Maxine A. Lesniak

Insulin interactions with its receptors: experimental evidence for negative cooperativity.

Summary A simple method is reported to detect cooperative interactions in the binding of polypeptide hormones to their membrane receptors. The dissociation of radioiodinated hormone from the receptor is studied under two conditions: first, by diluting the hormone-receptor complex sufficiently to prevent rebinding of the dissociated tracer; second, by dilution to the same extent in a medium containing an excess of unlabeled hormone. If the sites are independent, the dissociation rates must be the same in both cases. If the presence of unlabeled hormone increases the dissociation rate of the tracer, negatively cooperative interactions must occur. Insulin receptors on cultured lymphocytes and liver plasma membranes show negative cooperative interactions. Growth hormone receptor sites lack these interactions.

Receptors for insulin, NSILA-s, and growth hormone: applications to disease states in man.

Publisher Summary This chapter presents the definition and features of a receptor, and its historical aspects. Most contemporary workers use the term “receptor” to describe the natural molecular components of the cell that serve to recognize a biologically active chemical messenger or hormone. Recognition is manifested by binding of the hormone to the receptor. Another feature of the receptor is that in a normal target cell, the complex of hormone with receptor is capable of activating or initiating a chain of events that lead to a hormonal action. The chapter discusses the binding of peptide hormone to receptors and alterations in disease. The biologically important receptors for peptide and catecholamine hormones are largely or entirely on the outside surface of the cell. The number of receptors for each peptide hormone on a cell is finite, and the binding of these hormones to their receptors is saturable and reversible. The chapter also discusses alterations in receptor activity in vivo and in vitro. Hormone receptors may undergo conformational changes that result in a change in affinity of the receptor for the hormone. The chapter also explores the role of the cells receptor in determining the sensitivity of the cell to the hormone and applications of these hormone-receptor interactions to the measurement of plasma hormone concentrations and tissue receptor concentrations in disease states in man.

Insulin in Insects and Annelids

The fruitfly, Drosophila melanogaster, and the earthworm, Annelida oligocheta, were extracted with acid-ethanol by a classic method for recovering insulin from the pancreas. When each extract was filtered on a Sephadex G-50 column, a distinct peak of insulin immunoreactivity (equivalent to 0.1 to 2 ng of insulin/g wet weight) was recovered in the region typical of insulin. The material in this peak had reactivity in the insulin bioassay, measuring stimulation of glucose oxidation or lipogenesis by isolated rat adipocytes. The bioactivity was partially or largely neutralized by anti-insulin antibodies. In concordance with previous work showing the presence of material very similar to insulin in the blowfly and molluscs, we have confirmed the presence of insulin in insects and extended the observation to earthworms. These findings suggest that insulin is more widespread in invertebrates than was previously thought. In a companion study (Proc. Nati. Acad. Sci. USA 77:6184-88, 1980), we have demonstrated material similar to insulin in unicellular organisms.

Specificity spillover at the hormone receptor exploring its role in human disease

IN some disease states, one or more manifestations of hormonal excess may be caused by the interaction of one hormone with the receptor for a different hormone. When one receptor is activated by a ...

Developmental Regulation of Insulin and Type I Insulin-Like Growth Factor Receptors and Absence of Type II Receptors in Chicken Embryo Tissues

Chicken embryos are a suitable model for studying the role of insulin, insulin-like growth factors I and II (IGF-I and IGF-II), and their receptors in embryogenesis. We show that plasma membranes from heart, liver, and limb buds, as reported earlier for brain, each have a distinct developmental profile for insulin receptors and type I IGF receptors. In heart and limb buds, IGF binding is higher than insulin binding, but in liver, insulin receptors dominate. Expression of these receptors is, therefore, developmentally regulated and tissue specific. The wide distribution of high-affinity receptors capable of mediating insulin and IGF actions in early organogenesis further supports the possible importance of this family of peptides for differentiation and growth in vertebrates. In all chicken embryo tissues studied, both IGF-I and IGF-II appeared to bind to a type I IGF receptor. We have not detected a receptor with the peptide binding and structural characteristics of the mammalian type II IGF receptor. The type II receptor was absent in embryos, liver from newly hatched chicks, and adipocytes from older chicks, which suggests that the chicken may lack this subtype of IGF receptor.

Insulin Receptor Substrate-2 (IRS-2) Can Mediate the Action of Insulin to Stimulate Translocation of GLUT4 to the Cell Surface in Rat Adipose Cells

