2 Definition of Telomerase Telomerase is an alkaline nucleoprotein reverse transcriptase, which can add telomere DNA to the chromosome end of eukaryotic cells. Telomeres play an important role in maintaining chromosome stability and cell activity in cells of different species. Telomerase can prolong shortened telomeres (shortened telomeres have limited cell replication ability), thus enhancing cell proliferation ability in vitro. Telomerase activity is inhibited in normal human tissues and reactivated in tumors, and telomerase may participate in malignant transformation. Telomerase plays an important role in maintaining telomere stability, genome integrity, long-term cell activity and potential ability of continuous proliferation.
There is an enzyme in cells that is responsible for telomere elongation. Its name is telomerase. The existence of telomerase can make up for the defects of DNA cloning mechanism. By prolonging telomere repair, telomeres will not be lost due to cell division, thus increasing the number of cell division clones.
However, in normal human cells, telomerase activity is strictly regulated. Active telomerase can only be detected in hematopoietic cells, stem cells and germ cells that must be continuously divided and cloned. When cells differentiate and mature, they must be responsible for the needs of different tissues in the body and perform their duties, so the activity of telomerase will gradually disappear. It is not important for cells to continue to divide and clone, but differentiated cells will undertake a more important mission, that is, to make tissues and organs run and make life last, but not forever. This cycle of alternating generations is the creator's ingenious thinking on life design.
3 Application of Telomerase It is generally believed that the reactivation of telomerase activity can maintain the length of telomeres, and delaying the clonal aging of cells is the key step of cell aging. Restoring telomerase activity of epidermal fibroblasts can indeed prolong the life span of cell division and prolong the young cycle of cells.
In addition, in medical applications, taking vascular endothelial cells as an example, vascular endothelial cells are damaged very quickly under the constant scouring and flowing of blood flow. When an individual is young, the surrounding tissues can constantly provide new cells to repair the damage of the blood vessel wall. Once an individual is aging, the injured surrounding cells cannot provide new cells for repair, and the arteries will gradually harden. If the telomerase of cells in the surrounding tissues is activated, telomeres will be prolonged and the number of cell divisions will increase, so that the surrounding tissues will continue to provide new cells to fill the damage of blood vessels, thus delaying the signs of aging caused by arteriosclerosis. Just like the basic theory of finding telomerase inhibitors, scientists are actively using the same strategy to find telomerase activators.
Generally speaking, the mechanism of aging and cancer is more complicated than we thought. Because they are diseases caused by many factors, a single direction of prevention and treatment is not enough to cover all the causes. The study of telomere and telomerase is only a part of exploring the mechanism of aging.
Telomerase makes human beings see the dawn of eternal life.
4 Telomere DNA function and telomerase function and biological characteristics Telomere is a special structure at the chromosome end of eukaryotic cells. Human telomeres are composed of six base repeats (TTAGGG) and binding proteins. Telomere has important biological functions, which can stabilize chromosome function, prevent chromosome DNA degradation and terminal fusion, protect chromosome structural genes and regulate normal cell growth. With the disappearance of the 5' end of linear DNA replication in normal cells and the continuous proliferation of somatic cells, telomeres gradually become shorter. When telomeres contract to a certain extent, cells stop dividing and remain static. Therefore, some people call telomere the "biological clock" of normal cells. The length and stability of telomeres determine the life span of cells, which is closely related to cell aging and canceration. Telomerase is a reverse transcription DNA synthetase that extends telomeres. It is a ribonucleic acid protein complex composed of RNA and protein. Its RNA component is a template, and its protein component has catalytic activity. Telomere repeats are synthesized with the 3' end of telomere as primer. Telomerase activity can be detected in eukaryotic cells, and its function is to synthesize telomeres at the end of chromosomes, so that the telomere length gradually shortened due to each cell division can be compensated, and then the telomere length can be stabilized. Its main feature is to synthesize DNA by reverse transcription using its own RNA as a template.
