group 6-b2 - telomerase, aging and cancer
DESCRIPTION
Medicine handoutsTRANSCRIPT
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Telomerase, Cancer and Aging
Group no. 6
MED 1 -B2
Jamee Dela Rosa
Haiezel dela Cruz
Lalaine dela Cruz
Maureen dela Cruz
Erika dela Fuente
Mariel dela Cruz
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OBJECTIVES
1. Describe the physical structure of a chromosome and describe what makes up the centromere and telomeres of a chromosome
2. Briefly review the process of replication of a linear chromosome and explain what accounts for the natural shortening of the lagging strand
3. Explain Cellular Senescence, some mechanisms that accounts for it and how is it related to cancer
4. Describe the enzyme Telomerase and its structure.
5. Identify specific cell populations that express the enzyme h.
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6. Discuss the mechanism involve in Telometric
lengthening and of sealing the telometric ends.
7. Explain the role of telomere binding proteins in the
regulation of telomerase function.
8. Explain the relationship between telomeres in regards
to aging and cancer.
9. Discuss the potential advantages of using anti-
telomerase agents in treating cancer cells.
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CHROMOSOME
Tightly coiled DNA
Carriers of gene Unit of Heredity
2 pairs of 23 filamentous rod shape body
Present in the nucleus
Chromosomes are not visible in active nucleus, but are clearly seen during cell division
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PHYSICAL STRUCTURE Parts:
CHROMATIDS
Double Stranded DNA
Long arm (q)
Short arm (p)
CENTROMERE
Joins chromatids together
TELOMERE
Found at each end of Chromatid
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CENTROMERE
Part of a chromosome that links sister chromatids
Rich in adenine-thymine base pairs
Condensed regions within the chromosome that are responsible for the accurate segregation of the replicated
chromosome during mitosis and meiosis
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TELOMERE
Telos - END'
Mers -PART
Short thymine-guanine sequence
5-TTAGGG-3 Sequence
Found at each end of a chromatid, which protects the end of the
chromosome from deterioration or
from fusion with neighbouring
chromosomes
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DNA Replication: Review
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KEY POINTS
ORIGIN is the beginning
REPLICATION FORKS are the sites at which DNA
synthesis is occurring
New chains grow 5-3
Bidirectional
Semi-conservative
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ORDER OF ACTION
Unwinding proteins
Preventing the Reannealing
Primase makes RNA primer
DNA polymerase makes DNA
RNAse H removes RNA primer
DNA polymerase fills in gaps
DNA ligase joins gaps
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UNWINDING
OF PROTEINS
HELICASE
Made up of 6 proteins
arranged in a ring shape
Motor proteins
Unpackage an organisms gene
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PREVENTING THE
REANNEALING
SINGLE STRAND BINDING
PROTEINS
Tetramers
Attached to the post-replication fork single
strands of DNA,
preventing their
"reannealing
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PRIMASE MAKES
RNA PRIMER PRIMASE
A type of RNA Polymerase
Creates a RNA Primer
Key importance in DNA Replication
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DNA POLYMERASE MAKES DNA
DNA POLYMERASE
Creates DNA Molecules by assembling
nucleotides
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RNAse H
REMOVES RNA
PRIMER
RNAse H
Non- Specific Endonuclease that
catalyzes the cleavage
of RNA
Removing the RNA primer
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DNA POLYMERASE
FILLS IN THE GAPS
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DNA LIGASE JOINS
GAPS
DNA LIGASE
A ligase that facilitates the joining of DNA strand
together by catalyzing the
formation of a
phosphodiester bond.
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WHAT ACCOUNTS FOR THE NATURAL SHORTENING OF LAGGING STRAND?
During chromosome replication, the enzymes that duplicate the DNA cannot continue duplicating all the way to the end of the chromosome.
