Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0006142 (breast cancer)
 160,383 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

BRCA1 (Breast Cancer Susceptibility Gene 1) possesses an N-terminal Ring domain and tandem C-terminal BRCT motifs. While the Ring domain has E3 ubiquitin ligase activity, the BRCA1 BRCT domains specifically recognize phospho-serine motifs. Here, we demonstrate that BRCA1 Ring domain catalyzes CtIP ubiquitination in a manner that depends on a phosphorylation-mediated interaction between CtIP and BRCA1 BRCT domains. The BRCA1-dependent ubiquitination of CtIP does not target CtIP for degradation. Instead, ubiquitinated CtIP associates with chromatin following DNA damage and participates in G2/M checkpoint control. Thus, we propose that BRCA1 can regulate the functions of its substrates through nonproteasomal pathways that do not involve substrate degradation.
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PMID:BRCA1 ubiquitinates its phosphorylation-dependent binding partner CtIP. 1681 4

Gene amplification and protein overexpression of MDM2, which is often found in certain types of cancers, indicate that MDM2 plays an important role in tumorigenesis. Interestingly, several clinical reports have demonstrated that amplification of the MDM2 gene correlates with the metastatic stage. Using an antibody array assay, we identified E-cadherin as an MDM2-binding protein and confirmed that E-cadherin is a substrate for the MDM2 E3 ubiquitin ligase. We demonstrate that MDM2 interacts in vivo with E-cadherin, resulting in its ubiquitination and degradation. This regulation appears to be clinically relevant, as we found a significant correlation between high MDM2 and low E-cadherin protein levels in resected tumor specimens recovered from breast cancer patients with lymph node metastases. Ectopic expression of MDM2 in breast cancer cells was found to disrupt cell-cell contacts and enhance cell motility and invasive potential. We found that E-cadherin and MDM2 colocalized on the plasma membrane and in the early endosome, where ubiquitin moieties were attached to E-cadherin. Blocking endocytosis with dominant-negative mutants of dynamin abolished the association of MDM2 with E-cadherin, prevented E-cadherin degradation, and attenuated cell motility as observed by fluorescence microscopy. Thus, we provide evidence to support a novel role for MDM2 in regulating cell adhesions by a mechanism that involves degrading and down-regulating the expression of E-cadherin via an endosome pathway. This novel MDM2-regulated pathway is likely to play a biologically relevant role in cancer metastasis.
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PMID:MDM2 promotes cell motility and invasiveness by regulating E-cadherin degradation. 1698 Jun 28

The human P-glycoprotein (Pgp) is a drug-efflux pump responsible for innate or acquired multidrug resistance in many cancers. Pgp contains a unique approximately 75 amino acid long linker region in its middle, which is critically important for its drug transport and ATPase functions. To identify cellular proteins that bind to this linker region and modulate Pgp function, a yeast two-hybrid analysis was carried out. This procedure identified RNF2 (RING finger protein 2), an E3 ubiquitin ligase, as a prominent Pgp-interacting protein. Co-expression of RNF2 with Pgp in Sf9 insect cells resulted in decreased ATPase activity and proteolytic protection of the transporter protein. Immunoprecipitation experiments confirmed the physical interaction between these two proteins. Confocal microscopy showed the presence of RNF2 in the cytoplasm of the Pgp-negative, drug-sensitive MCF-7 breast cancer cells. However, it was undetectable in the Pgp-positive and drug-resistant MCF-7 cells. We suggest that RNF2 regulates the cellular abundance of Pgp, and plays a key role in the development of cancer drug resistance through its own down-regulation.
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PMID:RNF2 interacts with the linker region of the human P-glycoprotein. 1708 79

Dysregulation of ErbB receptor tyrosine kinases is thought to promote mammary tumor progression by stimulating tumor cell growth and invasion. Overexpression and aberrant activation of ErbB2/HER2 confer aggressive and malignant characteristics to breast cancer cells, and patients displaying ErbB2-amplified breast cancer face a worsened prognosis. Recent studies have established that ErbB2 and ErbB3 are commonly co-overexpressed in breast tumor cell lines and in patient samples. ErbB2 heterodimerizes with and activates the ErbB3 receptor, and the two receptors synergize in promoting growth factor-induced cell proliferation, transformation, and invasiveness. Our previous studies have shown that the neuregulin receptor degradation protein-1 (Nrdp1) E3 ubiquitin ligase specifically suppresses cellular ErbB3 levels by marking the receptor for proteolytic degradation. Here, we show that overexpression of Nrdp1 in human breast cancer cells results in the suppression of ErbB3 levels, accompanied by the inhibition of cell growth and motility and the attenuation of signal transduction pathways. In contrast, either Nrdp1 knockdown or the overexpression of a dominant-negative form enhances ErbB3 levels and cellular proliferation. Additionally, Nrdp1 expression levels inversely correlate with ErbB3 levels in primary human breast cancer tissue and in a mouse model of ErbB2 mammary tumorigenesis. Our observations suggest that Nrdp1-mediated ErbB3 degradation suppresses cellular growth and motility, and that Nrdp1 loss in breast tumors may promote tumor progression by augmenting ErbB2/ErbB3 signaling.
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PMID:Loss of Nrdp1 enhances ErbB2/ErbB3-dependent breast tumor cell growth. 1714 73

