scholarly journals Peptidic degron in EID1 is recognized by an SCF E3 ligase complex containing the orphan F-box protein FBXO21

2015 ◽  
Vol 112 (50) ◽  
pp. 15372-15377 ◽  
Author(s):  
Cuiyan Zhang ◽  
Xiaotong Li ◽  
Guillaume Adelmant ◽  
Jessica Dobbins ◽  
Christoph Geisen ◽  
...  
Keyword(s):  
Tumor Suppressor ◽  
Family Members ◽  
Binding Motif ◽  
Retinoblastoma Tumor Suppressor ◽  
Ubiquitin Ligase Complex ◽  
Retinoblastoma Tumor ◽  
F Box Protein ◽  
Necessary And Sufficient

EP300-interacting inhibitor of differentiation 1 (EID1) belongs to a protein family implicated in the control of transcription, differentiation, DNA repair, and chromosomal maintenance. EID1 has a very short half-life, especially in G0 cells. We discovered that EID1 contains a peptidic, modular degron that is necessary and sufficient for its polyubiquitylation and proteasomal degradation. We found that this degron is recognized by an Skp1, Cullin, and F-box (SCF)-containing ubiquitin ligase complex that uses the F-box Only Protein 21 (FBXO21) as its substrate recognition subunit. SCFFBXO21 polyubiquitylates EID1 both in vitro and in vivo and is required for the efficient degradation of EID1 in both cycling and quiescent cells. The EID1 degron partially overlaps with its retinoblastoma tumor suppressor protein-binding domain and is congruent with a previously defined melanoma-associated antigen-binding motif shared by EID family members, suggesting that binding to retinoblastoma tumor suppressor and melanoma-associated antigen family proteins could affect the polyubiquitylation and turnover of EID family members in cells.

scholarly journals Retinoblastoma Protein Contains a C-terminal Motif That Targets It for Phosphorylation by Cyclin-cdk Complexes

1999 ◽  
Vol 19 (2) ◽  
pp. 1068-1080 ◽  
Author(s):  
Peter D. Adams ◽  
Xiaotong Li ◽  
William R. Sellers ◽  
Kayla B. Baker ◽  
Xiaohong Leng ◽  
...  
Keyword(s):  
Site Directed Mutagenesis ◽  
Binding Motif ◽  
Retinoblastoma Tumor Suppressor Protein ◽  
Retinoblastoma Tumor Suppressor ◽  
C Terminus ◽  
Sequence Elements ◽  
Stable Association ◽  
Retinoblastoma Tumor

ABSTRACT Stable association of certain proteins, such as E2F1 and p21, with cyclin-cdk2 complexes is dependent upon a conserved cyclin-cdk2 binding motif that contains the core sequence ZRXL, where Z and X are usually basic. In vitro phosphorylation of the retinoblastoma tumor suppressor protein, pRB, by cyclin A-cdk2 and cyclin E-cdk2 was inhibited by a short peptide spanning the cyclin-cdk2 binding motif present in E2F1. Examination of the pRB C terminus revealed that it contained sequence elements related to ZRXL. Site-directed mutagenesis of one of these sequences, beginning at residue 870, impaired the phosphorylation of pRB in vitro. A synthetic peptide spanning this sequence also inhibited the phosphorylation of pRB in vitro. pRB C-terminal truncation mutants lacking this sequence were hypophosphorylated in vitro and in vivo despite the presence of intact cyclin-cdk phosphoacceptor sites. Phosphorylation of such mutants was restored by fusion to the ZRXL-like motif derived from pRB or to the ZRXL motifs from E2F1 or p21. Phospho-site-specific antibodies revealed that certain phosphoacceptor sites strictly required a C-terminal ZRXL motif whereas at least one site did not. Furthermore, this residual phosphorylation was sufficient to inactivate pRB in vivo, implying that there are additional mechanisms for directing cyclin-cdk complexes to pRB. Thus, the C terminus of pRB contains a cyclin-cdk interaction motif of the type found in E2F1 and p21 that enables it to be recognized and phosphorylated by cyclin-cdk complexes.

