Transcript Endocrine Receptors

Dr. C. Behrens
Dr. T. Mofokeng
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About 100 years ago Starling coined the term
“hormone” to describe secretin, a substance
secreted by the small intestine into the
bloodstream to stimulate pancreatic secretion.
The first connection between a viral oncogene,
a mutated receptor tyrosine kinase and human
cancer was made in 1984
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Neural
Endocrine,
Neuroendocrine
Paracrine
Autocrine
Tropic hormones
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Typical examples are luteinizing hormone, and folliclestimulating hormone, thyroid-stimulating hormone and
adrenocorticotrophic hormone (LH, FSH, TSH, ACTH)
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G protein coupled receptors
Tyrosine kinase receptors
Serine/threonine kinase receptors
Ion channels
Cytokine receptors
Nuclear receptors
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describes the affinity of the hormone for the
receptor.
It is usually a straight line, but several
mechanisms contribute to a non-linearity:
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More than one type of receptor that binds to
hormone
More than one binding site
Cooperative interactions among binding sites
3 general classes of hormones:
 Protein and polypeptides
 The steroids
 the amino acid tyrosine
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In or on the surface of the cell
membrane.
In the cell cytoplasm
In the cell nucleus (nuclear
receptor superfamily)
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These hormones bind to intracellular
receptors that function in the nucleus of
the target cell to regulate gene expression.
Classical hormones that utilize
intracellular receptors include thyroid and
steroid hormones.
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Change membrane permeability
Activate intracellular enzymes when they
combine with their receptors
Activate Genes by binding with intracellular
receptors
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Down Regulation: binding of a hormone with
its target cell receptors often causes the number
of active receptors to decrease
Up Regulation: The stimulating hormone
induces the formation of more receptor
molecules than normal by the proteinmanufacturing machinery of the target cell.
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Internalization:
Receptor endocytosis causes internalization of cellsurface receptor
 Hormone-receptor complex is subsequently
dissociated
 Receptor trafficking may then result in recycling
back to the cell-surface
 or internalized receptor may undergo lysosomal
degradation.
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Lead to impaired hormone signalling by down-
regulation.
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Common structural mechanisms :
an extracellular domain containing the
ligand-binding site,
 a single transmembrane domain
 and an intracellular portion that
includes the tyrosine kinase catalytic
domain.
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Once activated, they are capable of
phosphorylating other protein substrates.
There are at least two distinct mechanisms
whereby tyrosine phosphorylation regulates
protein function
Phosphatidylinositol 3-Kinase
 Grb-2 and the activation of RAS:
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Grb-2 and the activation of RAS:
 mSos is capable of activating the Ras, a small G protein
that plays an important role in intracellular signalling
pathways.
 mSos activates Ras by catalysing the exchange of GTP
to GDP in the guanine nucleotide-binding site of Ras.
 This in turn triggers the activation of a cascade of
serine/threonine-specific protein kinases including
Raf,
 These pathways downstream from Ras contribute to
theability of tyrosine kinases to promote cell growth
and regulate the expression of various genes.
Receptor tyrosine kinase and disease patterns:
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Overexpression or mutations are responsible for
oncogenic RTK’s
Alterations include deletions or mutation within
the extracellular region or alterations of the
catalytic domain result in a constitutive active
RTK.
Mutations within the transmembrane domain lead
to ligand-independent kinase activation as
reported for the RTK HER2/neu.
Intervention Strategies:
 Possibility for the development of target –
specific drugs and new anti-cancer therapies
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Promising approach: small molecule drugs
that selectively interfere with the intrinsic
tyrosine kinase activity and thereby block
receptor
The tyrphostins, which belong to the
quinazolines: specifically inhibit the EGFR
This family comprise of four members:
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EGFR/ErbB1, which was the first RTK to be
molecularly cloned
HER2/ErbB2
 HER3/ErbB3
 HER4/ErbB4
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The EGFR is frequently overexpressed in nonsmall cell lung, bladder, cervical, ovarian,
kidney and pancreatic cancer and occurs with
very high incidence in squamous cell
carcinomas of the head and neck.
