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出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/06/02 21:39:43」(JST)

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A tumor suppressor gene, or antioncogene, is a gene that protects a cell from one step on the path to cancer. When this gene mutates to cause a loss or reduction in its function, the cell can progress to cancer, usually in combination with other genetic changes. The loss of these genes may be even more important than proto-oncogene/oncogene activation for the formation of many kinds of human cancer cells.^[1] Tumor suppressor genes can be grouped into categories including caretaker genes, gatekeeper genes, and landscaper genes; the classification schemes are evolving as medicine advances, learning from fields including molecular biology, genetics, and epigenetics.

Two-hit hypothesis

Models of tumour suppression

Unlike oncogenes, tumor suppressor genes generally follow the "two-hit hypothesis," which implies that both alleles that code for a particular protein must be affected before an effect is manifested. This is because if only one allele for the gene is damaged, the second can still produce the correct protein. In other words, mutant tumor suppressors' alleles are usually recessive whereas mutant oncogene alleles are typically dominant.

The two-hit hypothesis was first proposed by A.G. Knudson for cases of retinoblastoma.^[2] Knudson observed that the age of onset of retinoblastoma followed 2nd order kinetics, implying that two independent genetic events were necessary. He recognized that this was consistent with a recessive mutation involving a single gene, but requiring biallelic mutation. Oncogene mutations, in contrast, generally involve a single allele because they are gain-of-function mutations.

There are exceptions to the "two-hit" rule for tumor suppressors, such as certain mutations in the p53 gene product. p53 mutations can function as a "dominant negative," meaning that a mutated p53 protein can prevent the function of normal protein from the un-mutated allele.^[3]

Other tumor-suppressor genes that are exceptions to the "two-hit" rule are those that exhibit haploinsufficiency, including PTCH in medulloblastoma and NF1 in neurofibroma. An example of this is the p27Kip1 cell-cycle inhibitor, in which mutation of a single allele causes increased carcinogen susceptibility.^[4]

Functions

Tumor-suppressor genes, or more precisely, the proteins they code for, either have a dampening or repressive effect on the regulation of the cell cycle or promote apoptosis, and sometimes do both. The functions of tumor-suppressor proteins fall into several categories including the following:^[5]

Repression of genes that are essential for the continuing of the cell cycle. If these genes are not expressed, the cell cycle does not continue, effectively inhibiting cell division.
Coupling the cell cycle to DNA damage. As long as there is damaged DNA in the cell, it should not divide. If the damage can be repaired, the cell cycle can continue.
If the damage cannot be repaired, the cell should initiate apoptosis (programmed cell death) to remove the threat it poses for the greater good of the organism.
Some proteins involved in cell adhesion prevent tumor cells from dispersing, block loss of contact inhibition, and inhibit metastasis. These proteins are known as metastasis suppressors.^[6]^[7]
DNA repair proteins are usually classified as tumor suppressors as well, as mutations in their genes increase the risk of cancer, for example mutations in HNPCC, MEN1 and BRCA. Furthermore, increased mutation rate from decreased DNA repair leads to increased inactivation of other tumor suppressors and activation of oncogenes.^[8]

Examples

The first tumor-suppressor protein discovered was the Retinoblastoma protein (pRb) in human retinoblastoma; however, recent evidence has also implicated pRb as a tumor-survival factor.

Another important tumor suppressor is the p53 tumor-suppressor protein encoded by the TP53 gene. Homozygous loss of p53 is found in 65% of colon cancers, 30–50% of breast cancers, and 50% of lung cancers. Mutated p53 is also involved in the pathophysiology of leukemias, lymphomas, sarcomas, and neurogenic tumors. Abnormalities of the p53 gene can be inherited in Li-Fraumeni syndrome (LFS), which increases the risk of developing various types of cancers.

PTEN acts by opposing the action of PI3K, which is essential for anti-apoptotic, pro-tumorogenic Akt activation.

As costs of DNA sequencing have diminished, many cancers have now been sequenced for the first time, revealing novel tumor suppressors. Among the most frequently mutated genes are components of the SWI/SNF chromatin remodeling complex, which are lost in about 20% of tumors.^[9]

Other examples of tumor suppressors include pVHL, APC, CD95, ST5, YPEL3, ST7, and ST14.

