Critical domains for NACC2-NTRK2 fusion protein activation.

Neurotrophic receptor tyrosine kinases (NTRKs) belong to the receptor tyrosine kinase (RTK) family. NTRKs are responsible for the activation of multiple downstream signaling pathways that regulate cell growth, proliferation, differentiation, and apoptosis. NTRK-associated mutations often result in oncogenesis and lead to aberrant activation of downstream signaling pathways including MAPK, JAK/STAT, and PLCγ1. This study characterizes the NACC2-NTRK2 oncogenic fusion protein that leads to pilocytic astrocytoma and pediatric glioblastoma. This fusion joins the BTB domain (Broad-complex, Tramtrack, and Bric-a-brac) domain of NACC2 (Nucleus Accumbens-associated protein 2) with the transmembrane helix and tyrosine kinase domain of NTRK2. We focus on identifying critical domains for the biological activity of the fusion protein. Mutations were introduced in the charged pocket of the BTB domain or in the monomer core, based on a structural comparison of the NACC2 BTB domain with that of PLZF, another BTB-containing protein. Mutations were also introduced into the NTRK2-derived portion to allow comparison of two different breakpoints that have been clinically reported. We show that activation of the NTRK2 kinase domain relies on multimerization of the BTB domain in NACC2-NTRK2. Mutations which disrupt BTB-mediated multimerization significantly reduce kinase activity and downstream signaling. The ability of these mutations to abrogate biological activity suggests that BTB domain inhibition could be a potential treatment for NACC2-NTRK2-induced cancers. Removal of the transmembrane helix leads to enhanced stability of the fusion protein and increased activity of the NACC2-NTRK2 fusion, suggesting a mechanism for the oncogenicity of a distinct NACC2-NTRK2 isoform observed in pediatric glioblastoma.

Nefarious NTRK oncogenic fusions in pediatric sarcomas: Too many to Trk.

Neurotrophic Tyrosine Receptor Kinase (NTRK) genes undergo chromosomal translocations to create novel open reading frames coding for oncogenic fusion proteins; the N-terminal portion, donated by various partner genes, becomes fused to the tyrosine kinase domain of either NTRK1, NTRK2, or NTRK3. NTRK fusion proteins have been identified as driver oncogenes in a wide variety of tumors over the past three decades, including Pediatric Gliomas, Papillary Thyroid Carcinoma, Spitzoid Neoplasms, Glioblastoma, and additional tumors. Importantly, NTRK fusions function as drivers of pediatric sarcomas, accounting for approximately 15% of childhood cancers including Infantile Fibrosarcoma (IFS), a subset of pediatric soft tissue sarcoma (STS). While tyrosine kinase inhibitors (TKIs), such as larotrectinib and entrectinib, have demonstrated profound results against NTRK fusion-positive cancers, acquired resistance to these TKIs has resulted in the formation of gatekeeper, solvent-front, and compound mutations. We present a comprehensive compilation of oncogenic fusions involving NTRKs focusing specifically on pediatric STS, examining their biological signaling pathways and mechanisms of activation. The importance of an obligatory dimerization or multimerization domain, invariably donated by the N-terminal fusion partner, is discussed using characteristic fusions that occur in pediatric sarcomas. In addition, examples are presented of oncogenic fusion proteins in which the N-terminal partners may contribute additional biological activities beyond an oligomerization domain. Lastly, therapeutic approaches to the treatment of pediatric sarcoma will be presented, using first generation and second-generation agents such as selitrectinib and repotrectinib.

Mechanisms of transplacental transport and barrier of polybrominated diphenyl ethers: A comprehensive human, Sprague-Dawley rat, BeWo cell and molecular docking study.

Although studies have reported that polybrominated diphenyl ethers (PBDEs) can transfer from mothers to fetuses, the underlying transplacental transport and barrier mechanisms are still unclear. Therefore, we conducted a series of comprehensive experiments in humans, Sprague-Dawley rats, and a BeWo cell monolayer model, as well as a molecular docking study. PBDEs in mothers can transfer to fetuses with a ratio of approximately 0.46, suggesting that the placenta could not efficiently acts as a barrier to PBDE transplacental transport. Similar results were observed in pregnant rats, although varying times were required for different congeners to reach a steady-state in fetuses. The transport ratios at pregnancy day 14 in rats were generally higher than those at pregnancy day 18, which demonstrated that the barrier capacity of immature placentas was lower than that of mature placentas. None concentration-dependent transplacental transport was observed in BeWo cells with efflux ratios of 1.73-2.32, which suggested passive diffusion mechanisms govern the influx of PBDEs through placenta. The accumulated ratios of PBDEs and the inhibitor assay indicated that the effluent channel of P-glycoprotein was partially inhibited by PBDEs. Using molecular docking studies, three pocket sites were identified for different congeners in P-glycoprotein, which demonstrated that the inhibition of P-glycoprotein efflux pump through the pocket sites.

