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

Previous studies have indicated that, in general, the insulin receptor gene is expressed at a level in cells reflecting the level of insulin receptors on the cellular surface. For instance, insulin-responsive tissues, such as hepatocytes, express high levels of both insulin receptor protein and mRNA relative to less responsive cells, such as fibroblasts. Moreover, in the cells of a patient (Minn1) with severe insulin resistance and very low levels of insulin receptors, it has been shown that insulin receptor gene transcripts are virtually undetectable. Our earlier studies of the insulin receptor gene promoter suggested that the differences in the steady state level of insulin receptor gene transcripts in different cells could be transcriptionally mediated. In this study we have attempted to assess the relative contribution of transcriptional and posttranscriptional mechanisms in determining steady state levels of insulin receptor mRNA in various cells, including Minn 1 fibroblasts. Using nuclear run-on assays, we have determined that the level of nascent insulin receptor gene transcripts is roughly equal in different cells, including Minn1 fibroblasts. Therefore, transcriptional differences do not seem to account for the dramatic differences in steady state levels of insulin receptor mRNA in different cells, and there is no evidence in support of a transcriptional defect in Minn1's insulin receptor gene alleles. However, the rate of insulin receptor mRNA turnover varies significantly in different cells, ranging from an mRNA half-life of as little as 2 h in fibroblast and IM9 (lymphocytic) cells up to 8 h in HepG2 (liver) cells, and accounts in part for the observed differences in steady state insulin receptor mRNA.(ABSTRACT TRUNCATED AT 250 WORDS)
Mol Endocrinol 1991 May
PMID:Posttranscriptional mechanisms account for differences in steady state levels of insulin receptor messenger RNA in different cells. 207 25

The human insulin receptor (hIR) is expressed in two variant forms that are generated by tissue-specific alternative splicing of the 11th exon of the IR gene. This leads to receptors that differ in their affinities for insulin based on the absence (hIR-A) or presence (hIR-B) of a 12-amino acid insert near the C-terminus of the alpha-subunit. To explore further the functional significance of the difference in these receptor subtypes, the properties of hIR-A(exon 11-) and hIR-B(exon 11+) receptors have been compared in parallel. Despite their different affinities for insulin, the receptor variants retain equivalent acid sensitivity for insulin binding and bind proinsulin with the same relative affinity. Both hIR-A and hIR-B are able to signal a variety of insulin's actions, but the insulin dose-response curves for receptor autophosphorylation and for mitogenesis and glycogen synthase stimulation in cells are shifted to the right for hIR-B receptors compared to hIR-A receptors. The magnitude of these rightward shifts, 1.5- to 3-fold in the assays listed above, are similar to and presumably accounted for by the 2-fold difference in insulin affinity exhibited by the receptor variants. Occupied hIR-A and hIR-B receptors undergo indistinguishable endocytotic itineraries after insulin binding. Both lead to insulin degradation that is quantitatively and kinetically similar, and both down-regulate when exposed to saturating insulin for 24 h. Thus, the functional consequences of the alternative splicing of IRs are limited to those related to the variants' differing affinities for insulin.
Mol Endocrinol 1991 May
PMID:Different ligand affinities of the two human insulin receptor splice variants are reflected in parallel changes in sensitivity for insulin action. 207 30

Homogeneous preparations of a protein phosphatase that is specific for phosphotyrosyl residues (protein tyrosine phosphatase [PTPase] 1B) were isolated from human placenta and microinjected into Xenopus oocytes. This resulted in an increase in activity of up to 10-fold over control levels, as measured in homogenates with use of an artificial substrate (reduced carboxamidomethylated and maleylated lysozyme). Microinjected PTPase was stable for at least 18 h. It is distributed within the oocyte in a manner similar to the endogenous activity and is suggestive of an interaction with cellular structures or molecules located predominantly in the animal hemisphere. The phosphatase markedly retarded (by up to 5 h) maturation induced by insulin. This, in conjunction with the demonstration that PTPase 1B abolished insulin stimulation of an S6 peptide (RRLSSLRA) kinase concomitant with a decrease in the phosphorylation of tyrosyl residues in a protein with the same apparent Mr as the beta subunit of the insulin and insulinlike growth factor 1 receptors (M. F. Cicirelli, N. K. Tonks, C. D. Diltz, E. H. Fischer, and E. G. Krebs, submitted for publication), provides further support for an essential role of protein tyrosine phosphorylation in insulin action. Furthermore, maturation was significantly retarded even when the PTPase was injected 2 to 4 h after exposure of the cells to insulin. PTPase 1B also retarded maturation induced by progesterone and maturation-promoting factor, which presumably do not act through the insulin receptor. These data point to a second site of action of the PTPase in the pathway of meiotic cell division, downstream of the insulin receptor and following the appearance of active maturation-promoting factor.
Mol Cell Biol 1990 Feb
PMID:Effect of microinjection of a low-Mr human placenta protein tyrosine phosphatase on induction of meiotic cell division in Xenopus oocytes. 215 16

