The human insulin receptor cDNA: the structural basis for hormone-activated transmembrane signalling

Developmental biochemistry of cottonseed embryogenesis and germination XVIII cDNA and amino acid sequences of members of the storage protein families

We have sequenced cDNA clones representing each of the three distinct groups of storage proteins of the cotton seed. Characteristics of their mRNAs and derived proteins are given. Dot matrix analysis of the nucleotide and amino acid sequences shows that 2 of these groups of proteins have a great deal of vestigial homology at low stringency and should be considered subfamilies of a single storage protein gene family. The remaining group is quite distinct and should be considered a separate multigene family. It also can be divived into 2 subfamilies based on the presence or absence of glycosyl residues and other sequence differences.These proteins are processed to smaller species during embryogenesis, and all of the mature storage proteins of cotton can be traced back to these 2 gene families.In view of these relationships we propose that these 2 families be called the α and β globulins of cotton storage proteins, each comprised of an A and B subfamily.

Linking functional domains of the human insulin receptor with the bacterial aspartate receptor

A hybrid receptor has been constructed that is composed of the extracellular domain of the human insulin receptor fused to the transmembrane and cytoplasmic domains of the bacterial aspartate chemoreceptor. This hybrid protein can be expressed in rodent (CHO) cells and displays several functional features comparable to wild-type insulin receptor. It is localized to the cell surface, binds insulin with high affinity, forms oligomers, and is recognized by conformation-specific monoclonal antibodies. Although most of the expressed protein accumulates as a 180-kDa proreceptor, some processed 135-kDa receptor can be detected on the cell surface by covalent cross-linking. Expression of the hybrid receptor inhibits the insulin-activated uptake of 2-deoxyglucose by CHO cells. Thus, this hybrid is partially functional and can be processed; however, it is incapable of native transmembrane signaling. The results indicate that the intact domains of different types of receptors can retain some of the native features in a hybrid molecule but specific requirements will need to be satisfied for transmembrane signaling.

Differential sensitivity of two functions of the insulin receptor to the associated proteolysis: kinase action and hormone binding

Since we observed that after purification the receptor kinase activity is rapidly lost under conditions where insulin binding function seems to be preserved, we have studied the cause(s) of receptor kinase inactivation. Highly purified placental insulin receptor preparations were analyzed by NaDodSO4/PAGE followed by silver staining or immunostaining using domain-specific antibodies raised against synthetic peptides corresponding to the amino acid sequences of the beta subunit. These studies revealed the intact 90-kDa beta subunit is degraded first to an 88-kDa form and then to a 50-kDa beta 1-subunit form by proteolysis even after purification when stored at 4 degrees C. The 88-kDa beta subunit, which lacks the carboxyl-terminal approximately equal to 2-kDa portion exhibits almost no autophosphorylation activity, nor does insulin stimulate autophosphorylation. The loss of kinase activity as measured by phosphorylation of the src-related peptide is correlated with the loss of the intact 90-kDa beta subunit. Degradation of the beta subunit to the 50-kDa form seems to be facilitated by the removal of the approximately equal to 2-kDa peptide. Present studies thus suggest that only the intact form of the beta subunit has full kinase activity in an insulin-dependent manner and that other forms, such as the 88-kDa beta subunit show little kinase activity. The inactivation appears to arise from a conformational change of the 90-kDa form, which makes it susceptible to proteolysis at the carboxyl-terminal end. These results imply that the carboxyl-terminal of the beta subunit is important for the manifestation of the tyrosine kinase activity of the insulin receptor.

Alternative splicing of RNAs transcribed from the human abl gene and from the bcr-abl fused gene

The primary structure of normal abl protein was determined by sequencing the coding region of its cDNA. abl contains two alternative 5' exons spliced to a common set of 3' exons to yield the two major abl RNA transcripts. These transcripts initiate in different promoter regions and give rise to proteins that vary in their N-termini. In the human cell line K562, abl is translocated from chromosome 9 to within the bcr gene on chromosome 22. Within the fused bcr-abl gene, abl exon II alternatively splices to two adjacent bcr exons. This phenomenon is seen in many patients with chronic myeloid leukemia.

Nucleotide sequence and expression in vitro of cDNA derived from mRNA of int-1, a provirally activated mouse mammary oncogene

The mouse int-1 gene is a putative mammary oncogene discovered as a target for transcriptionally activating proviral insertion mutations in mammary carcinomas induced by the mouse mammary tumor virus in C3H mice. We have isolated molecular clones of full- or nearly full-length cDNA transcribed from int-1 RNA (2.6 kilobases) in a virus-induced mammary tumor. Comparison of the nucleotide sequence of the cDNA clones with that of the int-1 gene (A. van Ooyen and R. Nusse, Cell 39:233-240, 1984) shows the following. The coding region of the int-1 gene is composed of four exons. The splice donor and acceptor sites conform to consensus; however, at least two closely spaced polyadenylation sites are used, and the transcriptional initiation site remains ambiguous. The major open reading frame is preceded by an open frame 10 codons in length. The mRNA encodes a 41-kilodalton protein with several striking features--a strongly hydrophobic amino terminus, a cysteine-rich carboxy terminus, and four potential glycosylation sites. There are no differences in nucleotide sequence between the known exons of the normal and a provirally activated allele. The length of the deduced open reading frame was further confirmed by in vitro translation of RNA transcribed from the cDNA clones with SP6 RNA polymerase.

Alternative 5' exons and tissue-specific expression of the Drosophila EGF receptor homolog transcripts

cDNA clones of the Drosophila epidermal growth factor receptor homolog (DER) gene were isolated and sequenced. The deduced amino acid sequence shows a similar degree of homology to the human epidermal growth factor receptor and to the rat and human neu proteins; the most striking difference is the addition of a third cysteine-rich extracellular domain in DER. The structure of the cDNA indicates the use of alternative 5' exons. Thus, the gene encodes three putative proteins differing at their N termini. The distribution of DER transcripts was analyzed by in situ hybridization. Transcripts are uniformly distributed in embryos, larval transcripts are primarily localized to proliferating tissues of the imaginal discs and brain cortex, and adult transcripts are detected mainly in the brain and ganglia. All three splicing alternatives show similar tissue distribution during development.

