EGF receptor induction and insulin-EGF overlap in Tetrahymena

Offspring generations of Tetrahymena pretreated (imprinted) with insulin showed a greater binding capacity for the hormone than offspring of untreated ones. The epidermal growth factor (EGF) imprinted for insulin to a greater degree than insulin itself, and vice versa: insulin imprinted for EGF more efficiently than EGF itself. These phenomena can be explained by the overlap of insulin and EGF on one another's receptors in Tetrahymena.     

The urokinase receptor and integrins in cancer progression

Enhanced levels of expression of urokinase receptor (uPAR) and certain integrins have been linked to cancer cell progression. This has classically been attributed to matrix degradation via the activation of the urokinase (uPA)/plasmin system and modulation of cell motility and survival through integrin engagement. More recently, uPAR has been shown to play multiple roles independent of protease activity. Specifically, uPAR has been shown to be intimately involved in the regulation of cell adhesion, migration and proliferation in part through interactions with other membrane partners, including integrins. The goal of this review is to summarize recent insights in the function of uPAR/integrin interactions, to provide a framework for understanding the importance of these interactions in the context of cancer, and to highlight its potential as a target for therapeutic intervention.     

Two phorbol ester receptor affinities in partially transformed human urothelial cells and decrease of receptor binding in desensitized cells

The presence of specific binding sites for phorbol esters was studied in a transformed but non-tumorigenic human urothelial cell line HCV-29 by assay of specific binding of³H-phorbol-12,13-dibutyrate (³H-PDBu) to intact living cells.³H-PDBu bound specifically to HCV-29 cells in a saturable and competitive manner. Scatchard plot analysis of specific binding yielded a curved plot consistent with two binding sites with K_d of 11 nM and 102 nM, respectively. At saturation the corresponding PDBu binding capacities (B_max) were 8.8 pmol/10⁶ cells (5.2×10⁶ molecules bound per cell) and 2.8 pmol/10⁶ cells (1.7×10⁶ molecules bound per cell).³H-PDBu binding was displaced by biologically active phorbol ester tumor promoters such as 12-O-tetradecanoylphorbol-13-acetate (TPA) and mezerein,but not by tumor promoters such as L-tryptophan, anthranilic acid and sodium saccharin. In cells desensitized by pretreatment with 1 g/ml (2M) TPA or PDBu for 24 h the level of binding was reduced to 28% of the level in non-exposed cells. The ability of desensitized cells to bind³H-PDBu was gradually restored within 5–6 days. At the same time the cells became sensitive to the morphological alteration induced by PDBu. This suggests that desensitization of HCV-29 cells is due to a decreased receptor-ligand binding capacity probably associated with down regulation of the phorbol ester receptors.     

Ethanol and opioid receptor signalling

Summary Ethanol may modulate endogenous opioid systems by disrupting opioid receptor signalling. Low concentrations of ethanol slightly potentiate -opioid receptor binding by increasing receptor B_max, and, in some cases, chronic ethanol exposure decreases the density or affinity of the -opioid receptors. By contrast, high concentrations of ethanol acutely decrease -opioid receptor binding by decreasing receptor affinity, whereas chronic exposure of animals and neuronal cell lines to lower concentrations of ethanol leads to possibly adaptive increases in the density or affinity of the -opioid receptors. In the neuronal cell line NG108-15, ethanol does not up-regulate the -opioid receptor by blocking receptor degradation or endocytosis, but protein synthesis is required for this response. Up-regulation of the -opioid receptor renders ethanol-treated NG108-15 cells 3.5-fold more sensitive to opioid inhibition of adenylyl cyclase. Long-term treatment with ethanol also increases maximal opioid inhibition in NG108-15 cells, possibly by decreasing levels of G_s and its mRNA. Ethanol differentially modulates signal transduction proteins in three additional neuronal cell lines, N18TG2, N4TG1, and N1E-115. Ethanol-treated N18TG2 cells show the least up-regulation of the -opioid receptor, little heterologous desensitization of adenylyl cyclase, and no changes in G_s or G_i. By contrast, ethanol-treated N1E-115 cells show the largest up-regulation of the -opioid receptor, the most heterologous desensitization of adenylyl cyclase, and concentration-dependent decreases in G_s and increases in G_i. Further analysis of these related neuronal cell lines may help to identify the molecular elements that endow some, but not all, neuronal cells with the capacity to adapt to ethanol.     

