DNA Damage Mediated S and G2 Checkpoints in Human Embryonal Carcinoma Cells

For mouse embryonic stem (ES) cells, the importance of the S and G2 cell cycle checkpoints for genomic integrity is increased by the absence of the G1 checkpoint. We have investigated ionizing radiation (IR)-mediated cell cycle checkpoints in undifferentiated and retinoic acid-differentiated human embryonal carcinoma (EC) cells. Like mouse ES cells, human EC cells did not undergo G1 arrest after IR but displayed a prominent S-phase delay followed by a G2-phase delay. In contrast, although differentiated EC cells also failed to arrest at G1-phase after IR, they quickly exited S-phase and arrested in G2-phase. In differentiated EC cells, the G2-M-phase cyclin B1/CDC2 complex was upregulated after IR, but the G1-S-phase cyclin E and the cyclin E/CDK2 complex were expressed at constitutively low levels, which could be an important factor distinguishing DNA damage responses between undifferentiated and differentiated EC cells. S-phase arrest and expression of p21 could be inhibited by 7-hydroxystaurosporine, suggesting that the ataxia-telangiectasia and Rad-3-related-checkpoint kinase 1 (ATR-CHK1), and p21 pathways might play a role in the IR-mediated S-phase checkpoint in EC cells. IR-mediated phosphorylation of ataxia-telangiectasia mutated, (CHK1), and checkpoint kinase 2 were distinctly higher in undifferentiated EC cells compared with differentiated EC cells. Combined with the prominent S and G2 checkpoints and a more efficient DNA damage repair system, these mechanisms operate together in the maintenance of genome stability for EC cells. Stem Cells 2009;27:568–57

Current techniques of liver transection

The operative mortality rate of liver resection has decreased from 10% to 20% before the 1980s to <5% in most specialized hepatobiliary centers nowadays. The most important factor for better outcome is reduced blood loss due to improvement in surgical techniques. Liver transection is the most challenging part of liver resection, associated with a risk of massive hemorrhage. Understanding the segmental anatomy of the liver and delineation of the proper transection plane using intraoperative ultrasound are prerequisites to safe liver transection. Clamp crushing and ultrasonic dissection are the two most widely used transection techniques. In recent years, new instruments using different types of energy for coagulation or sealing of vessels have been developed for liver transection. These include radiofrequency devices, Harmonic Scalpel, Ligasure and TissueLink dissecting sealer. Whether these new instruments, used alone or in combination with clamp crushing or ultrasonic dissection, improve the safety of liver transection has not been clearly demonstrated. The use of the vascular stapler for transection of major intrahepatic vascular trunks is also gaining popularity. These new instruments are particularly useful in liver transection during laparoscopic liver resection. Adjunctive measures such as intermittent Pringle maneuver and low central venous pressure anesthesia are also useful measures to reduce the risk of hemorrhage. This article reviews the safety and efficacy of different techniques of liver transection, with particular attention to evidence from randomized controlled trials available in the literature

Brain-Derived Neurotrophic Factor Promotes Tumorigenesis via Induction of Neovascularization: Implication in Hepatocellular Carcinoma

Purpose: Brain-derived neurotrophic factor (BDNF) has emerged as a novel angiogenic factor, and yet its impact on tumorigenesis is unclear. This study aimed at investigating the roles of BDNF in angiogenesis and tumor development. Experimental Design: BDNF was overexpressed in a mouse endothelial cell (EC) line by stable transfection, and angiogenic properties of the transfectants were assessed. Microarray analysis was employed to explore the molecular pathways. The impact of modulating BDNF levels in two mouse EC lines on tumorigenic potential of a transformed mouse liver cell line was evaluated by an in vivo cotransplantation model. BDNF and tropomyosin receptor kinase B (TrkB) protein levels were determined in 50 pairs of human hepatocellular carcinoma (HCC) tissues by Western blotting and immunohistochemistry. Survival analysis was carried out to determine their clinical significance. Results: Overexpression of BDNF could promote EC proliferation, migration, invasion, and survival. Microarray and molecular studies showed that RhoA, caspase-9, caspase-3, growth arrest specific 6, and VEGF could mediate BDNF/TrkB-induced angiogenesis. The cotransplantation experiment showed that high BDNF-expressing ECs could facilitate tumor angiogenesis and growth, whereas knockdown of BDNF by short hairpin RNAs impaired such effects. Furthermore, examination on human HCC tissues revealed upregulation of BDNF and TrkB protein levels in 46.0% and 33.3% of the cases studied, respectively. Immunohistochemistry disclosed strong BDNF reactivity in both tumor and endothelial cells. High TrkB expression was associated with shorter overall survival. Conclusions: BDNF/TrkB system was crucial for tumor angiogenesis and growth, which may represent a potential target for antiangiogenic therapy in HCC. ©2011 AACR.link_to_subscribed_fulltex