The main biological function of telomerase in cells is to stabilize the length of chromosome telomere DNA by its reverse transcriptase activity and by replicating and prolonging telomere DNA. The latest research progress on the relationship between telomerase and tumor shows that telomerase is also involved in the regulation of tumor cell apoptosis and genomic stability. Corresponding to the various biological activities of telomerase, there is also a complex telomerase regulatory network in tumor cells. Regulating the activity and function of telomerase at the post-translational level through protein-protein interaction is one of the hot spots in the research of telomerase regulation mechanism.
Telomeres exist to maintain the stability of chromosomes. Without telomere, the terminal is exposed, which is easily hydrolyzed by exonuclease.
Telomeres are not synthesized by DNA polymerase, but by telomerase, which contains RNA templates to synthesize telomeres.
5 aging mechanism and telomerase problem aging mechanism (link) The first question to be clear is why people die. It is not impossible to achieve immortality only if the mechanism of this process is thoroughly understood.
I know several mechanisms of human aging and death. For example, the mechanism of free radical scavenging and production in the body is unbalanced, which leads to the accumulation of harmful free radicals and then destroys organelles. Mitochondria have been proved to be involved in this process.
Your telomerase is also one of the explanations. Because normal human cells have no telomerase, it is impossible to repair the problem of dna shortening caused by DNA replication. Therefore, with the increase of cell replication times, DNA is short to a certain extent, which may trigger the death mechanism, or death is an asymptotic process.
5. 1 Mainstream hypothesis about the molecular mechanism of cell aging 1, oxidative damage. From the accumulation of free radicals.
2. rDNA. There may be a mismatch in chromosome replication, which makes the extra-chromosomal rDNA ring swell, which is called ERC. Its accumulation leads to cell senescence, accompanied by nucleolar division.
3. Silent information regulatory protein complex. It can prevent the transcription of DNA at its site.
4.SGS 1 gene and WRN gene. These two homologous genes are necessary to ensure the normal life cycle of cells, but they are easy to mutate and lead to premature aging.
5. Development plan.
6. Mitochondrial DNA. With the passage of time, the mutation of mitochondrial DNA is quite significant.
Life is the most magical magic. Intracellular movements are complex and precise, and it is often foreign * * * that causes protein to be phosphorylated, transmitted from one level to the next, activates some genes, and begins to transcribe and translate protein, which does not exist at ordinary times. This protein then causes a series of cascade reactions. Overturning the laws of nature and solving an enzyme problem is tantamount to a drop in the bucket.
But even assuming that the human body has telomerase, longevity is a question worth asking. Because telomerase only solves the problem of replication length, it cannot solve the problem of variation in DNA replication. Of course, there is a special agency responsible for this. However, it also shows that immortality is not as simple as imagined, and it can not be solved by a telomerase.
5.2 What are telomeres and anti-aging telomeres?
Telomeres are DNA fragments at the ends of chromosomes.
The DNA on the line determines the characteristics of human beings. They determine the straightness and radian of human hair, the blue-black eyes, the height of people, and even the temper and gentleness of personality.
In fact, telomeres are also DNA, except that telomeres are repetitive DNA at the head and tail of chromosomes. I imagine telomeres as a sweater, with a segment of the cuff falling off, and the sweater is like a tightly structured DNA. Cytologists are never interested in the DNA pulled from the tail of chromosome rods. They focused on 46 stained gene maps and made a fuss about the draft human genome.
Calvin Harley began to associate telomeres with human aging from 1990. He put forward three points, which I recorded as follows: first, the older the cell, the shorter the telomere length; The younger the cell, the longer the telomere, which is related to cell aging.
Some telomeres in aging cells have lost most of their telomere repeats. When the function of cell telomere is destroyed, aging occurs. When telomere is shortened to a critical length, aging accelerates and approaches death.
Second, normal cells have shorter telomeres. Cell division shortens telomeres, and it shortens them a little at a time, just like wearing an iron bar. If there is only one stump left, the cell will be close to aging. When a cell divides, its telomere DNA loses about 30200bp (base pairs), and some cells in mice and humans generally lose about 10000bp.