The human c-ros gene (ROS) is located at chromosome region 6q16----6q22

The human homolog, c-ros, of the transforming gene, v-ros, of the avian sarcoma virus, UR2, has been isolated from a human genomic library. A single-copy fragment from the human c-ros genomic clone has been used to map the human c-ros homolog (ROS) to human chromosome region 6q16----6q22 by somatic cell hybrid analysis and chromosomal in situ hybridization. Thus, the c-ros gene joins the c-myb oncogene, which is distal to the c-ros gene on the long arm of human chromosome 6, as a candidate for involvement in chromosome 6q deletions and rearrangements seen in various malignancies.

Purification and autophosphorylation of insulin receptors from rat skeletal muscle

Insulin receptors of rat skeletal muscle were purified by first extracting a plasma membrane-enriched pellet obtained from a muscle homogenate with Triton X-100, followed by WGA-Sepharose and insulin-Sepharose affinity chromatography. Routinely, 4-5 micrograms of purified receptor were obtained from 15 g of tissue. The purified receptors are composed of two major polypeptides with molecular weights of 130,000 and 95,000, respectively. The binding of [125I]insulin by the purified receptors was analyzed by a Scatchard plot. There are at least two binding components. The high-affinity component, with an apparent association constant (Ka) of 2.0 X 10(9) M-1, comprises 10% of the total insulin binding sites; while the low-affinity component, with a Ka value of 1.4 X 10(8) M-1, represents 90% of the binding sites. Assuming the insulin receptor to have a molecular weight of 300,000, the receptor binds 1.7 mol of insulin per mol at saturation. Insulin is capable of stimulating the autophosphorylation of the beta-subunit of the muscle insulin receptor (Mr 95,000) by 5-10-fold. The stoichiometry of this phosphorylation reaction was determined as 0.8 phosphate per insulin binding site after a 10 min incubation with 100 nM insulin. In a previous report, I showed that the insulin stimulation of glucose transport in diaphragms from neonatal rats was small, even although the diaphragms had normal levels of insulin receptors and glucose transporters (Wang, C. (1985). Proc. Natl. Acad. Sci. USA 82, 3621-3625). To determine whether or not receptor autophosphorylation might be related to this insensitivity to insulin, the level of receptor phosphorylation was quantitated in diaphragms from rats at different stages of development. Autophosphorylation remains unchanged from birth to 21 days of age, suggesting that the lower insulin-stimulated glucose uptake by diaphragms at early stages of postnatal development as compared to that by diaphragms of older rats, is not due to a difference in receptor kinase.

Characterization of affinity-purified type I insulin-like growth factor receptor from human placenta

The binding affinities of type I IGF receptor, purified to near homogeneity from human placental membranes, were characterized. For this receptor preparation, free of type II IGF receptor and essentially free of insulin receptor, dissociation constants of Kd = 0.05 nM for IGF I and of Kd = 0.2 nM for IGF II (linear Scatchard plots) were determined. Competitive binding studies indicated a cross-reactivity of approximately 40% for IGF II to the type I IGF receptor.

Human c-ros-1 gene homologous to the v-ros sequence of UR2 sarcoma virus encodes for a transmembrane receptorlike molecule

We isolated a human gene (designated c-ros-1) homologous to the v-ros sequence of UR2 sarcoma virus. Ten exons, 1,414 base pairs spanning 26 kilobases, contained a tyrosine kinase domain, a transmembrane domain, and a part of an extracellular domain carrying an N glycosylation site which was not acquired by UR2 sarcoma virus. The predicted structure of c-ros-1 is unique among the src family and clearly distinct from the human insulin receptor.

Structure and function of the interleukin 2 receptor: affinity conversion model

We cloned cDNAs of the human and mouse IL-2 receptors. Comparison of their structures allowed us to identify several conserved regions localized to exons 2 and 4, the cytoplasmic portion and the transmembrane portion. These regions might be important for the functions of the IL-2 receptor. The human IL-2 receptor, which was expressed on an IL-2-dependent murine T-cell line, CTLL-2, by cDNA transfection, was shown to be functionally active by blocking the endogenous mouse IL-2 receptor with monoclonal antibodies. On the other hand, the human IL-2 receptors expressed on non-lymphoid cells were functionally inactive. They were unable to mediate the growth signal, were of low affinity species and aberrant in internalization. We postulated that the dysfunction of the IL-2 receptors in non-lymphoid cells would be due to the absence of the putative converter protein which is expressed specifically in lymphoid cells. Since the human IL-2 receptor is active in the murine T cell, the converter may interact with the receptor at the portions conserved between man and mouse. We proposed the affinity conversion model that explained the high affinity state of the receptor by the ternary complex formation between IL-2, the IL-2 receptor and the converter.

Crystals of the Chlamydomonas reinhardtii cell wall: polymerization, depolymerization, and purification of glycoprotein monomers

Two of the three major outer layers of the Chlamydomonas reinhardtii cell wall (W6 and W4) can be solubilized from living cells with sodium perchlorate or other chaotropes and will repolymerize in vitro to form milligram amounts of wall crystals. Conditions for optimal crystalization are presented, and conditions that fail to induce polymerization are exploited to maintain monomers in aqueous solution for ion-exchange chromatography. The four major glycoproteins of the complex (GP1, 1.5, 2, and 3) have in this way been purified to apparent homogeneity and have been characterized morphologically by transmission electron microscopy using the quick-freeze, deep-etch technique and by amino acid composition. Three of the four are hydroxyproline-rich species that copolymerize to form the W6 layer. The fourth (GP1.5) is a glycine-rich species that binds to the interior of the in vitro crystal; it is apparently equivalent to the granules within the W4 layer in situ.