OKAZAKI FRAGMENTS
RNA Primers attached ahead on the lagging strand
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CELLULAR SENESCENCE
Latin: Senescere Grow Old
It is the phase or stage in which normal cells cease to divide
Associated with a loss of telomerase activity
As human telomeres grow shorter, eventually cells reach the limit of their replicative capacity and progress into senescence
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PROPERTIES OF CELLS IN CELLULAR SENESCENCE
Increase synthesis of proteases
Decrease in synthesis of pro-collagen and tissue inhibitors of metalloproteases
Irreversible growth arrest
Dramatic change in morphology
-lose original shape
-acquire distinct flattened cytoplasm
-change in nuclear structure, gene expression, protein processing and metabolism
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CELLULAR SENESCENCE Today it is known that somatic cells derived from
human newborns will usually divide 80 to 90 times in culture
Whereas those from a 70-year-old are likely to divide only 20 to 30 times
When human cells that are normally capable of dividing stop reproducingor, in Hay- flick's words, become "senescent"they look different and function less efficiently than they did in youth, and after a while they die.
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CELLULAR SENESCENCE: TELOMERE SHORTENING
Telomeres shorten because of the lagging strand phenomenon.
A section of telomeres is lost during each cycle of replication.
Progressively lose approximately 50-200 nucleotides during each mitotic replication.
Cellular senescence is triggered when cells acquire one or a few critically short telomeres
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CELLULAR SENESCENCE: ACCUMULATION OF DAMAGE
Major cause of aging which is due to highly reactive substances containing oxygen (oxygen free radicals)
Oxygen free radicals damages the DNA
Damaged DNA accumulate mutations with fewer proliferation
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CELLULAR SENESCENCE: GLYCATION
Glycation is the result of a sugar reducing molecule, such as fructose or glucose, bonding to a protein or Lipid molecule without the controlling action of an enzyme.
This reaction products [AGEs or advanced glycation end products] are irreversible and detrimental for extracellular protein function.
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CELLULAR SENESCENCE: MITOCHONDRIAL DNA DAMAGE
The mitochondria have their own genetic material (mtDNA), which is distinct from the nuclear DNA in the cell.
Mitochondria produce ATP (energy) and free radical (byproducts of respiration)
Aerobic condition 4% of oxygen are metabolize by mitochondria.
In normal condition, the oxygen is reduced to produce water.
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However, the oxygen is instead prematurely and incompletely reduced to give the superoxide ion.
The superoxide ion hydrogen peroxide hydroxyl radical Reactive oxygen species (ROS)
ROS leads to damage the cell membrane, structural protein and mitochondrial and nuclear DNA.
CELLULAR SENESCENCE: MITOCHONDRIAL DNA DAMAGE
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CELLULAR SENESCENCE SUMMARY
TELOMERE
SHORTENING MITOCHONDRIA
ROS
CELLULAR
SENESCENCE
OXIDATIVE STRESS
OXYGEN FREE RADICALS GLYCATION
AGEs
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CELLULAR SENESCENCE AND CANCER
Senescence involves p53 and pRb pathways and leads to the arrest of cell proliferation plays an important role in suppression of
emergence of cancer, although inheriting shorter telomeres probably does not protect against cancer. Why?
Because with critically shortened telomeres, further cell proliferation can be achieved by inactivation of p53 and pRb pathways.
Cells entering proliferation after inactivation of p53 and pRb pathways undergo crisis.
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CELLULAR SENESCENCE AND CANCER
Usually almost all cells die when it enters crisis but rare cells emerge from crisis and immortalized through telomere elongation by either activated telomerase (becomes cancer cells)
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WHAT IS TELOMERASE?
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TELOMERASE
Background
Telomerase is an enzyme, discovered by Elizabeth Helen Blackburn (professor of biochemistry and biophysics at the University of California, San Francisco School of Medicine) and Carol Greider (professor of molecular biology and genetics at the Johns Hopkins University School of Medicine ) in 1985.
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TELOMERASE
A ribonucleoprotein reverse transcriptase (enzyme) that synthezises telomeric DNA.
Tetrahymena in which the enzyme was first discovered.
Tetrahymena 5 TTGGGG 3
In humans 5 TTAGGG 3
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TELOMERASE
is an enzyme that adds telomeric sequences to the ends of each chromosome. Unlike most enzymes, which consist entirely of protein, telomerase is a combination of a protein and an RNA.
