User:Iris To/Retinoblastoma Protein Regulation

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==Retinoblastoma Protein==
==Retinoblastoma Protein==
{{STRUCTURE_3n5u| PDB=3n5u | SCENE= }}
{{STRUCTURE_3n5u| PDB=3n5u | SCENE= }}
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The retinoblastoma protein (Rb) is a suppressor protein, also known as a tumor suppressor, involved in negative regulation of the cell cycle[http://en.wikipedia.org/wiki/Cell_cycle] due to its ability to bind the transcription factor E2F[http://en.wikipedia.org/wiki/E2F]. It acts as a cell cycle checkpoint during the G1 phase, determining if the cell cycle should continue or stop. In its normal state, Rb is activated, which prevents the cell cycle to continue because it can recruit transcriptional co-repressors, blocking transcription<ref name=Change >PMID: 12502741 </ref>. Rb is deactivated after being phosphorylated by Cyclin-dependent kinases (Cdks)[http://en.wikipedia.org/wiki/Cyclin-dependent_kinase], and thus cannot associate factors that inhibit transcription factors that allow the cell cycle to continue. Unregulated deactivation of Rb can lead to uncontrolled growth of cells, which is why studying this protein is important in cancer research.
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The retinoblastoma protein (Rb) is a suppressor protein, also known as a tumor suppressor, involved in negative regulation of the cell cycle[http://en.wikipedia.org/wiki/Cell_cycle] due to its ability to bind the transcription factor E2F[http://en.wikipedia.org/wiki/E2F]. It acts as a cell cycle checkpoint during the G1 phase, determining if the cell cycle should continue or stop. In its normal state, Rb is activated, which prevents the cell cycle to continue because it can recruit transcriptional co-repressors, blocking transcription<ref name=Change >PMID: 12502741 </ref>. Rb is deactivated after being phosphorylated by Cyclin-dependent kinases (Cdks)[http://en.wikipedia.org/wiki/Cyclin-dependent_kinase], and thus cannot associate factors that inhibit transcription factors that allow the cell cycle to continue. Unregulated deactivation of Rb can lead to uncontrolled growth of cells, which is why studying this protein is important in cancer research. [[Image:http://www.grin.com/object/external_document.258080/2a0fcb4585f4d1ad9f55e6dec27a8792_LARGE.png]]
==Regulation of Rb==
==Regulation of Rb==

Revision as of 20:20, 30 November 2011

Contents

Retinoblastoma Protein

PDB ID 3n5u

Drag the structure with the mouse to rotate
3n5u, resolution 3.20Å ()
Ligands: ,
Gene: PPP1A, PPP1CA (Homo sapiens)
Activity: Phosphoprotein phosphatase, with EC number 3.1.3.16


Resources: FirstGlance, OCA, RCSB, PDBsum
Coordinates: save as pdb, mmCIF, xml


The retinoblastoma protein (Rb) is a suppressor protein, also known as a tumor suppressor, involved in negative regulation of the cell cycle[1] due to its ability to bind the transcription factor E2F[2]. It acts as a cell cycle checkpoint during the G1 phase, determining if the cell cycle should continue or stop. In its normal state, Rb is activated, which prevents the cell cycle to continue because it can recruit transcriptional co-repressors, blocking transcription[1]. Rb is deactivated after being phosphorylated by Cyclin-dependent kinases (Cdks)[3], and thus cannot associate factors that inhibit transcription factors that allow the cell cycle to continue. Unregulated deactivation of Rb can lead to uncontrolled growth of cells, which is why studying this protein is important in cancer research. Image:Http://www.grin.com/object/external document.258080/2a0fcb4585f4d1ad9f55e6dec27a8792 LARGE.png

Regulation of Rb

From previous studies, it has been determined that the phosphorylation state and activity of Rb are controlled by a balance of kinase and phosphatase activity, in which Cdks phosphorylate Rb from late G1 to mitosis and the enzyme protein phosphatase 1 (PP1c) dephosphorylates Rb for mitotic exit[2]. An enzyme-docking site for PP1c was determined to overlap with the docking site for Cdks, more specifically the RxL Cyclin binding site[3] that brings Cdk-Cyclins to Rb, through a crystal structure; this crystal structure initiated studies on phosphatase and kinase competition for the docking site. It has been found that PP1c directly inhibits phosphorylation of RbC from Cdk2-CycA[4]; it is not affected by phosphatase activity but by the presence of the KLRF docking site, which binds the catalytic subunit of PP1c to a specific site of Rb[2]. In addition, it has been observed that PP1c makes complexes with RbC when there are many phosphatases produced, thus overthrowing Cdk activity and inhibiting cell progression from the G1 phase. This competition is important in terms of cell signaling, which is affected by response to cellular stress, cell cycle exit, DNA damage, etc[2]. This is because the competition further controls cell overgrowth besides phosphorylation regulation. Studies determined a biochemical mechanism where directly competing kinases and phosphatase activity regulates Rb phosphorylation and activity, but there has not been an established study that defined a mechanism that controlled the outcome of the competition between each enzyme[2].

Relevance

While there are other characteristics of cancer cells, such as cell dispersal and apoptosis resistance, the foundation of cell proliferation is at the cell cycle[4]. Studying this competition in overlapping docking sites is important in cancer research because it can give a better understanding of how Rb can be manipulated if there is an error in regulation, leading to unwanted cell growth.


Structure of Rb-PP1c(PDB entry 3n5u)

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3D Structures

1o9k with E2F
1h25 with Cdk2/Cyclin A


References

  1. ↑ Lee C, Chang JH, Lee HS, Cho Y. Structural basis for the recognition of the E2F transactivation domain by the retinoblastoma tumor suppressor. Genes Dev. 2002 Dec 15;16(24):3199-212. PMID:12502741 doi:10.1101/gad.1046102
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Hirschi A, Cecchini M, Steinhardt RC, Schamber MR, Dick FA, Rubin SM. An overlapping kinase and phosphatase docking site regulates activity of the retinoblastoma protein. Nat Struct Mol Biol. 2010 Sep;17(9):1051-7. Epub 2010 Aug 8. PMID:20694007 doi:10.1038/nsmb.1868
  3. ↑ Lowe ED, Tews I, Cheng KY, Brown NR, Gul S, Noble ME, Gamblin SJ, Johnson LN. Specificity determinants of recruitment peptides bound to phospho-CDK2/cyclin A. Biochemistry. 2002 Dec 31;41(52):15625-34. PMID:12501191
  4. ↑ http://www.ias.ac.in/currsci/sep102001/515.pdf
  5. ↑ Terrak, Mohammed, Kerff, Frederic, Langsetmo, Knut, Tao, Terence, & Dominguez, Roberto Structural basis of protein phosphatase 1 regulation. Nature, 429, 780–784 (17 June 2004); 10.1038/nature02582

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