Cloning and expression of cDNA for anti-müllerian hormone

Messenger RNA, prepared from fetal bovine testicular tissue, was used to construct a cDNA library in lambda gt11 phage. The library was screened with an antibody probe directed against bovine anti-Müllerian hormone and three positive clones were isolated. Cross-hybridizing cDNA inserts carried by clones 4 and 5 (1.2 and 0.08 kilobases long, respectively) code for a fragment of authentic anti-Müllerian hormone, as shown by the ability of the anti-epitope antibodies eluted from fusion protein 4 to bind strongly to anti-Müllerian hormone on immunoblots and by the capacity of anti-epitope antibodies 4 and 5 to precipitate radioiodinated bovine anti-Müllerian hormone. A probe prepared from insert 4 hybridizes with an mRNA present only in tissues that are known producers of anti-Müllerian hormone, such as the fetal testis and adult ovarian follicles. The amount of specific mRNA in tissues of males and females is related to the rate of their anti-Müllerian hormone production. The 2.1-kilobase size of this mRNA species is large enough to code for the Mr 62,000 anti-Müllerian hormone polypeptide chain. Insert 4 also hybridizes with an mRNA of similar size in human and rat fetal testicular tissue. The third isolated clone, clone 8, which does not cross-hybridize with the others, carries a cDNA insert coding for a ubiquitous protein, smaller than anti-Müllerian hormone, with which it apparently shares an epitope.

Structure of integrin, a glycoprotein involved in the transmembrane linkage between fibronectin and actin

We describe the isolation, characterization, and sequence of cDNA clones encoding one subunit of the complex of membrane glycoproteins that forms part of the transmembrane connection between the extracellular matrix and the cytoskeleton. The cDNA sequence encodes a polypeptide of 89 kd that has features strongly suggesting the presence of a large N-terminal extracellular domain, a single transmembrane segment, and a small C-terminal cytoplasmic domain. The extracellular domain contains a threefold repeat of a novel 40 residue cysteine-rich segment, and the cytoplasmic domain contains a tyrosine residue that is a potential site for phosphorylation by tyrosine kinases. We propose the name integrin for this protein complex to denote its role as an integral membrane complex involved in the transmembrane association between the extracellular matrix and the cytoskeleton.

Antibodies to the ATP-binding site of the human epidermal growth factor (EGF) receptor as specific inhibitors of EGF-stimulated protein-tyrosine kinase activity

A region of the primary amino acid sequence of the epidermal growth factor receptor (EGF) protein-tyrosine kinase, which is involved in ATP binding, was identified using chemical modification and immunological techniques. EGF receptor was 14C-labelled with the ATP analogue 5'-p-fluorosulphonylbenzoyladenosine and from a tryptic digest a single radiolabelled peptide was isolated. The amino acid sequence was determined to be residues 716-724 and hence lysine residue 721 is located within the ATP-binding site. Antisera were elicited in rabbits to a synthetic peptide identical to residues 716-727 of the EGF receptor and the homologous sequence in v-erb B transforming protein from avian erythroblastosis virus. The affinity-purified antibodies precipitated human ECF receptor from A431 cells and placenta, and the v-erb B protein from erythroblasts. The antibodies inhibited EGF-stimulated receptor protein-tyrosine kinase autophosphorylation and phosphorylation of an exogenous peptide substrate containing tyrosine. The antibodies did not immunoprecipitate the transforming proteins pp60v-src or P120gag-abl or cAMP-dependent protein kinase, proteins which have homologous but not identical sequences surrounding the lysine residue within the ATP-binding site, nor did they react with the platelet-derived growth factor receptor. The antibodies had no effect on the kinase activity of purified v-abl protein in solution. The antibodies may therefore be a specific inhibitor of the tyrosine kinase of the EGF receptor.

Mechanisms of receptor-mediated transmembrane signalling

Although this paper has dealt with general mechanisms whereby a hormonal signal is transmitted across the cell membrane, advances in work with a number of receptors should permit a precision of description of these mechanisms that would have delighted both Langley and Ehrlich. For instance, the detailed sequences now known for the separate subunits of the nicotinic cholinergic receptor and the cellular manipulations made possible by the cloning of the separate subunit genes will make it possible to determine the precise receptor sequence involved either in acetylcholine binding or in ion channel function. The complete sequences and biochemical properties now known for the insulin and EGF-URO receptors to be dealt with in part by a subsequent article (van Obberghen and Gammeltoft, this series) should lay the groundwork for elucidating the transmembrane signalling mechanisms used by the kinase family of growth factor receptors. Continuing work on the structure of the beta-adrenergic receptor, and on the interaction of such receptors with guanine nucleotide regulatory complexes and on the detailed properties of the family of so-called G-proteins and their associated regulatory subunits should unravel the details for a variety of transmembrane signalling reactions. Thus, at least for three basic transmembrane signalling mechanisms: ligand modulated ion transport; ligand-modulated receptor enzyme activity (e.g. tyrosine kinase); and ligand-modulated liberation of cryptic mediators (like the alpha- and beta-subunits of the guanine nucleotide regulatory complexes) one can look forward with excitement to the elucidation in the not-too-distant future of a number of specific biochemical reaction pathways that lead to cell activation.

Insulin receptors: structure and function

The recent characterization of the human insulin receptor structure and its intrinsic tyrosine kinase activity represent major advances in our understanding of the mechanism of insulin action. It is reasonable to think that the insulin-induced autophosphorylation and activation of its receptor kinase represent an important event in the action of insulin on cell metabolism and growth. The fundamental research reviewed may be followed by the discovery of molecular receptor defects in clinical syndromes of insulin resistance.