Thirdly, it is found that there is an enzyme that synthesizes telomeres in cells. The length of telomeres is determined by enzymes. Too many enzymes in cells can predict the length of telomeres. Telomerase was not detected in normal human cells. Telomerase activity was not detected in some benign pathological cells and fibroblasts cultured in vitro. However, this enzyme is positive in germ cells testis, ovary, placenta and fetal cells. Remarkably, it is found that malignant tumor cells have high activity of telomerase. Telomerase-positive tumors include ovarian cancer, lymphoma, acute leukemia, breast cancer, colon cancer and lung cancer. High telomerase activity exists widely in human tumors. In this way, we found a specific substance of tumor cells.
5.3 Looking for the story of aging clock The human body is made up of cells. If people are aging, will cells also age? It is like a building, and its life is largely related to the bricks that make it up. Cells have longevity, which was discovered by cytologist Frick 40 years ago. Cultured human fibroblasts from generation to generation. However, in the case of adequate nutrition supply, cell division stopped around the 1950 s and really entered the aging period. This discovery seems to tell people that there is an aging clock in cells, which limits the number of cell divisions, thus limiting the life span of organisms. Because a long-lived creature is formed by the division of a fertilized egg cell, it splits into two, four, and so on, forming a fetus and then splitting into a youth. If cells can no longer divide, then individuals will be aging.
5.4 Promising Anti-aging Road Until today, I dare not say that scientists have determined the real cause of aging, but the discovery of telomere function has indeed opened up a new anti-aging road for us.
Telomere shortening leads to aging. If telomere length is not maintained, cells will stop dividing or dying. In some cases, dying cells become immortal cells, which are cancer cells.
The discovery of telomerase gives a logical explanation to the problems of normal cells, aging and cancer that have been puzzling for thousands of years. Simply put, it is possible to inject telomerase into aging cells, prolong telomere length and rejuvenate cells, which scientists have high hopes for. In the future, doctors will inject the elderly with preparations similar to telomerase to prolong the telomere length of the elderly and achieve the goal of rejuvenation.
Some scholars have suggested that telomerase inhibitors can be used as drugs to treat cancer. Because telomerase only exists in cancer cells, it seems that cancer cells will not reproduce if the enzyme is drained. Of course, there are still many difficulties to overcome.
As early as 1930s, geneticist Mullert discovered that the terminal structure of chromosome is very important for maintaining the stability of chromosome, and named it (telomeretm). Blackburn and Gall first discovered and confirmed the telomere structure of Tetrahymena. Telomeres consist of telomere DNA and telomere protein. They found that the end of each chain of this rDNA contains a large number of repeated fragments. Later, they found that the DNA end of eukaryotes is mostly composed of a large number of repetitive specific basic sequence units, that is, telomere sequences. For a given eukaryotic species, it must have a characteristic telomere DNA sequence.
Telomere is a special structure at the end of chromosome, which consists of many simple short repetitive sequences and telomere binding protein (TEBP). In normal human cells, telomeres can gradually shorten with cell division. Telomere is the basic genetic component of cells, because it can protect and compensate the loss of genetic information at the end of chromosomes. Protect it from nuclease recognition and degradation. However, in the process of replication, telomeres will be lost slowly due to the lack of replication mechanism or other reasons. In a new cell, every time a cell divides, the telomere at the top of the chromosome will be shortened once (every time a cell divides, its telomere DNA will be lost by about 30 ~ 200 bp). When the telomere can no longer be shortened, the cell cannot continue to divide. Further research shows that some telomeres in aging cells lose most telomere repeats. 1990, Calvin Haley found that the life span of human cells at different ages is obviously different, and the telomere length is also different. It gets shorter with age. The older a cell is, the shorter its telomere length is. The younger the cell, the longer the telomere, which is related to cell aging. So telomeres are used to explain the new mechanism of human aging. In addition, the loss of telomere is related to many reasons. Maria blasco and pierrot annas explored the role of telomere dysfunction in some cardiovascular diseases. Maria blasco and Piero versa constructed transgenic mice with telomere RNA deletion (Terc/) in the second generation G2 and the fifth generation G5. The researchers analyzed the cardiomyocytes of G5(Terc/) mice by in-situ quantitative fluorescence hybridization, and found that the telomeres of these cells were shorter than those of G2(Terc/) mice, and the telomeres of G2(Terc/) mice cardiomyocytes were also shorter than those of wild-type cells. Dr Shay and Dr Wright of UT Southwest Medical Center in Dallas reported the research results of changing the life span of human cells by controlling telomere length in March 1996 in the Journal of European Molecular Biology Organization. They found that by increasing telomere length, the life span of cell hybrid lines can be prolonged.
