Catabolic regulation analysis of Escherichia coli and its crp, mlc, mgsA, pgi and ptsG mutants

BACKGROUND

Most bacteria can use various compounds as carbon sources. These carbon sources can be either co-metabolized or sequentially metabolized, where the latter phenomenon typically occurs as catabolite repression. From the practical application point of view of utilizing lignocellulose for the production of biofuels etc., it is strongly desirable to ferment all sugars obtained by hydrolysis from lignocellulosic materials, where simultaneous consumption of sugars would benefit the formation of bioproducts. However, most organisms consume glucose prior to consumption of other carbon sources, and exhibit diauxic growth. It has been shown by fermentation experiments that simultaneous consumption of sugars can be attained by ptsG, mgsA mutants etc., but its mechanism has not been well understood. It is strongly desirable to understand the mechanism of metabolic regulation for catabolite regulation to improve the performance of fermentation.

RESULTS

In order to make clear the catabolic regulation mechanism, several continuous cultures were conducted at different dilution rates of 0.2, 0.4, 0.6 and 0.7 h⁻¹ using wild type Escherichia coli. The result indicates that the transcript levels of global regulators such as crp, cra, mlc and rpoS decreased, while those of fadR, iclR, soxR/S increased as the dilution rate increased. These affected the metabolic pathway genes, which in turn affected fermentation result where the specific glucose uptake rate, the specific acetate formation rate, and the specific CO₂ evolution rate (CER) were increased as the dilution rate was increased. This was confirmed by the ¹³C-flux analysis. In order to make clear the catabolite regulation, the effect of crp gene knockout (Δcrp) and crp enhancement (crp⁺) as well as mlc, mgsA, pgi and ptsG gene knockout on the metabolism was then investigated by the continuous culture at the dilution rate of 0.2 h⁻¹ and by some batch cultures. In the case of Δcrp (and also Δmlc) mutant, TCA cycle and glyoxylate were repressed, which caused acetate accumulation. In the case of crp⁺ mutant, glycolysis, TCA cycle, and gluconeogenesis were activated, and simultaneous consumption of multiple carbon sources can be attained, but the glucose consumption rate became less due to repression of ptsG and ptsH by the activation of Mlc. Simultaneous consumption of multiple carbon sources could be attained by mgsA, pgi, and ptsG mutants due to increase in crp as well as cyaA, while glucose consumption rate became lower.

CONCLUSIONS

The transcriptional catabolite regulation mechanism was made clear for the wild type E. coli, and its crp, mlc, ptsG, pgi, and mgsA gene knockout mutants. The results indicate that catabolite repression can be relaxed and crp as well as cyaA can be increased by crp⁺, mgsA, pgi, and ptsG mutants, and thus simultaneous consumption of multiple carbon sources including glucose can be made, whereas the glucose uptake rate became lower as compared to wild type due to inactivation of ptsG in all the mutants considered.

Disruption of Tacc3 function leads to in vivo tumor regression

The formation of the bipolar spindle is responsible for accurate chromosomal segregation during mitosis. The dynamic instability of microtubules has an important role in this process, and has been shown to be an effective target for cancer chemotherapy. Several agents that target non-microtubule mitotic proteins, including the motor protein Eg5, Aurora kinases and Polo-like kinases, are currently being developed as chemotherapeutic drugs. However, because the efficacies of these drugs remain elusive, new molecular targets that have essential roles in tumor cells are desired. Here, we provide in vivo evidence that transforming acidic coiled-coil-3 (Tacc3) is a potential target for cancer chemotherapy. Using MRI, we showed that Tacc3 loss led to the regression of mouse thymic lymphoma in vivo, which was accompanied by massive apoptosis. By contrast, normal tissues, including the thymus, showed no overt abnormalities, despite high Tacc3 expression. in vitro analysis indicated that Tacc3 depletion induced multi-polar spindle formation, which led to mitotic arrest, followed by apoptosis. Similar responses have been observed in Burkitt's lymphoma and T-ALL. These results show that Tacc3 is a vulnerable component of the spindle assembly in lymphoma cells and is a promising cancer chemotherapy target.