Novel in vitro method for measuring the mass fraction of bioaccessible atmospheric polycyclic aromatic hydrocarbons using simulated human lung fluids.

The bioaccessibility of organic pollutants is a key factor in human health risk assessments. We developed a novel in vitro method for determining the mass fraction of bioaccessible atmospheric polycyclic aromatic hydrocarbons (PAHs) using an air-washing device containing simulated human lung fluid. The experimental parameters were optimized based on the deposition fractions (DFs) of PAHs in human lung fluids. The DFs were measured for PAHs based on the mass of compounds in the mainstream and exhaled cigarette smoke. The mass fractions of bioaccessible PAHs were measured by passing the mainstream cigarette smoke through the air-washing device, and they were calculated via a simple mass balance equation based on the PAHs in the fluid and mainstream cigarette smoke. The DFs of individual PAHs ranged from 20.5% to 78.1%, and the bioaccessible mass fractions varied between 45.5% and 99.8%. The octanol-water partition coefficients (KOW) significantly influenced both the DFs and bioaccessible mass fractions of PAHs, and the optimized in vitro method could be used to estimate the bioavailable atmospheric PAHs. This in vitro method can potentially be used to measure the mass fraction of bioaccessible atmospheric PAHs and to assess the health risk related to human exposure to airborne PAHs.

Benzophenone-UV filters in personal care products and urine of schoolchildren from Shenzhen, China: Exposure assessment and possible source.

The use of benzophenone (BP)-type UV filters in personal care products (PCPs) has rapidly increased in China over the past decade, leading to growing concerns on the potential adverse effects associated with the usage. Urine analysis is an ideal non-invasive approach for human biomonitoring of xenobiotics that are excreted mainly through urinary system. To investigate human exposure of PCPs to children from South China, we determined BP-type UV filters in a total of 156 commercial PCP goods covering 11 categories, as well as 280 urine samples collected from elementary school students in Shenzhen, China. Five BP analogues (i.e., BP1, BP2, BP3, BP8, and 4HB) were frequently detected in both PCPs and urine, among which BP3 was the dominant analogue, accounting for 96.3% of the total BPs in PCPs and 53.2% in urine, respectively. Sunscreens contained the highest BP concentrations (mean: 2.15 × 104 ng g-1) among all PCP goods. Girls exhibited higher urinary BP concentrations than boys, and body mass index positively influenced BP concentrations. However, no regional difference in urinary BP concentration was observed. The estimated dermal uptake of BPs from PCPs after considering the percutaneous absorption rates was much lower than the estimated dermal intake. The total daily excretion doses estimated from urinary BPs were 74.4 and 47.4 ng·kg-1bw day-1 for girls and boys, respectively. The higher usage of body lotions, hand lotions, and sunscreens by girls than boys (1.49 vs. 1.03 times week-1) might play an important role.

Transplacental transfer characteristics of organochlorine pesticides in paired maternal and cord sera, and placentas and possible influencing factors.

Organochlorine pesticides (OCPs), including dichlorodiphenyltrichloroethane (DDT) and its metabolites [dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane], hexachlorocyclohexanes (HCHs), and hexachlorobenzene (HCB), are widely detected in humans despite the considerable decline in environmental concentrations. To understand the placental transfer of OCPs and the possible maternal influence on them, we measured the concentrations of DDTs, HCHs, and HCB in 102 paired samples of maternal and cord sera, and placentas collected in Shanghai, China. The median concentrations of DDTs and HCHs were the highest in maternal sera (601, 188 ng g-1 lipid), followed by umbilical cord sera (389, 131 ng g-1 lipid), and placentas (65, 37 ng g-1 lipid). 4,4'-DDE, ß-HCH, and HCB were the predominant contaminants in the three matrices. The ubiquitous existence of OCPs, and the significant concentration relationships of DDTs, HCHs, and OCPs in the three matrices suggested placental transfer from mother to fetus. The lipid-based concentration ratios of 4,4'-DDE, ß-HCH, and HCB in umbilical cord serum to those in maternal serum (F/M), and ratios of placenta to maternal serum (P/M) ranged from 0.66 to 1.01, and 0.12 to 0.25, respectively. Maternal variables affected the levels of fetal contamination. For primiparous women, significant correlations between maternal age and maternal HCHs, and between pre-pregnancy body mass index (BMI) and maternal HCHs were found. The negative effect of parity, and the positive effect of food consumption on maternal OCP concentrations were also observed, although there were no significant differences. The possible influence of parity on F/M and P/M of 4,4'-DDE suggested borderline significant differences between primiparous and multiparous women. Also, slight group differences were observed between elder and younger women, and between overweight and normal/underweight women. Parity seems to have a potential influence on transfer ratios of some OCP pollutants.