Mutations specifically affecting ligand interaction of the Trg chemosensory transducer

The Trg transducer mediates chemotactic response to galactose and ribose by interacting, respectively, with sugar-occupied galactose- and ribose-binding proteins. Adaptation is linked to methylation of specific glutamyl residues of the Trg protein. This study characterized two trg mutations that affect interaction with binding protein ligands but do not affect methylation or adaptation. The mutant phenotypes indicated that the steady-state activity of methyl-accepting sites is independent of ligand-binding activity. The mutation trg-8 changed arginine 85 to histidine, and trg-19 changed glycine 151 to aspartate. The locations of the mutational changes provided direct evidence for functioning of the amino-terminal domain of Trg in ligand recognition. Cross-inhibition of tactic sensitivity by the two Trg-linked attractants implies competition for a common site on Trg. However, the single amino acid substitution caused by trg-19 greatly reduced the response to galactose but left unperturbed the response to ribose. Thus Trg must recognize the two sugar-binding proteins at nonidentical sites, and the complementary sites on the respective binding proteins should differ. trg-8 mutants were substantially defective in the response to both galactose and ribose. An increase in cellular content of Trg-8 protein improved the response to galactose but not to ribose. It appears that Trg-8 protein is defective in the generation of the putative conformational change induced by ligand interaction. The asymmetry of the mutational defect implies that functional separation of interaction sites could persist beyond the initial stage of ligand binding.

Insulin receptors of chicken liver and brain. Characterization of alpha and beta subunit properties

Receptors on membranes of chicken liver and brain bound porcine 125I-insulin in a specific and temperature-dependent manner. Competition with unlabeled insulin derivatives exhibited typical insulin potency ratios, i.e. chicken greater than porcine insulin greater than human proinsulin (2.1/1/0.02). Apparent binding affinity was higher in brain with a 50% inhibition of tracer binding of 1.3 +/- 0.2 nM porcine insulin as compared to 2.8 +/- 0.3 nM in liver. The apparent molecular mass of the 125I-insulin cross-linked alpha subunit of the insulin receptor was 139 +/- 2 kDa for chicken liver and 127 +/- 2 kDa for chicken brain. These molecular masses were similar to those of rat liver and brain insulin receptors. Neuraminidase treatment of the cross-linked insulin receptor increased the mobility of the alpha subunit from liver but did not affect that from brain, suggesting a difference in the glycosylation of the chicken brain alpha subunit as previously described in the rat. Despite this change, both receptors could be purified on wheat germ agglutinin (WGA) chromatography after Triton solubilization. In the presence of CTP and vanadate (phosphatase inhibitors) insulin-stimulatable tyrosine-specific phosphorylation of exogenous substrates was demonstrated with chicken liver and brain receptors. The reaction was dependent on Mg2+ and Mn2+. As noted with other insulin receptors, the best artificial substrate for phosphorylation was poly(Glu,Tyr)4:1. In both chicken liver and brain the smallest effective insulin dose as well as maximal stimulation of phosphorylation of the substrate was similar to that seen with rat liver, and in all three tissues chicken insulin was more potent than porcine insulin. In chicken liver an active ATP hydrolytic activity copurified with the insulin receptors during WGA chromatography. Further purification using S-300 Sephacryl filtration or affinity (insulin-biotin-avidin) chromatography could dissociate the phosphorylation and the hydrolytic activities. Gel electrophoresis, under reducing conditions revealed beta subunits with apparent Mr of 97-99 kDa in chicken liver and brain, which were phosphorylated in the presence of insulin. Similar apparent molecular masses have been described for the beta subunit of rat liver receptors. These studies suggest that both chicken brain and liver insulin receptors exhibit coupling of alpha and beta subunits with fully active tyrosine kinase and that the structural difference of the brain insulin receptor is widespread and phylogenetically old.

Multiple restriction fragment length polymorphisms at the insulin receptor locus: a highly informative marker for linkage analysis

Although resistance to insulin action is a well-studied phenomenon in non-insulin-dependent diabetes and certain genetic syndromes, the role of inherited defects of the insulin receptor in these disorders is unknown. To facilitate the evaluation of that role, restriction fragment length polymorphisms (RFLPs) were identified using various portions of the insulin receptor cDNA to examine digested DNA from American Blacks, Pima Indians, and Caucasians. Five RFLPs were identified in Caucasians. Two of these were detected with a single 1.3-kilobase probe in Rsa I digests with minor allele frequencies of 0.48 and 0.23. An additional RFLP was noted with Bgl II and two more RFLPs with Sac I using a different 1.6-kilobase probe, with minor allele frequencies of 0.17 for Bgl II and 0.12 for both Sac I RFLPs. All RFLPs except for the second Sac I RFLP were present in American Blacks, while only the Rsa I RFLPs were present in Pima Indians. Pairwise analysis showed random association between all sites except for the Bgl II and second Rsa I sites, where the disequilibrium statistic, delta, was -0.70 (different from 0 at P less than 0.001). No association of any RFLP was noted with non-insulin-dependent diabetes in a small population. These studies show that this is a highly informative locus that should be important for mapping of chromosome 19p and for linkage studies.

Isolation of a Drosophila genomic sequence homologous to the kinase domain of the human insulin receptor and detection of the phosphorylated Drosophila receptor with an anti-peptide antibody

A Drosophila genomic fragment has been isolated with a deduced amino acid sequence that is strikingly homologous to that of the kinase domain of the human insulin receptor. The Drosophila DNA hybridizes with an 11-kilobase mRNA that is most prominent in 8- to 12-hr embryos. An anti-peptide antibody prepared to a sequence in the human insulin receptor kinase domain that is conserved in the Drosophila sequence immunoprecipitates a single 95-kDa Drosophila protein whose phosphorylation on tyrosine residues is dependent on insulin. We conclude that the DNA sequence is that of the kinase domain of the Drosophila insulin receptor and that the 95-kDa phosphoprotein is the autophosphorylated beta subunit of that receptor. The results are compatible with our previous reports demonstrating a specific insulin-binding Drosophila glycoprotein and an insulin-dependent tyrosine protein kinase whose activity is greatest during embryogenesis. The observations suggest a role for insulin-dependent protein tyrosine phosphorylation during embryogenesis.

