CXCR4 and TRN1 Demonstrate an Interaction.

<p><b><i>A</i></b>, Sixty micrograms of total protein were analyzed for TRN1 expression by western blot analysis using a TRN1 specific antibody. Alpha-tubulin served as a loading control. <b><i>B</i></b>, One milligram of PC3 whole cell lysate was immunoprecipitated with anti-CXCR4 and separated by SDS-PAGE. Immunocomplexes were probed with anti-TRN1 or anti-CXCR4 to ensure that CXCR4 interacted with TRN1 and was immunoprecipitated, respectively. Thirty micrograms of whole cell PC3 supernatant, post-immunoprecipitation, were separated by SDS-PAGE and harvested for western blot analysis to assess the efficiency of CXCR4 immunoprecipitation. <b><i>C and D</i></b>, Cells were transiently transfected with TRN1-specific siRNA to determine an effective concentration <i>(</i><b><i>C</i></b><i>)</i>, prior to harvesting for immunohistochemistry with anti-Lamin A/C and anti-CXCR4 <i>(</i><b><i>D</i></b><i>)</i>. Images were taken using Zeiss Axio Imager.z1 fluorescence microscope at 40× magnification at excitation 470 nm for FITC and 551 nm for Cy3. Small arrows indicate co-localization of CXCR4 with the nucleus (yellow/orange). Scale bar represents 50 µm.</p

Nuclear CXCR4 was Functional at the Nucleus.

<p><b><i>A</i></b>, Representative light images of whole cells and isolated nuclei confirmed the integrity of nuclear isolation at 20× magnification. <b><i>B</i></b>, Whole cells were treated with SDF1α prior to isolating and lysing intact nuclei. Nuclei lysates (1 mg) were immunoprecipitated with anti-CXCR4 and separated by SDS-PAGE. Immunocomplexes were probed for G_αi (first row) or CXCR4 antibody (second row), respectively. Anti-CD44 (non-nuclear) and anti-Topoisomerase1 (Topo1, nuclear) were used as markers for fractionation purity and as loading controls. <b><i>C</i></b>, PC3 nuclei were isolated, incubated with FluoForte dye Ca²⁺ probe, followed by incubation with AMD3100 or pertussis toxin (PTX) for 1 hr, then stimulated with SDF1α for 30 min. An increase in fluorescent-bound Ca²⁺ was measured on a microplate reader at ex = 490 nm/em = 525 nm.</p

Nuclear CXCR4 Expression in Prostate Cancer Cell Lines.

<p><b><i>A</i></b>, Normal prostate epithelial (RWPE1) and PCa (PC3, DU145, 22RV1) cells were stimulated with SDF1α (100 ng/ µl) prior to subcellular fractionation into non-nuclear and nuclear fractions. Immunoblots were probed with anti-CXCR4. Anti-CD44 (non-nuclear) and anti-Topoisomerase1 (Topo 1, nuclear) were used as markers for fractionation purity and as loading controls. The bar graphs are quantitative results of the band density representing expression of CXCR4 in each fraction. Data were mean <u>+</u>S.E. from three independent experiments. *, P<0.05. <b><i>B</i></b>, Immunocytochemistry of PCa cell lines for CXCR4. PCa cells were stimulated with SDF1α (100 ng/ µl), fixed with methanol, blocked then incubated with an antibody mixture containing a mouse anti-CXCR4 monoclonal antibody and a rabbit polyclonal anti-Lamin A/C antibody, followed by secondary mixture containing a Cy3-conjugated anti-mouse antibody and FITC-conjugated anti-rabbit antibody. Imaging was with a Zeiss LSM-510 UV Confocal Microscope using the 63× Plan-Apochromat 63x/1.40 Oil DIC objective at excitation 488 nm for FITC and 543 nm for Cy3. Confocal images demonstrating the plasma membrane and cytosolic localization of CXCR4 (red), intact nuclear membrane (green), and nuclear-associated localization of CXCR4 (yellow/orange) are shown. Small arrows indicate co-localization of CXCR4 with the nucleus (yellow/orange). Scale bars represent 50 µm.</p

A Putative Functional NLS within CXCR4.

