Project description:Studies were undertaken to determine whether oscillatory behavior in the extracellular signal regulated kinase (ERK) pathway results in unique gene regulation patterns. Microarray analysis was performed on three subcloned populations of human keratinocytes with distinct ERK signaling/oscillation phenotypes. Microarray analysis identified 45 genes that overlapped between 2 subclones with oscillation phenotypes but not in the subclone which is non-oscillatory. Transcription factor networks revealed a role for MED1 in mediating ERK oscillation-dependent gene expression, which was confirmed with Western blot analysis. Further experimentation confirmed a role for p38 in the mediation of MED1 phosphorylation and ERK oscillatory behavior. hTERT-immortalized normal human keratinocytes (provided by Dr. Jerry Shay, The University of Texas Southwestern Medical Center) were stably transfected with ERK1-green fluorescent protein chimera and stable subclones were isolated with distinct ERK activation/oscillation patterns: Clone #1 exhibits transient ERK activation with ligand activation but does not oscillate; Clone #2 exhibits persistent ERK oscillations that are dependent on ligand activation; and Clone #3 exhibits spontaneous ERK oscillations in the absence of ligand activation.
Project description:The purpose of this experiment is to determine the phosphorylation ratio of pT vs pY ERK present in ERK phosphorylation reaction by activated MEK E203K or MEK WildType. Aliquots were collected at 3 minutes 15 seconds, the time at which the mono-phosphorylated ERK is at its maximal. To determine the ratio between pT and pY ERK, synthetic AQUA peptides corresponding to the pY- and the pT-phosphorylated ERK were spiked into the sample. The two peptides have identical mass but they can be umabiguguously distinguished by their elution times and fragmentation spectra.
Project description:Identifying specific protein interactors and spatially or temporally restricted local proteomes contributes significantly to our understanding of cellular processes in virtually all aspects of life. Obtaining such data is challenging, especially when the protein, cell type or event of interest is rare. In recent years, different proximity labeling techniques have been developed that have greatly improved our ability to tackle these questions. However, while effective in mammalian systems, use in plants has been extremely limited due to technical challenges. Recent technological improvements in the form of two highly active versions of the biotin ligase BirA* (TurboID and miniTurboID), prompted us to test this new system on two challenging but widely asked questions in plants: what are interaction partners of low-abundant proteins and what are organellar proteomes in rare and transient cell types. To address the first question, we used the transcription factor FAMA as a test case. FAMA is a master regulator of guard cell development and promotes terminal differentiation of the guard cell precursor by both activating and repressing hundreds of genes. FAMA-expressing young guard cells are rare and restricted to the epidermis of developing aerial tissues, which makes them a good model system to test TurboID applicability under material-limiting conditions. For this experiment, young Arabidopsis seedlings expressing FAMA-TurboID were treated with biotin to label FAMA complexes. Col-0 wild type and seedlings expressing nuclear TurboID under the FAMA promoter were used as controls for unspecific binding of proteins to the beads and stochastic labeling of nuclear proteins, respectively. Biotinylated proteins were isolated by affinity purification with streptavidin-coupled beads and identified by LC-MS/MS. Analysis of proteins labeled by FAMA-TurboID fusions revealed known interactors of this late stomatal lineage specific transcription factor, as well as novel proteins that could explain its dual function as an activator and repressor. Comparison with proteins obtained from classical co-immunoprecipitation approaches with FAMA showed that proximity labeling is superior for identification of meaningful interaction partners of low-abundant proteins.
Project description:The aim of the study was to investigate gene expression tumour progression of KRas*/MYC driven lung tumours from adenocarcinoma in situ to invasive disease.
Project description:It has not been possible to view the transcriptional activity of a single gene within a living eukaryotic cell. It is therefore unclear how long and how frequently a gene is actively transcribed, how this is modulated during differentiation, and how transcriptional events are dynamically coordinated in cell populations. By means of an in vivo RNA detection technique , we have directly visualized transcription of an endogenous developmental gene. We found discrete "pulses" of gene activity that turn on and off at irregular intervals. Surprisingly, the length and height of these pulses were consistent throughout development. However, there was strong developmental variation in the proportion of cells recruited to the expressing pool. Cells were more likely to re-express than to initiate new expression, indicating that we directly observe a transcriptional memory. In addition, we used a clustering algorithm to reveal synchronous transcription initiation in neighboring cells. This study represents the first direct visualization of transcriptional pulsing in eukaryotes. Discontinuity of transcription may allow greater flexibility in the gene-expression decisions of a cell.
Project description:The tumor suppressor PTEN is mutated or deleted in many tumors, causing the activation of the PI3K pathway. Here, we show that the loss of PTEN increases the transcriptional activity of hypoxia-inducible factor 1 (HIF-1) through the inactivation of Forkhead transcription factors (FOXO) in PTEN-null cells. Reintroduction of PTEN into the nucleus, overexpression of a nonphosphorylatable FOXO3a, which accumulates in the nucleus, or inhibition of nuclear export of FOXO3a by leptomycin B represses HIF-1 transcriptional activity in PTEN-null cells. HIF-1 transcriptional activity increases in PTEN-positive cells depleted of FOXO3a with siRNA. PTEN and FOXO3a regulate the transactivation domain of HIF-1alpha. Chromatin immunoprecipitation indicates that FOXO3a complexes with HIF-1alpha and p300 on the Glut-1 promoter, a HIF-1 target gene. Overexpression of p300 reverses FOXO3a-mediated repression of HIF-1 transcriptional activity. Coimmunoprecipitation and GAL4-HIF-1alpha transactivation assays reveal that FOXO3a interferes with p300-dependent HIF-1 transcriptional activity. Thus, FOXO3a negatively regulates HIF-1 transcriptional activity.
Project description:To understand the molecular mechanism by which regulate skeletal development, we attempted to identify transcription factors that were highly expressed in developing cartilage during the embryonic stage. Col2a1-Venus-Tg mice in which chondrocytes were fluorescently labelled with the GFP-modified Venus gene. We purified total RNA from Venus-negative and Venus-positive cells and performed microarray analysis using an Affymetrix Mouse Genome 430 2.0 Array.