Insulin receptor substrates-1 and -2 (IRS-1 and -2) are important substrates of the insulin receptor tyrosine kinase. Previous studies have focused upon the role of IRS-1 in mediating the actions of insulin. In the present study, we demonstrate that IRS-2 can mediate translocation of the insulin responsive glucose transporter GLUT4 in a physiologically relevant target cell for insulin action. Co-immunoprecipitation experiments performed on cell lysates derived from freshly isolated rat adipose cells incubated in the presence or absence of insulin indicated that twice as much phosphatidylinositol 3-kinase was associated with endogenous IRS-1 as with IRS-2 after insulin stimulation. When rat adipose cells in primary culture were transfected with expression vectors for IRS-1 or IRS-2, we observed 40-fold overexpression of human IRS-1 or murine IRS-2. In addition, anti-phosphotyrosine immunoblotting experiments confirmed that the recombinant substrates were phosphorylated in response to insulin stimulation. To examine the role of IRS-2 in insulin-stimulated translocation of GLUT4, we studied the effects of overexpression of IRS-1 and -2 on translocation of a co-transfected epitope-tagged GLUT4 (GLUT4-HA). Overexpression of IRS-1 or IRS-2 in adipose cells resulted in a significant increase in the basal level of cell surface GLUT4 (in the absence of insulin). Interestingly, at maximally effective concentrations of insulin (60 nm), the level of cell surface GLUT4 in cells overexpressing IRS-1 or -2 significantly exceeded the maximal recruitment observed in the control cells (160 and 135% of control, respectively; p < 0.003). Our data directly demonstrate that IRS-2, like IRS-1, is capable of participating in insulin signal transduction pathways leading to the recruitment of GLUT4. Thus, IRS-2 may provide an alternative pathway for critical metabolic actions of insulin.

Insulin in Brain and Other Extrapancreatic Tissues of Vertebrates and Nonvertebrates

Publisher Summary This chapter focuses on insulin in brain and other extrapancreatic tissues of vertebrates and nonvertebrates. Insulin production is not unique to beta cells of the vertebrate pancreas. The levels of insulin are high in specific nerves but undetected in others. Insulin accumulates in nerves proximal to axonal clamps, and electrical stimulation of nerves results in release of insulin. Insulin content of brain and other extrapancreatic tissues of mammals is largely independent of the level of plasma insulin, that is, conditions characterized by sustained hyper- and hypoinsulinemia hardly alter tissue levels of insulin. Kidney is the only tissue whose insulin content parallels plasma levels of insulin. This suggests that only in kidney does the plasma-derived compartment contain the majority of tissue insulin. As in most tissues in vivo , levels of insulin in extracts of cultured cells are very poorly responsive to changes in the level of insulin in the medium. In guinea pigs, brain and other extrapancreatic tissues have a type of insulin that is distinct from the insulin found in abundance in its pancreas and plasma, again suggesting nonpancreatic sites of insulin production. It appears that some nonpancreatic tissues of both vertebrates and nonvertebrates can make material that is very similar to pancreatic insulin of vertebrates.

Evolutionary aspects of the endocrine and nervous systems.

Publisher Summary This chapter illustrates the evolutionary aspects of the endocrine and nervous systems. In mammals and other vertebrates, the major systems of intercellular communication are the endocrine and nervous systems. Intercellular communication is not unique to organisms which possess endocrine and nervous systems; rather it is essential to all forms of life including microbes. In the classic concept of the endocrine system the chemical messenger molecule, the hormone, is produced in a localized region, released into the general circulation, and acts on a target cell at a distance. In the nervous system, on the other hand, the secretory cell is a neuron and the messenger molecule a neurotransmitter. Many of the messenger molecules assigned to the endocrine or nervous systems reach their target tissues by other systems of intercellular communication such as exocrine and paracrine systems. Furthermore, a number of nonhormonal peptides which act on a target tissue have structural similarities to classic hormones and act on the target tissues in a manner almost identical to hormones. Interestingly, the biochemical elements necessary for the intercellular communication, that is, messenger molecules, their receptors, as well as post receptor intracellular components, are present in unicellular organisms and show distinct structural and functional similarities to their counterparts in vertebrate tissues.

Receptors for intercellular messenger molecules in microbes: similarities to vertebrate receptors and possible implications for diseases in man.

Our focus is on the evolutionary origins of receptors for vertebrate hormones, neuroactive peptides, and related messengers. The first part wiU survey the possible evolutionary origins and phylogenetic distribution of the vertebrate-type messenger peptides providing a possible clue or guide to the same speculation for the receptor. Also, we will explain current data which suggest why receptors might need to be at least as old or as widely distributed as the messengers. In the latter part we will survey examples of materials in microbes that resemble vertebrate-type receptors and also highlight some possible applications to an understanding of human disease problems.

An Introduction to Receptors and Receptor Disorders

Summary In the last decade reliable methods have been introduced to quantitate and characterize receptors for hormones and other biologically interesting ligands. Applied initially to hormone receptors on malignant cells and to androgen-resistant and insulin-resistant states, these methods have led to the identification of many disease processes where the receptor plays an important role. This includes not only endocrine-related diseases but also neurological, metabolic, infectious, and immune disorders as well. Note. On the basis of biological and chemical data, it appears that the 40 to 50 different hormones found in a given organism each evolved from a much smaller number of primordial hormones. Presumably, for the peptide hormones the gene for the primordial hormone was duplicated as was the gene for its cell surface receptor; the new hormone-receptor pair evolved to establish a second signaling system. The affinity of each hormone for its specific receptor was high but in many cases the ligand retained some finite (albeit low) affinity for the other receptor. Thus, teleologically, greater diversity was paid for by a small loss in specificity. The weak affinity of one hormone for the receptor of a closely related hormone forms the basis for specificity spillover. The modest impairment of specificity in endocrine systems, its postulated origins, and suggested consequences may have significant counterparts in other areas of biology where diversity coexists with modest degeneracies in specificity, e.g., the large series of trypsin-like proteases that regulate multiple extracellular events such as clotting and kinin generation; neurotransmitters and related drugs; cyclase and the nucleotide-stimulated kinases; autoantibodies and prostaglandins.