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

A tumor surface protein (TSP-180) that is highly expressed on highly malignant metastatic cells has been identified on murine lung carcinomas. On SDS-PAGE under reducing conditions, TSP-180 shows a complex banding pattern corresponding to 204, 183, 150, 135, and 116 kDa. All bands of the TSP-180 complex are glycosylated and are labeled by lactoperoxidase-catalyzed radioiodination of viable cells. The mouse TSP-180 complex described here is homologous to the human integrin alpha 6 beta 4 complex, and in particular it has been demonstrated that protein corresponding to 204 kDa is homologous to the beta 4 subunit of the integrin complex. It has been shown recently that monoclonal antibody to TSP-180 (MoAb 135-13C) stimulates cell growth in vitro and induces phosphorylation of the 204-kDa protein. We now report that insulin increases the phosphorylation of the 204-kDa protein 30-fold in intact carcinoma cells and epidermal growth factor (EGF) causes a threefold increase. Insulin-like growth factor (IGF-I) and platelet-derived growth factor have no effect. The effect of insulin and of IGF-I on phosphorylation of their own receptors was studied using solubilized cell membranes. Insulin and IGF-I each induced a fivefold increase in the phosphorylation of their respective receptor beta subunits. In order to test if phosphorylation of the 204-kDa protein was induced by direct binding of growth factors to TSP-180 and to identify growth factor receptors on line 1 cells, affinity cross-linking studies were performed. Affinity labeling of receptors demonstrated that insulin and IGF-I both bind to a 135-kDa protein that corresponds to the insulin and IGF-I receptor alpha subunits. Affinity labeling of EGF receptors failed to demonstrate EGF receptor molecules (175-kDa protein) on line 1 cells. Further investigations by using a different approach confirmed the very low amount of EGF receptors on line 1 cells. Direct phosphoamino acid analysis of the 204-kDa protein purified from insulin-stimulated cells demonstrated that this beta 4 integrin subunit is phosphorylated on serine and tyrosine. We conclude that beta 4 integrin molecule is a target for phosphorylation through an indirect receptor-mediated mechanism.
Mol Carcinog 1989
PMID:Insulin-induced phosphorylation of the beta-4 integrin subunit expressed on murine metastatic carcinoma cells. 269 4

Human fibroblasts, a cell type that is used extensively to determine the pleiotypic effects of the insulin-like growth factors, have been shown to secrete a 35K protein that binds somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) but not insulin. This 35 K protein is associated with the fibroblast surface and following transfer to the surface of cell types that do not have this protein on their surfaces, it alters the binding of radiolabeled Sm-C/IGF-I. In this study human fibroblast monolayers that were incubated with cyclohexamide (50 micrograms/ml) for 14 h at 37 C had no detectable 35 K protein on their cell surface, but type I Sm-C/IGF-I receptors were still present. Loss of the 35 K protein was associated with 60-70% increase in binding of Sm-C/IGF-I to type I receptors. The relative affinity of the type I receptor for Sm-C/IGF-I was apparently increased because unlabeled Sm-C/IGF-I (12 ng/ml) competitively displaced 63% of radiolabeled Sm-C/IGF-I after cycloheximide exposure, whereas in cultures not exposed to cycloheximide [125I]Sm-C/IGF-I binding was increased by 11%. Coincubation of fibroblast conditioned media containing the 35 K protein with cycloheximide-treated fibroblast monolayers resulted in restoration of the paradoxical increase in Sm-C/IGF-I binding and loss of sensitivity to competition by unlabeled Sm-C/IGF-I. Exposure of suspended fibroblasts, which do not have 35 K on their cell surface, to media conditioned by fibroblast monolayers also induced both of these changes.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1987 May
PMID:Alterations in the synthesis of a fibroblast surface associated 35 K protein modulates the binding of somatomedin-C/insulin-like growth factor I. 285 4

