Human Decision Making Based on Variations in Internal Noise: An EEG Study

Perceptual decision making is prone to errors, especially near threshold. Physiological, behavioural and modeling studies suggest this is due to the intrinsic or ‘internal’ noise in neural systems, which derives from a mixture of bottom-up and top-down sources. We show here that internal noise can form the basis of perceptual decision making when the external signal lacks the required information for the decision. We recorded electroencephalographic (EEG) activity in listeners attempting to discriminate between identical tones. Since the acoustic signal was constant, bottom-up and top-down influences were under experimental control. We found that early cortical responses to the identical stimuli varied in global field power and topography according to the perceptual decision made, and activity preceding stimulus presentation could predict both later activity and behavioural decision. Our results suggest that activity variations induced by internal noise of both sensory and cognitive origin are sufficient to drive discrimination judgments

Minimum Information about a Biosynthetic Gene cluster

A wide variety of enzymatic pathways that produce specialized metabolites in bacteria, fungi and plants are known to be encoded in biosynthetic gene clusters. Information about these clusters, pathways and metabolites is currently dispersed throughout the literature, making it difficult to exploit. To facilitate consistent and systematic deposition and retrieval of data on biosynthetic gene clusters, we propose the Minimum Information about a Biosynthetic Gene cluster (MIBiG) data standard.Chemistry and Chemical Biolog

The Effect of Antibiotic Selective Pressure on MDR1 and ASCT2 Expression in Human Hepatocellular Carcinoma

Our laboratory has used the CRISPR-Cas9 gene editing system to eliminate the expression of the SLC1A5 gene, which encodes the ASCT2 amino acid transporter, which is implicated in driving the glutamine-dependent growth of several cancers. At last year’s URAD event, the isolation of clones confirmed for knockout (KO) of ASCT2 in two human hepatocellular carcinoma (HCC) cell lines – Huh7 and SK-Hep1 - was described. As these ASCT2 knockout (ASCT2KO) cell lines are currently being deployed in studies assessing the role of this transporter in tumorigenesis, we asked two fundamental questions: 1) Does the removal of antibiotic selective pressure – under which ASCT2KO lines are selected – result in the re-appearance of ASCT2 in populations or selected clones of Huh7 and SK-Hep1? 2) Does the continuous exposure of populations or isolated clones of Huh7 or SK-Hep1 to lethal antibiotics used in selection of ASCT2KO lines lead to increased expression of the Multi-Drug Resistance Transporter MDR1? These two questions are fundamental to the interpretation of tumorigenesis results. ASCT2 and MDR1 expression was assessed by western blot analysis, and growth of the lines were measured by the colorimetric MTT assay. The results indicate that the SK-Hep1 cell lines targeted for ASCT2KO exhibited no transporter expression in the absence or presence of antibiotic selective pressure. Conversely, Huh7 populations targeted for ASCT2KO unexpectedly exhibited enhanced ASCT2 expression under antibiotic selection. Huh7 ASCT2KO clones in contrast showed no re-emergence of ASCT2 expression, suggesting that each was successfully “knocked out” for this transporter. Likewise, SK-Hep1 exhibited no MDR1 expression, but Huh7 significantly expressed this drug resistance transporter; its abundance was increased by Puromycin, the antibiotic used for selection of CRISPR-Cas9-mediated ASCT2KO lines. This drug-induced expression of MDR1 was blunted in Huh7 ASCT2KO lines, suggesting that ASCT2 might play a role in drug resistance in cancerous cells. Finally, studies were done to test the growth rate of Huh7 clonal cells lines compared to the population, as well as study the growth of the Huh7 and Sk-Hep ASCT2KO populations when grown in the presence of two drug therapies-Metformin and Sorafenib. It was found that the clonal cell population initially showed a slower growth rate, however the rate increased after 72 hours to become consistent with the population and control. It was also observed that Metformin and Sorafenib slightly slowed the growth of Huh7 cells, but neither drug had an effect on Sk-Hep cells overall. These results suggest that while ASCT2 elimination does not affect growth, it may render targeted cancer cells more vulnerable to certain chemotherapies. Further studies can be designed to test this hypothesis.B.S. (Bachelor of Science

Targeted Suppression and Knockout of ASCT2 or LAT1 in Epithelial and Mesenchymal Human Liver Cancer Cells Fail to Inhibit Growth

Amino acid transporters alanine-serine-cysteine transporter 2 (ASCT2) and L-Type Amino Acid Transporter 1 (LAT1) are coordinately enhanced in human cancers where among other roles, they are thought to drive mechanistic target-of-rapamycin (mTOR) growth signaling. To assess ASCT2 and LAT1 as therapeutic targets, nine unique short hairpin RNA (shRNA) vectors were used to stably suppress transporter expression in human epithelial (Hep3B) and mesenchymal (SK-Hep1) hepatocellular carcinoma (HCC) cell lines. In addition, six unique CRISPR-Cas9 vectors were used to edit the ASCT2 (SLC1A5) and LAT1 (SLC7A5) genes in epithelial (HUH7) and mesenchymal (SK-Hep1) HCC cells. Both approaches successfully diminished glutamine (ASCT2) and leucine (LAT1) initial-rate transport proportional to transporter protein suppression. In spite of profoundly reduced glutamine or leucine transport (up to 90%), transporter suppression or knockout failed to substantially affect cellular proliferation or basal and amino acid-stimulated mTORC1 growth signaling in either HCC cell type. Only LAT1 knockout in HUH7 slightly reduced growth rate. However, intracellular accumulation of radiolabeled glutamine and leucine over longer time periods largely recovered to control levels in ASCT2 and LAT1 knockout cells, respectively, which partially explains the lack of an impaired growth phenotype. These data collectively establish that in an in vitro context, human epithelial and mesenchymal HCC cell lines adapt to ASCT2 or LAT1 knockout. These results comport with an emerging model of amino acid exchangers like ASCT2 and LAT1 as “harmonizers”, not drivers, of amino acid accumulation and signaling, despite their long-established dominant role in initial-rate amino acid transport

“Click” Chemistry-Mediated Phenylene-Cored Carborane Dendrimers

Phenylene-cored small dendrimers containing three to nine peripheral <i>o</i>-carborane clusters were synthesized via Cu­(I)-catalyzed Huisgen-type azide alkyne cycloaddition reactions. The resulting dendrimers have been characterized by IR and NMR spectroscopy and MALDI-TOF mass spectral analysis. The biological evaluation of branched dendrimer <b>16</b> containing nine carborane cages has been carried out using human liver cancer cells (SK-Hep1). Dendrimer <b>16</b> was accumulated in the SK-Hep1 cancer cells in a concentration-dependent manner. The highest boron accumulation up to 2540 ng of boron/5 × 10⁵ cells was observed at a 50 μM concentration of <b>16</b> over a period of 20 h. The high accumulation of <b>16</b> into the tumor cell lines indicates that such dendritic boron drug delivery platforms could be possible for application in boron neutron capture therapy in cancer treatment