16 research outputs found

    Inhibition of Proliferation by PERK Regulates Mammary Acinar Morphogenesis and Tumor Formation

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    Endoplasmic reticulum (ER) stress signaling can be mediated by the ER kinase PERK, which phosphorylates its substrate eIF2α. This in turn, results in translational repression and the activation of downstream programs that can limit cell growth through cell cycle arrest and/or apoptosis. These responses can also be initiated by perturbations in cell adhesion. Thus, we hypothesized that adhesion-dependent regulation of PERK signaling might determine cell fate. We tested this hypothesis in a model of mammary acini development, a morphogenetic process regulated in part by adhesion signaling. Here we report a novel role for PERK in limiting MCF10A mammary epithelial cell proliferation during acinar morphogenesis in 3D Matrigel culture as well as in preventing mammary tumor formation in vivo. We show that loss of adhesion to a suitable substratum induces PERK-dependent phosphorylation of eIF2α and selective upregulation of ATF4 and GADD153. Further, inhibition of endogenous PERK signaling during acinar morphogenesis, using two dominant-negative PERK mutants (PERK-ΔC or PERK-K618A), does not affect apoptosis but results instead in hyper-proliferative and enlarged lumen-filled acini, devoid of proper architecture. This phenotype correlated with an adhesion-dependent increase in translation initiation, Ki67 staining and upregulation of Laminin-5, ErbB1 and ErbB2 expression. More importantly, the MCF10A cells expressing PERKΔC, but not a vector control, were tumorigenic in vivo upon orthotopic implantation in denuded mouse mammary fat pads. Our results reveal that the PERK pathway is responsive to adhesion-regulated signals and that it is essential for proper acinar morphogenesis and in preventing mammary tumor formation. The possibility that deficiencies in PERK signaling could lead to hyperproliferation of the mammary epithelium and increase the likelihood of tumor formation, is of significance to the understanding of breast cancer

    Expression pattern of glypican-3 -GPC3- during human embryonic and fetal development

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    Glypicans represent a family of cell surface proteoglycans. Loss-of-function mutations in the human glypican-3 (GPC3) gene results in the Simpson-Golabi- Behmel syndrome, characterized by severe malformations and pre- and postnatal overgrowth. Because the expression of GPC3 during human embryonic and fetal periods remains largely unknown, we investigated by immunohistochemistry its pattern of expression during four periods of human development covering the embryonic period (P1) from 5 to 8 weeks of development, and the fetal periods (P2, P3 and P4) from 9 to 28 weeks of development. Hepatocytes were homogeneously positive for GPC3 during the four periods while pancreatic acini and ducts showed a rather high staining only during P1. GPC3 was also detected in several kidney structures and in the genital system where the sex cords were weakly positive in P1 and P2. In later developmental stages the male’s genital system expressed GPC3 while the female’s did not. While the mesenchyme in the limbs showed positive staining in P1, GPC3 was not detected during the following stages. The mesenchymal tissue localized between the most caudal vertebrae was also positive in P1. A strong GPC3 signal was observed in neurons of the spinal cord and dorsal root ganglia in P2 and P3, while the brain was negative. In sum our studies revealed that GPC3 expression is highly tissue- and stage-specific during human development. The expression pattern of GPC3 is consistent with the abnormalities seen in the Simpson- Golabi-Behmel syndrome

    Downmodulation of Vaccine-Induced Immunity and Protection against the Intracellular Bacterium Francisella tularensis by the Inhibitory Receptor FcγRIIB

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    Fc gamma receptor IIB (FcγRIIB) is the only Fc gamma receptor (FcγR) which negatively regulates the immune response, when engaged by antigen- (Ag-) antibody (Ab) complexes. Thus, the generation of Ag-specific IgG in response to infection or immunization has the potential to downmodulate immune protection against infection. Therefore, we sought to determine the impact of FcγRIIB on immune protection against Francisella tularensis (Ft), a Category A biothreat agent. We utilized inactivated Ft (iFt) as an immunogen. Naïve and iFt-immunized FcγRIIB knockout (KO) or wildtype (WT) mice were challenged with Ft-live vaccine strain (LVS). While no significant difference in survival between naïve FcγRIIB KO versus WT mice was observed, iFt-immunized FcγRIIB KO mice were significantly better protected than iFt-immunized WT mice. Ft-specific IgA in serum and bronchial alveolar lavage, as well as IFN-γ, IL-10, and TNF-α production by splenocytes harvested from iFt-immunized FcγRIIB KO, were also significantly elevated. In addition, iFt-immunized FcγRIIB KO mice exhibited a reduction in proinflammatory cytokine levels in vivo at 5 days after challenge, which correlates with increased survival following Ft-LVS challenge in published studies. Thus, these studies demonstrate for the first time the ability of FcγRIIB to regulate vaccine-induced IgA production and downmodulate immunity and protection. The immune mechanisms behind the above observations and their potential impact on vaccine development are discussed

    GADD153 mRNA and Protein Levels Are Strongly Upregulated During Suspension Conditions.