INVESTIGATING THE ROLE AND REGULATION OF THE SPECIFIC ANDGENERAL PRB-E2F1 INTERACTIONS

2008 ◽  
Vol 31 (4) ◽  
pp. 6
Author(s):  
Matthew J Cecchini ◽  
Frederick A Dick
Keyword(s):  
Tumor Suppressor ◽  
Binding Site ◽  
Family Members ◽  
Retinoblastoma Tumor Suppressor Protein ◽  
Retinoblastoma Tumor Suppressor ◽  
C Terminus ◽  
Proliferation And Apoptosis ◽  
Retinoblastoma Tumor ◽  
And Control

Background/Purpose. The retinoblastoma tumor suppressor protein (pRB) plays a central role in proliferative control and is a frequent target for inactivation in cancer. The G1-Sphase transition of the cell cycle is regulated by pRB, which is capable of interacting with E2F family members and inhibiting the transcription of genesrequired to progress into S-phase. E2F1 is unique from other E2F family members as it can induce both apoptosis and proliferation. To control these contrasting functions of E2F1, a second E2F1 binding site exists in the C-terminus of pRB that can control apoptosis separately from proliferation. This anti-apoptotic function of pRBcan in some circumstances promote tumorigenesis, which leads to the question; is pRB a tumor suppressor or an oncogene? Methods. To investigate this, a gene-targeted mouse model is being engineered to selectively disrupt the ability of pRB to control proliferation through the general E2F binding site while still retaining the ability tocontrol apoptosis through the specific E2F1 site. Results. A series of novel mutants were engineered to selectively disrupt the binding of E2Fs at the general site, and prevent pRB from controlling proliferation. The mutants retain the ability to bind E2F1 and control apoptosis through thespecific binding site, which is not disrupted. Conclusions. By separating the ability of pRB to control proliferation and apoptosis under in vivo conditions, a better understanding into the significance of these two functions in development and tumorigenesis can be gained.

scholarly journals N6-Isopentenyladenosine Inhibits Colorectal Cancer and Improves Sensitivity to 5-Fluorouracil Targeting FBXW7 Tumor Suppressor

Cancers ◽  
2019 ◽  
Vol 11 (10) ◽  
pp. 1456 ◽  
Author(s):  
Donatella Fiore ◽  
Chiara Piscopo ◽  
Maria Proto ◽  
Michele Vasaturo ◽  
Fabrizio Dal Piaz ◽  
...  
Keyword(s):  
Colorectal Cancer ◽  
Tumor Suppressor ◽  
In Vitro Models ◽  
Antitumor Action ◽  
Cancer Proliferation ◽  
Ubiquitinated Proteins ◽  
Mutational Status ◽  
Ubiquitin Ligase Complex

N6-isopentenyladenosine has been shown to exert potent in vitro antitumor activity on different human cancers, including colorectal cancer. Although some potential biochemical targets have been identified, its precise mechanism of action remains unclear. We found that N6-isopentenyladenosine affects colorectal cancer proliferation in in vitro models carrying different mutational status of FBXW7 and TP53 genes, and in HCT116 xenografts in SCID mice, by increasing the expression of the well-established tumor suppressor FBXW7, a component of the SCF-E3 ubiquitin ligase complex that promotes degradation of various oncoproteins and transcription factors, such as c-Myc, SREBP and Mcl1. Corroborating our previous studies, we identified for the first time the FBXW7/SREBP/FDPS axis as a target of the compound. Pull down of ubiquitinated proteins, immunoprecipitation and luciferase assays, reveal that through the increase of FBXW7/c-Myc binding, N6-isopentenyladenosine induces the ubiquitination of c-Myc, inhibiting its transcriptional activity. Moreover, in FBXW7- and TP53-wild type cells, N6-isopentenyladenosine strongly synergizes with 5-Fluorouracil to inhibit colon cancer growth in vitro. Our results provide novel insights into the molecular mechanism of N6-isopentenyladenosine, revealing its multi-targeting antitumor action, in vitro and in vivo. Restoring of FBXW7 tumor-suppressor represents a valid therapeutic tool, enabling N6-isopentenyladenosine as optimizable compound for patient-personalized therapies in colorectal cancer.

scholarly journals The Corepressor mSin3a Interacts with the Proline-Rich Domain of p53 and Protects p53 from Proteasome-Mediated Degradation

2001 ◽  
Vol 21 (12) ◽  
pp. 3974-3985 ◽  
Author(s):  
Jack T. Zilfou ◽  
William H. Hoffman ◽  
Michael Sank ◽  
Donna L. George ◽  
Maureen Murphy
Keyword(s):  
Tumor Suppressor ◽  
Binding Domain ◽  
Protein Stabilization ◽  
Independent Manner ◽  
Retinoblastoma Tumor Suppressor Protein ◽  
Rich Domain ◽  
Retinoblastoma Tumor Suppressor ◽  
Retinoblastoma Tumor ◽  
Sin3 Complex

