Cytoplasmic TrkA Expression as a Screen for Detecting NTRK1 Fusions in Colorectal Cancer.

NTRK1 gene fusions, the targets of multikinase inhibitors, are promising therapeutic targets for colorectal cancer (CRC). However, screening methods for detecting NTRK1 gene fusions in CRC tissues have not been reported. In this study, we investigated the potential use of immunohistochemistry (IHC) for detecting NTRK1 gene fusions. We performed and compared IHC with fluorescence in situ hybridization (FISH) in 80 CRC patients. TrkA immunostaining was observed to be both membranous and cytoplasmic and was scored semiquantitatively using staining intensity and proportions. The tumors were observed to be NTRK1 gene fusion-positive when ≥20 out of 100 nuclei in FISH. A significant correlation between the IHC and FISH results for determination of the NTRK1 gene fusions was observed. We measured the cytoplasmic TrkA expression, which showed an area under the receiver operating characteristic (ROC) curve of 0.926 (range: 0.864-0.987, 95% CI, P=.001). By choosing 4.5 (sum of the intensity and proportion scores of cytoplasmic TrkA expression) as the cut-off value for the positive and negative NTRK1 gene fusion groups, the sensitivity and specificity for predicting lymph node metastasis were 100 and 83.8%, respectively (P=.001). Specifically, high cytoplasmic TrkA expression (sum of intensity and proportion scores >4) was associated with the presence of NTRK1 gene fusions (P<.0001, r=0.528). Taken together, our data showed that IHC for TrkA can be used as an efficient screening method for detecting NTRK1 gene fusions in CRC.

TWIST mediates resistance to paclitaxel by regulating Akt and Bcl-2 expression in gastric cancer cells.

The transcription factor TWIST has been reported to play an important role in tumor progression as well as resistance to anti-cancer drugs. However, the role of TWIST in gastric cancer and the molecular mechanisms by which this protein elicits drug resistance remain poorly understood. We transfected gastric cancer cell lines with lentiviral vector to generate TWIST-overexpressing stable cell lines. Our study showed that overexpression of TWIST not only increased cell migration and invasion but also induced resistance to the anti-cancer drug paclitaxel in gastric cancer. Paclitaxel increased gastric cancer cell death in dose-dependent manner; this was decreased following TWIST overexpression. Furthermore, treatment with paclitaxel decreased Akt phosphorylation and Bcl-2 expression, whereas these effects were suppressed by TWIST overexpression. Treatment of cells with Akt inhibitor or small interfering RNA targeting for Bcl-2 led to increased paclitaxel-induced cell death, indicating that TWIST elicits resistance to paclitaxel via the regulation of the Akt and Bcl-2 pathway. Our results suggest an underlying mechanism for TWIST-mediated paclitaxel resistance and indicate that TWIST represents a potential target for overcoming paclitaxel resistance in gastric cancer cells.

Low-dose irradiation promotes Rad51 expression by down-regulating miR-193b-3p in hepatocytes.

Current evidence indicates that there is a relationship between microRNA (miRNA)-mediated gene silencing and low-dose irradiation (LDIR) responses. Here, alterations of miRNA expression in response to LDIR exposure in male BALB/c mice and three different types of hepatocytes were investigated. The miRNome of the LDIR-exposed mouse spleens (0.01 Gy, 6.5 mGy/h) was analyzed, and the expression of miRNA and mRNA was validated by qRT-PCR. Western blotting, chromatin immunoprecipitation (ChIP), and luciferase assays were also performed to evaluate the interaction between miRNAs and their target genes and to gain insight into the regulation of miRNA expression. The expression of miRNA-193b-3p was down-regulated in the mouse spleen and liver and in various hepatocytes (NCTC, Hepa, and HepG2 cell lines) in response to LDIR. The down-regulation of miR-193b-3p expression was caused by histone deacetylation on the miR-193b-3p promoter in the HepG2 cells irradiated with 0.01 Gy. However, the alteration of histone deacetylation and miR-193b-3p and Rad51 expression in response to LDIR was restored by pretreatment with N-acetyl-cyctein. In conclusion, we provide evidence that miRNA responses to LDIR include the modulation of cellular stress responses and repair mechanisms.

Purine biosynthesis, biofilm formation, and persistence of an insect-microbe gut symbiosis.

