Basic Science

Mechanism of Rnf2 in Tumor Formation is Discovered

As the primary E3 ligase responsible for H2A modification in the PRC1 complex, Rnf2 plays important roles in early development, ES cell maintenance and tissue homeostasis. The overexpression of Rnf2 has also been documented in clinical gastrointestinal tumors and lymphomas. Despite these findings, the mechanisms of Rnf2 in tumor formation remain poorly understood. Using cell culture, tissue array and mouse xenograft models, Zhang Jian’s lab from the Institute of genetics and developmental biology identify Rnf2 as an E3 ligase that targets p53 for degradation. The E3 ligase activity of Rnf2 requires Bmi1 protein, a component of the polycomb group (PcG) complex. Unlike Mdm2, Rnf2 only degrades p53 in selective cell lines, such as those from germ-cell tumors. The knockdown of Rnf2 induces apoptosis, which can be rescued through the reduction of p53 expression. Moreover, the down-regulation of Rnf2 expression in germ-cell tumors significantly reduces tumor cell growth, while the simultaneous down-regulation of both genes restores tumor cell growth in vitro and in tumor xenograft models. Furthermore, a reverse correlation between Rnf2 and p53 expression was detected in human ovarian cancer tissues. Together, these results indicate that Rnf2 is an E3 ligase for p53 degradation in selective cells, implicating Rnf2 as a therapeutic target to restore tumor suppression through p53 in certain tumor cells. The results published online on January 14, 2013 in PNAS (doi:10.1073/pnas.1211604110). Su Wenjing, a graduate student from Zhang’s lab is the first author of the paper.

New Achievement on Smart Magnetic Resonance Contrast Agents

On Jan. 3 of 2013, the journal Scientific Reports (Nature Publishing Group, NPG) published a research article entitled "Controlled intracellular self-assembly of gadolinium nanoparticles as smart molecular MR contrast agents" that was contributed by the research team led by Prof. Liang Gaolin from the University of Science and Technology of China (USTC) in collaboration with a research group led by Prof. Li Li from Sun Yat-Sen University Cancer Center. The co-first authors of this paper are Ph. D. student Cao Chunyan from USTC and Ph. D. student Shen Yingying from Sun Yat-Sen University. This paper reported the development of a new type of smart tumor-targeted magnetic resonance (MR) contrast agents that have greatly enhanced MR signal in tumors on nude mice. After the invention of the first generation of smart MR contrast agents by Dr. Liang with a unique platform of condensation reaction, this time by collaborating with the Sun Yat-Sen University Cancer Center and Nanjing University Jinling Hospital, Liang’s group successfully developed the second generation of tumor-targeted smart contrast agents for magnetic resonance imaging (MRI). They conjugated the two functional groups for condensation to one Gd-based magnetic small molecule. Under the action of the reducing agents and proteases over-expressed in tumor cells, the small molecule condenses to form dimers and the latter self-assemble into gadolinium nanoparticles (Gd-NPs), resulting in greatly enhanced MRI signal than that of the small molecular precursor.

Breakthrough on Pulsed Optically Pumped Rb Atomic Clock

Prof. Wang Yuzhu and his team of novel satellite atomic clock, from the Shanghai Institute of Optics and Fine Mechanics (SIOM, CAS), have made a breakthrough on pulsed optically pumped (POP) Rb atomic clock [Opt. Lett. 37, 5036 (2012)]. In the work, the clock transition signal of a vapor cell rubidium atomic clock, for the first time, was observed by the orthogonal-polarized detection based on magneto-optical rotation and the ultrahigh signal contrast up to 90% was reported. Therefore, shot noise and laser fluctuation noise have been suppressed as much as possible. As a result, the signal-to-noise ratio of the clock transition and the frequency stability of the atomic clock have been improved by about an order of magnitude. The referee of Opt. Lett. gives high appraisal of the result: “the authors attempt to improve the well-studied pulsed optically pumped clock by changing the detection technique to one based on dispersion rather than absorption (the resonant Faraday effect). This leads to an improvement in the signal-to-noise ratio (SNR). This is an interesting idea which should be brought to the notice of the optical-clock community.”