Ethanol and opioid receptor signalling

Ethanol may modulate endogenous opioid systems by disrupting opioid receptor signalling. Low concentrations of ethanol slightly potentiate mu-opioid receptor binding by increasing receptor Bmax, and, in some cases, chronic ethanol exposure decreases the density or affinity of the mu-opioid receptors. By contrast, high concentrations of ethanol acutely decrease delta-opioid receptor binding by decreasing receptor affinity, whereas chronic exposure of animals and neuronal cell lines to lower concentrations of ethanol leads to possibly adaptive increases in the density or affinity of the delta-opioid receptors. In the neuronal cell line NG108-15, ethanol does not up-regulate the delta-opioid receptor by blocking receptor degradation or endocytosis, but protein synthesis is required for this response. Up-regulation of the delta-opioid receptor renders ethanol-treated NG108-15 cells 3.5-fold more sensitive to opioid inhibition of adenylyl cyclase. Long-term treatment with ethanol also increases maximal opioid inhibition in NG108-15 cells, possibly by decreasing levels of G alpha s and its mRNA. Ethanol differentially modulates signal transduction proteins in three additional neuronal cell lines, N18TG2, N4TG1, and N1E-115. Ethanol-treated N18TG2 cells show the least up-regulation of the delta-opioid receptor, little heterologous desensitization of adenylyl cyclase, and no changes in G alpha s or G alpha i. By contrast, ethanol-treated N1E-115 cells show the largest up-regulation of the delta-opioid receptor, the most heterologous desensitization of adenylyl cyclase, and concentration-dependent decreases in G alpha s and increases in G alpha i. Further analysis of these related neuronal cell lines may help to identify the molecular elements that endow some, but not all, neuronal cells with the capacity to adapt to ethanol.     

Kainate receptor pharmacology and physiology

Glutamate is the primary neurotransmitter in the central nervous system. One of the classes of ionotropic glutamate receptors is kainate receptors. Recent developments in the pharmacology of kainate receptors have resulted in the emergence of several selective agonists and antagonists. These compounds have allowed scientists to begin to probe the functional properties of these receptors in neurons and gain a better understanding of the role of these receptors in the nervous system.     

The TSH receptor and its role in thyroid disease

The thyrotropin (TSH) receptor plays a preeminent role in thyroid physiology and disease. TSH, acting through the TSH receptor, is the major stimulator of thyroid cell growth, differentiation and function. In Graves' disease, the TSH receptor is the target of stimulating antibodies that cause hyperthyroidism. Although still a topic of debate, the TSH receptor has been implicated in the pathogenesis of the endocrine ophthalmopathy associated with Graves' disease. Blocking antibodies against the TSH receptor are involved in the development of hypothyroidism in a subset of patients with autoimmune hypothyroidism. Transplacental passage of stimulating or blocking TSH receptor antibodies from a mother with autoimmune thyroid disease may result in transient hyper- or hypothyroidism in early infancy. During pregnancy, the placental hormone human choriogonadotropin (hCG) can cause gestational hyperthyroidism through cross-reaction with the TSH receptor. Gestational hyperthyroidism may also be involved in the pathogenesis of hyperemesis gravidarum. Trophoblast tumors secreting hCG are a rare cause of hyperthyroidism. Somatic activating mutations of the TSH receptor have been identified as a molecular cause of toxic adenomas, whereas activating mutations in the germline give rise to nonautoimmune familial hyperthyroidism or sporadic congenital hyperthyroidism. These gain-of-function mutations are dominant, and one mutated allele is sufficient to result in disease. Inactivating germline mutations of both TSH receptor alleles lead to variable degrees of resistance to TSH, encompassing a spectrum ranging from euthyroid hyperthyrotropinemia to overt hypothyroidism with thyroid hypoplasia. Received 31 January 2001; received after revision 3 April 2001; accepted 3 April 2001     

Low-density lipoprotein receptor structure and folding

The endoplasmic reticulum (ER) is a major cellular 'production factory' for many membrane and soluble proteins. A quality control system ensures that only correctly folded and assembled proteins leave the compartment. The low-density lipoprotein receptor (LDLR) is the prototype of a large family of structurally homologous cell surface receptors, which fold in the ER and function as endocytic and signaling receptors in a wide variety of cellular processes. Patients with familial hypercholesterolemia carry single or multiple mutations in their LDLR, which leads to malfunction of the protein, in most patients through misfolding of the receptor. As a result, clearance of cholesterol-rich LDL particles from the circulation decreases, and the elevated blood cholesterol levels cause early onset of atherosclerosis and an increased risk of cardiac disease in these patients. In this review, we will elaborate on the structural aspects of the LDLR and its folding pathway and compare it to other LDLR family members.     

Transient receptor potential canonical channels in angiogenesis and axon guidance

Wiring of vascular and neural networks requires precise guidance of growing blood vessels and axons, respectively, to reach their targets during development. Both of the processes share common molecular signaling pathways. Transient receptor potential canonical (TRPC) channels are calcium-permeable cation channels and gated via receptor- or store-operated mechanisms. Recent studies have revealed the requirement of TRPC channels in mediating guidance cue-induced calcium influx and their essential roles in regulating axon navigation and angiogenesis. Dissecting TRPC functions in these physiological processes may provide therapeutic implications for suppressing pathological angiogenesis and improving nerve regeneration.     