ABSTRACT While the transactivation function of the tumor suppressor p53 is well understood, less is known about the transrepression functions of this protein. We have previously shown that p53 interacts with the corepressor protein mSin3a (hereafter designated Sin3) in vivo and that this interaction is critical for the ability of p53 to repress gene expression. In the present study, we demonstrate that expression of Sin3 results in posttranslational stabilization of both exogenous and endogenous p53, due to an inhibition of proteasome-mediated degradation of this protein. Stabilization of p53 by Sin3 requires the Sin3-binding domain, determined here to map to the proline-rich region of p53, from amino acids 61 to 75. The correlation between Sin3 binding and stabilization supports the hypothesis that this domain of p53 may normally be subject to a destabilizing influence. The finding that a synthetic mutant of p53 lacking the Sin3-binding domain has an increased half-life in cells, compared to wild-type p53, supports this premise. Interestingly, unlike retinoblastoma tumor suppressor protein, MDMX, and p14ARF, Sin3 stabilizes p53 in an MDM2-independent manner. The ability of Sin3 to stabilize p53 is consistent with the model whereby these two proteins must exist on a promoter for extended periods, in order for repression to be an effective mechanism of gene regulation. This model is consistent with our data indicating that, unlike the p300-p53 complex, the p53-Sin3 complex is immunologically detectable for prolonged periods following exposure of cells to agents of DNA damage.

scholarly journals RBP1 Recruits the mSIN3-Histone Deacetylase Complex to the Pocket of Retinoblastoma Tumor Suppressor Family Proteins Found in Limited Discrete Regions of the Nucleus at Growth Arrest

2001 ◽  
Vol 21 (8) ◽  
pp. 2918-2932 ◽  
Author(s):  
Albert Lai ◽  
Brian K. Kennedy ◽  
David A. Barbie ◽  
Nicholas R. Bertos ◽  
Xiang Jiao Yang ◽  
...  
Keyword(s):  
Cell Cycle ◽  
Tumor Suppressor ◽  
Histone Deacetylase ◽  
Family Members ◽  
Growth Stimulation ◽  
Stable Complex ◽  
Induce Cell Cycle Arrest ◽  
Retinoblastoma Tumor Suppressor ◽  
Retinoblastoma Tumor ◽  
Class I Hdacs

ABSTRACT Retinoblastoma (RB) tumor suppressor family pocket proteins induce cell cycle arrest by repressing transcription of E2F-regulated genes through both histone deacetylase (HDAC)-dependent and -independent mechanisms. In this study we have identified a stable complex that accounts for the recruitment of both repression activities to the pocket. One component of this complex is RBP1, a known pocket-binding protein that exhibits both HDAC-dependent and -independent repression functions. RB family proteins were shown to associate via the pocket with previously identified mSIN3-SAP30-HDAC complexes containing exclusively class I HDACs. Such enzymes do not interact directly with RB family proteins but rather utilize RBP1 to target the pocket. This mechanism was shown to account for the majority of RB-associated HDAC activity. We also show that in quiescent normal human cells this entire RBP1-mSIN3-SAP30-HDAC complex colocalizes with both RB family members and E2F4 in a limited number of discrete regions of the nucleus that in other studies have been shown to represent the initial origins of DNA replication following growth stimulation. These results suggest that RB family members, at least in part, drive exit from the cell cycle by recruitment of this HDAC complex via RBP1 to repress transcription from E2F-dependent promoters and possibly to alter chromatin structure at DNA origins.

scholarly journals The Mus musculus papillomavirus type 1 E7 protein binds to the retinoblastoma tumor suppressor - implications for viral pathogenesis

2021 ◽  
Author(s):  
Tao Wei ◽  
Miranda Grace ◽  
Aayushi Uberoi ◽  
James C Romero-Masters ◽  
Denis Lee ◽  
...  
Keyword(s):  
Tumor Suppressor ◽  
Mus Musculus ◽  
Model Organisms ◽  
Retinoblastoma Tumor Suppressor ◽  
C Terminus ◽  
E6 And E7 ◽  
Retinoblastoma Tumor ◽  
E7 Proteins

