Dynamic Regulation of Tgf-B Signaling by Tif1γ: A Computational Approach

TIF1γ (Transcriptional Intermediary Factor 1 γ) has been implicated in Smad-dependent signaling by Transforming Growth Factor beta (TGF-β). Paradoxically, TIF1γ functions both as a transcriptional repressor or as an alternative transcription factor that promotes TGF-β signaling. Using ordinary differential-equation models, we have investigated the effect of TIF1γ on the dynamics of TGF-β signaling. An integrative model that includes the formation of transient TIF1γ-Smad2-Smad4 ternary complexes is the only one that can account for TGF-β signaling compatible with the different observations reported for TIF1γ. In addition, our model predicts that varying TIF1γ/Smad4 ratios play a critical role in the modulation of the transcriptional signal induced by TGF-β, especially for short stimulation times that mediate higher threshold responses. Chromatin immunoprecipitation analyses and quantification of the expression of TGF-β target genes as a function TIF1γ/Smad4 ratios fully validate this hypothesis. Our integrative model, which successfully unifies the seemingly opposite roles of TIF1γ, also reveals how changing TIF1γ/Smad4 ratios affect the cellular response to stimulation by TGF-β, accounting for a highly graded determination of cell fate

Altered Intracellular Localization and Mobility of SBDS Protein upon Mutation in Shwachman-Diamond Syndrome

Shwachman-Diamond Syndrome (SDS) is a rare inherited disease caused by mutations in the SBDS gene. Hematopoietic defects, exocrine pancreas dysfunction and short stature are the most prominent clinical features. To gain understanding of the molecular properties of the ubiquitously expressed SBDS protein, we examined its intracellular localization and mobility by live cell imaging techniques. We observed that SBDS full-length protein was localized in both the nucleus and cytoplasm, whereas patient-related truncated SBDS protein isoforms localize predominantly to the nucleus. Also the nucleo-cytoplasmic trafficking of these patient-related SBDS proteins was disturbed. Further studies with a series of SBDS mutant proteins revealed that three distinct motifs determine the intracellular mobility of SBDS protein. A sumoylation motif in the C-terminal domain, that is lacking in patient SBDS proteins, was found to play a pivotal role in intracellular motility. Our structure-function analyses provide new insight into localization and motility of the SBDS protein, and show that patient-related mutant proteins are altered in their molecular properties, which may contribute to the clinical features observed in SDS patients

The Human Nucleolar Protein FTSJ3 Associates with NIP7 and Functions in Pre-rRNA Processing

NIP7 is one of the many trans-acting factors required for eukaryotic ribosome biogenesis, which interacts with nascent pre-ribosomal particles and dissociates as they complete maturation and are exported to the cytoplasm. By using conditional knockdown, we have shown previously that yeast Nip7p is required primarily for 60S subunit synthesis while human NIP7 is involved in the biogenesis of 40S subunit. This raised the possibility that human NIP7 interacts with a different set of proteins as compared to the yeast protein. By using the yeast two-hybrid system we identified FTSJ3, a putative ortholog of yeast Spb1p, as a human NIP7-interacting protein. A functional association between NIP7 and FTSJ3 is further supported by colocalization and coimmunoprecipitation analyses. Conditional knockdown revealed that depletion of FTSJ3 affects cell proliferation and causes pre-rRNA processing defects. The major pre-rRNA processing defect involves accumulation of the 34S pre-rRNA encompassing from site A′ to site 2b. Accumulation of this pre-rRNA indicates that processing of sites A0, 1 and 2 are slower in cells depleted of FTSJ3 and implicates FTSJ3 in the pathway leading to 18S rRNA maturation as observed previously for NIP7. The results presented in this work indicate a close functional interaction between NIP7 and FTSJ3 during pre-rRNA processing and show that FTSJ3 participates in ribosome synthesis in human cells

Capreomycin-induced serum electrolyte abnormalities

Gross electrolyte disturbances including hypokalaemia, hypomagnesaemia, hypocalcaemia, and alkalosis have developed in tuberculous patients who were being treated with capreomycin. Similar abnormalities have also occurred when the drug gentamicin was used and were found to be due to secondary hyperaldosteronism. In this paper a detailed description of the changes induced by capreomycin is given. The evidence available strongly suggests a similar aetiology for the biochemical changes, but the precise pathophysiology is unknown. Caution should be exercised when capreomycin is used and the drug should be withdrawn if any of these abnormalities develop

The Shwachman-Bodian-Diamond syndrome associated protein interacts with HsNip7 and its down-regulation affects gene expression at the transcriptional and translational levels

The Shwachman-Bodian-Diamond syndrome (SDS) is an autosomal disorder with pleiotropic phenotypes including pancreatic, skeletal and bone marrow deficiencies and predisposition to hematological dysfunctions. SDS has been associated to mutations in the SBDS gene, encoding a highly conserved protein that was shown to function in ribosome biogenesis in yeast. in this work, we show that SBDS is found in complexes containing the human Nip7 ortholog. Analysis of pre-rRNA processing in a stable SBDS knock-down HEK293-derivative cell line revealed accumulation of a small RNA which is a further indication of SBDS involvement in rRNA biosynthesis. Global transcription and polysome-bound mRNA profiling revealed that SBDS knock-down affects expression of critical genes involved in brain development and function, bone morphogenesis, blood cell proliferation and differentiation, and cell adhesion. Expression of a group of growth and signal transduction factors and of DNA damage response genes is also affected. in SBDS knockdown cells, 34 mRNAs showed decreased and 55 mRNAs showed increased association to polysomes, among which is a group encoding proteins involved in alternative splicing and RNA modification. These results indicate that SBDS is required for accurate expression of genes important for proper brain, skeletal, and blood cell development. (c) 2007 Elsevier Inc. All rights reserved.Brazilian Synchroton Light Lab, Ctr Struct Mol Biol, BR-13084971 Campinas, SP, BrazilUniv São Paulo, Inst Chem, Dept Biochem, BR-05508900 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Microbiol Immunol & Parasitol, BR-04023062 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Microbiol Immunol & Parasitol, BR-04023062 São Paulo, BrazilWeb of Scienc

The Shwachman-Bodian-Diamond syndrome associated protein interacts with HsNip7 and its down-regulation affects gene expression at the transcriptional and translational levels (vol 313, pg 4180, 2007)

Ctr Struct Mol Biol, Brazilian Synchroton Light Lab, BR-13084971 Campinas, SP, BrazilUniv São Paulo, Inst Chem, Dept Biochem, BR-05508900 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Microbiol Immunol & Parasitol, BR-04023062 São Paulo, BrazilUniversidade Federal de São Paulo, Dept Microbiol Immunol & Parasitol, BR-04023062 São Paulo, BrazilWeb of Scienc