A very potent mechanism of constitutive EGFR
activation in a variety of human cancers is
autocrine stimulation via growth factor loops
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Since aberrant EGFR signalling is implicated in
many cancers and seems to correlate with poor
prognosis, it is an excellent target for anti-cancer
therapy
Currently the monoclonal antibody-based
treatments using cetuximab (C225) represent the
most successful anti-EGFR therapies
C225 is directed against the extracellular domain of
the EGFR and inhibits receptor activation and
downstream signalling by blocking ligand binding
to the EGFR and inducing receptor internalization.
The RTK HER2 was originally identified at both
the transforming gene in a chemically transformed
rat neuroblastoma cell line and has been most
frequently implicated in human neoplasias and
cancer
The role of HER2 in tumour growth:
 The transforming ability of HER2 is linked to cell
survival
 Progression through the cell cycle is critically
dependent on active complex formation of CDK
with cyclin D1
 key regulator of G1/S phase transition of the cell
cycle.
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Overexpression of HER2 increases the
metastatic potential of human potential of
human breast and lung cancer cells and
correlates with the number of lymph node
metasteses in node-positive breast cancer
patients
Elevated levels of a processed HER2
extracellular domain metastatic breast cancer
patients seem to reduce the efficacy of certain
chemotherapy combinations
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consist of two extracellular α subunitsand two
membrane spanning β subunits bearing the
tyrosine kinase domain and the
autophosphorylation site
While insulin is mostly a metabolic hormone,
IGF-I and IGF-II are crucial for normal
development and carcinogenesis
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The insulin receptor closely resembles the type 1
receptor for IGFs.
In the inactive form of insulin receptor kinase,
TYR1162 is located in a position so that it blocks
protein substrates from binding to the active site,
When the three tyrosine residues in the activation
loop become phosphorylated by autophosporylation of three tyrosine residues (Tyr1158,
Tyr1162,Tyr1163) in the activation loop,
an important conformation change occurs
as a result the ability to bind both ATP and protein
substrates.
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They are expressed on endothelial cells during
embryonic development and are the key
regulators for angiogensis, a process which
leads to the formation of new blood vessels
developing from pre-existing ones
solid tumours beyond a diameter of 1-2mm
requires de novo formation of a vascular
network
http://www.bumc.bu.edu/busm-pathology/busm-faculty-profiles/naderrahimi-phd/
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The FGFs and their designated receptors play
roles in normal development but also in
tumour formation and progression.
Suramin, a compound that complexes heparinbinding growth factors, such as FGF-2, has
been shown to inhibit cell migration and FGF-2
mediated induction of urokinase-plasminogen
activator.
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The gene responsible for MEN2 was identified
as the Rearranged during transformation (RET)
RTK
Has intra and extracellular codons
expressed during embryogenesis in the
peripheral nervous system and in the
development of the neural crest and the
kidneys
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Men 2A : Autosomal dominant
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Men and women equally effected
Medullary Thyroid carcinoma
Pheochromocytoma
Primary Parathyroid hyperplasia
Men 2B: Autosomal dominant
Medullary Thyroid carcinoma
 Pheochromocytoma
 NOT HYPERPARATHYROIDISM
 The tumour develops at an earlier age and is more
aggressive than in MEN2A
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Several features in common with Receptor
Tyrosine kinase:
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N-terminal extracellular domains, which bind ligand
A single transmembrane domain
C-terminal intracellular domains, which possess
protein kinase activity
The two classes of differ with respect to
enzymatic specificity
Mediate the biological actions of the
transforming growth factor (TGF)-β family of
ligands
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Cytokine receptors activate members of the Janus family of
tyrosine kinases:
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four known JAKs (JAK1, JAK2, JAK3, TYK2).
