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  • Over-accumulation of nuclear IGF-1 receptor in tumor cells requires elevated expression of the receptor and the SUMO-conjugating enzyme Ubc9. 21147068

    The insulin-like growth factor 1 receptor (IGF-1R) plays crucial roles in tumor cell growth and is overexpressed in many cancers. IGF-1R's trans-membrane kinase signaling pathways have been well characterized. Very recently, we showed that SUMOylation mediates nuclear translocation of the IGF-1R, and that nuclear IGF-1R (nIGF-1R) binds to enhancer regions and activates transcription. We identified three lysine residues in the ?-subunit of the receptor and that mutation of these blocks nuclear translocation and gene activation. Furthermore, accumulation of nIGF-1R was proven strongly dependent on the specific SUMO-conjugating enzyme Ubc9. Here we show that nIGF-1R originates solely from the cell membrane and that phosphorylation of the core tyrosine residues of the receptor kinase is crucial for nuclear accumulation. We also compared the levels of nIGF-1R, measured as nuclear/membrane ratios, in tumor and normal cells. We found that the breast cancer cell line MCF-7 has 13-fold higher amounts of nIGF-1R than breast epithelial cells (IME) which showed only a small amount of nIGF-1R. In comparison, the total expression of IGF-1R was only 3.7- higher in MCF-7. Comparison of several other tumor and normal cell lines showed similar tumor cell over-accumulation of nIGF-1R, exceeding the total receptor expression substantially. Ectopic overexpression (>10-fold) of the receptor increased nIGF-1R in IME cells but not to that high level as in wild type MCF-7. The levels of Ubc9 were higher in all tumor cell lines, compared to the normal cells, and this probably contributes to over-accumulation of nIGF-1R. Over-accumulation of nIGF-1R may contribute to deregulated gene expression and therewith play a pathophysiological role in cancer cells.
    Document Type:
    Reference
    Product Catalog Number:
    LP1
    Product Catalog Name:
    VLDL, human

  • XRCC1 suppresses somatic hypermutation and promotes alternative nonhomologous end joining in Igh genes. 21967769

    Activation-induced deaminase (AID) deaminates cytosine to uracil in immunoglobulin genes. Uracils in DNA can be recognized by uracil DNA glycosylase and abasic endonuclease to produce single-strand breaks. The breaks are repaired either faithfully by DNA base excision repair (BER) or mutagenically to produce somatic hypermutation (SHM) and class switch recombination (CSR). To unravel the interplay between repair and mutagenesis, we decreased the level of x-ray cross-complementing 1 (XRCC1), a scaffold protein involved in BER. Mice heterozygous for XRCC1 showed a significant increase in the frequencies of SHM in Igh variable regions in Peyer's patch cells, and of double-strand breaks in the switch regions during CSR. Although the frequency of CSR was normal in Xrcc1(+/-) splenic B cells, the length of microhomology at the switch junctions decreased, suggesting that XRCC1 also participates in alternative nonhomologous end joining. Furthermore, Xrcc1(+/-) B cells had reduced Igh/c-myc translocations during CSR, supporting a role for XRCC1 in microhomology-mediated joining. Our results imply that AID-induced single-strand breaks in Igh variable and switch regions become substrates simultaneously for BER and mutagenesis pathways.
    Document Type:
    Reference
    Product Catalog Number:
    12-371
    Product Catalog Name:
    Normal Mouse IgG

  • The histone demethylase JARID1A regulates progesterone receptor expression. 21348942

    Transcriptional control of the progesterone receptor gene by estrogen is a complex mechanism. It involves estrogen receptor α which uses several enzymes that locally modify histone tails as cofactors. Using MCF-7 cells as a model, we found that Jumonji AT-rich interactive domain 1A (JARID1A; KDM5A/RBP2), an enzyme that removes the activating H3K4 di- and trimethylation marks, was involved in the fine-tuning of progesterone receptor gene expression. Reduction of JARID1A led to enhanced progesterone receptor expression, at both the basal and estrogen-stimulated levels. Conversely, overexpression of JARID1A wild-type, but not the enzymatically inactive mutant, suppressed progesterone receptor promoter activity. Chromatin immunoprecipitation experiments showed JARID1A to bind in a ligand-independent manner to a progesterone receptor gene upstream region that contains an estrogen response element half-site as well as the CCGCCC sequence, which is potentially recognized by JARID1A. Estrogen treatment led to RNA polymerase II recruitment to this region and to increased estrogen receptor α binding to the PR enhancer region 1. In addition, elevation of H3K4 trimethylation was detected at the estrogen response element half-site region. Reduction of JARID1A expression was followed by higher H3K4 trimethylation in this region. Analysis of MDA-MB-231 cells, which do not express the progesterone receptor, indicated that H3K4 trimethylation did not take place in the regulatory regions examined. Taken together, the results underscore the importance of epigenetic modifications for regulation of progesterone receptor expression. They suggest that H3K4 tri- and dimethylation play an important role and that JARID1A is the histone-demethylating enzyme responsible for removal of this mark.
    Document Type:
    Reference
    Product Catalog Number:
    PP64
    Product Catalog Name:
    IgG, Rabbit

  • A novel mechanism for target gene-specific SWI/SNF recruitment via the Snf2p N-terminus. 21278159

    Chromatin-remodeling complexes regulate the expression of genes in all eukaryotic genomes. The SWI/SNF complex of Saccharomyces cerevisiae is recruited to its target promoters via interactions with selected transcription factors. Here, we show that the N-terminus of Snf2p, the chromatin remodeling core unit of the SWI/SNF complex, is essential for the expression of VHT1, the gene of the plasma membrane H(+)/biotin symporter, and of BIO5, the gene of a 7-keto-8-aminopelargonic acid transporter, biotin biosynthetic precursor. chromatin immunoprecipitation (ChIP) analyses demonstrate that Vhr1p, the transcriptional regulator of VHT1 and BIO5 expression, is responsible for the targeting of Snf2p to the VHT1 promoter at low biotin. We identified an Snf2p mutant, Snf2p-R(15)C, that specifically abolishes the induction of VHT1 and BIO5 but not of other Snf2p-regulated genes, such as GAL1, SUC2 or INO1. We present a novel mechanism of target gene-specific SWI/SNF recruitment via Vhr1p and a conserved N-terminal Snf2p domain.
    Document Type:
    Reference
    Product Catalog Number:
    MAB3580
    Product Catalog Name:
    Anti-Green Fluorescent Protein Antibody
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