Regulation of rDNA Transcription by Proto-Oncogene PELP1

Proline-, glutamic acid-, and leucine-rich protein (PELP1) is a novel nuclear receptor coregulator with a multitude of functions. PELP1 serves as a scaffolding protein that couples various signaling complexes with nuclear receptors and participates as a transcriptional coregulator. Recent data suggest that PELP1 expression is deregulated in hormonal cancers, and that PELP1 functions as a proto-oncogene; however, the mechanism by which PELP1 promotes oncogenesis remains elusive.Using pharmacological inhibitors, confocal microscopy and biochemical assays, we demonstrated that PELP1 is localized in the nucleolus and that PELP1 is associated with the active ribosomal RNA transcription. Cell synchronization studies showed that PELP1 nucleolar localization varies and the greatest amount of nucleolar localization was observed during S and G2 phases. Using pharmacological compounds and CDK site mutants of PELP1, we found that CDK's activity plays an important role on PELP1 nucleolar localization. Depletion of PELP1 by siRNA decreased the expression of pre-rRNA. Reporter gene assays using ribosomal DNA (pHrD) luc-reporter revealed that PELP1WT but not PELP1MT enhanced the expression of reporter. Deletion of nucleolar domains abolished PELP1-mediated activation of the pHrD reporter. ChIP analysis revealed that PELP1 is recruited to the promoter regions of rDNA and is needed for optimal transcription of ribosomal RNA.Collectively, our results suggest that proto-oncogene PELP1 plays a vital role in rDNA transcription. PELP1 modulation of rRNA transcription, a key step in ribosomal biogenesis may have implications in PELP1-mediated oncogenic functions

ABA perception and signalling

Plant productivity is continuously challenged by pathogen attack and abiotic stress such as drought and salt stress. The phytohormone abscisic acid (ABA) is a key endogenous messenger in plants' responses to such stresses and understanding ABA signalling is essential for improving plant performance in the future. Since the discovery of ABA as a leaf abscission- and seed dormancy-promoting sesquiterpenoid in the 1960s, our understanding of the action of the phytohormone ABA has come a long way. Recent breakthroughs in the field of ABA signalling now unfold a unique hormone perception mechanism where binding of ABA to the ABA receptors RCARs/PYR1/PYLs leads to inactivation of type 2C protein phosphatases such as ABI1 and ABI2. The protein phosphatases seem to function as coreceptors and their inactivation launches SNF1-type kinase action which targets ABA-dependent gene expression and ion channels

Nitric oxide production occurs downstream of reactive oxygen species in guard cells during stomatal closure induced by chitosan in abaxial epidermis of Pisum sativum

The effects of chitosan (β-1,4 linked glucosamine, a fungal elicitor), on the patterns of stomatal movement and signaling components were studied. cPTIO (NO scavenger), sodium tungstate (nitrate reductase inhibitor) or l-NAME (NO synthase inhibitor) restricted the chitosan induced stomatal closure, demonstrating that NO is an essential factor. Similarly, catalase (H2O2 scavenger) or DPI [NAD(P)H oxidase inhibitor] and BAPTA-AM or BAPTA (calcium chelators) prevented chitosan induced stomatal closure, suggesting that reactive oxygen species (ROS) and calcium were involved during such response. Monitoring the NO and ROS production in guard cells by fluorescent probes (DAF-2DA and H2DCFDA) indicated that on exposure to chitosan, the levels of NO rose after only 10 min, while those of ROS increased already by 5 min. cPTIO or sodium tungstate or l-NAME prevented the rise in NO levels but did not restrict the ROS production. In contrast, catalase or DPI restricted the chitosan-induced production of both ROS and NO in guard cells. The calcium chelators, BAPTA-AM or BAPTA, did not have a significant effect on the chitosan induced rise in NO or ROS. We propose that the production of NO is an important signaling component and participates downstream of ROS production. The effects of chitosan strike a marked similarity with those of ABA or MJ on guard cells and indicate the convergence of their signal transduction pathways leading to stomatal closure

Trafficking-Mediated STING Degradation Requires Sorting to Acidified Endolysosomes and Can Be Targeted to Enhance Anti-tumor Response

STING is an endoplasmic reticulum (ER)-associated transmembrane protein that turns on and quickly turns off downstream signaling as it translocates from the ER to vesicles. How STING signaling is attenuated during trafficking remains poorly understood. Here, we show that trafficking-mediated STING degradation requires ER exit and function of vacuolar ATPase complex. Late-stage STING vesicles are sorted to Rab7-positive endolysosomes for degradation. Based on analysis of existing structures, we also identified the helix amino acid 281 (aa281)–297 as a motif required for trafficking-mediated STING degradation. Immuno-electron microscopy (EM) reveals the size and clustering of STING vesicles and topology of STING on the vesicle. Importantly, blockade of trafficking-mediated STING degradation using bafilomycin A1 specifically enhanced cyclic guanosine monophosphate (GMP)-AMP (cGAMP)-mediated immune response and anti-tumor effect in mice. Together, our findings provide biochemical and imaging evidence for STING degradation by the lysosome and pinpoint trafficking-mediated STING degradation as a previously unanticipated therapeutic target for enhancing STING signaling in cancer therapy

Action of natural abscisic acid precursors and catabolites on abscisic acid receptor complexes

The phytohormone abscisic acid (ABA) regulates stress responses and controls numerous aspects of plant growth and development. Biosynthetic precursors and catabolites of ABA have been shown to trigger ABA responses in physiological assays, but it is not clear whether these are intrinsically active or whether they are converted into ABA in planta. In this study, we analyzed the effect of ABA precursors, conjugates and catabolites on hormone signalling. The compounds were also tested in vitro for their ability to regulate the phosphatase moiety of ABA receptor complexes consisting of the protein phosphatase 2C ABI2 and the co-receptors RCAR1/PYL9, RCAR3/PYL8 or RCAR11/PYR1. Using mutants defective in ABA biosynthesis, we show that the physiological activity associated with ABA precursors derives predominantly from their bioconversion to ABA. The ABA glucose ester conjugate, which is the most widespread storage form of ABA, showed weak ABA-like activity in germination assays and in triggering ABA-signaling in protoplasts. The ABA conjugate and precursors showed negligible activity as a regulatory ligand of the ABI2/RCAR receptor complexes. The majority of ABA catabolites were inactive in our assays. To analyze the chemically unstable 8'- and 9'-hydroxylated ABA catabolites, we used stable tetralone derivatives of these compounds, which did trigger selective ABA responses. ABA synthetic analogues exhibited differential activity as regulatory ligands of different ABA receptor complexes in vitro. The data show that ABA precursors, catabolites and conjugates have limited intrinsic bioactivity and that both natural and synthetic ABA-related compounds can be used to probe the structural requirements of ABA ligand-receptor interactions.Peer reviewed: YesNRC publication: Ye

PELP1 nucleolar localization depends on cell cycle progression.

<p>(<b>A</b>) HeLa cells were arrested in G1-S boundary by a double thymidine block and cells were released to progress into the S and G2 phases of the cell cycle. PELP1 localization was visualized by using confocal microscopy. (<b>B</b>) ZR-75 cells were synchronized to G2/M phase using nocodazole (15 µM) for 18 h and released to progress into the cell cycle by addition of 10% serum. PELP1 localization was monitored with confocal microscopy by colocalizing with nucleolin. (<b>C</b>) ZR-75 cells were synchronized to G1 phase by serum starvation and released to progress into the cell cycle by addition of 10% serum. PELP1 localization was monitored by using confocal microscopy in different time intervals by colocalizing with nucleolin.</p