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前回の記事に出てくるガン抑制遺伝子p53関連です ^^v
画像:p53: A Gatekeeper of Life and Death
http://www.emdbiosciences.com/html/cbc/p53_apoptosis_cancer_spotlight.htm より Orz〜
「p53, a tumor suppressor phosphoprotein is present at low concentrations in normal cells. The low concentration is maintained by MDM2-mediated ubiquitination and resulting proteolysis. HAUSP/USP7, a newly identified ubiquitin hydrolase, is thought to regulate MDM2 and help stabilize p53. When cells are subjected to stress, such as hypoxia or UV radiation, p53 is activated, its protein levels are elevated and its ubiquitin-dependent degradation is blocked. The resulting increase in p53 leads either to the induction of cell cycle arrest or apoptosis. Cell cycle arrest allows DNA repair to proceed before mitosis. If the damage is severe, p53 activation results in apoptosis. Hence, functional p53 provides a protective effect against tumor growth. Mutations in the p53 gene are commonly seen in various types of human cancers. Any successful response to chemo- or radiation therapy is reduced in tumors containing mutant forms of p53. While significant progress has been made in our understanding of the regulation and activation of p53, the role of post-translational modifications and the precise control of the interaction among p53, HAUSP, and MDM2 remains to be elucidated.」
画像:p53 Function
画像:Thus p53 unleashes cascading events via p21 to shut down cell cycle and initiate cell suicide.
http://www.cancerwatch.org/index.cfm?d=3005&c=4038&p=10661&do=detail より Orz〜
「Binding of p53 to DNA. The p53 tetramer (shown in gold, blue, green and magenta) binds to DNA (in silver at bottom) and causes the expression of the p21 proteiin.
p53 is a tumor suppressor protein which modulates cell cycle and induces potentially cancerous cells to commit suicide.
When cellular DNA is damaged, p53 gene is activated, resulting in the production of p53 protein which binds to DNA causing the expression of the p21 gene. Now p21 protein is produced whic h has two roles.
It inhibits the proteins cyclin dependent kinases (Cdk2-cyclin E) which are necessary for the passage of cells from G1 to the DNA synthesis (S) phase in the cell cycle. Thus p21 protein prevents the G1 to S passage in the cell cycle. This is G1 arrrest.
If the cells were already in the S phase, p21 will block the activity of a small nuclear protein PCNA (Proliferating Cell Nuclear Antigen) involved in DNA replication and repair in cells. 」
イメージだけでも...^^;v
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