Novel estrogen receptor coregulators and signaling molecules in human diseases

The steroid hormone estrogen and signaling from its receptors are increasingly recognized as critical mediators of a variety of organ-specific biological processes. Recent advances in the identification and functional characterization of novel estrogen receptor interacting proteins clearly show the complexity of hormonal signaling regulation, but may also contribute to our understanding of the roles of estrogen signaling in normal physiology and the pathobiology of human disease.Received 12 June 2003; received after revision 21 July 2003; accepted 29 July 2003     

Functional interaction between calsequestrin and ryanodine receptor in the heart

Evidence obtained in the last two decades indicates that calsequestrin (CSQ2), as the major Ca²⁺-binding protein in the sarcoplasmic reticulum of cardiac myocytes, communicates changes in the luminal Ca²⁺ concentration to the cardiac ryanodine receptor (RYR2) channel. This review summarizes the major aspects in the interaction between CSQ2 and the RYR2 channel. The single channel properties of RYR2 channels, discussed here in the context of structural changes in CSQ2 after Ca²⁺ binding, are particularly important. We focus on five important questions concerning: (1) the method for reliable detection of CSQ2 on the reconstituted RYR2 channel complex; (2) the power of the procedure to strip CSQ2 from the RYR2 channel complex; (3) structural changes in CSQ2 upon binding of Ca²⁺ which cause CSQ2 dissociation; (4) the potential role of CSQ2-independent regulation of the RYR2 activity by luminal Ca²⁺; and (5) the vizualization of CSQ2 dissociation from the RYR2 channel complex on the single channel level. We discuss the potential sources of the conflicting experimental results which may aid detailed understanding of the CSQ2 regulatory role. Although we mainly focus on the cardiac isoform of the proteins, some aspects of more extensive work carried out on the skeletal isoform are also discussed.     

Regulation of estrogen receptor beta activity and implications in health and disease

Together with the estrogen receptor (ER) alpha, estrogen receptor beta (ERβ) mediates many of the physiological effects of estrogens. As ERβ is crucially involved in a variety of important physiological processes, its activity should be tightly regulated. ERβ regulation is achieved by hormone binding as well as by posttranslational modifications of the receptor. Furthermore, ERβ expression levels are under circadian control and can be regulated by DNA methylation of the ERβ promoter region. There are also a number of factors that can interfere with ERβ activity, such as phytoestrogens, endocrine disruptive chemicals, and growth factors. In this article, we outline different mechanisms of ERβ regulation and how they are implicated in various diseases. We also discuss how these insights might help to specifically target ERβ in drug design.     

Opiate receptor sites in neuronal and glial cell lines in culture]

A stereospecific saturable high affinity binding of 3H-naloxone has been found in 3 glial and 2 neuronal cell lines. Kinetic study of binding seems to indicate only one class of receptor sites in the 5 cell lines. Acute exposure to morphine (1 X 10(-5)M) concurrent with PGE1-induced stimulation of adenylate cyclase did not result in a decrease of the cAMP level in any cell line tested.     

Internalization of polypeptide hormones and receptor recycling

Conclusion The insulin receptor is an integral protein of the plasma membrane of the cell. It is composed of two subunits: an subunit, which binds the hormone, and a subunit which is a tyrosine specific protein kinase capable of undergoing autophosphorylation. These independent subunits are synthesized by way of a higher molecular weight single chain precursor and thus are the product of a single gene^{29, 49, 85} localized to chromosome 19^{29, 91}. Assuming that the insulin receptor is synthesized in the same fashion as other integral membrane glycoproteins, then the nucleus, the rough endoplasmic reticulum, and the Golgi apparatus are involved in its biosynthesis. Further, there must be some form of transport of the mature receptor subunits to the plasma membrane where they are inserted.By contrast, the endocytotic route involves coated pits, coated vesicles, large clear vesicles or endosomes, multivesicular bodies and other lysosomal forms. In addition, it is possible that some other as yet unidentified organelle is involved in recycling (fig. 8). At the present time, with respect to the insulin receptor, the biosynthetic pathway and the endocytotic pathway appear to be separate. Further, it does not appear that either pathway, i. e. synthesis or endocytosis, exerts a regulatory function over the other.     

H2 receptor antagonists and human granulopoiesis

Summary The effect of 2 H₂ receptor antagonists (ranitidine and cimetidine) on the in vitro growth of human granulomonopoietic precursors (CFU-GM) was studied. Ranitidine, although having an anti H₂ receptor activity much greater than that of cimetidine, displays the same toxicity for CFU-GM.Acknowledgments. This work was supported by CNR, Rome, PFCCN and AIRC, Milan.     

H2 receptor antagonists and human granulopoiesis

The effect of 2 H2 receptor antagonists (ranitidine and cimetidine) on the in vitro growth of human granulomonopoietic precursors (CFU-GM) was studied. Ranitidine, although having an anti H2 receptor activity much greater than that of cimetidine, displays the same toxicity for CFU-GM.