However, it should be mentioned that whether telomere reduction leads to atherosclerosis needs further study.
Studies have found that there is an enzyme in cells that can synthesize telomeres. Telomere replication can not be catalyzed by classical DNA polymerase, but by a special reverse transcriptase-telomerase. Telomerase is an enzyme that uses RNA as a template to synthesize DNA. Telomerase is a ribonucleoprotein composed of RNA and protein. Its RNA component is a template for telomere sequence synthesis. Telomerase in different organisms has different RNA templates and different telomere sequences. Telomerase RNA mutation; The new telomere sequence corresponding to the mutated RNA sequence can be synthesized in vivo, which proves the template function of RNA. Telomerase synthesizes telomere DNA fragment TTAGGG, and its gene is located in 3q .26.3 of human chromosome. Telomerase is not detected in normal human cells. Telomerase activity was not detected in some benign pathological cells and fibroblasts cultured in vitro. But this enzyme is positive in germ cells, testis, ovary, placenta and fetal cells, which explains why scientists began to study how telomeres in cancer cells and cancer cells do not shorten for a long time.
It is worth noting that malignant tumor cells have highly active telomerase (it can maintain the telomere length of cancer cells and make them expand indefinitely). Haleri put forward the hypothesis of telomere telomerase in 199 1 year about how cancer cells achieve immortality. It is considered that the decline and death of normal cells should go through the first death stage (MortalityStage 1+0) and the second death stage (M2). That is to say, telomere DNA is constantly lost during cell mitosis, which makes telomeres shorter. When telomeres are shortened to a certain length (2 KB ~ 4 KB), the stability of chromosomes is destroyed, cells are aging, and cells enter the first consistent death stage M 1. At this time, cells no longer divide, but quit the cell cycle, aging and dying. If the cell has been transfected by virus (SV40, human papillomavirus), oncogene is activated or tumor suppressor gene (P53, Rb) is inactivated, the cell can go beyond M 1 phase, continue to divide for 2030 times, telomere continues to shorten, and finally enter the M2 phase of the second lethal phase. Most cells lose their function and die because their telomeres are too short. Only a few cells have telomere telomerase activated, which can repair and maintain the telomere length, and make the cells break away from M2 phase and gain eternal life. This is also a research hotspot in the field of contemporary scientific research. Hiyama et al. [8] confirmed that 90% of tumor tissues expressed telomerase activity in the study of 100 cases of fibroneuroblastoma. However, the tumor tissues with low telomerase activity have no corresponding changes and the prognosis is good. Even 3 cases with no telomerase activity in IVS showed tumor regression. This seems to indicate that there is a correlation between telomerase and cancer, but it is difficult to determine whether it is causal.