The Riptortus-Burkholderia symbiotic system is an experimental model system for studying the molecular mechanisms of an insect-microbe gut symbiosis. When the symbiotic midgut of Riptortus pedestris was investigated by light and transmission electron microscopy, the lumens of the midgut crypts that harbor colonizing Burkholderia symbionts were occupied by an extracellular matrix consisting of polysaccharides. This observation prompted us to search for symbiont genes involved in the induction of biofilm formation and to examine whether the biofilms are necessary for the symbiont to establish a successful symbiotic association with the host. To answer these questions, we focused on purN and purT, which independently catalyze the same step of bacterial purine biosynthesis. When we disrupted purN and purT in the Burkholderia symbiont, the ΔpurN and ΔpurT mutants grew normally, and only the ΔpurT mutant failed to form biofilms. Notably, the ΔpurT mutant exhibited a significantly lower level of cyclic-di-GMP (c-di-GMP) than the wild type and the ΔpurN mutant, suggesting involvement of the secondary messenger c-di-GMP in the defect of biofilm formation in the ΔpurT mutant, which might operate via impaired purine biosynthesis. The host insects infected with the ΔpurT mutant exhibited a lower infection density, slower growth, and lighter body weight than the host insects infected with the wild type and the ΔpurN mutant. These results show that the function of purT of the gut symbiont is important for the persistence of the insect gut symbiont, suggesting the intricate biological relevance of purine biosynthesis, biofilm formation, and symbiosis.

Purine biosynthesis-deficient Burkholderia mutants are incapable of symbiotic accommodation in the stinkbug.

The Riptortus-Burkholderia symbiotic system represents a promising experimental model to study the molecular mechanisms involved in insect-bacterium symbiosis due to the availability of genetically manipulated Burkholderia symbiont. Using transposon mutagenesis screening, we found a symbiosis-deficient mutant that was able to colonize the host insect but failed to induce normal development of host's symbiotic organ. The disrupted gene was identified as purL involved in purine biosynthesis. In vitro growth impairment of the purL mutant and its growth dependency on adenine and adenosine confirmed the functional disruption of the purine synthesis gene. The purL mutant also showed defects in biofilm formation, and this defect was not rescued by supplementation of purine derivatives. When inoculated to host insects, the purL mutant was initially able to colonize the symbiotic organ but failed to attain a normal infection density. The low level of infection density of the purL mutant attenuated the development of the host's symbiotic organ at early instar stages and reduced the host's fitness throughout the nymphal stages. Another symbiont mutant-deficient in a purine biosynthesis gene, purM, showed phenotypes similar to those of the purL mutant both in vitro and in vivo, confirming that the purL phenotypes are due to disrupted purine biosynthesis. These results demonstrate that the purine biosynthesis genes of the Burkholderia symbiont are critical for the successful accommodation of symbiont within the host, thereby facilitating the development of the host's symbiotic organ and enhancing the host's fitness values.

Polyester synthesis genes associated with stress resistance are involved in an insect-bacterium symbiosis.

Many bacteria accumulate granules of polyhydroxyalkanoate (PHA) within their cells, which confer resistance to nutritional depletion and other environmental stresses. Here, we report an unexpected involvement of the bacterial endocellular storage polymer, PHA, in an insect-bacterium symbiotic association. The bean bug Riptortus pedestris harbors a beneficial and specific gut symbiont of the ß-proteobacterial genus Burkholderia, which is orally acquired by host nymphs from the environment every generation and easily cultivable and genetically manipulatable. Biochemical and cytological comparisons between symbiotic and cultured Burkholderia detected more PHA granules consisting of poly-3-hydroxybutyrate and associated phasin (PhaP) protein in the symbiotic Burkholderia. Among major PHA synthesis genes, phaB and phaC were disrupted by homologous recombination together with the phaP gene, whereby ΔphaB, ΔphaC, and ΔphaP mutants were generated. Both in culture and in symbiosis, accumulation of PHA granules was strongly suppressed in ΔphaB and ΔphaC, but only moderately in ΔphaP. In symbiosis, the host insects infected with ΔphaB and ΔphaC exhibited significantly lower symbiont densities and smaller body sizes. These deficient phenotypes associated with ΔphaB and ΔphaC were restored by complementation of the mutants with plasmids encoding a functional phaB/phaC gene. Retention analysis of the plasmids revealed positive selection acting on the functional phaB/phaC in symbiosis. These results indicate that the PHA synthesis genes of the Burkholderia symbiont are required for normal symbiotic association with the Riptortus host. In vitro culturing analyses confirmed vulnerability of the PHA gene mutants to environmental stresses, suggesting that PHA may play a role in resisting stress under symbiotic conditions.