Precise regulation of the cytokine receptors is required for normal
function
Ligand binding to cytokine receptors normally activates JAKs
rapidly and transiently.
Activated JAKs and STATs are associated with cellular
transformation.
For example, a single acquired activating point mutation in JAK2 is
present in the majority of patients with a myeloproliferative disorder.
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G protein-coupled receptors (GPCR) are an e
evolutionarily conserved gene superfamily
with members in all eukaryotes from yeast to
mammals.
All share a common structural feature,
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seven membrane-spanning helices,
but various subfamilies diverge in primary amino
acid sequence and in the domains that serve in
ligand binding, G prot coupling and interaction with
other effector proteins.
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All GPCR act as guanine nucleotide
exchange factors
G protein- regulated effectors include
enzymes of second messenger metabolism
such as adenyl cyclase and phospholipase
effect on hormone secretion, muscle
contraction and a variety of other
physiologic functions.
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Hormones bind receptor: coupling of the
receptor to a G-protein
This receptor becomes the activated
enzyme adenyl cyclase,
Protrudes to the inside of the cell.
Catalyzes the formation of cAMP,
and cAMP has a multitude of effects
inside the cell to control cell activity
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Adrenocorticotropic Hormone (ACTH)
Angiotensin II (epithelial)
Calcitonin
Catecholamines (B receptors)
Corticotropin –releasing hormone (CRH)
Follicle –stimulating Hormone (FSH)
Glucagon
Human Chorionic Gonadotropin (HCG)
Luteinizing hormone (LH)
Secretin
Thyroid Stimulating Hormone (TSH)
Vasopressin
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Angiotensin II (vascular smooth muscle)
Catecholamines
Gonadotropin-releasing hormone
Growth Hormone releasing hormone
Oxytocin
Thyroid releasing hormone (TRH)
Vasopressin
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GPCRs have long been a major targer for drug
development.
Defects in GPCRs are an important cause of a
wide variety of human diseases.
Diseases caused by G protein
coupled receptor loss of function
mutations
Receptor
Disease
Inheritance
V2: Vasopressin
Nephrogenic diabetes insipidus
X-linked
ACTH
Familial ACTH Resistance
Autosomal recessive
GHRH
Familial GH deficiency
Autosomal recessive
GnRH
Hypogonadotropic Hypogonadism
Autosomal recessive
GPR54
Hypogonadotropic Hypogonadism
Autosomal recessive
FSH
Autosomal recessive
LH
Hypergonodadotropic ovarian
dysgenesis
Male pseudohermaphroditism
TSH
Familial Hypothyroidism
Autosomal recessive
CA 2+ sensing
Autosomal dominant
Autosomal recessive
Melanocortin 4
Familial Hypocalcuric hypercalcemia,
Neonatal severe primary
hyperparathyroidism
Obesity
PTH/PTHrP
Blomstrand Chondrodysplasia
Autosomal recessive
Autosomal recessive
Autosomal recessive
Receptor
Diseases caused by G
protein coupled receptor
gain-of-function mutations
Disease
Inheritance
LH
Familial male precocious
puberty
Autosomal dominant
TSH
Sporadic hyper functional
thyroid modules
Noninherited (somatic)
TSH
Familial nonautoimmune
hyperthyroidism
Autosomal dominant
Ca2+ sensing
Familial hypocalcemic
hypercalcuria
Autosomal dominant
PTH/PTHrP
Jansen’s metaphyseal
chondrodysplasia
Autosomal dominant
V2 vasopressin
Nephrogenic inappropriate Autosomal dominant
antidiuresis
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Bind to intracellular receptors
Regulate gene expression.
Lipophilic: readily absorbed from GIT
Excellent targets for pharmaceutical
interventions.
Range from those used to treat specific
hormone deficiencies to those used to treat
common multigenic diseases such as
inflammation, cancer and type 2 Diabetes.
