Mitogen- and Stress-Activated Protein Kinases 1 and 2 Are Required for Maximal Trefoil Factor 1 Induction

<div><p>Mitogen- and stress-activated protein kinases 1 and 2 (MSK1 and MSK2), activated downstream of the ERK- and p38-mitogen-activated protein kinase pathways are involved in cell survival, proliferation and differentiation. Following mitogenic or stress stimuli, they mediate the nucleosomal response, which includes phosphorylation of histone H3 at serine 10 (H3S10ph) coupled with transcriptional activation of immediate-early genes. While MSK1 and MSK2 are closely related, their relative roles may vary with cellular context and/or stimuli. However, our knowledge of MSK2 recruitment to immediate-early genes is limited, as research has primarily focused on MSK1. Here, we demonstrate that both MSK1 and MSK2, regulate the phorbol ester 12-O-tetradecanoylphorbol-13-acetate induced expression of the breast cancer marker gene, trefoil factor 1 (<i>TFF1</i>), by phosphorylating H3S10 at its 5′ regulatory regions. The MSK-mediated phosphorylation of H3S10 promotes the recruitment of 14-3-3 isoforms and BRG1, the ATPase subunit of the BAF/PBAF remodeling complex, to the enhancer and upstream promoter elements of <i>TFF1</i>. The recruited chromatin remodeling activity leads to the RNA polymerase II carboxy-terminal domain phosphorylation at the <i>TFF1</i> promoter, initiating <i>TFF1</i> expression in MCF-7 breast cancer cells. Moreover, we show that MSK1 or MSK2 is recruited to <i>TFF1</i> regulatory regions, but as components of different multiprotein complexes.</p></div

FOS and JUN levels do not change with MSK1 or MSK2 knockdown in MCF-7 cells.

<p>MCF-7 cells were treated with scramble, MSK1, or MSK2 siRNA, serum starved for 72 h, and treated with TPA for 0 or 45 min. Protein lysates were analyzed by immunoblotting using antibodies against MSK1 (rabbit, Sigma), MSK2 (rabbit, Abcam ab99411), JUN, or FOS. Actin was used as a loading control.</p

Effect of H89 on TPA-induced expression, nucleosomal response and chromatin remodeling of <i>TFF1</i>.

<p>Serum-starved MCF-7 cells were pre-treated or not with H89 prior to TPA stimulation for 15, 30, 45 and 60 min. A. Total RNA was isolated and quantified by real time RT-PCR. Fold change values, normalized to <i>CYP33</i> expression levels and time 0 values, are the mean of three independent experiments, and the error bars represent the standard deviation. B. Formaldehyde-crosslinked mononucleosomes were prepared and used in ChIP assays with antibodies against RNAPII S5ph. Equal amounts of input and immunoprecipitated DNAs were quantified by real-time quantitative PCR. The enrichment values of the <i>TFF1</i> enhancer (−10476) and UPE (−429) sequences are the mean of three independent experiments, and the error bars represent the standard deviation. C. Serum-starved MCF-7 cells were pre-treated or not with H89 prior to TPA stimulation for 15, 30, 45 and 60 min. Formaldehyde-crosslinked mononucleosomes were prepared and used in ChIP assays with antibodies against MSK1, MSK2, H3S10ph, H3S10phK14ac, 14-3-3ε, 14-3-3ζ, and BRG1. Equal amounts of input and immunoprecipitated DNAs were quantified by real-time quantitative PCR. The enrichment values of the <i>TFF1</i> enhancer (-10476) and UPE (-429) sequences are the mean of three independent experiments, and the error bars represent the standard deviation. *P≤0.05, **P≤0.01, ***P≤0.001, ns = P≥0.05 (Student’s paired t-test).</p

MSK1 and MSK2 are in different complexes.