In addition to the well-known growth stimulating effects of insulin-like growth factors (IGFs), recent studies suggest that these peptides may also modulate the differentiated functions of endocrine cells. Thus, in the present studies, we have investigated the actions of IGFs on androgen biosynthesis by cultured testicular cells. Treatment of cells obtained from adult hypophysectomized rats with LH (1 ng/ml) stimulated testosterone production 60-fold over basal levels. In contrast, treatment with either synthetic human IGF-I or IGF-II failed to stimulate androgen production. However, concomitant treatment of the LH-containing cultures with increasing doses of IGF-I (10-500 ng/ml) augmented testosterone production up to 70% over that seen with LH alone (ED50 = 67 ng/ml). Similar effects were obtained with IGF-II but this peptide was about 10-fold less potent than IGF-I. In addition, these peptides also stimulated the accumulation of pregnenolone and progesterone in the culture medium. Additional studies demonstrated specific binding of [125I]iodo-IGF-I to testicular cells. This binding was competed by IGF-related peptides with the potency order IGF-II = IGF-I greater than insulin whereas unrelated peptides did not compete. The cellular localization of these receptors was examined in testicular cells separated on a metrizamide density gradient. IGF-I receptors were evenly distributed between two cell peaks containing subpopulations of Leydig cells whereas much less binding was found in other testicular cell types. Coupled with recent findings indicating testicular production of IGF-I, the present results suggest that this peptide may act as a positive intratesticular modulator of Leydig cell differentiation.
Mol Cell Endocrinol 1987 Jul
PMID:Insulin-like growth factor-I augments gonadotropin-stimulated androgen biosynthesis by cultured rat testicular cells. 295 58

The in vitro secretion of immunoreactive somatomedin C/insulin-like growth factor I (IR Sm-C/IGF-I) by two human breast cancer cell lines, MCF-7 and EVSA-T has been studied. IR Sm-C/IGF-I concentration showed a linear increase in serum-free culture media over 72 h of incubation for both cell lines, and a close correlation with cell number (P less than 0.001). To characterize this immunoreactivity, a pool of conditioned media collected after 72 h of incubation was dialyzed overnight against 1 M acetic acid, lyophilized, and gel filtered on a Sephadex G-50 column. Fractions were determined for Sm-C/IGF-I content and for the presence of a specific carrier for Sm-C/IGF-I. Two peaks of Sm-C/IGF-I-like immunoreactivity were evidenced, the first in the high molecular weight region and the second corresponding to the molecular weight of the free peptide. The first peak evidenced also a specific binding ability for radioiodinated Sm-C/IGF-I, suggesting that the activity found in this region could be interpreted as interference of the specific free binding sites in the immunoassay. Analysis of this peak by polyacrylamide gel electrophoresis demonstrated the presence of a specific binding for Sm-C/IGF-I in a molecular weight range between 35,000 and 45,000 Da, which was not modified in reducing conditions. The binding activity was competitively inhibited by addition of cold Sm-C/IGF-I but not by insulin excess.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Cell Endocrinol 1987 Dec
PMID:Partial characterization of somatomedin C-like immunoreactivity secreted by breast cancer cells in vitro. 296 40

Erythroleukemia cells (K562) were found to bind insulin-like growth factor-II (IGF-II) about 10 times as much as IGF-I, insulin and human growth hormone. The specific binding of IGF-II increased as a function of cell number in a range of 0.5-6 X 10(6) cell/ml. Kinetic studies revealed that binding was time and temperature dependent and showed a broad pH optimum. Specificity studies showed no inhibition of 125I-IGF-II binding by insulin or unrelated peptide hormones. The half-maximal inhibition of 125I-IGF-II binding to K562 cells was achieved at 87 and 28 ng/ml of IGF-I and IGF-II respectively. However, the addition of 7.5 and 1.7 ng/ml of unlabeled IGF-I and IGF-II respectively increased the binding of 125I-IGF-II by 55%. This 'hook' effect was greatly reduced when K562 cell membranes were used. Scatchard analysis of IGF-II binding showed a comparable equilibrium constant with either intact cells (Ka = 8.9 X 10(8) M-1) or microsomal membranes (Ka = 5.4 X 10(8) M-1). Cross-linking studies indicated that both 125I-IGF-II and 125I-IGF-I bound to an entity of 215 kDa which increased to 260 kDa under reducing conditions. Both IGF-I and II stimulated 3H-thymidine incorporation into K562 cells whereas insulin was without effect. These data show that both IGF-I and II bind predominantly to a type II-IGF receptor in K562 cells. Since both peptides stimulate 3H-thymidine incorporation in these cells it is possible that the type II-IGF receptor is mediating an anabolic biological response in these cells.
Mol Cell Endocrinol 1988 Apr
PMID:Characterization of the insulin-like growth factor (IGF) receptor in K562 erythroleukemia cells; evidence for a biological function for the type II IGF receptor. 296 13