The molecular mechanisms underlying epidermal growth factor (EGF) receptor tyrosine kinase down-regulation in response to growth factor binding are coming into focus and involve cbl-mediated receptor ubiquitination followed by lysosomal degradation. However, mechanisms underlying the ligand-stimulated degradation of the related receptor tyrosine kinases of the ErbB family do not involve cbl and remain unexplored. Previous studies have demonstrated that the E3 ubiquitin ligase Nrdp1 contributes to the maintenance of steady-state ErbB3 levels by mediating its growth factor-independent degradation. Here we demonstrate that treatment of cells with the ErbB3 ligand neuregulin-1 (NRG1) stabilizes the deubiquitinating enzyme USP8, which in turn stabilizes Nrdp1. The catalytic activity of USP8 is required for NRG1-induced Nrdp1 stabilization. We provide evidence that Akt-mediated phosphorylation of USP8 threonine residue T907 contributes to USP8 stability. Finally, we demonstrate that Nrdp1 or USP8 knockdown suppresses NRG1-induced ErbB3 ubiquitination and degradation in MCF7 breast cancer cells. We conclude that an NRG1-induced protein stability cascade involving USP8 and Nrdp1 mediates the down-regulation of ErbB3. Our observations raise the possibility that the ligand-induced augmentation of pathways involved in the maintenance of basal levels of receptor tyrosine kinases can contribute to ligand-stimulated down-regulation.
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PMID:Neuregulin-induced ErbB3 downregulation is mediated by a protein stability cascade involving the E3 ubiquitin ligase Nrdp1. 1721 Jun 35

The selective ubiquitination of proteins by ubiquitin E3 ligases plays an important regulatory role in control of cell differentiation, growth, and transformation and their dysregulation is often associated with pathologic outcomes, including tumorigenesis. RNF5 is an E3 ubiquitin ligase that has been implicated in motility and endoplasmic reticulum stress response. Here, we show that RNF5 expression is up-regulated in breast cancer tumors and related cell lines. Elevated expression of RNF5 was seen in breast cancer cell lines that became more sensitive to cytochalasin D- and paclitaxel-induced apoptosis following its knockdown with specific short interfering RNA. Inhibition of RNF5 expression markedly decreased cell proliferation and caused a reorganization of the actin cytoskeleton in response to stress in MCF-7 but not in p53 mutant breast cancer cells, suggesting a p53-dependent function. Significantly, high levels of RNF5 were associated with decreased survival in human breast cancer specimens. Similarly, RNF5 levels were higher in metastatic melanoma specimens and in melanoma, leukemia, ovarian, and renal tumor-derived cell lines, suggesting that increased RNF5 expression may be a common event during tumor progression. These results indicate that RNF5 is a novel regulator of breast cancer progression through its effect on actin cytoskeletal alterations, which also affect sensitivity of breast cancer cells to cytoskeletal targeting antineoplastic agents.
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PMID:Increased expression of the E3 ubiquitin ligase RNF5 is associated with decreased survival in breast cancer. 1780 30

Keap1 is the substrate recognition module of a Cullin 3-based E3 ubiquitin ligase. Its primary role is to catalyze the ubiquitylation of the Nrf2 transcription factor. Oxidative stress blocks the E3 ligase activity of Keap1 which stabilizes Nrf2 allowing it to drive the expression of certain antioxidant and drug metabolizing enzymes. A recent study identified a mutation in the Keap1 gene (Keap1C23Y) that is present in breast cancer. Using reporter gene assays we show that Keap1C23Y is impaired in its ability to repress Nrf2 dependent transcription. Unlike wild-type Keap1, we found that Keap1C23Y failed to stimulate the degradation of Nrf2. Co-immunopreciptation experiments showed that Keap1C23Y retains its ability to interact with Nrf2 and Cullin 3. In contrast, we found that Keap1C23Y could not efficiently promote the ubiquitylation of Nrf2, suggesting that its intrinsic biological activity might have been compromised. These results revealed an unexpected role for the N-terminal region of Keap1 in regulating its E3 ligase activity. Importantly, our findings suggest that a paradox exists whereby Nrf2 activity is beneficial in non-malignant cells but in cancer cells it may provide a selective advantage for clonal expansion.
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PMID:A mutation of Keap1 found in breast cancer impairs its ability to repress Nrf2 activity. 1782 77

