the potent variant des(1-3) IGF-I in Chinese hamster ovary cells. 188 85

The importance of the ovarian insulin-like growth factors (IGFs) has been suggested by data from numerous laboratories and several approaches in the last several years. In the aggregate, these data indicate that this system could function as an important local amplification mechanism for steroidogenesis and gonadotropin action. Studies supporting this hypothesis have described several interacting components of this autocrine/paracrine system. First, the several types of ovarian cells possess an IGF-response system, which includes receptors for IGFs and an effective intracellular transduction system. The IGFs can promote growth and/or differentiation of ovarian cells, and their predominant actions depend on the nature of the cells and the presence of additional modulating factors. The biochemical events leading to enhanced steroidogenesis are now understood in considerable detail and include induction of several steps in the cAMP-dependent steroidogenic cascade. The second component of the ovarian IGF system comprises hormone-responsive local production of IGFs. Both IGF-I and IGF-II may be secreted; gonadotropins, gonadal steroids and locally produced growth factors can regulate the IGF system at this level. Finally, ovarian cells secrete a heterogeneous and complex family of IGF-binding proteins (IGFBPs). These proteins can impact on multiple ovarian functions in a manner which is generally opposite to that of the IGFs themselves. As is the case for the IGFs, the secretion of these proteins by ovarian cells is regulated by gonadotropins and locally produced ovarian factors. Collectively, these several components provide an integrated, synergistically cooperative local network to promote gonadotropin-dependent growth and differentiation in the ovary.
J Steroid Biochem Mol Biol 1991
PMID:The ovarian insulin-like growth factors, a local amplification mechanism for steroidogenesis and hormone action. 195 42

In humans, the plasma level of sex hormone binding globulin (SHBG) is regulated by several hormones. We have now accumulated evidence that SHBG is also intimately related to nutritional state. However, we do not yet know what specific signal, if any, may be the regulator of SHBG. There is a strong and negative correlation between fasting insulin level and SHBG in obese as in hyperandrogenic women. Under such circumstances, a high fasting insulin level, normal glycemia and a low SHBG level suggest insulin resistance in terms of glucose disposal but not in terms of SHBG inhibition. This is a rather complex situation. It is too early to judge the importance of IGF-I in the regulation of SHBG. But it may turn out that IGF-I is the main regulator of SHBG and that, by interaction with the IGF-I receptors, insulin carries on its inhibitory activity on SHBG.
J Steroid Biochem Mol Biol 1991
PMID:Pathophysiology of sex hormone binding globulin (SHBG): relation to insulin. 195 79

The human uterus repeatedly exhibits cyclic biochemical and cytological changes during the reproductive period of life. These changes are the result of a well-characterized endocrine network involving the hypothalamus, pituitary, and ovary. The exact nature of the mechanism(s) by which the sex steroids act on the uterus remains to be elucidated. Possible local mediators of hormonal action on the uterus include polypeptide growth factors. Using the method of RNA transfer blot hybridization, we have analyzed tissue samples from the cycling human endometrium and tissue samples of human myometrium and myometrial benign tumor (leiomyoma) for the presence of platelet-derived growth factor (PDGF) and insulin-like growth factor (IGF) RNA. All the uterine tissues examined possessed RNA for PDGF-B chain and IGF-I and -II. Two transcripts were observed for PDGF-B chain, four were observed for IGF-I, and eight were observed for IGF-II. Overall, the relative abundance of PDGF-B chain RNA was consistent in all of the uterine tissues examined. In contrast, IGF RNA relative abundance varied. IGF-I RNA was highest in late proliferative stage endometrium, and IGF-II RNA was highest in early proliferative stage endometrium. Both IGF-I and IGF-II RNAs were greater in amount of leiomyoma than in myometrium. The increased IGF-I RNA in late proliferative-stage human endometrium correlates with the known elevation of estradiol secretion by the ovary and the increased concentration of uterine estradiol receptors during this stage of the menstrual cycle.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Reprod Dev 1990 Oct
PMID:Expression of the insulin-like and platelet-derived growth factor genes in human uterine tissues. 197 7

