Structure and regulation of the anthranilate synthase genes in Pseudomonas aeruginosa: II. Cloning and expression in Escherichia coli

The genes for the large and small subunits of anthranilate synthase (trpE and trpG, respectively) have been cloned from Pseudomonas aeruginosa PAC174 into E. coli by R-prime formation with the broad-host- range plasmid R68.44. Sequential subcloning into plasmid vectors reduced the active Pseudomonas DNA fragment to a length of 3.1 kb. We obtained evidence that this region contains the promoter for its own expression and retains a vestigial regulatory response to tryptophan scarcity or excess.      

Mycosin-1, a subtilisin-like serine protease of Mycobacterium tuberculosis, is cell wall-associated and expressed during infection of macrophages

Background  

Exported proteases are commonly associated with virulence in bacterial pathogens, yet there is a paucity of information regarding their role in Mycobacterium tuberculosis. There are five genes (mycP1-5) present within the genome of Mycobacterium tuberculosis H37Rv that encode a family of secreted, subtilisin-like serine proteases (the mycosins). The gene mycP1 (encoding mycosin-1) was found to be situated 3700 bp (four ORF's) from the RD1 deletion region in the genome of the attenuated vaccine strain M. bovis BCG (bacille de Calmette et Guérin) and was selected for further analyses due to the absence of expression in this organism.     

Macromolecular changes caused by formalin fixation and antigen retrieval

Although the mechanics of formalin fixation and antigen retrieval have been studied extensively and reviewed periodically, little attention has been directed toward conformational changes in target molecules. Formaldehyde changes the shape of tissue molecules by appending small hydroxymethyl groups to them. These adducts, in turn, can react with other tissue molecules to form crosslinks, or they can participate in a variety of reactions during tissue processing, including formation of imines, ethoxymethyl adducts, and further crosslinks. Under the influence of alcohol dehydration, fixed DNA may fragment and form a variety of depurination products. The situation becomes even more complex with short fixation times because under these conditions, the dehydrating agent used for tissue processing denatures macromolecules in other ways, most notably through rearrangement of molecular shape to move hydrophobic realms outward and hydrophilic areas inward (hydrophobic inversions). How tissue molecules are modified affects the outcome of immunohistochemical staining and prospects for restoration of antigenicity. Immunoreacitivity may be compromised because epitopes are either sterically hidden, but otherwise unaffected, or they have been altered more directly. Enzyme-based retrieval methods are best suited for the former because they literally snip the molecule apart to reveal the portions of interest. Heat-induced retrieval with buffers can demodify affected epitopes by removing adducts and breaking crosslinks. The choice of temperature and pH is usually critical for optimal retrieval. Effective temperatures are directly related to the strength of bonds-higher temperatures are needed to break stronger bonds. The pH of the retrieval solution determines the charge on the tissue molecule; the goal is to create a charge that causes the demodified molecule to assume a near natural conformation. Rational use of these concepts should lead to better control of immunohistochemical reactions.     

Dyes from a twenty-first century perspective

In June 2008, the Biological Stain Commission sponsored A Seminar on Dyes and Staining the purpose of which was twofold: first, to show that very useful information applicable to biomedical dyes and staining is available from unrelated disciplines and second, to summarize modern thinking on how dyes, solvents, and tissues interact to produce selective staining. In this introduction to the papers from the symposium, we acknowledge that biomedical dye research has declined as newer technologies have gained importance. We should point out, however, that dyes and staining still are vitally important. Moreover, needs abound for innovative studies concerned with dye analysis, synthesis, and mode of action. Concepts and tools from unrelated fields hold promise for significant breakthroughs in many areas of interest.     

Regulation of homeostasis and oncogenesis in the intestinal epithelium by Ras

Much of our current state of knowledge pertaining to the mechanisms controlling intestinal epithelial homeostasis derives from epidemiological, molecular genetic, cell biological, and biochemical studies of signaling pathways that are dysregulated during the process of colorectal tumorigenesis. Activating mutations in members of the RAS oncoprotein family play an important role in the progression of colorectal cancer (CRC) and, by extension, intestinal epithelial homeostasis. Mutations in K-RAS account for 90% of the RAS mutations found in CRC. As such, the study of RAS protein function in the intestinal epithelium is largely encompassed by the study of K-RAS function in CRC. In this review, we summarize the data available from genetically defined in vitro and in vivo models of CRC that aim to characterize the oncogenic properties of mutationally activated K-RAS. These studies paint a complex picture of a multi-functional oncoprotein that engages an array of downstream signaling pathways to influence cellular behaviors that are both pro- and anti-tumorigenic. While the complexity of K-RAS biology has thus far prevented a comprehensive understanding of its oncogenic properties, the work to date lays a foundation for the development of new therapeutic strategies to treat K-RAS mutant CRC.     

