Εισαγωγή στην Ενδοκρινολογία -Ορμόνες-Μηχανισμοί Δράσης

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1 Εισαγωγή στην Ενδοκρινολογία -Ορμόνες-Μηχανι σμοί Δράσης Ιφιγένεια Κώστογλου-Αθανασίου, MSc, MD, PhD Διδάκτωρ Πανεπιστημίου Αθηνών Διδάκτωρ Πανεπιστημίου Λονδίνου MSc Διοίκησης Μονάδων Υγείας Ενδοκρινολόγος Διευθύντρια ΕΣΥ Γ.Ν. Ασκληπιείο Βούλας

2 Ενδοκρινικό σύστημα Ορμόνες Μηχανισμοί δράσης ορμονών

3 Ενδοκρινικό σύστημα ΕΝΔΟΚΡΙΝΙΚΟ ΟΣΥΣΤΗΜΑ

4 Το Ενδοκρινικό Σύστημα Το ενδοκρινικό και το νευρικό σύστημα συνεργάζονται και ενορχηστρώνουν την απάντηση για τη διατήρηση της ομοιοστασίας στον οργανισμό για την απάντηση η σε ερεθίσματα

5 Ενδοκρινικό σύστημα Η κύρια διαφορά μεταξύ νευρικού και ενδοκρινικού συστήματος βρίσκεται στο χρόνο που απαιτείται για την απάντηση σε ερεθίσματα Μικρός χρόνος άμεση απάντηση για το νευρικό σύστημα Μεγάλος χρόνος μη άμεση απάντηση η για το ενδοκρινικό σύστημα

6 Ενδοκρινικό σύστημα Κύρια δράση του συστήματος είναι η διατήρηση σταθερού εσωτερικού περιβάλλοντος ήτοι ομοιοστασίας

7 Ενδοκρινικό σύστημα Ο στόχος του ενδοκρινικού συστήματος ορμονών επιτυγχάνεται με την έκκριση Ορμόνες είναι χημικές ουσίες που εκκρίνονται από αδένα και εισέρχονται στη συστηματική κυκλοφορία και δρούν σε άλλη περιοχή στον οργανισμό

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10 Ορμόνες ΟΡΜΟΝΕΣ Ο

11 Ορμόνες Δράση Ενδοκρινής Παρακρινής Αυτοκρινής

12 Ομάδες ορμονών Παράγωγα αμινοξέων Πεπτιδικές ορμόνες Παράγωγα λιπιδίων στεροειδείς ορμόνες

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14 Παράγωγα αμινοξέων Μελατονίνη είναι παράγωγο του αμινοξέος τρυπτοφάνη

15 Πεπτιδικές ορμόνες Παράδειγμα πεπτιδικής ορμόνης Προλακτίνη Αυξητική ορμόνη Ωκυτοκίνη

16 Στεροειδείς ορμόνες Παράδειγμα στεροειδούς ορμόνης Κορτιζόλη

17 Μηχανισμοί δράσης ΜΗΧΑΝΙςΜΟΙ ΔΡΑςΗς ΟΡΜΟΝΩΝ ορμονών

18 Μηχανισμός δράσης ορμονών Μηχανισμός δράσης μη στεροειδών ορμονών Μηχανισμός δράσης στεροειδών ορμονών

19 Μηχανισμός δράσης μη στεροειδών ορμονών Παράγωγα αμινοξέων και πεπτιδικές ορμόνες Δρουν σε υποδοχείς στην επιφάνεια του μεμβράνης Συνδέονται με υποδοχείς κυττάρου ή εντός της κυτταρικής Οι υποδοχείς είναι συνδεδεμένοι με πρωτείνες ειδικότερα με G-πρωτείνες Οι G-πρωτεΐνες μεταβάλλουν ένζυμα που τελικά μετατρέπουν το ATP σε camp Το camp μεταβάλλει την ενζυματική δραστηριότητα στο κύτταρο και επιτρέπει να γίνουν μεταβολές για να επέλθει η δράση της ορμόνης στο κύτταρο

20 Μηχανισμός μη στεροειδών δράσης ορμονών Ορμόνη Πεπτιδική ορμόνη Παράγωγο αμινοξέος first messenger Μεμβρανικός υποδοχέας G-πρωτεΐνηρ η Ενζυμο ATP camp second messenger

21 Μηχανισμός δράσης σεροεδώ στεροειδών ορμονών Εισέρχονται στο κύτταρο Δεσμεύονται σε ενδοκυτταροπλασματικό υποδοχέα Δεσμεύονται σε ενδοπυρηνικό υποδοχέα Το σύμπλεγμα δεσμεύεται στο DNA και μεταβάλλει τη μεταγραφική δραστηριότητα και ακολούθως την παραγωγή πρωτεινών

22 How Do Hormones Target Cells? Change Their Hormones are chem ical messengers that invoke profound changes within target t cells How is this accomplished?