<p><b><i>A</i></b>, GFP-CXCR4 fusion protein localized similar to endogenous CXCR4. CXCR4-pEGFPN1 transfected PC3 cells were stimulated with SDF1α, fixed with methanol, blocked then incubated with a mouse anti-CXCR4 monoclonal antibody, followed by a Cy3-conjugated anti-mouse secondary antibody. Nuclei were stained with DAPI (blue). Images were taken at 40× maginification using Axiovision software 4.8.2 with a Zeiss Axio Imager.z1 fluorescence microscope at ex = 470 nm for FITC, ex = 358 nm for DAPI and ex = 551 nm for Cy3. Images demonstrate the co-localization (yellow) of endogenous CXCR4 (red) with GFP-tagged CXCR4 (green). <b><i>B</i></b>, Localization analysis of wild type CXCR4 (CXCR4-pEGFPN1), NLS-mutant of CXCR4 (pEGFPN1-CXCR4<b>R146A</b>,) and deleted NLS of CXCR4 (CXCR4<b>ΔNLS</b>) by immunocytochemistry in PC3 cells. Nuclei were stained with propidium iodide (red) and CXCR4 was detected as the fusion protein GFP-CXCR4 (green). Imaging was with a Zeiss LSM-510 UV Confocal Microscope using the 63× Plan-Apochromat 63x/1.40 Oil DIC objective at ex = 488 nm for FITC and ex = 543 nm for Cy3. Scale bars represent 50 µm. <b><i>C</i></b>, Transfected cells were stimulated with SDF1α prior to subcellular fractionation into non-nuclear and nuclear fractions. Immunoblots were probed with anti-GFP to detect the fusion protein GFP-CXCR4. Anti-CD44 (non-nuclear) and anti-Topoisomerase1 (Topo 1, nuclear) were used as markers for fractionation purity and as loading controls.</p

Immunohistochemical (IHC) Staining of Prostate Tissues for CXCR4.

<p><b><i>A</i></b>, A human prostate tissue array, ranging from normal to high-grade prostate cancer, was evaluated by IHC for CXCR4 expression using standard methods. Samples were evaluated at magnification 40X, using a Q-Imaging camera of Olympus BX51 Microscope with Bioquant® Image Analysis Software (RtmBometrics). Normal prostate tissues demonstrated slightly weak or undetectable brown staining for CXCR4 (positive cells<5%), and no CXCR4 expression in the nucleus. Representative low grade prostate tissue (grade 2, stage II, T₂N₀M₀, adenocarcinoma) demonstrated random/focal positive staining for CXCR4 in the nucleus (positive cells >11%, but less than 50%), indicating low expression of CXCR4. Representative high grade metastatic prostate tissue (grade 4, stage IV, T₄N₁M₁, adenocarcinoma) demonstrated diffuse/intense staining (positive cells >50%), indicating high expression for CXCR4 in the nucleus. Scale bar represents 50 µm. <b><i>B</i></b>, CXCR4 IgG2B mouse monoclonal antibody was evaluated for specificity to CXCR4 protein by western blot analysis in PC3 (CXCR4 positive) or 293T (CXCR4 null) cell lines. <b><i>C</i></b>, CXCR4 antibody was evaluated for specificity to CXCR4 protein by immunoprecipitation for CXCR4 and western blot analysis for CXCR4. <b><i>D</i></b>, CXCR4 IgG2B antibody was evaluated for specificity to CXCR4 protein by immunoprecipitation with Fibronectin IgG2B mouse monoclonal antibody (unrelated isotype control) and western blot analysis for CXCR4; expression of Fibronectin protein was confirmed by western blot analysis. Beta-actin was used as a loading control.</p

Germ-line variants of human N-methylpurine DNA glycosylase show impaired DNA repair activity and facilitate 1,N6 ethenoadenine induced mutations.

Human N-methylpurine DNA glycosylase (hMPG) initiates base excision repair of a number of structurally diverse purine bases including 1,N(6)-ethenoadenine, hypoxanthine, and alkylation adducts in DNA. Genetic studies discovered at least eight validated non-synonymous single nucleotide polymorphisms (nsSNPs) of the hMPG gene in human populations that result in specific single amino acid substitutions. In this study, we tested the functional consequences of these nsSNPs of hMPG. Our results showed that two specific arginine residues, Arg-141 and Arg-120, are important for the activity of hMPG as the germ line variants R120C and R141Q had reduced enzymatic activity in vitro as well as in mammalian cells. Expression of these two variants in mammalian cells lacking endogenous MPG also showed an increase in mutations and sensitivity to an alkylating agent compared with the WT hMPG. Real time binding experiments by surface plasmon resonance spectroscopy suggested that these variants have substantial reduction in the equilibrium dissociation constant of binding (K(D)) of hMPG toward 1,N(6)-ethenoadenine-containing oligonucleotide (ϵA-DNA). Pre-steady-state kinetic studies showed that the substitutions at arginine residues affected the turnover of the enzyme significantly under multiple turnover condition. Surface plasmon resonance spectroscopy further showed that both variants had significantly decreased nonspecific (undamaged) DNA binding. Molecular modeling suggested that R141Q substitution may have resulted in a direct loss of the salt bridge between ϵA-DNA and hMPG, whereas R120C substitution redistributed, at a distance, the interactions among residues in the catalytic pocket. Together our results suggest that individuals carrying R120C and R141Q MPG variants may be at risk for genomic instability and associated diseases as a consequence