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FUNdamentals 1
09/24/08 (Dr. Whikehart)
10:00 – 11:00
Note: Bolded material is information directly off slide.
Slide 1 - STEROID & THYROID HORMONES
 Unique problems are involved in the delivery of these hormones to their target tissues as well as the
difference in the way that they are processed in comparison to peptide hormones.
Slide 2 - INTRODUCTION:
 TYPES of hormones involve AND their ORIGINS (how they are made)
 SYNTHESIS: STEROIDS, T3/ T4 (TSH)
 CARRIER MOLECULES (BOUND VS. UNBOUND) and the degree to which they are bound
 LISTING OF SOME IMPORTANT TYPES
 RECEPTORS & MECHANISMS OF ACTION
Slide 3 - STEROID TYPES
 EVEN THOUGH THERE ARE LITERALLY HUNDREDS OF DIFFERENT STEROIDAL
HORMONES SYNTHESIZED IN THE BODY, THEY CAN ALL BE CLASSIFIED INTO THE
FOLLOWING 3 GENERAL CATEGORIES:
 GLUCOCORTICOIDS (originally named because they were thought to increase the metabolism of
glucose, but they support more than just glucose metabolism):
o SUPPORT INCREASED METABOLISM OF CARBOHYDRATES, LIPIDS AND PROTEINS
AS WELL AS INFLAMMATORY REACTIONS AND STRESS COPING.
 MINERALOCORTICOIDS: REGULATE SALT RECOVERYAND WATER VOLUME (VIA THE
KIDNEYS).
o Done by means of reuptake of sodium ions and then removal of potassium ions in the kidneys
 ANDROGENS & ESTROGENS: AFFECT SEXUAL DEVELOPMENT AND FUNCTION AS WELL
AS TO SUPPORT PREGNANCY.
o Not all androgens and estrogens, but some
Slide 4 - ORIGINS
 STEROIDS ARE MADE FROM CHOLESTEROL ON THE OUTER MITOCHONDRIAL SURFACE
IN THE ADRENAL GLANDS AND GONADS.
 THIS IS DONE UNDER THE INFLUENCE OF ADRENOCORTICO TROPIC HORMONE (ACTH)
FROM THE ANTERIOR PITUITARY GLAND.
 THE ADRENAL GLANDS MAKE (synthesize) THREE STEROIDS:
o CORTICOSTERONE
o CORTISOL
o ANDROGENS
 ACTH IS LARGELY INVOLVED IN MAKING GLUCO-CORTICOIDS (MORE TO FOLLOW as we
go along)
 The diagram in the lower right hand corner shows you the location of the adrenal glands, which are right
above the kidneys on the left and right sides. They are fairly close to one another.
Slide 5 - STEROID SYNTHETIC PATHWAYS
 General synthetic scheme to show you how these are manufactured.
 They all begin with cholesterol and go through several different pathways.
 Will end up with either a corticosterone, cortisol or an aldosterone.
 Corticosterone really isn’t a final product. It goes on to form aldosterone.
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o Cholesterol  Corticosterone  Aldosterone
Cortisol and aldosterone are really the steroids that I want you to know about.
The reason for all the intermediates is because several different kinds of enzymes that are considered to
be oxidases (oxygen-adding) are involved in this process.
In addition we need NADPH (obtained from pentose shunt pathway) to be a source of electrons that is
needed for the synthesis of these particular steroids.
These enzymes, which are oxidases in nature are complex and are referred to as P450 series of enzymes.
o Notice on left hand side the different P450 enzymes.
o They are all a series of closely related enzymes found in the mitochondria.
o Iron complexes that are similar to the heme groups you find in hemoglobin are present on these
oxidases
What you need to know about this diagram:
o the enzyme class that is necessary for this to take place
o the two products (aldosterone and cortisol)
o NADPH required to carry out synthesis
Example: Pregnenolone (on slide)
o Shifts in the double bonds are important and need to be considered
o From ring B (which has the double bond) moves to ring A
o In Deoxycorticosterone (third intermediate here) you see that there has been a hydroxy group
added to replace the methyl group on the upper portion the extension off of the D-ring (right
hand ring)
o It is a series of oxidations that take place
o Finally when you get down to corticosterone the next product, you see that a hydroxy group has
been added to the C-ring.
o Aldosterone (notice thin blue line transition) has a methyl group added
o Again, most of the time you have oxidations, but you may also have shifts in double bonds or the
addition of a methyl group to form the final product
Slide 6 - Notes
 1. SYNTHETIC PATHWAYS OCCUR IN THE ADRENAL CORTEX
o DO NOT MEMORIZE STRUCTURES! (even the product structures)
 2. MUCH OF THE SYNTHESES INVOLVE OXIDATION AND REQUIRES NADPH (WHERE
DOES THAT COME FROM?)