High Resolution Emission and Transmission Imaging Using the Same Detector

We demonstrate the capability of one detector, the Micro-Angiographic Fluoroscope (MAF) detector, to image for two types of applications: nuclear medicine imaging and radiography. The MAF has 1024 × 1024 pixels with an effective pixel size of 35 microns and is capable of real-time imaging at 30 fps. It has a CCD camera coupled by a fiber-optic taper to a light image intensifier (LII) viewing a 300-micron thick CsI phosphor. The large variable gain of the LII provides quantum-limited operation with little additive instrumentation noise and enables operation in both energy-integrating (EI) and sensitive low-exposure single photon counting (SPC) modes. We used the EI mode to take a radiograph, and the SPC mode to image a custom phantom filled with 1 mCi of I-125. The phantom is made of hot rods with diameters ranging from 0.9 mm to 2.3 mm. A 1 mm diameter parallel hole, medium energy gamma camera collimator was placed between the phantom and the MAF and was moved multiple times at equal intervals in random directions to eliminate the grid pattern corresponding to the collimator septa. Data was acquired at 20 fps. Two algorithms to localize the events were used: 1) simple threshold and 2) a weighted centroid method. Although all the hot rods could be clearly identified, the image generated with the simple threshold method shows more blurring than that with the weighted centroid method. With the diffuse cluster of pixels from each single detection event localized to a single pixel, the weighted centroid method shows improved spatial resolution. A radiograph of the phantom was taken with the same MAF in EI mode without the collimator. It shows clear structural details of the rods. Compared to the radiograph, the sharpness of the emission image is limited by the collimator resolution and could be improved by optimized collimator design. This study demonstrated that the same MAF detector can be used in both radioisotope and x-ray imaging, combining the benefits of each.

Adhesion and junction molecules in embryonic and adult lens cell differentiation

The expression of the neural cell adhesion molecule NCAM and its polysialic acid (PSA) moiety was documented during embryonic development and adult differentiation of chicken lens cells. In both the embryo and adult, NCAM is predominantly found in the epithelium and the zone of young elongating cells of the annular pad. NCAM abundance drops markedly in the cortical fibers and is further reduced in the lens nucleus. Epithelial cell NCAM is more highly poly-sialylated in the adult than in the embryonic lens. Three isoforms of NCAM at 180, 140, and 120 kDa were detected in the lens and predominantly associated with the unit membrane-enriched plasma membranes of fiber cells. The distribution of NCAM relative to MP26 and the adherence junction-associated glycoprotein N-cadherin suggests that NCAM could influence the formation of fiber cell gap junctions and adherence junctions.

Identification of urinary biomarkers to distinguish tumor bearing and control rats in the methylnitrosourea (MNU) – induced model of mammary carcinogenesis: use of label-free, comparative, ultra-high resolution nano-LC mass spectrometry

Abstract #1109

In the MNU induced model of mammary cancer, rats given a single dose of MNU (75 mg/kg BW), via the jugular vein, at 50 days of age develop multiple ER+ mammary cancers. These cancers appear similar to highly differentiated ER+ human breast cancers, and have been shown to be sensitive to many of the same chemotherapeutic agents that are effective in women. When a female rat developed its first palpable cancer, it was placed in a metabolic cage and urine collected overnight on dry ice. The urine from these rats were compared to those obtained from control rats. Using a new sample preparation protocol, peptides were prepared from the urines of control (n = 4 individual animals) and rats bearing induced mammary tumors (n = 4). The peptide pools were analyzed using nano-LC-LTQ-FT-MS. The 8 LC-MS analyses were aligned and the integrated accurate mass signals were quantified using Rosetta ElucidatorTM software. The ion currents from 4430 peptides (charge state > +2) were analyzed between the two groups using ANOVA. Two hundred and twenty nine peptides were found to be significantly different (P< 0.01) between the two groups, with clear distinction between the urines from control and experimental animals being observed using hierarchical clustering and principal component analysis. The protein identifications that were significantly increased in the tumor-bearing urines were confirmed by targeted tandem mass spectrometry. Further studies relating the altered expression of these peptides to differences in tumor size, the effects of therapeutic agents, etc will also be presented.

Citation Information: Cancer Res 2009;69(2 Suppl):Abstract nr 1109.