Fetal growth and development are dependent upon the growth and development of the placenta. Control of placental growth and development is little understood. Immunoreactive insulin-like growth factor-I and -II (IGF-I and IGF-II) have been shown to be released by human placental tissue and human placental membranes have been observed to contain specific receptors for these growth factors. Furthermore, we have demonstrated the presence of IGF-II mRNA transcripts in the developing human placenta and at gestational term in placentae of diabetics. Thus, the IGFs may have a regulatory role in the growth and development of the placenta via autocrine and/or paracrine mechanism(s) of action. In this report we demonstrate the presence of four differing size species of placental poly(A)+ RNA which specifically hybridize to an IGF-I probe originally isolated from an adult human liver cDNA library and localize IGF-I and IGF-II mRNA to syncytiotrophoblasts and fibroblasts, respectively, of the placenta by in situ hybridization. The major transcript is 7500 bases in size and the remaining three transcripts are 5000, 1100, and 900 bases in length with no apparent changes from these sizes throughout gestation and at term in diabetics. Quantification by densitometry of placental IGF-I mRNA detected by dot blot hybridization indicated that first and second trimester placentae each express more IGF-I mRNA relative to that expressed in placenta at term. These results suggest that there are developmental changes in the relative amount of IGF-I mRNA expressed in the human placenta. IGF-I is, therefore, most likely important early in gestation as a placental growth factor. This time period is critical for fetal development and growth, when embryonic induction, organogenesis, and rapid cell proliferation occur.
Mol Endocrinol 1988 Mar
PMID:Insulin-like growth factor-I messenger ribonucleic acid in the developing human placenta and in term placenta of diabetics. 339 51

The GH dependence of somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) and insulin like growth factor II (IGF-II) mRNAs was investigated by Northern blot hybridizations of polyadenylated RNAs from liver, pancreas, and brain of normal rats, untreated hypophysectomized rats, and hypophysectomized rats 4 h or 8 h after an ip injection of human GH (hGH). Using a 32P-labeled human Sm-C/IGF-I cDNA as probe, four Sm-C/IGF-I mRNAs of 7.5, 4.7, 1.7, and 1.2 kilobases (kb) were detected in rat liver and pancreas but were not detectable in brain. In both liver and pancreas, the abundance of these Sm-C/IGF-I mRNAs was 8- to 10-fold lower in hypophysectomized rats than in normal rats. Within 4 h after injection of hGH into hypophysectomized animals, the abundance of liver and pancreatic Sm-C/IGF-I mRNAs was restored to normal. A human IGF-II cDNA was used as a probe for rat IGF-II mRNAs which were found to be very low in abundance in rat liver and showed no evidence of regulation by GH status. In pancreas, IGF-II mRNA abundance was below the detection limit of the hybridization procedures. The brain contained two IGF-II mRNAs of 4.7 and 3.9 kb that were 5-fold lower in abundance in hypophysectomized rats than in normal rats. These brain IGF-II mRNAs were not, however, restored to normal abundance at 4 or 8 h after ip hGH injection into hypophysectomized animals. To investigate further, the effect of GH status on abundance of Sm-C/IGF-I and IGF-II mRNAs in rat brain, a second experiment was performed that differed from the first in that hypophysectomized rats were given an injection of hGH into the lateral ventricle (intracerebroventricular injection) and a rat Sm-C/IGF-I genomic probe was used to analyze Sm-C/IGF-I mRNAs. In this experiment, a 7.5 kb Sm-C/IGF-I mRNA was detected in brain polyadenylated RNAs. The abundance of the 7.5 kb mRNA was 4-fold lower in hypophysectomized rats than in normal rats and was increased to 80% of normal within 4 h after icv administration of hGH to hypophysectomized animals. As in the first experiment, the abundance of the 4.7 and 3.9 kb brain IGF-II mRNAs was lower than normal in hypophysectomized rats. Brain IGF-II mRNAs were increased to 50% of normal in hypophysectomized rats given an icv injection of hGH but within 8 h after the injection rather than at 4 h as with Sm-C/IGF-I mRNAs.
Mol Endocrinol 1987 Mar
PMID:Growth hormone dependence of somatomedin-C/insulin-like growth factor-I and insulin-like growth factor-II messenger ribonucleic acids. 345 90