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The carboxyl (C-) terminus of the
nuclear receptor is responsible for
hormone binding.
Major structural change: internal
folding of the most C-terminal helix
(H12)
Class
Hormone
Receptor
Classical Hormones
Thyroid Hormone
Thyroid hormone receptor Subtype α, β
Estrogens
Estrogens Receptor (ER) subtype α, β
Testosterone
Androgen receptor (AR)
Progesterone
Progesterone receptor (PR)
Aldosterone
Mineralocorticoid receptor (MR)
Cortisol
Glucocorticoid receptor (GR)
1,25-(OH)2-vit.D
Vit.D receptor (VDR)
All-trans-retinoic
acid
9-cis-retinoic acid
retinoid acid receptor , subtypes α, β and γ
Fatty acids
Peroxisome proliferators activated receptor (PPAR) , subtypes
α, β and γ
Oxysterols
Liver X receptor (LXR) , subtypes α, β
Bile acids
Bile acid receptor (BAR)
Vitamins
Metabolic
intermediates and
products
Xenobiotics
Retinoid X receptor (RXR) , subtypes α, β and γ
Pregnane X receptor (PXR)
Constitutive androstane receptor (CAR)
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Vitamin D are synthesized and stored in the
skin and activated by ultraviolet light;
vit D can also be derived from dietary sources.
Vit D is then converted in the liver to 25(OH)
Vitamin D and in the kidney to 1-25(OH)2Vitamin D3.
1-25(OH)2-Vitamin D3 is the most potent
natural ligand of vitamin D receptor (VDR).
Up to date version 18.2
Steroid Hormones increase protein synthesis
The sequence of events:
1. Steroid hormone enter cytoplasm
2. Bind to specific receptor protein
3. Combined receptor protein-hormone then
diffuses into or is transported into nucleus
4. Bind to a specific points on the DNA strands
5. Activates the transcription process of mRNA
6. mRNA diffuses into cytoplasm
7. Translation at ribosomes to form new proteins
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Hormone overproduction
Hormone underproduction
Altered tissue responses to hormones
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Resistance to hormones can be causes by a variety of
genetic disorders.
Tumours of the endocrine glands
Genetic Defects in Receptor function
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Mutations can lead to a decrease in the number of receptors by
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Impairing receptor biosynthesis
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Inhibiting the transport of receptors to their normal location in the plasma membrane
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Accelerating the rate of receptor degradation
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Mutations can impair the intrinsic activities of the receptor.
Auto-antibodies directed against Cell-surface receptors
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Inhibitory anti-receptor autoantibodies were first identified in myasthenia gravis (where
nicotinic acetylcholine receptor impair neuromuscular transmission, apparently by
accelerating receptor degradation)
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Insulin resistance is caused by at least two mechanisms:
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The anti-receptor antibodies inhibit insulin binding to the receptor
The antibodies accelerate receptor degradation
Graves-disease provided the first example of stimulatory anti-receptor antibodies, where
there are auto-antibodies directed against the thyroid-stimulating hormone (TSH)
receptor. These anti-receptor antibodies activate the TSH receptor, thereby stimulating
growth of the thyroid gland as well as hypersecretion of the hormone.
IGF
AKROMEGALY
Pegvisomant
RECEPTOR
TYROSINE
KINASE
HER 2
BREAST CANCER
Trastuzumab
cAMP
G-COUPLED
PROTEIN
RECEPTORS
Secondary
messenger
systems
SERINE
KINASE
TGF
NEPHROGENIC SYSTEMIC
FYBROSIS IN ADVANCED
RENAL FAILURE
NUCLEAR
HORMONE
VIT D
OSTEOPOROSIS
CYTOKINE
RECEPTORS
JAK
POLYCYTEMIA VERA
HORMONE
RECEPTORS
Calciumcalmodulin
complex
?? Imatinib
Imatinib trials
busy