Cell cycle - Role of SCF complex in cell cycle regulation

Role of SCF complex in cell cycle regulation

The events controlling cell division are governed by the degradation of different regulatory proteins by the Ubiquitin-dependent pathway. Ubiquitin, a small protein of 76 amino acids is found in all eukaryotic cells. In the Ubiquitin-dependent pathway, the attachment of a polyubiquitin chain to a substrate is realized by an ubiquitin-ligase targets this substrate for degradation by the 26S proteasome. The ubiquitination pathway sequentially involves the E1 Ub-activating enzyme, E2 Ub-conjugating enzymes, and E3 Ub-ligases [1].

E1 Ub-activating enzyme (e.g. ubiquitin-activating enzyme E1 (UBE1)) activates Ubiquitin in the ATP-dependent manner [2] and transfers it to E2 Ub-conjugating enzyme through thioester bond formation. E2 Ub-conjugating enzyme (e.g. cell division cycle 34 ubiquitin-protein ligase (CDC34)) activates ubiquitin-polymerization [3]. E3 Ub-ligase mediates the transfer of Ubiquitin from E2 Ub-conjugating enzyme to the substrate protein [1].

S-phase kinase-associated protein 1 p19 (SKP1)/ Cullin/F-box complex (SCF complex) is one of E3-ubiquitin ligases, which play a very important role in the cell cycle. SCF complex consists of Cullin 1, SKP1, F-box proteins (e.g. S-phase kinase-associated protein 2 p45 (Skp2), beta-transducin repeat containing protein (TrCP) or F-box protein FBW7 (FBXW7)) and RING-box protein 1. The Cullin 1/ RING-box protein 1 components are associated with E2 Ub-conjugating enzymes [1]. Ubiquitin-lake protein NEDD8 charged surface residues mediates activation of Cullin 1 / RING-box protein 1, which is needed to specifically support Cdc34-catalyzed ubiquitin polymerization [3]. F-box proteins directly recruit ubiquitination substrates and bridge the interaction between E2 Ub-conjugating enzyme and the substrate [1].

SCF complex participates in cell cycle regulation by stimulating ubiquitination of the cell cycle proteins and their degradation by the 26S proteasome. Most substrates require phosphorylation to interact with the F-box protein in an SCF complex [1].

Cell division cycle 25A phosphotase (CDC25A), Cyclin D, Cyclin E, cyclin-dependent kinase 2 (CDK2), DNA replication factor (Cdt1), cyclin-dependent kinase inhibitor 1A (p21), cyclin-dependent kinase inhibitor 1B (p27KIP1), E2F transcription factor 1 (E2F1) and retinoblastoma-like 2 (p130) bind to SCF complex and degrade during interphase [1], [4].

CDC25A is phosphorylated by some kinases in response to DNA damage (e.g. cell cycle checkpoint kinase 1 (Chk1). Phosphorylated CDC25A is ubiquitinated by SCF complex in late S and G2 phases [5]. Stimulation of the growth factor beta (TGF-beta)/ SMAD family member 3 (Smad3) pathway promotes SCF complex-mediated CDC25A ubiquitination [6]. Moreover, SCF complex may promote ubiquitin-proteasome degradation of Smad3 [7].

Phosphorylated by cyclin-dependent kinases (e.g. cyclin-dependent kinase 4 (CDK4)) p130 is ubiquitinated by SCF complex in G1 phase [8].

CDK2 binds to SCF complex and is degraded during late S or G2 phase. At the same time, phosphorylation of p27KIP1 [9], Cyclin E [10] and Cdt1 [11] by CDK2 promotes their SCF complex-mediated destruction during G1 and S phases [1]. Ubiquitination of p27KIP1 requires the SCF complex and Skp2 F-box binding protein CKS1 [12]. SKP2 and CKS1 are negatively regulated by Anaphase-promoting/ cell division cycle 20 related 1 protein complex (APC/hCdh1)-mediated ubiquitination. Targeting of SKP2 and CKS1 by APC/hCdh1 stabilizes p27KIP1, subsequently leading to the maintenance of G1 phase and blocking premature S-phase initiation [13], [14].

Cyclin D1 [15] and p21 bind to the SCF complex and get degraded during interphase too [16].

Tyrosine kinase Wee1 and F-box protein 5 (Emi1) bind to SCF complex and degrade during mitosis.

Major M-phase kinases Polo-like kinase 1 (Plk1) and Cdk1 phosphorylate WEE1 [17] and Emi1 [18], [19]. The phosphorylation makes WEE1 and Emi1 accessible to SCF complex-mediated degradation. Emi1 promotes S phase entry in somatic cells by inhibiting the APC/hCdh1 complex [20].