23 How Do Hormones Target Cells? Change Their Activation of enzymes and other dynamic molecules Most enzymes shuttle between conformational states that are catalytically active versus inactive, on versus off Many hormones affect their target cells by inducing such transitions, usually causing an activation of one of more enzymes Because enzymes are catalytic and often serve to activate additional enzymes, a seemingly small change induced by hormone-receptor binding can lead to widespread consequences within the cell Modulation of gene expression Stimulating transcription of a group of genes clearly can alter a cell's phenotype by leading to a burst of synthesis of new proteins Similarly, if transcription of a group of previously proteins will soon disappear from the cell active genes is shut off, the corresponding

24 Mechanism of Action Hormones o with Cell Surface Receptors

25 Mechanism of Action Hormones with Cell Surface Receptors Protein and peptide hormones, catecholamines like epinephrine, and eicosanoids such as prostaglandins find their receptors decorating the plasma membrane of target cells

26 Mechanism of Action Hormones with Cell Surface Receptors Binding of hormone to receptor initiates a series of events which leads to generation of so-called second messengers within the cell (the hormone is the first messenger) The second messengers then trigger a series of molecular interactions that alter the physiologic state of the cell Another term used to describe this entire process is signal transduction

27 Structure of Cell Surface Receptors Extracellular domains Some of the residues exposed to the outside of the cell interact with and bind the hormone - another term for these regions is the ligand-binding domain Transmembrane domains Hydrophobic stretches of amino acids are "comfortable" in the lipid bilayer and serve to anchor the receptor in the membrane Cytoplasmic or intracellular domains Tails or loops of the receptor that are within the cytoplasm react to hormone binding by interacting in some way with other molecules, leading to generation of second messengers Cytoplasmic residues of the receptor are thus the effector region of the molecule

28 Cell surface receptors

29 Cell surface receptors Receptor molecules are neither isolated by themselves nor fixed in one location of the plasma membrane In some cases, other integral membrane receptor to modulate its activity Some types of receptors cluster together hormone proteins interact with the in the membrane after binding Finally, as elaborated below, interaction of the hormone-bound receptor with other membrane or cytoplasmic proteins is the key to generation of second messengers and transduction of the hormonal signal

30 Second Messenger Systems Currently, four second messenger systems are recognized in cells Note that not only do multiple l hormones utilize the same second messenger system, but a single hormone can utilize more than one system Understanding how cells integrate signalss from several hormones into a coherent biological response remains a challenge

31 Second messenger systems Cyclic AMP Protein kinase activity Calcium and/or phosph hoinositides Cyclic GMP

32 Second messenger sy stems camp Epinephrine and norep pinephrine, glucagon, luteinizing hormone, follicle stimulating hormone, thyroid- stimulating hormone, calcitonin, parathyroid hormone, antidiuretic hormone

33 Second messenger sy stems Protein kinase activity Insulin, growth hormo one, prolactin, oxytocin, erythropoietin, several growth factors

34 Second messenger sy stems Calcium and/or phosphoinositides Epinephrine and nore epinephrine, angiotensin II, antidiuretic hormone, gonadotropin-releas sing hormone, thyroid-releasing hormone

35 Second messenger sy stems cgmp Atrial naturetic horm one, nitric oxide

36 Second messenger systems

37 Cyclic AMP Second Messenger Systems Cyclic adenosine monophosph hate (camp) is a nucleotide generated from ATP through the action of the enzyme adenylate cyclase The intracellular concentration of camp is increased or decreased by a variety of hormones and such fluctuations affect a variety of cellular processes One prominent and important effect of elevated concentrations of camp is activation of a camp- protein kinase dependent protein kinase called A