We have reported the presence of insulin-related poly A+ RNA sequences in human placenta by RNA to DNA hybridization. In this study we have used a monoclonal antibody to somatomedin C/insulin-like growth factor I (Sm-C/IGF-I) to identify somatomedin-like proteins whose synthesis is directed by placental mRNA. Poly A+ RNA from first trimester and term placenta was translated in a cell-free system using micrococcal nuclease-treated reticulocyte-lysate and [35S]methionine as a label. From 2.0 X 10(6) cpm of specifically incorporated [35S]methionine labeled protein, an immunoprecipitate with an apparent molecular weight of 14,000 represented about 0.1% of total radioactivity in the translational products of poly A+ RNA of first trimester placenta. A less prominent band (0.006%) of the same apparent molecular weight was also evident from translational products of term placental mRNAs. This protein could be competed with either acromegalic serum or synthetic Sm-C/IGF-I when added prior to immunoprecipitation. Translational products synthesized from mRNA of term placenta showed a second labeled band of 24,000 daltons. This band was less effectively competed by acromegalic serum and not competed with either Sm-C/IGF-I or IGF-II and therefore its identity is uncertain. A protein similar to Sm-C/IGF-I is, therefore synthesized in first trimester placenta and to a lesser extent at term, suggesting developmental changes in Sm-C/IGF-I synthesis. Because Sm-C/IGF-I may act in a paracrine fashion, our findings suggest a role for Sm-C/IGF-I in growth of the placenta during early gestation.
Mol Biol Rep 1986
PMID:Synthesis of somatomedin C/insulin-like growth factor I by human placenta. 354 54

Insulin is able to stimulate a growth response in a variety of different cell types. However, the role of the insulin receptor in mediating this response is not clear. Indeed, it has been reported that the ability of insulin to stimulate a growth response is a result of its interaction with other growth factor receptors rather than the insulin receptor. We have previously reported that the H-35 hepatoma cell line responded to physiological concentrations of insulin as a growth factor and that the relative potency of proinsulin suggested that this response was mediated by the insulin receptor. In this report, two experimental approaches are used to demonstrate the involvement of the insulin receptor in mediating the growth response. Two different preparations of antibody to the insulin receptor are found to be capable of stimulating this response. In addition, the human insulin-like growth factors (IGF-I and II) show very low cross-reactivity with the insulin receptor and are significantly less potent than insulin in stimulating the growth response.
Mol Cell Biochem 1984
PMID:The role of the insulin receptor in mediating the insulin-stimulated growth response in Reuber H-35 cells. 614 51

Insulin-like growth factor II (IGF-II)-overexpressing NIH 3T3 cells were used to examine regulation of insulin-like growth factor binding protein (IGFBP) and mannose 6-phosphate (M6P)/IGF-II receptor expression. Ligand blot analysis of conditioned media indicated a predominant IGFBP of 26-28 kilodaltons the abundance of which is 3- to 10-fold higher in media of IGF-II-overexpressing cells. The IGFBP level in control cell medium was increased by incubation in the presence of IGF-II, IGF-I, and mutant IGF-II forms with reduced affinities for IGF-I or M6P/IGF-II receptors. Further proof that IGF-II regulated the IGFBP was obtained by incubation of IGF-II overexpressing cells in the presence of antisense IGF-II oligomers or anti-IGF-II antibodies, which resulted in significant reduction of the IGFBP in conditioned medium. Mouse IGFBP-6 mRNA expression was increased in IGF-II-overexpressing or IGF-II-treated control cells. The IGFBP contained O-linked carbohydrate residues and was recognized by an antiserum to rat IGFBP-6. To determine whether IGFs were influencing proteolytic degradation of IGFBPs, cell-free conditioned media were incubated at 37 C with recombinant human IGFBPs. At neutral pH proteolysis of IGFBP-5 occurred during incubation in conditioned media from control and IGF-II-overexpressing cells. Upon acidification of the medium samples, only the degradation of IGFBP-6 was prevented in IGF-II-overexpressing cell-conditioned medium.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1995 Jul
PMID:Regulation of insulin-like growth factor (IGF)-binding protein-6 and mannose 6-phosphate/IGF-II receptor expression in IGF-IL-overexpressing NIH 3T3 cells. 747 72


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