References

^ Weinberg, Robert A (2014). "The Biology of Cancer." Garland Science, page 231.
^ Knudson AG (1971). "Mutation and Cancer: Statistical Study of Retinoblastoma". Proc Natl Acad of Sci 68 (4): 820–3. doi:10.1073/pnas.68.4.820. PMC 389051. PMID 5279523.
^ Baker SJ, Markowitz S, Fearon ER, Willson JK, Vogelstein B. (1990). "Suppression of human colorectal carcinoma cell growth by wild-type p53". Science 249 (4971): 912–5. doi:10.1126/science.2144057. PMID 2144057.
^ Fero ML, Randel E, Gurley KE, Roberts JM, Kemp CJ (1998). "The murine gene p27Kip1 is haplo-insufficient for tumour suppression". Nature 396 (6707): 177–80. doi:10.1038/24179. PMID 9823898.
^ Sherr CJ (January 2004). "Principles of tumor suppression". Cell 116 (2): 235–46. doi:10.1016/S0092-8674(03)01075-4. PMID 14744434.
^ Yoshida BA, Sokoloff MM, Welch DR, Rinker-Schaeffer CW (November 2000). "Metastasis-suppressor genes: a review and perspective on an emerging field". J. Natl. Cancer Inst. 92 (21): 1717–30. doi:10.1093/jnci/92.21.1717. PMID 11058615.
^ Hirohashi S, Kanai Y (2003). "Cell adhesion system and human cancer morphogenesis". Cancer Sci 94 (7): 575–81. doi:10.1111/j.1349-7006.2003.tb01485.x. PMID 12841864.
^ Markowitz S (November 2000). "DNA repair defects inactivate tumor suppressor genes and induce hereditary and sporadic colon cancers". J. Clin. Oncol. 18 (21 Suppl): 75S–80S. PMID 11060332.
^ Shain, AH; Pollack, JR (2013). "The spectrum of SWI/SNF mutations, ubiquitous in human cancers.". PLoS ONE 8 (1): e55119. doi:10.1371/journal.pone.0055119. PMC 3552954. PMID 23355908. Cite uses deprecated parameters (help)

External links

TCF21 gene discovery at Ohio State University
Drosophila Oncogenes and Tumor Suppressors - The Interactive Fly
Online book: Tumor Suppressor Genes, published in 2012
Tumor Suppressor Gene Database, published in 2012

English Journal

Differential gene expression profile in monocytic myeloid-derived suppressor cells at maternal-fetal interface in a mouse model of spontaneous abortion.

Ren J, Zeng W, Tian F, Wu F, Zhang S, Liu X, Lin Y.
Journal of cellular physiology. 2019 Jul;234(7)10789-10799.
Monocytic myeloid-derived suppressor cells (MO-MDSCs) play an important role in maintaining normal pregnancy. However, it is still not clear what kind of changes in MO-MDSCs may lead to miscarriage, and which gene expression changes take place when MO-MDSCs migrate to the uterus as bone marrow-deriv
PMID 30549043

Synergistic anticancer action of quercetin and curcumin against triple-negative breast cancer cell lines.

Kundur S, Prayag A, Selvakumar P, Nguyen H, McKee L, Cruz C, Srinivasan A, Shoyele S, Lakshmikuttyamma A.
Journal of cellular physiology. 2019 Jul;234(7)11103-11118.
Women with the breast cancer type 1 susceptibility protein (BRCA1) mutation and loss of BRCA1 expression are reported to have an increased risk of triple-negative breast cancer (TNBC). Targeting BRCA1 modulation might offer a therapeutic option to treat TNBC patients. Our studies detected that BRCA1
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UHRF1 promotes aerobic glycolysis and proliferation via suppression of SIRT4 in pancreatic cancer.

Hu Q, Qin Y, Ji S, Xu W, Liu W, Sun Q, Zhang Z, Liu M, Ni Q, Yu X, Xu X.
Cancer letters. 2019 Jun;452()226-236.
UHRF1 (ubiquitin like with plant homeodomain and ring finger domains 1) is an epigenetic modifier that is overexpressed in some cancers, including pancreatic cancer, and mediates silencing of tumor suppressor genes. However, the role of UHRF1 in regulating pancreatic cancer metabolism and metastasis
PMID 30905812