Replacement of insulin receptor tyrosine residues 1162 and 1163 compromises insulin-stimulated kinase activity and uptake of 2-deoxyglucose

Insulin stimulates the autophosphorylation of tyrosine residues of the beta subunit of the insulin receptor (IR); this modified insulin-independent kinase has increased activity toward exogenous substrates in vitro. We show here that replacement of one or both of the twin tyrosines (residues 1162 and 1163) with phenylalanine results in a dramatic reduction in or loss of insulin-activated autophosphorylation and kinase activity in vitro. In vivo, these mutations not only result in a substantial decrease in insulin-stimulated IR autophosphorylation but also in a parallel decrease in the insulin-activated uptake of 2-deoxyglucose. Furthermore, a truncated IR protein (lacking the last 112 amino acids) has an unstable beta subunit; this mutant has no kinase activity in vitro or in vivo and does not mediate insulin-stimulated uptake of 2-deoxyglucose. IR autophosphorylation is thus implicated in the regulation of IR activities, with tyrosines 1162 and 1163 as major sites of this regulation.

An atypical insulin receptor with high affinity for insulin-like growth factors copurified with placental insulin receptors

Insulin receptors purified from human placenta by sequential affinity chromatography on wheat germ lectin-agarose and insulin coupled to 1,1'-carbonyldiimidazole-activated agarose (CDI-agarose) retained full binding activity but bound a greater than predicted amount of 125I-labeled insulin-like growth factor I (IGF-I). IGF-I and multiplication-stimulating activity (MSA; the rat homologue of IGF-II) were equipotent in displacing either 125I-labeled IGF-I or 125I-labeled MSA from the purified receptors; insulin was 5-15 times more potent. Competitive binding studies indicated that this IGF binding activity could not be explained by cross-reaction with classical insulin receptors or by coelution of IGF-I or IGF-II receptors. Instead, it was due to a minor population of discrete atypical insulin receptors (6-18% total insulin receptors) with moderately high affinity (Kd = 2-4 X 10(-9) M) for IGF-I and MSA. These receptors were not an artifact of insulin-CDI-agarose chromatography, since they were present in wheat germ lectin-agarose-purified preparations and could also be purified from insulin-succinyldiaminodipropylamino-agarose. Affinity labeling with 125I-labeled MSA revealed that these atypical receptors had the same binding subunit (Mr 140,000) as classical insulin and IGF-I receptors. They displayed intermediate reactivity with polyclonal and monoclonal antibodies to the insulin and IGF-I receptors. It is therefore likely that insulin receptors purified by immunoadsorption would also contain atypical insulin receptors. The finding of more than one type of insulin receptor might relate to the slight variations in the cDNA nucleotide sequences and the multiple mRNA species reported for the insulin receptor [Ebina, Y., Ellis, L., Jarnagin, K., Edery, M., Graf, L., Clauser, E., Ou, J.-H., Masiarz, F., Kan, Y. W., Goldfine, I. D., Roth, R. A. & Rutter, W. J. (1985) Cell 40, 747-758].

Proto-oncogene c-ros codes for a molecule with structural features common to those of growth factor receptors and displays tissue specific and developmentally regulated expression

A recombinant DNA clone containing cellular sequences homologous to the transforming sequence, v-ros, of avian sarcoma virus UR2 was isolated from a chicken genomic DNA library. Heteroduplex mapping and nucleotide sequencing reveal that the v-ros sequences are distributed in nine exons ranging from 65 to 204 nucleotides on cellular ros (c-ros) DNA over a range of 11 kilobases. Comparison of the deduced amino acid sequences of c-ros and v-ros shows two differences: v-ros contains a three-amino-acid insertion within the hydrophobic domain presumed to be involved in membrane association, and (ii) the carboxyl 12 amino acids of v-ros are completely different from those of the deduced c-ros sequence. The deduced amino acid sequence of c-ros bears striking structural features similar to those of insulin and epidermal growth factor receptors, including the presumed hydrophobic membrane binding domain, amino acids flanking the domain, and the distance between the domain and the catalytic region of the kinase activity. The expression of c-ros appears to be under a very stringent control. When tissues at various stages of chicken development were analyzed, only kidney was found to contain a significant level of c-ros RNA. The level of c-ros RNA in kidney tissue is most abundant in 7- to 14-day-old chickens. Finally, nucleotide sequences of c-ros DNA and UR2-associated helper viral genome at regions corresponding to the gag ros recombination site suggest that the junction has been formed by RNA splicing.

Insulin receptors in lizard brain and liver: structural and functional studies of alpha and beta subunits demonstrate evolutionary conservation

Specific insulin receptors are present in the liver and brain of the lizard Anolis carolinesis. In this study, the specific binding of 125I-insulin to the receptors showed time, temperature and pH dependency. Specific binding to crude membranes prepared from brain was 1-2% of the total radioactivity added compared to 4-5% in the crude membranes prepared from liver. Solubilization and wheat germ agglutinin purification of the membranes resulted in an increase in the specific binding (per mg of protein) between 6 and 32 times for liver membranes and 13-186 for brain membranes. Binding inhibition of tracer insulin by unlabeled porcine insulin was characteristic for insulin receptors with 50% inhibition for liver crude membranes at 60 ng/ml of porcine insulin and 0.7 ng/ml for purified brain insulin receptors. Chicken insulin was 2- to 3-fold more potent and proinsulin about 100 times less potent than porcine insulin. The alpha-subunits of liver and brain had apparent molecular weights on sodium dodecyl sulfate polyacrylamide gel electrophoresis of 135 kDa and 120 kDa respectively. Apparent molecular weights of beta subunits were 92 kDa for both tissues. Insulin stimulated phosphorylation of the beta subunit of both brain and liver receptors. Both tissues demonstrated tyrosine-specific phosphorylation, which was stimulated by insulin, of exogenously added artificial substrates. In addition, purified brain insulin receptor preparations contained an endogenous protein with apparent molecular weight of 105 kDa, whose phosphorylation was stimulated by insulin (10(-7) mol/l). This phosphoprotein was not immunoprecipitated by anti-insulin receptor antibodies. These studies suggest that the structural differences between brain and liver receptors previously demonstrated in the rat are also present in the lizard, which is about 300,000,000 years older than the mammalian species. Thus, there is strong evolutionary conservation of the brain insulin receptor.