Comparative Analysis of Radiosensitizers for K-RAS Mutant Rectal Cancers

Approximately 40% of rectal cancers harbor activating K-RAS mutations, and these mutations are associated with poor clinical response to chemoradiotherapy. We aimed to identify small molecule inhibitors (SMIs) that synergize with ionizing radiation (IR) (“radiosensitizers”) that could be incorporated into current treatment strategies for locally advanced rectal cancers (LARCs) expressing mutant K-RAS. We first optimized a high-throughput assay for measuring individual and combined effects of SMIs and IR that produces similar results to the gold standard colony formation assay. Using this screening platform and K-RAS mutant rectal cancer cell lines, we tested SMIs targeting diverse signaling pathways for radiosensitizing activity and then evaluated our top hits in follow-up experiments. The two most potent radiosensitizers were the Chk1/2 inhibitor AZD7762 and the PI3K/mTOR inhibitor BEZ235. The chemotherapeutic agent 5-fluorouracil (5-FU), which is used to treat LARC, synergized with AZD7762 and enhanced radiosensitization by AZD7762. This study is the first to compare different SMIs in combination with IR for the treatment of K-RAS mutant rectal cancer, and our findings suggest that Chk1/2 inhibitors should be evaluated in new clinical trials for LARC.     

Succinate dehydrogenase is a direct target of sirtuin 3 deacetylase activity

Background

Sirtuins (SIRT1-7) are a family of NAD-dependent deacetylases and/or ADP-ribosyltransferases that are involved in metabolism, stress responses and longevity. SIRT3 is localized to mitochondria, where it deacetylates and activates a number of enzymes involved in fuel oxidation and energy production.

Methodology/Principal Findings

In this study, we performed a proteomic screen to identify SIRT3 interacting proteins and identified several subunits of complex II and V of the electron transport chain. Two subunits of complex II (also known as succinate dehydrogenase, or SDH), SDHA and SDHB, interacted specifically with SIRT3. Using mass spectrometry, we identified 13 acetylation sites on SDHA, including six novel acetylated residues. SDHA is hyperacetylated in SIRT3 KO mice and SIRT3 directly deacetylates SDHA in a NAD-dependent manner. Finally, we found that SIRT3 regulates SDH activity both in cells and in murine brown adipose tissue.

Conclusions/Significance

Our study identifies SDHA as a binding partner and substrate for SIRT3 deacetylase activity. SIRT3 loss results in decreased SDH enzyme activity, suggesting that SIRT3 may be an important physiological regulator of SDH activity.     

Systemic elevation of PTEN induces a tumor-suppressive metabolic state

Decremental loss of PTEN results in cancer susceptibility and tumor progression. PTEN elevation might therefore be an attractive option for cancer prevention and therapy. We have generated several transgenic mouse lines with PTEN expression elevated to varying levels by taking advantage of bacterial artificial chromosome (BAC)-mediated transgenesis. The "Super-PTEN" mutants are viable and show reduced body size due to decreased cell number, with no effect on cell size. Unexpectedly, PTEN elevation at the organism level results in healthy metabolism characterized by increased energy expenditure and reduced body fat accumulation. Cells derived from these mice show reduced glucose and glutamine uptake and increased mitochondrial oxidative phosphorylation and are resistant to oncogenic transformation. Mechanistically we find that PTEN elevation orchestrates this metabolic switch by regulating PI3K-dependent and -independent pathways and negatively impacting two of the most pronounced metabolic features of tumor cells: glutaminolysis and the Warburg effect.     

Metabolic regulation by SIRT3: implications for tumorigenesis

Cancer cells meet their needs for energy and biomass production by consuming high levels of nutrients and rewiring metabolism to support macromolecular biosynthesis. Mitochondrial enzymes play central roles in anabolic growth, and acetylation may provide a key layer of regulation over mitochondrial metabolic pathways. As a major mitochondrial deacetylase, SIRT3 regulates the activity of enzymes to coordinate global shifts in cellular metabolism. SIRT3 promotes the function of the tricarboxylic acid (TCA) cycle and the electron transport chain and reduces oxidative stress. Loss of SIRT3 triggers oxidative damage, reactive oxygen species (ROS)-mediated signaling, and metabolic reprogramming to support proliferation and tumorigenesis. Thus, SIRT3 is an intriguing example of how nutrient-sensitive, post-translational regulation may provide integrated regulation of metabolic pathways to promote metabolic homeostasis in response to diverse nutrient signals.