<p>A. MCF-7 cell lysate (500 µg) was incubated with anti-MSK1 (rabbit, Sigma; 4 µg) or anti-MSK2 (rabbit, Invitrogen; 2 µg) antibodies. The immunoprecipitates (<i>IP</i>) and equivalent volumes of lysate (Input), immunodepleted (<i>ID</i>) fractions, and IgG control (<i>IgG)</i>, corresponding to 50 µg of lysate, were loaded onto SDS-8% polyacrylamide gels, transferred to nitrocellulose membranes, and immunochemically stained with anti-MSK1 or anti-MSK2 antibodies. B. MCF-7 cells grown on coverslips were serum starved and then treated with or without TPA as described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0063189#s2" target="_blank"><i>Materials and Methods</i></a>. The cells were fixed and immunostained with antibodies against MSK1 and MSK2, and co-stained with DAPI. Spatial distribution was visualized by fluorescence microscopy and image deconvolution was done by AxioVision software. Yellow signal in the merged images indicates colocalization. Bar, 5 µm.</p

MSK1 and MSK2 activity contribution to TPA-induced <i>TFF1</i> expression.

<p>A. Levels of MSK1 and MSK2 in transient MSK1 or MSK2 knockdown and scramble control (SC) MCF-7 cells were analyzed by immunoblotting. Actin was used as loading control. Note that MSK1 (7 µg, rabbit, Sigma) antibody was used at a higher titer than MSK2 (2.5 µg, rabbit, Invitrogen). B, C. Serum-starved transient MSK1 or MSK2 knockdown and scramble control MCF-7 cells were treated with TPA for 0, 15, 30, 45 and 60 min. Total RNA was isolated and quantified by real time RT-PCR. Fold change values, normalized to <i>GAPDH</i> expression levels and time 0 values, are the mean of three independent experiments, and the error bars represent the standard deviation. *P≤0.05 (Student’s paired t-test).</p

TPA-induced co-occupancy of MSK1/H3S10ph, MSK2/H3S10ph and 14-3-3ζ/BRG1 at regulatory regions of <i>TFF1</i>.

<p>Re-ChIP experiments were performed on formaldehyde-crosslinked mononucleosomes prepared from serum-starved MCF-7 cells either untreated or treated with TPA for 30 min. The antibodies were used as indicated in the graph. Equal amounts of input and immunoprecipitated DNA were quantified by real-time quantitative PCR. The enrichment values of the <i>TFF1</i> enhancer (-10476) and UPE (-429) sequences are the mean of three independent experiments, and the error bars represent the standard deviation. *P≤0.05, **P≤0.01, ***P≤0.001 (Student’s paired t-test).</p

Distribution of MSK1/2, H3S10ph, H3S10phK14ac, 14-3-3ε/ζ, BRG1, RNAPolIIS5ph, and RNAPolII at regulatory and coding regions of <i>TFF1</i> in response to TPA.

<p>A. Schematic representation of <i>TFF1</i> gene structure. Black bars underneath the map show regions amplified in the ChIP assay. Each region is labeled according to the 5′ position of the forward primer relative to the transcription start site. The exons are represented by black boxes, while the binding sites of relevant transcription factors located in the amplified enhancer (−10476) and UPE (−429) regions are displayed. C/EBP, CCAAT-enhancer binding protein; Sp1, GC box that is a binding site for the Sp family of transcription factors; ERE, estrogen response element; AP1 constitutes a combination of dimers formed of members of the JUN, FOS and ATF families of transcription factors. Asterisk indicates a putative binding site. B. ChIP assays were performed using antibodies against MSK1, MSK2 or H3S10ph on formaldehyde-crosslinked mononucleosomes prepared from serum-starved MCF-7 cells either untreated (0′ TPA) or treated with TPA for 15, 30, 45 and 60 min. Equal amounts of input and immunoprecipitated DNA were quantified by real-time quantitative PCR. Enrichment values are the mean of three independent experiments, and the error bars represent the standard deviation. C. ChIP experiments were performed as in B, using antibodies against H3S10phK14ac, 14-3-3ε or 14-3-3ζ. D. ChIP experiments were performed as in B and C, using antibodies against BRG1, RNAPII S5ph or total RNAPII. *P≤0.05, **P≤0.01, ***P≤0.001, ns = P≥0.05 (Student’s paired t-test).</p