The ligand binding subunit of the insulin-like growth factor 1 receptor has properties of a peripheral membrane protein

125I-insulin-like growth factor 1 was cross-linked to its receptor in human placenta microsomal membranes. The microsomes were treated with urea, with dithiothreitol or with both reagents prior to centrifugation at 100,000 X g. We found that greater than 80% of the label was membrane-associated following separate treatment with urea or dithiothreitol, but greater than 80% of the radioactivity remained in the supernatant after simultaneous exposure to both reagents. In identical experiments employing 125I-epidermal growth factor, no condition led to the release of greater than 10% of label from the membrane. We conclude that the ligand binding subunit of the insulin-like growth factor 1 receptor, like peripheral membrane proteins, lacks a membrane anchoring domain.

Heterologous transmembrane and cytoplasmic domains direct functional chimeric influenza virus hemagglutinins into the endocytic pathway

Chimeric genes were created by fusing DNA sequences encoding the ectodomain of the influenza virus hemagglutinin (HA) to DNA coding for the transmembrane and cytoplasmic domains of either the G glycoprotein of vesicular stomatitis virus or the gC glycoprotein of Herpes simplex virus 1. CV-1 cells infected with SV40 vectors carrying the recombinant genes expressed large amounts of the chimeric proteins, HAG or HAgC on their surfaces. Although the ectodomains of HAG and HAgC differed in their immunological properties from that of HA, the chimeras displayed the biological functions characteristic of the wild-type protein. Both HAG and HAgC bound erythrocytes as efficiently as HA did and, after brief exposure to an acidic environment, induced the fusion of erythrocyte and CV-1 cell membranes. However, the behavior of HAG and HAgC at the cell surface differed from that of HA in several important respects. HAG and HAgC were observed to collect in coated pits whereas wild-type HA was excluded from those structures. In the presence of chloroquine, which inhibits the exit of receptors from endosomes, HAG and HAgC accumulated in intracellular vesicles. By contrast, chloroquine had no effect on the location of wild-type HA. HAG and HAgC labeled at the cell surface exhibited a temperature-dependent acquisition of resistance to extracellular protease at a rate similar to the rates of internalization observed for many cell surface receptors. HA acquired resistance to protease at a rate at least 20-fold slower. We conclude that HAG and HAgC are efficiently routed into the endocytic pathway and HA is not. However, like HA, HAG was degraded slowly, raising the possibility that HAG recycles to the plasma membrane.

Protein kinase activity of the insulin receptor

The insulin receptor is an integral membrane glycoprotein (Mr approximately 300,000) composed of two alpha-subunits (Mr approximately 130,000) and two beta-subunits (Mr approximately 95,000) linked by disulphide bonds. This oligomeric structure divides the receptor into two functional domains such that alpha-subunits bind insulin and beta-subunits possess tyrosine kinase activity. The amino acid sequence deduced from cDNA of the single polypeptide chain precursor of human placental insulin receptor revealed that alpha- and beta-subunits consist of 735 and 620 residues, respectively. The alpha-subunit is hydrophilic, disulphide-bonded, glycosylated and probably extracellular. The beta-subunit consists of a short extracellular region which links the alpha-subunit through disulphide bridges, a hydrophobic transmembrane region and a longer cytoplasmic region which is structurally homologous with other tyrosine kinases like the src oncogene product and EGF receptor kinases. The cellular function of insulin receptors is dual: transmembrane signalling and endocytosis of hormone. The binding of insulin to its receptor on the cell membrane induces transfer of signal from extracellular to cytoplasmic receptor domains leading to activation of cell metabolism and growth. In addition, hormone-receptor complexes are internalized leading to intracellular proteolysis of insulin, whereas receptors are recycled to the membrane. These phenomena are kinetically well-characterized, but their molecular mechanisms remain obscure. Insulin receptor in different tissues and animal species are homologous in their structure and function, but show also significant differences regarding size of alpha-subunits, binding kinetics, insulin specificity and receptor-mediated degradation. We suggest that this heterogeneity of receptors may be linked to the diversity in insulin effects on metabolism and growth in various cell types. The purified insulin receptor phosphorylates its own beta-subunit and exogenous protein and peptide substrates on tyrosine residues, a reaction which is insulin-sensitive, Mn2+-dependent and specific for ATP. Tyrosine phosphorylation of the beta-subunit activates receptor kinase activity, and dephosphorylation with alkaline phosphatase deactivates the kinase. In intact cells or impure receptor preparations, a serine kinase is also activated by insulin. The cellular role of two kinase activities associated with the insulin receptor is not known, but we propose that the tyrosine- and serine-specific kinases mediate insulin actions on metabolism and growth either through dual-signalling or sequential pathways.(ABSTRACT TRUNCATED AT 400 WORDS)

Antipeptide antiserum identifies a widely distributed cellular tyrosine kinase related to but distinct from the c-fps/fes-encoded protein

We raised antibodies directed against a synthetic peptide representing an amino acid sequence of the conserved kinase domain of the transforming protein of Fujinami sarcoma virus (FSV) (P140). The antiserum obtained specifically recognized FSV-P140 and its cellular homolog and in addition, it recognized a new cellular protein of 94,000 daltons (NCP94) in avian and mammalian cells. NCP94 was found to be associated with a cyclic nucleotide-independent protein kinase activity that was specific for tyrosine residues. Although NCP94 and FSV-P140 share antigenic determinants, NCP94 is not a cellular homolog of FSV-P140: NCP94 and the previously identified c-fps/fes product were different in their tryptic fingerprints and in their tissue specificities. Thus, the function of NCP94 in normal cells is probably different than that of the c-fps/fes product. NCP94 was expressed in every tissue and cell line that was examined. In chickens, NCP94 levels were highest during embryonic development and NCP94 expression was high in gizzard, brain, and spleen throughout embryonic and adult life. The universal expression of NCP94 suggests that this protein may be involved in an essential function of normal cells. NCP94 may be a new cellular tyrosine kinase of the src gene family.

