this ppt provides information about steroid hormone, their receptors, structure of receptors, and their role in gene expression

1. BIOCHEMICAL ASPECTS
(B) Mechanism of Action of Steroid Hormones
• STEROID HORMONE RECEPTORS – Expression
, Distribution, Regulation, Interaction with DNA (post-
translational & post - transcriptional)

2. SYNOPSIS
• Steroid hormones- A brief introduction
• Steroid hormone receptor
 Types & structure
• Mechanism of hormone action
• Role in gene expression
 Expression
 Distribution
 Regulation
 Interaction with DNA
• Refrences
• Conclusion

3. Steroid hormones
• The steroid hormones are synthesized by endocrine glands such as
the gonads (testis and ovary), the adrenals and (during gestation)
by the fetoplacental unit, and are then released into the blood
circulation.
• Steroid hormones are lipophilic molecules having low-molecular
weight hence it enters the by simple diffusion.
• The parent compound from which all steroid hormones are derived
is cholesterol.
• They all contain the same cyclopentanophenanthrene ring and
atomic numbering system as cholesterol.

4. STEROID HORMONE AND GENE EXPRESSION
• SH can have an activating or inhibiting effect on the genes.
• Not all genes are regulated by SH but a particular set of genes.
• These genes contain specific DNA sequences that are located in multiple copies in the
promoter region and are called as Hormone Response Elements (HREs).
• The unique action of each type of steroid results from the different receptor proteins
and HREs involved.
• In different types of cells, the same steroid hormone may activate different set of
genes.
• The genetic programs that they establish or modify affect virtually all aspects of the
life, covering such diverse aspects as embryogenesis, homeostasis, reproduction, cell
growth, or death.

5. STRUCTURE
• As all the steroid hormones are derived from cholesterol their basic structure is
similar.
• They contain three hexagonal carbon rings and a pentagonal carbon ring to which
a side-chain is attached.
PROGESTERONE ALDESTERONE CORTISOL

6. FUNCTIONS
• They act both on peripheral target tissues and the central nervous system (CNS).
• GONADAL STEROIDS influence the sexual differentiation of the genitalia and of the
brain, determine secondary sexual characteristics during development and sexual
maturation, contribute to the maintenance of their functional state in adulthood and control or
modulate sexual behaviour.
• ADRENAL STEROIDS modulate metabolism of carbohydrates, act as immunosuppressive and
anti inflammatory components, control excretion of electrolytes, etc.
CLASSIFICATION
• Steroid hormones can be grouped into five groups by the receptors to which they bind:
 Glucocorticoids
 Mineralocorticoids
 Androgens
 Estrogens
 Progestagens

7. STEROID HORMONE RECEPTOR
• Steroid hormone receptors are proteins that have a binding site for a
particular steroid molecule.
• Steroid hormone receptors are found in the cytosol and also in the nucleus of
target cells.
• Steroid hormone receptor belong to NUCLEAR RECEPTOR FAMILY.
• They are ligand-activated proteins that regulate transcription of selected
genes.
• Their response elements are DNA sequences that are bound by the Hormone-
Receptor complex.

8. TYPES OF STEROID HORMONE RECEPTORS

9. MOLECULAR STRUCTURE OF SHR
• The molecular structure of SHR shows presence of five distinct regions :
• Two end terminals – N terminal & C terminal.
• A hinge region
• Two domains – DNA binding domain & Ligand binding domain.
DNA Ligand
binding binding
domain domain
N terminal C terminal
Hinge
region
DIAGRRAMATIC REPRESENTATION OF SRUCTURE OF SHR

10. N TERMINAL
• It is also called as VARIABLE terminal as the length of this terminal is variable for every
hormone.
• Its length ranges between 100 to 500 amino acids.
• It contains several autonomous transactivation domain.
DNA BINDING DOMAIN
• About 59-76% of amino acid sequences are similar in all SHRs.
• It consists of zinc fingers and forms a highly conserved residue core.
• Usually present in the centre of receptor molecule.
• This is the region that interacts with the HRE.
HINGE REGION
• It is a poorly conserved region, serves as a connection between the DBD and LBD.
• It allows the DBD and LBD to adopt different conformations without creating a steric
hindrance.
• Domain also harbors a nuclear localization signal.

11. LIGAND BINDING DOMAIN
• Largest domain of SHR and forms 30% part of the receptor
• It is moderately conserved.
• It consists of about 290 amino acids.
• This domain with the heat shock proteins (chaperone proteins) in cytoplasm.
C Terminal
• the C-terminal is present at the end of LBD.
• It is a highly variable terminal with amino acids ranging from 530 to 984.
• The terminal connects the molecule to its pair in the homodimer or heterodimer. It may affect
the magnitude of the response.

12. SEQUENCE OF ACTION OF STERIOD HORMONE
Steroid Hormone enter cell & bind to receptor
Translocation of activated receptor- ligand complex into nucleus
Binds to another specific receptor on the chromatin.
Steroid receptors form dimers
Act on DNA
Augmentation or Suppression of transcription

13. EXPRESSION
• When the steroid hormone passes through the cell
membrane it enters cytoplasm and binds to steroid
hormone receptor.
• Both the components undergo conformational and
structural changes to become activated.
• The activation step is critical as it prepares the complex to
bind to DNA sequence.

14. DISTRIBUTION
• Once the hormone receptor complex gets activated it
enters the nucleus.
• 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.

15. REGULATION
• 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.

16. INTERACTION WITH DNA

17. • Within the nucleus along with the DNA, the hormone-receptor complex also interacts
with the transcription machinery, regulatory proteins, etc.
• There two models about how the hormone interacts with the DNA.
Ist Model
• The DNA is wrapped tightly in nucleosome which is composed of histone fold domains.
• The nucleosome also consists an amino terminal tail rich in lysine .
• Acetylation of tail lysines reduces the affinity of histone to DNA, thus making it
accessible to transcription factors.
• The architecture of the nucleosome is also maintained.
IInd Model
• According to the 2nd model NURF induces an ATP dependent remodeling of chromatin
resulting in an unstable or transient opening of promoter nucleosome.
• In this case,NF1 acts as a wedge to stabilize the open conformation of chromatin.

18. REGULATION
• The action of steroid hormones is regulated by the presence of two components- Coactivators
and Corepressors.
• The activation or inhibition f transcription of genes by SH depend on the presence of these
components.
• They are a class of protein whose mechanism & function is synonymous to that of coenzymes &
inhibittors in case of enzyme action .
 Corepressors
• Not much known about them.
• Antagonizes the effect of hormone to stimulate transcription from reporter genes.

19.  COACTIVATORS
• Made up of amino acid motif.
• It is distinguished into two classes ;
i. Interacts with sequence specific transcription factors.
ii. Interacts with general machinery on core promoter elements. Eg. TATA box binding
protein.

20. REFERENCES
• BOOKS
Endocrinology by Hadley
Clinical endocrinology
General endocrinology by Bagrara & Tumer