References:

1. Ang XL, Wade Harper J
   SCF-mediated protein degradation and cell cycle control. Oncogene 2005 Apr 18;24(17):2860-70
2. Handley PM, Mueckler M, Siegel NR, Ciechanover A, Schwartz AL
   Molecular cloning, sequence, and tissue distribution of the human ubiquitin-activating enzyme E1. Proceedings of the National Academy of Sciences of the United States of America 1991 Jan 1;88(1):258-62
3. Wu K, Chen A, Tan P, Pan ZQ
   The Nedd8-conjugated ROC1-CUL1 core ubiquitin ligase utilizes Nedd8 charged surface residues for efficient polyubiquitin chain assembly catalyzed by Cdc34. The Journal of biological chemistry 2002 Jan 4;277(1):516-27
4. Ohta T, Xiong Y
   Phosphorylation- and Skp1-independent in vitro ubiquitination of E2F1 by multiple ROC-cullin ligases. Cancer research 2001 Feb 15;61(4):1347-53
5. Busino L, Chiesa M, Draetta GF, Donzelli M
   Cdc25A phosphatase: combinatorial phosphorylation, ubiquitylation and proteolysis. Oncogene 2004 Mar 15;23(11):2050-6
6. Ray D, Terao Y, Nimbalkar D, Chu LH, Donzelli M, Tsutsui T, Zou X, Ghosh AK, Varga J, Draetta GF, Kiyokawa H
   Transforming growth factor beta facilitates beta-TrCP-mediated degradation of Cdc25A in a Smad3-dependent manner. Molecular and cellular biology 2005 Apr;25(8):3338-47
7. Fukuchi M, Imamura T, Chiba T, Ebisawa T, Kawabata M, Tanaka K, Miyazono K
   Ligand-dependent degradation of Smad3 by a ubiquitin ligase complex of ROC1 and associated proteins. Molecular biology of the cell 2001 May;12(5):1431-43
8. Bhattacharya S, Garriga J, Calbo J, Yong T, Haines DS, Gra?a X
   SKP2 associates with p130 and accelerates p130 ubiquitylation and degradation in human cells. Oncogene 2003 Apr 24;22(16):2443-51
9. Carrano AC, Eytan E, Hershko A, Pagano M
   SKP2 is required for ubiquitin-mediated degradation of the CDK inhibitor p27. Nature cell biology 1999 Aug;1(4):193-9
10. Yeh KH, Kondo T, Zheng J, Tsvetkov LM, Blair J, Zhang H
    The F-box protein SKP2 binds to the phosphorylated threonine 380 in cyclin E and regulates ubiquitin-dependent degradation of cyclin E. Biochemical and biophysical research communications 2001 Mar 9;281(4):884-90
11. Nishitani H, Taraviras S, Lygerou Z, Nishimoto T
    The human licensing factor for DNA replication Cdt1 accumulates in G1 and is destabilized after initiation of S-phase. The Journal of biological chemistry 2001 Nov 30;276(48):44905-11
12. Wang W, Ungermannova D, Chen L, Liu X
    A negatively charged amino acid in Skp2 is required for Skp2-Cks1 interaction and ubiquitination of p27Kip1. The Journal of biological chemistry 2003 Aug 22;278(34):32390-6
13. Bashir T, Dorrello NV, Amador V, Guardavaccaro D, Pagano M
    Control of the SCF(Skp2-Cks1) ubiquitin ligase by the APC/C(Cdh1) ubiquitin ligase. Nature 2004 Mar 11;428(6979):190-3
14. Wei W, Ayad NG, Wan Y, Zhang GJ, Kirschner MW, Kaelin WG Jr
    Degradation of the SCF component Skp2 in cell-cycle phase G1 by the anaphase-promoting complex. Nature 2004 Mar 11;428(6979):194-8
15. Maeda I, Ohta T, Koizumi H, Fukuda M
    In vitro ubiquitination of cyclin D1 by ROC1-CUL1 and ROC1-CUL3. FEBS letters 2001 Apr 13;494(3):181-5
16. Yam CH, Ng RW, Siu WY, Lau AW, Poon RY
    Regulation of cyclin A-Cdk2 by SCF component Skp1 and F-box protein Skp2. Molecular and cellular biology 1999 Jan;19(1):635-45
17. Watanabe N, Arai H, Nishihara Y, Taniguchi M, Watanabe N, Hunter T, Osada H
    M-phase kinases induce phospho-dependent ubiquitination of somatic Wee1 by SCFbeta-TrCP. Proceedings of the National Academy of Sciences of the United States of America 2004 Mar 30;101(13):4419-24
18. Margottin-Goguet F, Hsu JY, Loktev A, Hsieh HM, Reimann JD, Jackson PK
    Prophase destruction of Emi1 by the SCF(betaTrCP/Slimb) ubiquitin ligase activates the anaphase promoting complex to allow progression beyond prometaphase. Developmental cell 2003 Jun;4(6):813-26
19. Moshe Y, Boulaire J, Pagano M, Hershko A
    Role of Polo-like kinase in the degradation of early mitotic inhibitor 1, a regulator of the anaphase promoting complex/cyclosome. Proceedings of the National Academy of Sciences of the United States of America 2004 May 25;101(21):7937-42
20. Hsu JY, Reimann JD, S?rensen CS, Lukas J, Jackson PK
    E2F-dependent accumulation of hEmi1 regulates S phase entry by inhibiting APC(Cdh1). Nature cell biology 2002 May;4(5):358-66