S-phase kinase-associated protein 2 (SKP2) is a component of the E3 ubiquitin ligase SKP1-Cul1-Fbox complex. Overexpression of SKP2 results in cell cycle dysregulation and carcinogenesis; however, the genetic lesions that cause this upregulation are poorly understood. We recently demonstrated that forkhead box P3 (FOXP3) is an X-linked breast cancer suppressor and an important repressor of the oncogene ERBB2/HER2. Since FOXP3 suppresses tumor growth regardless of whether the tumors overexpress ERBB2/HER2, additional FOXP3 targets may be involved in its tumor suppressor activity. Here, we show that mammary carcinomas from mice heterozygous for a Foxp3 mutation exhibited increased Skp2 expression. Ectopic expression of FOXP3 in mouse mammary cancer cells repressed SKP2 expression with a corresponding increase in p27 and polyploidy. Conversely, siRNA silencing of the FOXP3 gene in human mammary epithelial cells increased SKP2 expression. We also show that Foxp3 directly interacted with and repressed the Skp2 promoter. Moreover, the analysis of over 200 primary breast cancer samples revealed an inverse correlation between FOXP3 and SKP2 levels. Finally, we demonstrated that downregulation of SKP2 was critical for FOXP3-mediated growth inhibition in breast cancer cells that do not overexpress ERBB2/HER2. Our data provide genetic, biochemical, and functional evidence that FOXP3 is a novel transcriptional repressor for the oncogene SKP2.
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PMID:FOXP3 is a novel transcriptional repressor for the breast cancer oncogene SKP2. 1800 5

Breast cancer-associated gene 1 (BRCA1) regulates the duplication and the function of centrosomes in breast cells. We have previously shown that BRCA1 ubiquitin ligase activity directly inhibits centrosome-dependent microtubule nucleation. However, there is a paradox because centrosome microtubule nucleation potential is highest during mitosis, a phase when BRCA1 is most abundant at the centrosome. In this study, we resolve this conundrum by testing whether centrosomes from cells in M phase are regulated differently by BRCA1 when compared with other phases of the cell cycle. We observed that BRCA1-dependent inhibition of centrosome microtubule nucleation was high in S phase but was significantly lower during M phase. The cell cycle-specific effects of BRCA1 on centrosome-dependent microtubule nucleation were detected in living cells and in cell-free experiments using centrosomes purified from cells at specific stages of the cell cycle. We show that Aurora-A kinase modulates the BRCA1 inhibition of centrosome function by decreasing the E3 ubiquitin ligase activity of BRCA1. In addition, dephosphorylation of BRCA1 by protein phosphatase 1 alpha enhances the E3 ubiquitin ligase activity of BRCA1. These observations reveal that the inhibition of centrosome microtubule nucleation potential by the BRCA1 E3 ubiquitin ligase is controlled by Aurora-A kinase and protein phosphatase 1 alpha-mediated phosphoregulation through the different phases of the cell cycle.
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PMID:Aurora-A kinase regulates breast cancer associated gene 1 inhibition of centrosome-dependent microtubule nucleation. 1805 43

NUMB is a cell fate determinant, which, by asymmetrically partitioning at mitosis, controls cell fate choices by antagonising the activity of the plasma membrane receptor of the NOTCH family. NUMB is also an endocytic protein, and the NOTCH-NUMB counteraction has been linked to this function. There might be, however, additional functions of NUMB, as witnessed by its proposed role as a tumour suppressor in breast cancer. Here we describe a previously unknown function for human NUMB as a regulator of tumour protein p53 (also known as TP53). NUMB enters in a tricomplex with p53 and the E3 ubiquitin ligase HDM2 (also known as MDM2), thereby preventing ubiquitination and degradation of p53. This results in increased p53 protein levels and activity, and in regulation of p53-dependent phenotypes. In breast cancers there is frequent loss of NUMB expression. We show that, in primary breast tumour cells, this event causes decreased p53 levels and increased chemoresistance. In breast cancers, loss of NUMB expression causes increased activity of the receptor NOTCH. Thus, in these cancers, a single event-loss of NUMB expression-determines activation of an oncogene (NOTCH) and attenuation of the p53 tumour suppressor pathway. Biologically, this results in an aggressive tumour phenotype, as witnessed by findings that NUMB-defective breast tumours display poor prognosis. Our results uncover a previously unknown tumour suppressor circuitry.
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PMID:NUMB controls p53 tumour suppressor activity. 1817 99


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