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    <p>(A) RT-PCR analysis of GADD153 mRNA levels in MCF10A (left panel) and HEK293T (right panel) cells at different time points in either adhered (A) or suspended (S) conditions. Adhered MCF10A cells treated with 2mM DTT for 4h were used as positive control and GAPDH was used as a loading control. (B) MCF10A cells were transiently transfected with a GADD153 promoter-driven-EGFP reporter plasmid and EGFP fluorescence was analyzed 48 h post-transfection by FACS; total events captured: 2×10<sup>4</sup>. The graph shows the number of GFP-positive events in FLH2>10 (mean±SD). (C) Western blot for GADD153 protein in adhered (A) or suspended (S) MCF10A cells. (D and E) Immunofluorescence (D) and FACS (E) analysis of GADD153 (red) expression in MCF10A cells following growth in adhered or suspension conditions for the indicated times. Secondary antibody was used as negative control in E. (F) MCF10A (top) and HEK293T (lower) cells were transiently co-transfected with the GADD153-EGFP reporter plasmid and either a full-length Flag-tagged GADD34 plasmid or an empty vector as control for 24 hrs before being detached and left to reattach or put into suspension for an additional 48 hrs before FACS analysis. GFP fluorescence was analyzed 48 h post transfection by FACS where a total 2×10<sup>4</sup> events were captured. The graphs show the number of GFP positive events in FLH2>10 or the mean fluorescence intensity (MFI) in the PMT2-FITC channel (mean±SD). (G) RT-PCR for XBP-1 splicing (top panel) in MCF10A cells at different time points either adhered (A) or suspended (S). Adhered MCF10A cells treated with 2mM DTT for 4 hrs was used as positive control and GAPDH, shown in (A) was used as a loading control. Lower panels show RT-PCR for BiP, Hsp47 and Erp72/PDI chaperone mRNA levels in adhered (Adh) or suspended (Sus) MCF10A cells. GAPDH was used as a loading control.</p

    Suspension Induces Phosphorylation of eIF2α and Translation Repression in Mammary and Kidney Epithelial Cells.

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    <p>(A) Whole cell lysates from MCF10A (upper left), HEK293T (upper right) and primary HMEC (lower panels) cells grown either in adhered (A) or suspended conditions (S) as described in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0000615#s4" target="_blank">methods</a> section for the indicated time points, were immunoblotted for p-eIF2α and total eIF2α levels. Adhered MCF10A or HEK293T cells treated with 2 mM DTT or 5 µg/ml tunicamycin (Tn) respectively, were used as positive controls. (B) Quantification of the rate of DNA synthesis using a BrdU incorporation assay and flow cytometry to measure the percentage of BrdU-positive cells (filled diamonds) at different time points in suspension. The percentage of apoptotic cells was measured using propidium iodide staining and flow cytometry to identify the sub-G0 apoptotic fraction for adhered (dashed line) or suspended (dotted line) MCF10A cells for different time points. Data points show the mean±SD for BrdU–positive cells in each sample as a percentage of the total. (C) Autoradiogram of [<sup>35</sup>S] Met/Cys incorporation (right panel) into newly synthesized proteins in MCF10A cells adhered or suspended for 24 hrs (two independent samples). Coomassie Blue staining of an identical gel (left panel) shows equal protein loading. (D) Polysome profiles from 24 hr adhered (left) and suspended (right) MCF10A cells showing an increase and decrease in the monosome and polysome peaks, respectively in suspended cells. Absorbance at 254 nm (Y-axis, RNA concentration) was plotted against migration in the sucrose gradient (X-axis, bottom to top). Total RNA was isolated from individual fractions to visualize the 18S and 28S rRNAs by ethidium bromide staining.</p

    Unscheduled Activation of PERK Restricts Acinar Growth and Promotes Apoptosis in 3D Matrigel.

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    <p>(A) Time-dependent increase in phosphorylation of eIF2α in MCF10A cells expressing an Fv2E-ΔNPERK construct, upon treatment with the dimerizing drug, AP20187 (2 nM). AP20187 has no effect on P-eIF2α levels in β-Gal cells. Total eIF2α was used as loading control. (B) Photomicrographs of Fv2E-ΔNPERK cells in 3D Matrigel treated with 2 nM AP20187 or equal volume of ethanol as control, added every 24 hrs from Day 4 up to Day 6 of morphogenesis; representative phase-contrast images depict the effect of forced PERK activation on acini development; (B-a and B-e) A×10 magnification image of several developing acini; (B-b) Normal acinus, (B-c) 2 cell cluster, (B-f) 4 cell cluster, (B-g) 4 cell cluster containing apoptotic cells. (B-d and h) Confocal images through the equatorial region of Fv2E-ΔNPERK cells in 3D Matrigel immunostained for active caspase-3 (red) or LN-5 (green) with (B-h) and without (B-d) treatment with 2nM AP20187 every 24 hrs, (B-h) cell cluster where the majority of cells have entered apoptosis. (C) Quantitation of phase contrast images of Fv2E-ΔNPERK cells on Day 6, treated every 24 hrs with or without 2nM AP20187. Over 400 acini were visually scored for the presence of apoptotic or growth arrested 2–4 celled acini and calculated as a percentage of the total number of acini; graph shows mean±SD. (D) Photomicrographs of β-Gal vector control cells treated with 2nM AP20187 or with equal volume EtOH as control, every 24 hrs from Day 4 up to Day 6 in Matrigel. Note that AP20187 treatment caused no noticeable changes in acini size or morphology, consistent with the absence of modulation of P-eIF2α levels in the same cells (<i>A</i>). (E) Confocal images showing Fv2E-ΔNPERK cells treated with (+AP) or without (-AP) AP20187 every 12 hrs stained for LN-5 (green) to delineate the acini and active caspase-3 (red). Note that a majority of cells even in large acini can be pushed into apoptosis by strong activation of PERK signaling. Scale bars = 10 µm.</p
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