Telomere DNA includes nonspecific DNA and specific DNA sequences composed of highly repetitive sequences. It usually consists of short tandem repeats rich in guanine nucleotide (G), extending to the 3' end of chromosome. Tetrahymena telomere repetitive DNA fragment (TTGGGG) is artificially synthesized. The telomere DNA sequence of human and mouse is TTGGG. The length of human telomere is about 15Kb. Due to the problem of terminal replication of dsDNA, cells lose about one Okazaki fragment length of DNA every time they divide, that is, 25 ~ 100 pairs of bases. Telomerase adds the DNA repetitive sequence synthesized by its own RNA template to the 3' end of the mother chain of the subsequent chain, and then uses the extended mother chain as a template to synthesize the daughter chain by DNA polymerase, but due to the incompleteness of the replication mechanism (or is this incompleteness preserved by evolution? This mechanism ensures the periodic aging and death of cells? ). Telomeres are still lost at a certain rate. Telomerase is a nuclear protein (RNP), which is mainly composed of RNA and protein. Telomerase is a special DNA polymerase necessary for telomere replication. At present, telomerase RNA of many organisms has been cloned, but the nucleotide sequences of different species are very different. Telomerase RNA template of Tetrahymena is 160~200 nucleotides long, encoding telomere repeat sequence of 1.5 copy. Its 43~5 1 bit sequence is CAACCCCAA, which just encodes a GGGGTT. Telomerase RNA genes in mice and humans are 65% identical. The template is 89 nucleotide sequences, and human telomerase RNA(hTR) consists of 450 nucleotide groups. The template area is CUAACCCUAAC(5'3'). ShippenLentz( 1990) cloned the telomerase RNA sequence of Eupolyphaga, including the template sequence 5' caacccaaaa3'. The template also synthesized RNA sequence with telomere repeat sequence (TTTTGGGG)n) N) n by base complementation. It is also considered that the template in telomerase RNA is complementary to the repeat sequence of 1.5 (TTTTGGGGG) once, and then the template slides for further synthesis.
As far as telomere binding proteins are concerned, as early as 1986, Gottschling et al. have confirmed that telomeres of Acuminatum have a relative molecular weight of 55,000 and 26,000, and the protein-specific recognition and binding of PAP 1 (repressor-activating protein 1) in megakaryon is a necessary factor to participate in telomere length regulation. 1 RAP 1 molecule integrates with 18 telomere DNA sequences on average, and negative feedback regulates telomere length. After the coding gene of partial catalytic subunit of telomerase protein was cloned and identified in yeast, the coding gene of partial catalytic subunit of human telomerase protein was also cloned and identified, named hTERT (human telomerase reverse transcriptase) gene. The gene contains a telomerase-specific motif, which translates into a protein sequence of 48 amino acids. The comparative study of hTR and hTERT gene expression shows that hTR gene can be expressed in lethal cells forced by proliferation, while hTERT gene is only expressed in immortalized cells of tumor cells. Therefore, hTERT gene shows the potential application value of tumor-specific diagnosis and treatment.
In addition, human papillomavirus (HPV) can cause human cervical cancer. The oncogene E6 in the genome of human papillomavirus plays an important role in tumorigenesis. It is the first oncogene that can activate telomerase. The expression product of this gene can regulate the expression of MYC at the post-transcriptional level, and then telomerase is activated by MYC. Recently, it has been found that estrogen in human body can combine with an incomplete palindrome structure at position 2677 in the promoter region of TERT gene, and directly regulate the activity of TERT gene. In addition, estradiol can indirectly promote the expression of TERT gene and improve the activity of telomerase by activating the expression of myc gene.
Recent comparative studies have found that many telomere proteins have similar structures and functions. In short, with the deepening of research, the characteristics and functions of telomere binding proteins that bind to telomere sequences will be gradually discovered and clarified.
6 Nobel Prize According to the official website news of the Nobel Foundation, Karolinska Medical College in Sweden announced that the 2009 Nobel Prize in Physiology or Medicine will be awarded to Liz Helen Blackburn of the University of San Francisco in California, carol greider of Johns Hopkins Medical College in Baltimore and Jack Szostak of Harvard Medical College. They found that telomerase produced by the root cap of chromosome can lead to aging and cancer.
7. Laboratory test 7. 1 normal dot blot method: none.
7.2 The detection results increased significantly: liver cancer (93.88OD/30μg protein) and adjacent tissues (24.09OD/30μg protein).
7.3 Test blood samples
7.4 Analysis Methods Tumor Immunoassay
7.5 Test Category
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