The objective of the present study was to develop a chemically-defined medium in which early stages of testicular differentiation can be investigated in an organ culture system. Mouse gonadal primordia were explanted before and after initiation of morphological sex differentiation, i.e. 11 and 12 day of gestation (d.g.), respectively. We found that a combination of human albumin fraction, insulin (or IGF-I), and sodium pyruvate promoted testicular organization of gonadal explants of 11 d.g., but not those of 12 d.g. Insulin also increased the production of testosterone from testicular explants of 11 d.g., but not those of 12 d.g. For the younger explants, progesterone was more efficient than pregnenolone as a steroid precursor during the first day of culture, but the maximum effect of pregnenolone was much higher than that of progesterone in later stages. The responsiveness to human chorionic gonadotropin increased gradually along with testicular organization. The addition of either serum or pregnenolone prominently increased the activity of delta 5-3 beta hydroxysteroid dehydrogenase in testicular explants of 11 d.g., but not the number of positive cells as demonstrated by histochemical staining. These results suggest that insulin (or IGF-I) is required during the initial phase of testicular organization, which is reflected by an increase in testosterone production and sensitivity to gonadotropins.
J Steroid Biochem Mol Biol 1991 Apr
PMID:Regulation of testicular differentiation and testosterone production in the fetal mouse gonad in vitro. 203 66

In Xenopus oocytes, insulin or IGF-I activated glucose transport and maturation, but not amino acid transport, as measured by the uptake of alanine. Glucose transporter identical or closely related to the mammalian erythroid/brain transporter (Glut-1/EGT) were found in oocyte membranes. The EC50 for stimulation of glucose uptake and of maturation were similar (1-5 x 10(-8) M for insulin and 2-8 x 10(-10) M for IGF-I), confirming that these effects were mediated through IGF-I receptors. Other agents, such as phorbol 12-myristate 13-acetate (TPA) (0.5 microM) and vanadate (2 mM) evoked only part of the insulin effect on glucose uptake (50% and 65%, respectively), without being additive to insulin. In contrast, progesterone at 1 microM, a potent inducer of maturation, inhibited at least partially the insulin-induced glucose uptake. Uptake of alanine and glucose was decreased after prolonged incubations (3-6 h) with agents that trigger maturation, and was dramatically reduced in oocytes that have undergone maturation (unfertilized eggs). Maturation is thus accompanied by a reduction in glucose and amino acid transports. These result further document the validity of Xenopus oocytes as a model to study insulin and IGF-I signalling.
Mol Cell Endocrinol 1991 Feb
PMID:Effects of insulin, insulin-like growth factor-I (IGF-I) and progesterone on glucose and amino acid uptake in Xenopus laevis oocytes. 205 Feb 72

Administration of ovine GH to immature domestic fowl blunted their subsequent GH response to thyrotrophin-releasing hormone (TRH), a GH secretagogue in birds. The in-vivo administration of GH also reduced the ability of radiolabelled TRH to bind to plasma membranes of the pituitary caudal lobe, in which GH cells predominate. These inhibitory effects of GH were mediated by extrapituitary actions, since GH had no direct inhibitory effects on TRH-induced GH release or on pituitary TRH binding in vitro. GH inhibition of GH secretion and TRH binding would not appear to be mediated by hypothalamic somatostatin (SRIF) or peripheral somatomedin (IGF-I), since SRIF and IGF-I had no direct effects in vitro.
J Mol Endocrinol 1990 Feb
PMID:Feedback-inhibition of growth hormone (GH) secretion in fowl: GH-induced down-regulation of thyrotrophin-releasing hormone binding to pituitary membranes. 210 92

The hypothesis has been advanced that Sertoli cells produce one or more follicle-stimulating hormone (FSH)-dependent paracrine factors which stimulate Leydig cell maturation and steroidogenesis. In an attempt to identify these factors we studied the effect of coculture with Sertoli cells on the steroidogenic capacity of immature Leydig cells. It is demonstrated that coculture, during a period of 6 days, markedly increases the capacity of the Leydig cells to secrete C21-steroids (progesterone, 17 alpha-hydroxyprogesterone, 20 alpha-hydroxypregn-4-en-3-one) and C19-steroids (testosterone, androst-4-ene-3,17-dione) in response to stimulation with luteinizing hormone (LH). Pretreatment of the cocultures on days 4, 5 and 6 with low concentrations of gonadotropins further enhances the steroidogenic response to LH. This pretreatment results in an overall increase in steroid output. At low concentrations of Sertoli cells and when short incubation times are used, pretreatment with FSH is clearly more effective than pretreatment with LH. Pretreatment with gonadotropins also results in a disproportionate increase in C19 output caused by increased conversion of C21 precursors into C19-steroids. This effect is also observed in Leydig cell monocultures and is mainly due to LH action on Leydig cells. Finally pretreated cocultures display a selective increase in testosterone output. The latter effect is caused by FSH-dependent conversion of androstenedione into testosterone in Sertoli cells. Pretreated cocultures can be maintained for at least 28 days. During this entire period their basal steroid output increases. Using a two-chamber culture system it is demonstrated that direct cell-cell interactions are not required to observe the stimulatory effects of coculture. One or more diffusible factors are involved and continuous contact with these factors is required to maintain the effect. Immunoneutralization experiments using an insulin-like growth factor (IGF-I) antiserum show that IGF-I is an important permissive factor to maintain steroidogenesis in isolated Leydig cells and in cocultures. Under none of the conditions studied, however, does the antiserum neutralize the stimulatory effect of coculture. It is concluded that the stimulatory effects of coculture on the testosterone output of Leydig cells are complex and that important diffusible mediators still remain to be identified.
Mol Cell Endocrinol 1990 Jul 09
PMID:Influence of coculture with Sertoli cells on steroidogenesis in immature rat Leydig cells. 212 92