38 Cyclic AMP Second Messenger Systems Protein kinase A is nominally in an catalytically-inactive inactive state, but becomes active when it binds camp Upon activation, protein kinase A phosphorylates a number of other proteins, many of which are themselves enzymes that are either activated or suppressed by being phosphor rylated Such changes in enzymatic activity within the cell clearly alter its state

39 Το παράδειγμα του γλουκαγόνου ucagon binds its receptor in the pl lasma membrane of target s (e.g. hepatocytes) und receptor interacts with and, through a set of G proteins, s on adenylate cyclase, which is also an integral membrane tein tivated adenylate cyclase begins to convert ATP to cyclic P, resulting in an elevated intracell lular concentration of camp

40 Το παράδειγμα του γλουκαγόνου High levels of camp in the cyto osol make it probable that protein kinase A will be bound by camp and therefore catalytically active Active protein kinase A "runs around the cell" adding phosphates to other enzymes, thereby changing their conformation and modulating their catalytic activity -- Levels of camp decrease due to destruction by camp- of adenylate phosphodiesterase and the inactivation cyclase

41 Το παράδειγμα του γλουκαγόνου

42 Tyrosine Kinase Second Messenger Systems The receptors for several protein hormones are themselves protein kinases which are switched on by binding of hormone The kinase activity associated with such receptors results in phosphorylation of tyrosine residues on other proteins Insulin is an example of a hormone whose receptor is a tyrosine kinase

43 Tyrosine Kinase Second Messenger Systems The hormone binds to domains expos sed on the cell's surface, resulting in a conformational change that activates kinase domains located in the cytoplasmic regions of the receptor In many cases, the receptor phosphorylates itself as part of the kinase activation process. The activated receptor phosphorylates a variety of intracellular targets, man y of which are enzymes that become activated or are inactivated upon phosphorylation

44 Tyrosine Kinase Second Messenger Systems Insulin uses a tyrosine kinase receptor Following binding of hormone, the receptor undergoes a conformational change, phosphorylates itself, then phosphorylates h a variet ty of intracellular l targets

45 Tyrosine Kinase Second Messenger Systems As was seen with camp second messenger systems, activation of receptor tyrosine kinases leads to rapid modulation in a number of target proteins within the cell Interestingly, some of the targets of receptor kinases are protein phosphatases which, upon activation by receptor tyrosine kinase, become competent to remove phosphates from other proteins and alter their activity Again, a seemingly small change due to hormone binding is amplified into a multitude of effects within the cell

46 Tyrosine Kinase Second Messenger Systems In some cases, binding of horm mone to a surface receptor induces a tyrosine kinase cascade even through the receptor is not itself a tyrosine kinase The growth hormone receptor is one example of such a system - the interaction of growth hormone with its receptor leads to activation of cytoplasmic tyrosine kinases, with results conceptually similar to that seen with receptor kinases

47 Fate of the Hormone-Rec ceptor Complex Normal cell function depends upon second messenger cascades being transient events Indeed, a number of cancers are associated with receptors that continually stimulate second messenger systems. One important part of negative regulation on hormone action is that cell surf face receptors are internalized In many cases, internalization is stimulated by hormone binding

48 Fate of the Hormone-Rec ceptor Complex Internalization occurs by endoc cytosis through structures called coated pits The resulting endosomes (sometimes called "receptosomes") may fuse with lysosomes, leading to destruction of the receptor and hormone In other cases, it appears that the hormone dissociates and the receptor is recycled by fusion of the endosome back into the plasma membrane

49 Mechanism of Action Hormone o es with Intracellular Receptors

50 Mechanism of Action Hormones with Intracellular Receptors Receptors for steroid and thyro id hormones are located inside target cells, in the cytoplasm or nucleus, and function as ligand-dependent transcription factors That is to say, the hormone-receptor complex binds to promoter regions of responsivee genes and stimulate or sometimes inhibit transcription from those genes

51 Mechanism of Action Hormones with Intracellular Receptors Thus, the mechanism of action of steroid hormones is to modulate gene expression in target cells By selectively affecting transcription from a battery of genes, the concentration of those respective proteins are altered, which clearly can change the phenotype of the cell

52 Structure re of Intracellula la ar Receptors Steroid and thyroid hormone re eceptors are members of a large group ("superfamily") of transcription factors In some cases, multiple forms of a given receptor are expressed in cells, adding to the complexity of the response All of these receptors are comp posed of a single polypeptide chain that has, in the simplest analysis, three distinct domains

