Molecular Mechanisms of TRAF6 Ubiquitination and Activation

The Tumor Necrosis Factor (TNF) Receptor Associated Factor 6 (TRAF6) is an intracellular signal transducers, being responsible for mediating many of the activation events initiated by TNF receptor (TNFR) and Toll-like/Interleukin-1 and 18 receptor (TIR) families, in which TRAF6 plays central roles in numerous biological processes including innate and adaptive immunity, osteoclastogenesis and bone development, CD40 signaling, neuronal cell development, and cancer cell progression. Acting as an E3 ubiquitin ligase, TRAF6 catalyzes lysine 63 linked poly-ubiquitination of itself and many other signal transducers upon association with upstream effectors possessing a short TRAF Interaction Motif (TIM) peptide sequence in the NF-KappaB signal transduction pathway. Ectopic over-expression of TRAF6 acts as a dominant-positive. However, the mechanism of TRAF6 activation by upstream activators or over-expression is unclear. This motivated our enthusiasm to study the role played by ubiquitination for TRAF6 in NF-KappaB signaling. We now demonstrate that two critical regions of TRAF6, the MATH domain required for TIM activator binding and the RING-Zinc region for downstream signaling, mutually interact and render the molecule structurally closed and inactive. Our results implicate that auto-ubiquitination disrupts such interaction, thus providing a means of sustaining the open conformation necessary for downstream signaling. However, excessive ubiquitination induced by TRAF6 over-expression results in formation of large cytoplasmic sequestosomes and its inactivation. Furthermore, the inferred cis nature of TRAF auto-ubiquitination is now demonstrated to act in trans and is regulated via its RING-Zinc and coiled-coil domains. We also demonstrate that both the RING-Zinc region and MATH domain of TRAF6 can be targeted for ubiquitination, but trans-ubiquitination of TRAF6 muteins is incapable of activating the NF-KappaB pathway, suggesting that ubiquitination, alone, is insufficient for activity

Finishing the euchromatic sequence of the human genome

The sequence of the human genome encodes the genetic instructions for human physiology, as well as rich information about human evolution. In 2001, the International Human Genome Sequencing Consortium reported a draft sequence of the euchromatic portion of the human genome. Since then, the international collaboration has worked to convert this draft into a genome sequence with high accuracy and nearly complete coverage. Here, we report the result of this finishing process. The current genome sequence (Build 35) contains 2.85 billion nucleotides interrupted by only 341 gaps. It covers ∼99% of the euchromatic genome and is accurate to an error rate of ∼1 event per 100,000 bases. Many of the remaining euchromatic gaps are associated with segmental duplications and will require focused work with new methods. The near-complete sequence, the first for a vertebrate, greatly improves the precision of biological analyses of the human genome including studies of gene number, birth and death. Notably, the human enome seems to encode only 20,000-25,000 protein-coding genes. The genome sequence reported here should serve as a firm foundation for biomedical research in the decades ahead

MiR-145 inhibits tumor angiogenesis and growth by N-RAS and VEGF

MiR-145 is known as a tumor suppressor in numerous human cancers. However, its role in tumor angiogenesis remains poorly defined. In this study, we found that miR-145 was significantly downregulated in breast cancer tissues by using 106 cases of normal and cancer tissues as well as in breast cancer cells. MiR-145 exhibited inhibitory role in tumor angiogenesis, cell growth and invasion and tumor growth through the post-transcriptional regulation of the novel targets N-RAS and VEGF-A. In addition, we provide evidence that the expression levels of miR-145 correlate inversely with malignancy stages of breast tumors, although there is no association between miR-145 levels and hormone receptor levels in breast cancer. Taken together, these results demonstrate that miR-145 plays important inhibitory role in breast cancer malignancy by targeting N-RAS and VEGF-A, which may be potential therapeutic and diagnostic targets