 3. MANY OF THE ENZYMES ARE MEMBERS OF THE CYTOCHROME P450 FAMILY OF
OXIDASES
o NOTED INHABITANTS OF MITOCHONDRIA.
 4. MAJOR STEROID PRODUCTS ARE UNDERLINED.
 5. CORTCOSTERONE (BLUE ARROW) HAS WEAK MINERALO- GLUCORTICOID-LIKE
ACTIVITY. (interesting because when we get to distinguish between the two of them you will find that
most steroids dominate in either one of these activities or the other…some have mixed activities as well)
o ALDOSTERONE HAS A SIMILAR STRUCTURE & IS PRODUCED AFTERWARDS. (the
illustration shows this concept)
 6. CORTISOL (RED ARROW) IS A GLUCOCORTICOID CONCERNED WITH ENERGY
PRODUCTION.
o ALDOSTERONE IS A MINERALOCORTICOID.
Slide 7 - GLUCOCORTICOID VS. MINERALOCORTICOID ACTIVITY
 Comparison of the two activities.
 STEROID HORMONES HAVE NUMEROUS EFFECTS ON CELLULAR FUNCTIONS THAT
INCLUDE:
o METABOLISM
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o ION TRANSPORT (WATER RETENTION)
o IMMUNE FUNCTIONS
o SEXUAL CHARACTERISTICS.
TWO VERY DOMINANT CHARACTERISTICS ARE GLUCOCORTICO- AND
MINERALOCORTICO FUNCTIONS.
o GLUCOCORTICO- FUNCTIONS PRIMARILY INVOLVE INCREASING THE ENERGY
LEVELS OF CELLS (1ST SEEN AS INCREASING AVAILABLE GLUCOSE).
 [CORTISOL]
o MINERALOCORTICO- FUNCTIONS PRIMARILY INVOLVE THE RETENTION OF IONS
IN THE BLOOD THROUGH KIDNEY REABSORPTION OF Na+.
 [ALDOSTERONE]
 means that K+ is not reabsorbed but is past out in the urine
“If you miss this on the exam I will be very very disappointed.”
Slide 8 - TRANSPORT
 There is a problem in transporting the steroid hormones in the blood because steroid hormones are lipid
soluble and they are not soluble in aqueous medium.
 The hormones are made in the adrenal glands and put out into the blood and they are not going to go
anywhere by themselves because they are insoluble and would adhere to the blood vessels and produce
plaque that would lead to a possible heart attack.
 STEROID HORMONES ARE NOTORIOUSLY INSOLUBLE IN BLOOD. THEY REQUIRE A
CARRIER PROTEIN TO MAKE THEM ENERGETICALLY COMPATIBLE (the amount of energy
necessary has to be minimized) WITH THE AQUEOUS ENVIRONMENT OF PLASMA.
 What is the difference between blood plasma and blood serum?
o Serum does not have cells
 TWO PROTEINS ARE KNOWN TO TAKE ON THAT ROLE of transport of these steroids:
TRANSCORTIN AND ALBUMIN (well known serum protein)
 TRANSCORTIN, ON THE RIGHT of slide, HAS A MOLECULAR WT. OF ~45.7 kD.
 ABOUT 75% OF ALL CORTISOL of one of these steroids BINDS TO THIS PROTEIN. THE
REMAINDER BINDS TO ALBUMIN.
 The percentage that is bound to transcortin as to the percentage that binds to the albumin varies a little
bit, but these proteins have to be bound to a carrier protein.
 Transcortin is a mixture of 3 different kinds of structures Beta-pleated sheets (yellow), alpha helices
(red), random coil structures (green).
Slide 9 - SYNTHESIS OF T3 & T4
 Synthesis of Thyroxine (T4) and Triiodothyronine (T3)
o Note: Professor stated “Thyroglobulin” as T4, but common literature sites TG being used by the
thyroid gland to produce the T3 & T4.