The enhanced phosphorylations via cAMP, Ca2+ mobilization, and diacyl glycerol formation via the activation of the respective kinases is now classical. The decreased phosphorylation via inhibition of adenylate cyclase via the alpha adrenergic receptor is also becoming understood. What the insulin studies on the control of glycogen synthesis have taught us is that the rate limiting enzyme glycogen synthase is regulated by multiple covalent phosphorylation in an elegant but complex manner. The overall pattern of dephosphorylation is influenced by effecting both phosphatase and kinase activities in a set of interrelated mechanisms. In the presence of glucose, in muscle, fat, and liver under physiological conditions G-6-P acts as a signal to stimulate the phosphatase. An additional stimulation could occur via a novel insulin phosphatase stimulatory mediator. The phosphatase is also stimulated by at least three covalent mechanisms involving altered phosphorylation state. In one there is a decreased phosphorylation of the phosphatase inhibitor 1 potentially related to decreased cAMP-dependent protein kinase activity. In the second, there is decreased phosphorylation of the deinhibitor also potentially related to decreased cAMP-dependent protein kinase phosphorylation. In the third, an increased activity of casein kinase 2 could activate the ATP-Mg dependent phosphatase by an increased phosphorylation of phosphatase inhibitor 2 (modulatory subunit). In the liver, allosteric control of the phosphatase by G-6-P and nucleotides is of great importance. Insulin also stimulates the phosphatase in long-term experiments via increased protein synthesis. It is clear that future work will be required to determine which species of the various classes of phosphatases are regulated in short-term and long-term regulation by insulin. In terms of kinases, the effects of insulin to inactivate and desensitize the cAMP-dependent protein kinase are established. The molecular mechanisms of this effect remain to be worked out. The enhanced activity of MAP and S-6 kinase would appear to be part of a cascade of reactions perhaps originating in the autophosphorylation and activation of the insulin receptor tyrosine kinase. The mechanism of the short-term activation of casein kinase 2 remains to be elucidated. A cAMP-dependent protein kinase inhibitory mediator, which also inhibits adenylate cyclase is an important element in the regulation of kinase and adenylate cyclase activity by insulin. Its physiological significance must be established in the future, in terms of its control of glycogen synthase activation by insulin. Clearly this kinase inhibitor as well as the phosphatase stimulator are potential regulators of glycogen synthase activity by insulin.
Adv Enzymol Relat Areas Mol Biol 1990
PMID:Insulin and the stimulation of glycogen synthesis. The road from glycogen structure to glycogen synthase to cyclic AMP-dependent protein kinase to insulin mediators. 215 10

BC3H-1 mouse muscle cells in culture were employed to study the mechanisms which regulate insulin receptor gene expression during differentiation. When BC3H-1 myoblasts were plated in low serum media (1% fetal bovine serum), cell division ceased. Within 1 week cells had the morphological features of myocytes and expressed muscle specific proteins such as creatine phosphokinase and the nicotinic acetylcholine receptor. It is known that following incubation in low serum media, the steady state mRNA levels for the key muscle transcription factor, myogenin are increased. Exposure of BC3H-1 cells to a 20-base myogenin antisense oligomer blocked morphological differentiation, and resulted in nearly complete inhibition of the expression of the acetylcholine receptor but not the insulin receptor(IR). In order to study further the relationship between differentiation and IR gene expression, fibroblast growth factor (FGF), a known inhibitor of myogenic differentiation, was employed. FGF treatment inhibited the transcription of both myogenin and the acetylcholine receptor. However FGF did not inhibit the transcription of the IR. These studies indicate therefore that IR transcription increases during muscle cell differentiation, and suggest that during differentiation the control of IR gene expression differs from the control of muscle specific proteins.
Mol Endocrinol 1990 Jun
PMID:Differential effects of fibroblast growth factor on insulin receptor and muscle specific protein gene expression in BC3H-1 myocytes. 217 94

