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Showing content from https://pubmed.ncbi.nlm.nih.gov/22405651/ below:

The glomuvenous malformation protein Glomulin binds Rbx1 and regulates cullin RING ligase-mediated turnover of Fbw7

. 2012 Apr 13;46(1):67-78. doi: 10.1016/j.molcel.2012.02.005. Epub 2012 Mar 8. The glomuvenous malformation protein Glomulin binds Rbx1 and regulates cullin RING ligase-mediated turnover of Fbw7

Affiliations

Affiliation

¹ Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02215, USA.

PMID: 22405651
PMCID: PMC3336104
DOI: 10.1016/j.molcel.2012.02.005

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The glomuvenous malformation protein Glomulin binds Rbx1 and regulates cullin RING ligase-mediated turnover of Fbw7

Adriana E Tron et al. Mol Cell. 2012.

. 2012 Apr 13;46(1):67-78. doi: 10.1016/j.molcel.2012.02.005. Epub 2012 Mar 8. Affiliation

¹ Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, MA 02215, USA.

PMID: 22405651
PMCID: PMC3336104
DOI: 10.1016/j.molcel.2012.02.005

Item in Clipboard

Abstract

Fbw7, a substrate receptor for Cul1-RING-ligase (CRL1), facilitates the ubiquitination and degradation of several proteins, including Cyclin E and c-Myc. In spite of much effort, the mechanisms underlying Fbw7 regulation are mostly unknown. Here, we show that Glomulin (Glmn), a protein found mutated in the vascular disorder glomuvenous malformation (GVM), binds directly to the RING domain of Rbx1 and inhibits its E3 ubiquitin ligase activity. Loss of Glmn in a variety of cells, tissues, and GVM lesions results in decreased levels of Fbw7 and increased levels of Cyclin E and c-Myc. The increased turnover of Fbw7 is dependent on CRL and proteasome activity, indicating that Glmn modulates the E3 activity of CRL1(Fbw7). These data reveal an unexpected functional connection between Glmn and Rbx1 and demonstrate that defective regulation of Fbw7 levels contributes to GVM.

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Conflict of interest statement

The authors declare that they have no competing financial interests.

Figures
Figure 1. Glmn binds specifically to Rbx1…

Figure 1. Glmn binds specifically to Rbx1 and Cullins

( A ) Extracts from HEK293T…

Figure 1. Glmn binds specifically to Rbx1 and Cullins

(A) Extracts from HEK293T cells transfected with myc-tagged cullins or empty vector (EV) were immunoprecipitated with Myc antibody and western blotted (WB). (B) U-2OS cell extracts were immunoprecipitated with antibodies against Rbx1, Glmn or control IgG and WB. (C) Lysates of HeLa cells transfected with HA-Rbx1, HA-Rbx2 or EV were immunoprecipitated with HA antibody and WB. (D) Extracts from HEK293T cells transfected with EV, or HA-wild type or -mutant Glmn were immunoprecipitated with HA antibody and WB.

Figure 2. Glmn Binds the RING Domain…

Figure 2. Glmn Binds the RING Domain of Rbx1 and Inhibits E3 Ligase Activity

(…

Figure 2. Glmn Binds the RING Domain of Rbx1 and Inhibits E3 Ligase Activity

(A) Extracts from HEK293T cells transfected with HA-Rbx1 wild type (wt) or mutants were immunoprecipitated with HA antibody and WB. (B) Upper - Glmn was mixed with purified Rbx1^RING and analyzed by gel filtration chromatography. Eluted proteins were detected by spectrophotometry. AU: arbitrary units. Bottom - Coomassie-stained SDS-PAGE gel of the eluted fractions. (C) Lysates from U-2OS cells transfected with the indicated siRNAs were immunoprecipitated and WB. Immunoprecipitation with Nedd8 and Cul1 antibodies were included as controls. Black and gray arrows indicate neddylated and un-neddylated Cul1, respectively. (D) Glmn was mixed with purified Cul1-Rbx1 (blue) or Cul1-Rbx1-Skp1-Fbw7 (red) complexes prior to gel filtration chromatography. Eluted proteins were detected by spectrophotometry (upper panel) and WB (bottom panel). (E) In vitro ubiquitination reactions with biotin-labeled Cyclin E phosphopeptide and neddylated CRL1^Fbw7, in the absence (-, left) or presence (+, right) of Glmn were WB with biotin antibody. Extracts from HEK293T cells co-transfected with HA-Rbx1 and Flag-Glmn or EV (F) or HA-Cul1 and Flag-Glmn or EV (G) were immunoprecipitated with Flag antibody. Flag-Glmn-associated proteins were eluted with Flag peptide, re-immunoprecipitated with Rbx1 (F) or HA (G) antibody, followed by ubiquitination assay and WB. Increasing amounts of HA-Rbx1 (F) or HA-Cul1 (G) expressing HEK293T lysates immunoprecipitated with Rbx1 or HA antibody, respectively, and subjected to an ubiquitination reaction were included as positive controls. See also Figure S1