 These thyroid hormones are manufactured in the thyroid gland.
 THE THYROID GLAND IS A BUTTERFLY SHAPED ORGAN THAT WRAPS ITSELF AROUND
THE TRACHEA AS SHOWN ON THE RIGHT (ARROW).
 THE SOLE PURPOSE OF THE ORGAN IS TO PRODUCE THYROID HORMONES THAT ARE
INVOLVED IN ESTABLISHING AND MAINTAINING AN OPTIMAL METABOLIC RATE FOR
THE CELLS IN THE BODY.
Slide 10 - THYROGLOBULIN,
 Diagram of some of the cells that make up thyroid gland
 Notice at the top at the region beyond these cells in the colloid area and a lot of transport between the
colloid area and the epithelial cells take place
 These cells have an important job: take up iodine in the iodide form (occurs in the basal region)
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o Iodide leaves the blood, goes through the epithelial cells, and is transported out the opposite side
o At the same time protein synthesis is occurring to synthesize a protein called thyroglobulin (A
LARGE PROTEIN THAT CONTAINS TYROSINE PRECURSORS FOR T3/ T4. (SEE
ARROW))
CUBOIDAL EPITHELIAL CELLS IN THE GLAND MAKE AND IODINATE THYROGLOBULIN
IODINATION OCCURS IN THE COLLOID SPACE OUTSIDE THE CELLS.
Summary: Thyroglobulin, the large protein containing the tyrosine precursors, occurs in the colloid
space outside the cells
Slide 11 - HOW IODINE IS ADDED TO TYROSINE ON TG (Thyroglobulin)
 THIS SCHEME SHOWS HOW IODINE IS ADDED TO TYROSINE ON TG (Thyroglobulin)
 There are 3 enzymes involved in this entire process
o NOTE THE KEY ENZYMES:
 IODOPEROXIDASE
 Takes and adds iodine to tyrosine residues that are present on one molecule
 In order for this to take place, we need a negatively charged iodine, as the iodide
anion and hydrogen peroxide…when that takes place iodine is added to either one
location or two locations on the ring of the tyrosine residue
 Squiggly line on slide represents the remainder of the thyroglobulin molecule
 Summary: iodination process
 COUPLING ENZYME
 Two tyrosine residues (that are now iodinated from the first step) are coupled
(“piggybacked”) one on top of the other and you now have either unreleased T3
or T4 hormones.
 TG PROTEASE.
 Then the thyroglobulin is broken down.
 The result of this will be the release of the particular amino acids that are now no
longer amino acids and are now no longer amino acids, but are now hormones
that are to be released into the body
 Summary: THE TYROSINE IS PIGGYBACKED ONTO ANOTHER TYROSINE; AND THE TG IS
HYDROLYSED.
Slide 12 - T3/ T4 RELEASE
 IODINATED THYRO-GLOBULIN (TG) IS TAKEN BACK INTO THE CELL (at this point the
iodination has taken place from the previous reactions) INTO LYSOSOMES WHERE THE TG IS
DIGESTED (ARROW).
 T3/ T4 IS RELEASED FROM ITS LYSOSOMES (ARROW) UNDER THE “INFLUENCE” OF TSH
(causes a number of things: uptake of iodine, regulation of the volume of the cell to indicate how much
hormone to intake, release of the hormone itself, etc.)
o T3 & T4 now remaining in these lysosomes usually, but not always, are taken to a point on the
plasma membrane of the cell where they will be released into the blood stream
o 2 possible mechanisms:
 early release of T3 & T4
 the retention of T3 & T4 in the lysosome and then they are released into the bloodstream
Slide 13 - THYROID HORMONES RELEASED INTO THE BLOOD
 There are about 8 kinds of thyroid hormones.
 We’ve already seen 2 types and these are the important ones for this class.