The insulin-like growth factors (IGF-I and IGF-II) are peptides of about 7,500 D with structural homology to proinsulin that are capable of stimulating cellular proliferation and inducing differentiation. They are each encoded by single, large, complex genes that direct the transcription of multiple mRNAs. Both genes are expressed in most organs and tissues, predominantly by cells of mesenchymal origin. Developmental factors are important in their regulation, with IGF-II's expression predominantly prenatally and IGF-I's postnatally. In the fetus, placental lactogen can stimulate the synthesis of both IGF-I and IGF-II. After birth, however, growth hormone and nutritional status are the major regulators of IGF-I. In addition, a variety of other factors exert tissue-specific stimulation of IGF-I and IGF-II expression. The actions of the IGFs are mediated by interaction with the type 1 IGF cell surface receptor, which, like the IGFs, is expressed in most tissues. The biologic effects of the IGFs are modulated by IGF binding proteins, which can both augment and inhibit IGF effects, depending on the nature of the binding protein and other factors. IGF actions are also influenced by other regulatory agents that appear to act in concert with the IGFs; for example, IGF-I's capacity to stimulate DNA synthesis in Balb-C 3T3 and FRTL5 cells requires other growth factors and TSH, respectively. The widespread expression of the IGFs, IGF receptors, and IGF binding proteins, taken together with the findings that the IGFs can act on many cell types, suggests that the IGFs have an important role in the growth and development of many organs, including lung.(ABSTRACT TRUNCATED AT 250 WORDS)
Am J Respir Cell Mol Biol 1990 Aug
PMID:The insulin-like growth factors and the lung. 216 91

Disaggregated airway epithelial cells replicate in serum-free media containing supraphysiologic concentrations of insulin. To examine the hypothesis that the type 1 insulin-like growth factor (IGF) receptor mediates the mitogenic action of insulin on these cells, we studied the mitogenic effects of IGF-I and insulin, and the expression of type 1 IGF receptors in primary cultures of adult canine tracheal epithelial cells. Isolated tracheal epithelial cells were grown in varying concentrations of IGF-I or insulin in Ham's F12 medium supplemented with transferrin, cholera toxin, and endothelial cell growth supplement. Both IGF-I and insulin increased DNA synthesis (measured as [3H]thymidine incorporation into DNA) and cell number in a concentration-dependent fashion, but IGF-I was at least 20 to 60 times more potent than insulin in its mitogenic effects. No additive or synergistic effect was observed with the simultaneous addition of IGF-I and insulin in maximally effective doses. A monoclonal antibody directed against the type 1 IGF receptor (alpha IR3) blocked the mitogenic activity of both IGF-I and insulin. Affinity labeling of type 1 IGF receptors by covalent cross-linking with disuccinimidyl suberate demonstrated the tracheal epithelial cell IGF-I binding moiety to have a relative molecular weight of 130,000 D. Binding of [125I]IGF-I to this protein was inhibited by low concentrations of IGF-I, relative to insulin, and by alpha IR3. An 11-kb transcript characteristic of mRNA for the type 1 IGF receptor was recognized in poly(A+) RNA derived from cultured canine tracheal epithelial cells.(ABSTRACT TRUNCATED AT 250 WORDS)
Am J Respir Cell Mol Biol 1990 Sep
PMID:Canine tracheal epithelial cells express the type 1 insulin-like growth factor receptor and proliferate in response to insulin-like growth factor I. 216 99


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