Figure 3. Glmn -Null Embryos Have Severe…

Figure 3. Glmn -Null Embryos Have Severe Developmental Defects

( A ) Genotype of Glmn ^+/−…

Figure 3. Glmn-Null Embryos Have Severe Developmental Defects

(A) Genotype of Glmn^+/− intercrosses. % −/−, Proportion of total Glmn^−/− embryos or pups at each stage. (B) Gross appearance of Glmn^−/− E9.5 embryos. Glmn^−/− embryos showed vast pools of embryonic blood, pericardial effusion (arrow) and asymmetrical open neural tube (arrow head) compared with Glmn^+/+ littermate. Scale bars, 1 mm (C) Yolk sacs of Glmn^−/− embryos presented disorganized vascular structures. A yolk sac of Glmn^+/+ littermate was included as control. Scale bars, 1 mm (D) Glmn^−/− E9.5 yolk sacs stained for PECAM-1 showed a primitive vascular plexus compared to wild type control. Scale bars, 0.5 mm Sections of H&E (E) or Caspase-3 (F) stained head regions of the Glmn^−/− E9.5 embryo demonstrated cystic degeneration (asterisk, E), low cellularity in mesenchyme (E), and massive apoptosis (F) compared with Glmn^+/+ littermate. Scale bars, 300 μm (E) and 100 μm (F)

Figure 4. Loss of Glmn Leads to…

Figure 4. Loss of Glmn Leads to Decreased Levels of Rbx1 and Cullins and Increased…
Figure 4. Loss of Glmn Leads to Decreased Levels of Rbx1 and Cullins and Increased Abundance of Cyclin E

(A) Lysates from E9.5 Glmn^+/+, Glmn^+/− and Glmn^−/− embryo and yolk sac were WB. (B) Relative mRNA levels for indicated genes in Glmn^+/+, Glmn^+/− and Glmn^−/− embryos. Results are shown as means ± standard error, calculated from three independent experiments. (C) Sections of Glmn^+/+ and Glmn^−/− placentas at E9.5 were stained with Cyclin E antibody (200x). (D) Lysates from U-2OS cells transfected with Glmn, Rbx1 or control siRNA were WB. (E) Extracts from Glmn^+/+ or Glmn^−/− ES cells stably expressing HA-Glmn, HA-m-d393, or EV were WB. See also Figure S2

Figure 5. Reduced Stability of Fbw7 in…

Figure 5. Reduced Stability of Fbw7 in Glmn Depleted Cells Contributes to Cyclin E and…
Figure 5. Reduced Stability of Fbw7 in Glmn Depleted Cells Contributes to Cyclin E and c-Myc Accumulation

(A) Lysates from E9.5 Glmn^+/+, Glmn^+/− and Glmn^−/− embryo and yolk sac were WB. (B) Extracts from U-2OS cells transfected with Glmn, Fbw7 or control siRNA were WB. Fbw7 was immunoprecipitated with Fbw7 antibody followed by WB. (C) Lysates from U-2OS cells transfected with Glmn or control siRNA and treated with CHX for the indicated time were WB. To normalize the amount of protein at time zero, blots highlighted in boxes were exposed for different times. Fbw7 was immunoprecipitated with Fbw7 antibody prior to WB. (D) Extracts from U-2OS transfected with Glmn siRNA and EV, HA-Fbw7 or HA-Gsk3 plasmids were WB. Sections of GVM were stained with H&E or immunostained with smooth muscle (SM) α-actin, Cyclin E (E), c-Myc (G), Rbx1 (I) or Cul1 (K) antibody. Squares in green outline fields enriched for glomus cells; squares in black shows field with normal VSMCs. Percentage of Cyclin E (F), c-Myc (H), Rbx1 (J), or Cul1 (L) positive cells present in sections of different GVM patients was quantified by Aperio analysis. See also Figure S3

Figure 6. Glmn Inhibits Rbx1-Mediated Ubiquitination of…

Figure 6. Glmn Inhibits Rbx1-Mediated Ubiquitination of Fbw7

( A ) Lysates from U-2OS cells…

Figure 6. Glmn Inhibits Rbx1-Mediated Ubiquitination of Fbw7

(A) Lysates from U-2OS cells transfected with Glmn or control siRNA were treated with 0.02, 0.2 or 2 μM Bortezomib for 9 hrs and WB. Fbw7 was immunoprecipitated with an Fbw7 antibody prior to WB. Extracts from U-2OS cells stably expressing HA-wild type Fbw7 (B), HA-Fbw7^{Y545A, L583S} (C), or HA-Fbw7^{D560S, D600S} (D) and treated with 100 μg/ml CHX for the indicated time were WB. To normalize the amount of protein at time zero, blots highlighted in boxes were exposed for different times. (E) U-2OS cells transfected with Glmn or control siRNA were treated with 0.075, 0.3 or 1 μM MLN4924 for 20 hrs and WB. (F) Extracts from U-2OS cells transfected with the indicated siRNAs were WB. See also Figure S4

Figure 7. Glmn Controls the Protein Stability…

Figure 7. Glmn Controls the Protein Stability of Rbx1 and Cullins

( A ) Extracts…

Figure 7. Glmn Controls the Protein Stability of Rbx1 and Cullins

(A) Extracts from U-2OS cells transfected with Glmn or control siRNA and treated with 50 μg/ml CHX for the indicated time were WB. To normalize the amount of protein at time zero, blots highlighted in boxes were exposed for different times. (B) Graphical representation of Rbx1 abundance in U-2OS cells transfected with Glmn or control siRNA after CHX for the indicated times. Data are shown as means ± standard error, calculated from three independent experiments p< 0.0001. (C) Lysates from U-2OS cells transfected with the indicated siRNAs were WB. See also Figure S5

Comment in

Cullin RING ligases: glommed by glomulin.
Hristova VA, Stringer DK, Weissman AM. Hristova VA, et al. Mol Cell. 2012 Aug 10;47(3):331-2. doi: 10.1016/j.molcel.2012.07.025. Mol Cell. 2012. PMID: 22883621 Free PMC article.