 This slide shows 4 of the 8 forms called thyroxine (T4) (note 4 iodines attached)
 T3 has a iodine missing (blue arrow)
 We can also have an iodine missing from an opposite ring – reverse T3 (2 types)
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We can also have it missing from two of the ring structures
Reason for this slide: Look at the biological activity of these hormones. If thyroxine, first known of
these thyroid hormones, has a biological activity equivalent to 1, then T3 has a biological activity
between 300-800%.
o T3 is the more potent of the two
The reverse T3 has a potency of less than 1%
The diiodothyronine has less than 1-3%
THE HORMONES ARE CARRIED BY THYROXINE BINDING GLOBULIN (TBG),
THRYROXINE BINDING PREALBUMIN (due to migration in electrophoretic field, it is not a
precursor for albumin), AND ALBUMIN.
o These are 3 carrier proteins that bring these hormones to the target tissues
Slide 14 - WHEN Thyroid HORMONES ARRIVE AT THEIR TARGET CELLS
 Mechanism is the same for all of the steroid and thyroid hormones
 SINCE THESE HORMONES (BOTH STEROIDS AND THYROID HORMONES ARE LIPID
SOLUBLE, THEY IMMEDIATELY CROSS THE PLASMA MEMBRANE OF THE CELLS (as soon
as they are released by their carrier proteins).
 AT THAT POINT THEY ENCOUNTER AND ARE BOUND BY A RECEPTOR PROTEIN.
o The receptor protein has domains that you don’t find in any other protein
o The hormone binds to one area (right hand side) called the hormone binding site near the
carboxyl end of the protein
o Also see a blocking protein here
o Also an area called a gene activating/inhibiting domain
o 3-4 domain areas (binding areas)
 Hormone binding domain – ligand binding domain (LBD)
 Where the hormone binds to the protein
 Twisting/flexibility area (not shown here)
 DNA binding area (DBD – DNA binding domain)
 Activating/inhibiting domain
 Ligand-independent transactivation domain
o Normally when the steroid hormone or the hormone from the thyroid gland is not bound to the
protein, another protein binds called a blocking protein, which prevents the protein from binding
to DNA until it is ready
Slide 15 – SCHEME OF A STEROID/THYROID RECEPTOR PROTEIN
 GENERAL SCHEME OF A STEROID/THYROID RECEPTOR PROTEIN. THE LIGAND
TRANSACTIVATION DOMAIN (LEFT) HAS A VARIABLE LENGTH (RED ARROW).
 Review slide of what has already been discussed.
Slide 16 - MECHANISM FOR TRANSCRIPTION ACTIVATION
 The transactivation area is going to go from one area of DNA to another of DNA.
 There are 2 binding sites for DNA on this protein.
 None of this can take place until the steroid binds to the LBD area.
 Note illustration on the right: LBD and DBD areas with steroids.
o Binds to the LBD area.
o Small section of DNA bound to DBD.
o Remainder of the transactivation domain would exist further back in the figure.
 This is the actual activation process
o Before binding takes place, the steroid-bound protein it present.
o The DBD area is going to bind to an enhancer region for which it is specific on double stranded
DNA.
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o At the same time RNA polymerase is binding to a promoter region.
o Once the RNA polymerase is bound, nothing is going to take place because it needs another
enhancer in order for RNA transcription to take place
o The area of the transcription (N-terminal end of protein) will bind first and then extend into the
area of the promoter region and interact with something on the promoter or with RNA
polymerase to give a signal to begin transcription
o This is the way that steroid hormones and thyroid hormones cause some activation of cells to
take place
2-3 different modes of change in RNA promotion that are achieved by these hormones
o the most obvious one is activation
o another is inhibition
o another is a modulation of activity causing either to transcribe faster or slower than it normally
does
IN THIS DIAGRAM, THE LIGAND INDEPENDENT DOMAIN MUST BE ABLE TO REACH
FROM THE ENHANCER REGION TO THE PROMOTER REGION TO INFLUENCE
TRANSCRIPTION (RED ARROW)
Slide 17 - SUMMARY
 STEROID HORMONES FALL INTO THREE GENERAL CLASSIFICATIONS.
o THEY ARE MADE IN THE ADRENAL GLANDS AND SEX ORGANS.
 CHOLESTEROL IS THE PARENT COMPOUND FOR STEROIDS THAT ARE PRODUCED BY
OXIDATION IN THE MITOCHONDRIA.
 CARRIER PROTEINS ARE NEEDED FOR STEROIDS AND THYROID HORMONES.
 THYROID HORMONES SUPPORT GENERAL METABOLISM
o SEVERAL FORMS EXIST.
 Most active form is T3
 STEROID & THYROID HORMONES USE RECEPTOR PROTEINS THAT ARE
TRANSACTIVATORS FOR RNA POLYMERASE.
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