The species specificity of papillomaviruses has been a significant roadblock for performing in vivo pathogenesis studies in common model organisms. The Mus musculus papillomavirus type 1 (MmuPV1) causes cutaneous papillomas that can progress to squamous cell carcinomas in laboratory mice. The papillomavirus E6 and E7 genes encode proteins that establish and maintain a cellular milieu that allows for viral genome synthesis and viral progeny synthesis in growth-arrested, terminally differentiated keratinocytes. The E6 and E7 proteins provide this activity by binding to and functionally reprogramming key cellular regulatory proteins. The MmuPV1 E7 protein lacks the canonical LXCXE motif that mediates the binding of multiple viral oncoproteins to the cellular retinoblastoma tumor suppressor protein, RB1. Our proteomic experiments, however, revealed that MmuPV1 E7 still interacts specifically with RB1. We show that MmuPV1 E7 interacts through its C-terminus with the C-terminal domain of RB1. Binding of MmuPV1 E7 to RB1 did not cause significant activation of E2F-regulated cellular genes. MmuPV1 E7 expression was shown to be essential for papilloma formation. Experimental infection of mice with MmuPV1 virus expressing an E7 mutant that is defective for binding to RB1 caused delayed onset, lower incidence, and smaller sizes of papillomas. Our results demonstrate that the MmuPV1 E7 gene is essential and that targeting non-canonical activities of RB1, which are independent of RB1's ability to modulate the expression of E2F-regulated genes, contribute to papillomavirus-mediated pathogenesis.

scholarly journals Retinoblastoma Tumor Suppressor: Analyses of Dynamic Behavior in Living Cells Reveal Multiple Modes of Regulation

2003 ◽  
Vol 23 (22) ◽  
pp. 8172-8188 ◽  
Author(s):  
Steven P. Angus ◽  
David A. Solomon ◽  
Lioba Kuschel ◽  
Robert F. Hennigan ◽  
Erik S. Knudsen
Keyword(s):  
Cell Cycle ◽  
Tumor Suppressor ◽  
Dynamic Behavior ◽  
Transcriptional Repression ◽  
Fluorescent Protein ◽  
Dynamic Equilibrium ◽  
Living Cells ◽  
Retinoblastoma Tumor Suppressor ◽  
Retinoblastoma Tumor

ABSTRACT The retinoblastoma tumor suppressor, RB, assembles multiprotein complexes to mediate cell cycle inhibition. Although many RB binding partners have been suggested to underlie these functions, the validity of these interactions on the behavior of RB complexes in living cells has not been investigated. Here, we studied the dynamic behavior of RB by using green fluorescent protein-RB fusion proteins. Although these proteins were universally nuclear, phosphorylation or oncoprotein binding mediated their active exclusion from the nucleolus. In vivo imaging approaches revealed that RB exists in dynamic equilibrium between a highly mobile and a slower diffusing species, and genetic lesions associated with tumorigenesis increased the fraction of RB in a highly mobile state. The RB complexes dictating cell cycle arrest were surprisingly dynamic and harbored a relatively short residence time on chromatin. In contrast, this rapid exchange was attenuated in cells that are hypersensitive to RB, suggesting that responsiveness may inversely correlate with mobility. The stability of RB dynamics within the cell was additionally modified by the presence and function of critical corepressors. Last, the RB-assembled complexes present in living cells were primarily associated with E2F binding sites in chromatin. In contrast to RB, E2F1 consistently maintained a stable association with E2F sites regardless of cell type. Together, these results elucidate the kinetic framework of RB tumor suppressor action in transcriptional repression and cell cycle regulation.

A Critical Role for the Retinoblastoma Tumor Suppressor Gene in Hematopoietic Stem Cells.

Blood ◽  
2006 ◽  
Vol 108 (11) ◽  
pp. 2548-2548
Author(s):  
Hartmut Geiger ◽  
Marie-Dominique Filippi ◽  
Theodosia A. Kalfa ◽  
Deidre Daria
Keyword(s):  
Cell Cycle ◽  
Tumor Suppressor ◽  
Cell Function ◽  
Fetal Liver ◽  
Critical Role ◽  
Lymphoid Cells ◽  
Hematopoietic Stem ◽  
Retinoblastoma Tumor Suppressor ◽  
Retinoblastoma Tumor