The enzyme is a protein and RNA complex called
telomere terminal transferase, or telomerase. Telomerase is present in most fetal tissues, normal
adult male germ cells, stem cells, in proliferative cells of renewal tissues, and in most tumor cells.
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TELOMERASE STRUCTURE
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TELOMERASE STRUCTURE
Human telomerase is composed of at least two sub-units:
human Telomerase Reverse Transcriptase (hTERT) - protein component
human Telomerase RNA (hTR or hTERC)
- RNA Component
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human Telomerase Reverse Transcriptase (hTERT)
Protein Component
The coding region of the hTERT gene is 3396bp, and translates to a protein of 1131 amino acids
The hTERT gene maps to chromosome band 5p15.33.
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RNA component
referred to as the RNA guide
template region of hTR is
3'-CAAUCCCAAUC-5'
sequence complementary to telomere repeat [TTAGGG]
serve as template for telomere synthesis and elongation
human Telomerase RNA (hTR or hTERC)
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MECHANISM OF TELOMERIC LENGTHENING
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CAAUCCCAAUC
3
5
hRNA
hTERT
GGTTAGGGTTAGGG
CCAAUCC
3
3 5
5
TELOMERE
TELOMERASE
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CAAUCCCAAUC
3
5
GGTTAGGGTTAGGG
CCAAUCC
3
3 5
5
STEP 1: BINDING
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CAAUCCCAAUC
3
5
GGTTAGGGTTAGGG
CCAAUCC 3 5
5 TTAGGG TTAG
STEP 2: ELONGATION
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GGTTAGGGTTAGGG
CCAAUCC 3 5
5
CAAUCCCAAUC
3
5
TTAGGG TTAG
STEP 3: TRANSLOCATION
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GGTTAGGGTTAGGG
CCAAUCC 3 5
5
CAAUCCCAAUC
3
5
TTAGGG TTAG TTAGGG TTAG
STEP 4: ELONGATION
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MECHANISM OF SEALING THE TELOMERIC ENDS
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T-loop
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HETERO-DUPLEX OR T-LOOP
It was proposed that the t-loop is formed by strand invasion of the 3' G-rich overhang into the preceding telomeric tract to form a lariat with a D-loop at the looptail junction .
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Importance of T-loop
stabilizes the telomere
prevents the telomere ends from being recognized as break points by the DNA repair machinery thus it gives protection from exonucleases.
preventing the telomere from eliciting a DNA damage response manifested as cell-cycle arrest or apoptosis
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Importance of T-loop
prevention of chromosome end fusions or non homologous end joining (NHEJ)
prevention of homologous recombination between telomeric regions
regulation of telomere length homeostasis.
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What prevents the telomerase from over-extending the ends of a linear chromosome?
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Shelterin Complex
The T-loop is held together by six known proteins:
TRF1, TRF2, POT1, TIN2, RAP 1 and TPP1,
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Shelterin Complex 1. TRF 1 (Telomeric Repeat
binding Factor 1)
It binds along the length of the T-loop.
along with TRF2, it normally prevents telomerase from adding more telomere units to telomeres.
But when telomere lengthening is required, TRF1 recruits helicases to facilitate the process.
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Shelterin Complex 2. TRF2 (Telomeric Repeat binding Factor 2)
It appears to promote formation of D-loop
prevents ataxia telangiectasia mutated (ATM) activation, which is a DNA damage response (DDR) to DNA double strand breaks.
But when DNA repair of telomeres is required, TRF2 recruits DNA repair proteins.
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Shelterin Complex 3. TIN 2 (TRF1 Interacting
Nuclear factor 2)
links TRF1 with TRF2, and connects both to TPP1 .
TIN2 is believed to facilitate recruitment oft single-stranded telomere-binding proteins to telomeres.
TIN2 interacts with TRF1 and has been suggested to stabilize the T-loop.