53 Structure of Intracellular Receptors The amino-terminus In most cases, this region is involv ed in activating or stimulating transcription by interacting with other components of the transcriptional machinery. The sequence is highly variable among different receptors DNA binding domain Amino acids in this region are responsible for binding of the receptor to specific sequences of DNA The carboxy-terminus or ligand-binding domain This is the region that binds hormo one

54 Structure of Intracellular Receptors

55 Structure of Intracellular Receptors In addition to these three core domains, two other important regions of the receptor protein are a nuclear localization sequence, which targets the protein to nucleus a dimerization domain, which is responsible for latching two receptors together in a form capable of binding DNA

56 Hormone-Receptor Binding and Interactions with DNA Being lipids, steroid hormones enter the cell by simple diffusion across the plasma membrane Thyroid hormones enter the cell by fa acilitated t diffusion i The receptors exist either in the cytop plasm or nucleus, which is where they meet the hormone

57 When hormone binds to receptor, a characteristic series of events occurs Receptor activation is the term used to describe conformational changes in the receptor induced by binding hormone The major consequence of activation is that the receptor becomes competent to bind DNA Activated receptors bind to "hormone response elements", which are short specific sequences of DNA which are located in promoters of hormone- responsive genes In most cases, hormone-receptor complexes bind DNA in pairs, as shown in the figure below Transcription from those genes to which the receptor is bound is affected Most commonly, receptor binding stimulates transcription The hormone-receptor complex thus functions as a transcription factor

58 Hormone-Receptor Binding and Interactions with DNA As might be expected, there are a number of variations on the themes described above, depending on the specific receptor in question For example, in the absense of hormone, some intracellular receptors do bind their hormone response elements loosely and silence transcription, but, when complexed to hormone, become activated and strongly stimulate t transcription ti Some receptors bind DNA not with another of their kind, but with different intracellular re eceptor

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61 Membrane Glucocorticoid Rece eptor Activation Induces Proteomic Changes Aligning with Classical Glucocorticoid Effects Vemmochi et al, Mol Cell Proteomics 2013; 12(7):

62 Ανίχνευση μεμβρανι ικού υποδοχέα κορτικοστεροειδών σε κυτταρικές σειρές

63 Γονιδιακές και μη γονιδιακές δράσεις των γλυκοκορτικοειδών Genomic and nongenomic effects of glucocorticoids. Stahn et al. Nat Clin Pract Rheumatol 2008; 4(10):

64 Γονιδιακές και μη γονιδιακές δράσεις των γλυκοκορτικοειδών The strong anti-inflammatory and immunosuppressive effects of glucocorticoids are mediated primarily by the cytosolic glucocorticoid receptors These receptors are members of the steroid hormone receptor family, a superfamily of ligand-inducible inducible transcript tion factors, and exert genomic effects that can result in increased expression of regulatory-including antior decreased production of inflammatory-proteins (transactivation), proinflammatory proteins (transrepression)

65 Γονιδιακές και μη γονιδιακές δράσεις των γλυκοκορτικοειδών Transactivation is thought to be responsible for numerous adverse effects of glucocorticoids; transrepression is thought to be responsible for many of the clinically desirable anti-inflinfl ammatory and immunosuppressive effects of glucocorticoids Optimized glucocorticoids, suc ch as selective glucocorticoid receptor agonists, are being developed to try to minimize the adverse effects many patients experience

66 Γονιδιακές και μη γονιδιακές δράσεις των γλυκοκορτικοειδών Glucocorticoids also exert their effects via rapid, nongenomic mechanisms that can be classified as involving nonspecific interactions of glucocorticoids with cellular membranes, nongenomic effects that are mediated by cytosolic glucocorticoid receptors, or specific interactions with membrane-bound b glucocorticoid id receptors Increased understanding of these mechanisms of glucocorticoid action could enable the development of novel drugs with which to treat patients with inflammatory and autoimmune disease

67 Μηχανισμοί δράσης ορμονών Οι ορμόνες δρουν είτε μεταβάλλοντας τη δράση ενζύμων είτε μεταβάλλοντας τη δράση του DNA ήτοι τη μεταγραφική δραστηριότητα στο κύτταρο Πολλές ορμόνες έχουν πολλαπλούς μηχανισμούς δράσης