Monoclonal antibodies reacting with multiple epitopes on the human insulin receptor

Monoclonal antibodies for the human insulin receptor were produced following immunization of mice with IM-9 lymphocytes and/or purified placental receptor. Four separate fusions yielded 28 antibodies, all of which reacted with receptor from human placenta, liver and IM-9 cells. Some antibodies cross-reacted to varying degrees with receptor from rabbit, cow, pig and sheep, but none reacted with rat receptor. At least 10 distinct epitopes were recognized as indicated by species specificity and binding competition experiments. All of these epitopes appeared to be on extracellular domains of the receptor as shown by binding of antibodies to intact cells. In some cases the epitopes were further localized to alpha or beta subunits by immunoblotting. Several antibodies inhibited binding of 125I-insulin to the receptor, some had no effect on binding, and others enhanced the binding of 125I-insulin. It is concluded that these antibodies will be valuable probes of receptor structure and function.

Mapping surface structures of the human insulin receptor with monoclonal antibodies: localization of main immunogenic regions to the receptor kinase domain

A panel of 37 monoclonal antibodies to the human insulin receptor has been used to characterize the receptor's major antigenic regions and their relationship to receptor functions. Three antibodies recognized extracellular surface structures, including the insulin binding site and a region not associated with insulin binding. The remaining 34 monoclonal antibodies were directed against the cytoplasmic domain of the receptor beta subunit. Competitive binding studies demonstrated that four antigenic regions (beta 1, beta 2, beta 3, and beta 4) are found on this domain. Sixteen of the antibodies were found to be directed against beta 1, nine against beta 2, seven against beta 3, and two against beta 4. Antibodies to all four regions inhibited the receptor-associated protein kinase activity to some extent, although antibodies directed against the beta 2 region completely inhibited the kinase activity of the receptor both in the autophosphorylation reaction and in the phosphorylation of an exogenous substrate, histone. Antibodies to the beta 2 region also did not recognize autophosphorylated receptor. In addition, antibodies to this same region recognized the receptor for insulin-like growth factor I (IGF-I) as well as the insulin receptor. In contrast, antibodies to other cytoplasmic regions did not recognize the IGF-I receptor as well as the insulin receptor. These results indicate that the major immunogenic regions of the insulin receptor are located on the cytoplasmic domain of the receptor beta subunit and are associated with the tyrosine-specific kinase activity of the receptor. In addition, these results suggest that a portion of the insulin receptor is highly homologous to that of the IGF-I receptor.

Characterization of phosphatidylinositol kinase activity associated with the insulin receptor

Various lipids were tested as substrates for the insulin receptor kinase using either receptor partially purified from rat hepatoma cells by wheat-germ-agglutinin-Sepharose chromatography or receptor purified from human placenta by insulin-Sepharose affinity chromatography. Phosphatidylinositol was phosphorylated to phosphatidylinositol 4-phosphate by the partially purified insulin receptor. In contrast, phosphatidylinositol 4-phosphate and diacylglycerol were not phosphorylated. In some, but not all preparations of partially purified insulin receptor, the phosphatidylinositol kinase activity was stimulated by insulin (mean effect 33%). Phosphatidylinositol kinase activity was retained in insulin receptor purified to homogeneity. Insulin regulation of the phosphatidylinositol kinase was lost in the purified receptor; however, dithiothreitol stimulated both autophosphorylation of the purified receptor and phosphatidylinositol kinase activity in parallel about threefold. (Glu80Tyr20)n, a polymeric substrate specific to tyrosine kinases, inhibited the phosphatidylinositol kinase activity of the purified receptor by greater than 90% and inhibited receptor autophosphorylation by 67%. Immunoprecipitation by specific anti-receptor antibodies depleted by greater than 90% the phosphatidylinositol kinase activity in the supernatant of the purified receptor and the phosphatidylinositol kinase activity was recovered in the precipitate in parallel with receptor autophosphorylation activity. These characteristics of the phosphatidylinositol kinase activity of the purified insulin receptor and its metal ion preference paralleled those of the receptor tyrosine kinase activity and differed from bulk phosphatidylinositol kinase activity in cell extracts, which was not significantly inhibited by (Glu80Tyr20)n, stimulated by dithiothreitol or depleted by immunoprecipitation with anti-(insulin receptor) antibody. These results suggest that the insulin receptor is associated with a phosphatidylinositol kinase activity; however, this activity is not well regulated by insulin. This kinase appears to be distinct from the major phosphatidylinositol kinase(s) of cells. Its relationship to insulin action needs further study.