Abstract The retinoblastoma tumor suppressor protein (RB) plays important roles in the control of the cell cycle, DNA-damage checkpoint, differentiation and apoptosis. It is estimated that RB is dysfunctional/inactivated in up to 40% of human leukemias. Positive as well as inhibitory signals are integrated into the phosphorylation of the RB protein to regulate the G1 to S-phase progression of the cell cycle. Despite the importance of RB in leukemia, the consequences of loss of RB on hematopoietic stem and progenitor cell (HSPC) function in vivo are still not clear and have been controversially discussed. Using Cre-enzyme expression driven by the hematopoietic specific Vav1-promotor, we generated mice that are constitutively deficient in RB (hemRb−/− animals) in HSPCs. HemRb−/− mice showed anemia with an increased number of reticulocytes in PB, consistent with a published role of RB in erythroid differentiation. In addition, the frequency of Mac-1 positive cells in BM was increased to 67% compared to 47% in control animals, whereas the frequency of B220 positive B-lymphoid cells was almost 10-fold reduced, without affecting the T-lymphoid compartment. HemRb−/− mice possessed a 3-fold enlarged spleen with a 5-fold increased number of colony-forming cells (CFCs) and severe extramedullary hematopoiesis, a phenotype also reported for animals transplanted with Rb−/− fetal liver cells. BM of hemRb−/− mice showed an almost 3-fold reduction of HSC frequency, measured by the cobblestone-area forming cell assay (CAFC) assay, but not a decrease in the number of HSCs determined by cell surface staining and flow cytometry. Upon transplantation into NOD/SCID animals or upon competitive transplantation into C57BL/6. CD45.1 animals, HSPCs from hemRb−/− mice contributed 4 to 6-fold less to hematopoiesis. HSPCs from hemRb−/− animals were neither impaired in their ability to home to the BM, nor did they show increased apoptosis. Finally, we detected a significant 4-fold decrease in stem cell function/numbers upon stress caused by 5-FU treatment in hemRB−/− mice compared to control animals. We conclude that upon transplantation/stress, HSPCs from hemRb−/− animals are impaired in their self-renewal function. HemRb−/− animals also showed a 2-fold increase in the frequency of CFCs in peripheral blood. As we detected no increased leukemia incidence in the hemRb−/− animals (now up to 1 year of age), loss of the tumor suppressor RB in hematopoietic cells might be regarded as necessary, but not sufficient for causing early onset leukemia. In summary, loss of RB results in context/localization dependent phenotypes in the hematopoietic hierarchy, influencing stem and progenitor cells in function, localization and differentiation ability.

Relationship between the loss of the retinoblastoma tumor suppressor and radiosensitivity.

2011 ◽  
Vol 29 (7_suppl) ◽  
pp. 34-34 ◽  
Author(s):  
R. B. Den ◽  
S. Ciment ◽  
A. Sharma ◽  
H. Mellert ◽  
S. Mc-Mahon ◽  
...  
Keyword(s):  
Prostate Cancer ◽  
Cell Cycle ◽  
Dna Damage ◽  
Tumor Suppressor ◽  
Ionizing Radiation ◽  
Cell Survival ◽  
Retinoblastoma Tumor Suppressor ◽  
Clonogenic Cell ◽  
Retinoblastoma Tumor

34 Background: Prostate cancer is the most frequently diagnosed malignancy and the second leading cause of cancer death in U.S. men. The retinoblastoma tumor suppressor protein, RB, plays a critical role in cell cycle regulation. Loss of RB has been observed in 25–30% of prostate cancers and is correlated with increasing tumor stage and grade. The clinical consequences of RB loss are unknown. We have previously shown that RB loss results in a castrate resistant phenotype. We hypothesized that RB loss would downregulate the G1-S cell cycle arrest normally induced by irradiation, inhibit DNA repair, and subsequently sensitize cells to mitotic catastrophe. Methods: Experimental work was performed with multiple isogenic prostate cancer cell lines (hormone sensitive: LNCaP and LAP-C4 cells and hormone resistant C42 cells; stable knockdown of RB using shRNA). Gamma H2AX assays were used to quantitate DNA damage and PARP cleavage and Caspase 3 were used to quantitate apoptosis. FACS analysis with BrdU was used to assess the cell cycle. Cell survival was measured using the clonogenic cell survival assay. In vivo work was performed in nude mice with tumor xenografts. Results: We observed that loss of RB increased radioresponsiveness in both transient and clonogenic cell survival assays in all cell lines (p<0.05). Cell death was not mediated through increased apoptosis, however, there was increased cell cycling despite the presence of DNA damage in the RB knockdown cells. In vivo xenografts of the RB deficient tumors exhibited diminished tumor mass, lower PSA kinetics and decreased tumor growth after treatment with single fraction of ionizing radiation in comparison to RB intact tumors (p<0.05). Conclusions: Loss of RB results in a differential response to ionizing radiation. Isogenic cells with RB knockdown are more sensitive to DNA damage and result in reduced cell survival. RB status is integral to determining which therapeutic modality should be employed in the management of prostate cancer. No significant financial relationships to disclose.

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