Insulin internalization and degradation, insulin receptor internalization and recycling, as well as long term receptor down-regulation were comparatively studied in Chinese hamster ovary (CHO) cell lines, either parental or expressing the wild-type human insulin receptor (CHO.R) or a mutated receptor in which the tyrosine residues in positions 1162 and 1163 were replaced by phenylalanines (CHO.Y2). The two transfected cell lines presented very similar binding characteristics, and their pulse labeling with [35S]methionine revealed that the receptors were processed normally. As expected, the mutation of these twin tyrosines resulted in a defective insulin stimulation of both receptor kinase activity and glycogen synthesis. We now present evidence that compared to CHO.R cells, which efficiently internalized and degraded insulin, CHO.Y2 cells exhibited a marked defect in hormone internalization, leading to impaired insulin degradation. Moreover, the mutated receptors were found to be less effective than the wild-type receptors in transducing the hormone signal for receptor internalization, whereas the process of receptor recycling after internalization seemed not to be altered. In parental CHO cells, insulin induced long term receptor down-regulation, but was totally ineffective in both transfected cell lines. These results reveal that the tyrosines 1162 and 1163 in the kinase regulatory domain of the receptor beta-subunit play a pivotal role in insulin and receptor internalization.
Mol Endocrinol 1990 Feb
PMID:Mutation of tyrosine residues 1162 and 1163 of the insulin receptor affects hormone and receptor internalization. 218 49

Structure-function studies of the insulin molecule indicate that an insulin B chain domain comprising residues 22-26 is involved both in binding to the insulin receptor (INSR) and in insulin dimer formation, suggesting that this domain might also interact with a structure resembling the insulin dimer interface in the INSR. Expression of a mutant INSR cDNA with a deletion of the region corresponding to exon 2 of the INSR gene produces a protein devoid of insulin-binding activity, although the mutant protein is processed appropriately to alpha- and beta-subunits, suggesting that the insulin-binding domain is encoded at least in part by exon 2. Within this region of the INSR molecule, the sequence 83-103 fulfills the structural criteria for a dimer interface. Studies of mutant INSRs with substitutions for phenylalanine 88 or 89 show that the presence of phenylalanine at position 89 is essential for full binding affinity.
Mol Endocrinol 1990 Mar
PMID:Identification of a ligand-binding region of the human insulin receptor encoded by the second exon of the gene. 218 17

The insulin receptor plays a critical role in the maintenance of glucose homeostasis. Regulation of this key function must be under stringent controls. In order to study the regulation of insulin receptor gene expression, we have cloned, sequenced and characterized its promoter. The first exon of the insulin receptor gene is embedded in an unusual segment of DNA composed of Alu repeats. The promoter has the characteristics typical of a housekeeping gene. It is GC-rich and has multiple start sites of transcription. A 574 base pair fragment immediately upstream of the translation initiation site contains promoter activity when transfected into eukaryotic cell lines. Deletion analysis was performed to study promoter function. These studies showed that only 150 base pairs of promoter sequence were necessary for promoter function. This region contains three potential binding sites for the transcription factor, Sp1 and a TC box sequence. Furthermore, the fragment functions equally well in either orientation. We have defined an element in this region with enhancer function for both its homologous and a heterologous promoter. In addition, this region seems to contribute some degree of tissue specificity to insulin receptor gene expression.
Mol Endocrinol 1990 Apr
PMID:Structural and functional analysis of the insulin receptor promoter. 228 Jul 79

Insulin and phorbol esters rapidly induce the transcription and cytoplasmic accumulation of a specific mRNA (p33) in rat hepatoma cells. We have studied the effects of insulin desensitization on the regulation of p33 gene expression by insulin and phorbol esters. Insulin desensitization is associated with down-regulation of the insulin receptor and post-receptor defects. When cells were treated with insulin (5 x 10(-7) M) for 24 h, a greater than 50% reduction in insulin binding was observed and insulin's stimulation of p33 transcription and cytoplasmic mRNA levels was prevented. The induction of p33 gene transcription and mRNA levels by phorbol esters was also decreased. Beta-tubulin gene expression was unaffected by insulin or phorbol esters and the stimulatory effect of dexamethasone on p33 gene expression was not impaired. Since insulin desensitization impaired phorbol esters' induction of p33 gene expression, one intracellular defect in insulin-desensitized cells may include an alteration in protein kinase C-dependent events.
Mol Cell Endocrinol 1990 Aug 20
PMID:Decreased induction of an hepatic mRNA by phorbol esters after insulin desensitization. 228 74

The structure and the regulatory mechanisms of insulin gene expression as well as the structure of the 5'-regulatory region of its gene are reviewed. Protein binding sites of the 5'-enhancer area of the insulin gene were identified by methods of site mutation, footprinting and competitive amplification in several papers. Diabetes induced by site mutation of the insulin gene is considered. Some viruses and viral proteins suppress the regulatory region of the insulin gene and induce diabetes symptoms. Transgenic animals carrying the natural human insulin gene together with the 5'-regulatory sequence in their genome show elevated human insulin and C-peptide secretion in response to high blood glucose concentration. The insulin receptor gene structure and mechanisms of insulin receptor functioning are discussed.
Mol Biol (Mosk)
PMID:[Recombinant DNA in the study of diabetes mellitus]. 229 Apr 17


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