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Shelterin Complex 4. POT 1 (Protector Of
Telomeres 1)
only binds to the single-stranded 3-end DNA overhang.
POT1 prevents ataxia telangiectasia and Rad3 related (ATR) activation, which is a DNA damage response (DDR) to DNA double strand breaks.
Humans only have a single POT1, whereas mice have POT1a and POT1b.
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Shelterin Complex 5. RAP1 (Repressor/Activator Protein 1)
binds to TRF2, and facilitates TRF2 function.
RAP1 protects telomeres from non homologous end joining (NHEJ).
Unlike the other shelterin proteins, RAP1 has functions independent of its function within the shelterin complex: RAP1 regulates transcription and affects NF- kb signaling.
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Shelterin Complex
6. TPP1 (TINT1, PTOP, PIP1 POT1-TIN2 organizing protein)
interacts with POT1 and regulates its function.
When telomeres are to be lengthened, TPP1 is a central factor in recruiting telomerase to telomeres.
Deletion of TPP1 from shelterin elicits an ATR-mediated DDR.
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AGING
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What is aging?
Aging is a degenerative process that is
associated with progressive accumulation of
deleterious changes with time, reduction of
physiological function and increase in the
chance of disease and death.
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Telomeres alone do not reduce lifespan but there are some factors that also plays an important role in aging.
According to geneticist Richard Cawthon and
the colleagues at the University of Utah, Shorter telomeres are associated with shorter lives. Among people older than 60, those with shorter telomeres were three times more likely to die from heart disease and eight times more likely to die from infectious disease.
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Telomere shortening
When people are divided into two groups based on telomere length, the half with longer telomeres lives an average of five years longer than those with shorter telomeres.
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Chronological Age After age 60, the risk of death doubles every 8 years. So a
68-year-old has twice the chance of dying within a year compared with a 60-year-old.
Oxidative Stress Oxidative stress is the damage to DNA, proteins, and
lipids (fats) caused by oxidants, which are highly reactive substances containing oxygen
Glycation Glycation happens when glucose, the main sugar we use
as energy, binds to some of our DNA, proteins, and lipids, leaving them unable to do their jobs.
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Is it possible to revert old cells into young cells again?
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Is it possible to revert old cells into young cells again?
No. Why?
Using that in humans will be more difficult because Mice make telomerase throughout their lives but the enzyme is switched off in adult humans.
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Telomerase and Cancer
Telomerase is expressed in almost all human cancers but is inactive in most normal cells.
Cancer cells are malignant cells which multiply until they form a tumor that grows uncontrollably.
Telomerase is a good biomarker for cancer detection because most human cancers cells express high levels of telomerase.
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Telomerase as an Agent to Extend Cellular Life Span
Telomere shortening has been observed in most dividing somatic cells, eventually leading to cell senescence when critically short telomeres are reached.
Telomerase has been identified as a ribonucleoprotein enzyme that can synthesize telomeric repeats onto chromosomes.
Telomerase can be an agent to extend cellular life span especially in cancer cells.
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Telomerase as an Agent to Extend Cellular Life Span
ADVANTAGES DISADVANTAGES
If telomerase are activated in somatic cell, human cells will not
age.
If telomerase are inactivated, telomeres in cancer cells would
shorten, just like they do in normal
body cells
It will be able to mass produce cells for transplantation
If telomerase are inactivated, telomere shortening can be
anticipated.
Telomerase has been detected in human cancer cells and is found
to be 10-20 times more active
than in normal body cells
Blocking telomerase could impair fertility, wound healing and
production of blood cells and
immune cells
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Anti-telomerase Agents to Treat Cancer Cells
Harley & Greider
inhibitory agent could
cause the telomeres of
cultured tumor cells to
shrink
Apoptosis
Blackburn
cells sometimes
compensate for the loss
of telomerase, repair
shorter ends for
Recombination
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Potential advantages of anti-telomerase agents
SPECIFICITY
Anti-telomerase treatment would be very selective in that only cells with an activated telomerase would be affected (most normal adult tissues have NO telomerase activity).
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THANK YOU!