Receptor-mediated endocytosis

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Biochemical characterization of the 9.3 antigens of human T-cells: simultaneous expression of disulfide-bonded 90-kilodalton dimers and free subunits at the cell surface

Human T-lymphocytes express a heterogeneous family of 90/45-kilodalton (kDa) glycoproteins which bind the 9.3 monoclonal antibody. It was found in previous functional tests carried out with cultures of mononuclear cells or antigen-specific T-cell clones that these glycoproteins have a specific receptor function in early T-cell activation [Gmünder and Lesslauer, Eur. J. Biochem. (1984); Ottenhoff et al., (1985)]; their membrane-biochemical properties are therefore investigated. By screening a number of lines, one continuously growing human T-cell line, HPB-ALL, was identified which expresses the 9.3 antigens in a manner comparable to normal T-cells. Monomeric 45-kDa and dimeric disulfide-bonded 90-kDa forms are precipitated from alkylated surface-iodinated and [35S]methionine-cysteine-labelled cells. The labelled tryptic fragments of surface-iodinated 9.3 antigens have isoelectric points of 4.8 (17-kDa), 4.8 (3-kDa) and 6.0 (17-kDa). By limited proteolysis the 45-kDa monomers are free subunits. The subunits of the 90-kDa dimer appear to be identical. The dimer and the free subunits coexist at the native cell surface and may be in dynamic chemical equilibrium. Human T-cells thus express--in addition to the T-cell antigen receptor--a further disulfide-bonded 90-kDa (homo-) dimeric receptor molecule.

Alternative 5' exons in c-abl mRNA

The cellular abl proto-oncogene encodes a protein-tyrosine kinase and is expressed in many cell types in two or three mRNA size species. Four types of mouse c-abl cDNAs have been cloned from 70Z/3 lymphoid cells that have different 5' sequences encoding predicted N-terminal regions of 20-45 amino acids. One of the four cDNAs has a predicted N-terminal sequence of met-gly-gln in common with the gag N terminus of v-abl. The 5' heterogeneity appears to be generated by alternative addition of 5' exons onto a common set of 3' exons. Alternative splicing occurs at the same site at which bcr sequences join to abl sequences in the Philadelphia chromosome translocation.

Unusual phylogenetic conservation of the N-terminal amino acid sequence of the central nervous system-specific membrane glycoprotein F3-87-8 (CNSgp130)

CNSgp130 is a CNS-specific membrane glycoprotein abundantly expressed throughout the mature mammalian CNS. The molecule is recognised by the mouse monoclonal antibody F3-87-8, which reacts with a determinant of CNSgp130 common to all mammals tested to date. Rat and human CNSgp130 were purified by a combination of F3-87-8 monoclonal antibody affinity and gel permeation chromatography, and the N-terminal amino acid sequence was determined by gas-phase sequencing techniques. The results show a remarkable conservation of the N terminus of the CNSgp130 polypeptide between rats and humans, with complete identity of the first 20 amino acid residues. There was an unusually high and phylogenetically conserved number of cysteines in this region. The sequence showed no homology to other known sequences and should prove useful in precisely identifying the relationship of CNSgp130 to other CNS membrane molecules.

Similarity of protein encoded by the human c-erb-B-2 gene to epidermal growth factor receptor

A novel v-erb-B-related gene, c-erb-B-2, which has been identified in the human genome, maps to human chromosome 17 at q21 (ref. 40), and seems to encode a polypeptide with a kinase domain that is highly homologous with, but distinct from, that of the epidermal growth factor (EGF) receptor. The c-erb-B-2 gene is conserved in vertebrates and it has been suggested that the neu gene, detected in a series of rat neuro/glioblastomas, is, in fact, the rat c-erb-B-2 gene. Amplification of the c-erb-B-2 gene in a salivary adenocarcinoma and a gastric cancer cell line MKN-7 suggests that its over-expression is sometimes involved in the neoplastic process. To determine the nature of the c-erb-B-2 protein, we have now molecularly cloned complementary DNA for c-erb-B-2 messenger RNA prepared from MKN-7 cells. Its sequence shows that the c-erb-B-2 gene encodes a possible receptor protein and allows an analysis of the similarity of the protein to the EGF receptor and the neu product. As a consequence of chromosomal aberration in MKN-7 cells, a 4.6-kilobase (kb) normal transcript and a truncated 2.3-kb transcript of c-erb-B-2 are synthesized at elevated levels. The latter transcript presumably encodes only the extracellular domain of the putative receptor.

The neu oncogene encodes an epidermal growth factor receptor-related protein

The neu oncogene is repeatedly activated in neuro- and glioblastomas derived by transplacental mutagenesis of the BDIX strain of rat with ethylnitrosourea. Foci induced by the DNAs from such tumours on NIH 3T3 cells contain the neu oncogene and an associated phosphoprotein of relative molecular mass 185,000 (p185). Previous work has shown that the neu gene is related to, but distinct from, the gene encoding the EGF receptor (c-erb-B). Here we describe a neu complementary DNA clone isolated from a cell line transformed by this oncogene; the clone has biological activity in a focus-forming assay. The nucleotide sequence of this clone predicts a 1,260-amino-acid transmembrane protein product similar in overall structure to the EGF receptor. We found that 50% of the predicted amino acids of neu and the EGF receptor are identical; greater than 80% of the amino acids in the tyrosine kinase domain are identical. Our results suggest strongly that the neu gene encodes the receptor for an as yet unidentified growth factor.

Messenger RNA for plasminogen activator inhibitor

We report here the identification and preliminary characterization of the messenger RNA coding for a Mr 50,000 plasminogen activator inhibitor (PAI) synthesized by cultured bovine aortic endothelial cells. Polyadenylated RNA was prepared from these cells and translated in a rabbit reticulocyte lysate in vitro translation system. When the 35S methionine labeled translation products were immunoprecipitated with monospecific antiserum to PAI and analyzed by SDS-PAGE and autoradiography, a single major polypeptide of Mr 40,000 was revealed. Competition experiments were performed to determine the relationship of the immunoprecipitated polypeptide to the PAI. The amount of 35S-labeled immunoprecipitate was greatly decreased by the presence of the purified PAI, consistent with the conclusion that the Mr 40,000 band represented the translation product of PAI mRNA. This mRNA migrated with a sedimentation coefficient of 22s when analyzed by sucrose gradient centrifugation. The in vitro translation assay was used to determine the relative amount of PAI mRNA in cells cultured in calf serum purchased from different vendors. The level of PAI mRNA varied by at least eight-fold depending on the serum employed, suggesting that expression of the PAI gene is subject to regulation by external factors.