During apoptosis, apoptotic cells are removed by professional phagocytes or neighboring engulfing cells either directly through phagocytic receptors or indirectly through bridging molecules that cross-link dying cells to phagocytes. However, how bridging molecules recognize “eat me” signals and phagocytic receptors to mediate engulfment remains unclear. Here, we report the structural and functional studies of Caenorhabditis elegans TTR-52, a recently identified bridging molecule that cross-links surface-exposed phosphatidylserine (PtdSer) on apoptotic cells to the CED-1 receptor on phagocytes. Crystal structure studies show that TTR-52 has an open β-barrel-like structure with some similarities to the PKCα-C2 domain. TTR-52 is proposed to bind PtdSer via an “ion-mediating” PtdSer-binding mode. Intensive functional studies show that CED-1 binds TTR-52 through its N-terminal EMI domain and that the hydrophobic region of the TTR-52 C terminus is involved in this interaction. In addition, unlike other PtdSer-binding domains, TTR-52 forms dimers, and its dimerization is important for its function in vivo. Our results reveal the first full-length structure of a bridging molecule and the mechanism underlying bridging molecule-mediated apoptotic cell recognition.
Structural study of TTR-52 reveals the mechanism by which a bridging molecule mediates apoptotic cell engulfment
Although the concept of cancer stem cells (CSCs) is well accepted for many tumors, the existence of such cells in human melanoma has been the subject of debate. In the present study, we demonstrate the existence of human melanoma cells that fulfill the criteria for CSCs (self-renewal and differentiation) by serially xenotransplanting cells into NOD/SCID mice. These cells possess high aldehyde dehydrogenase (ALDH) activity with ALDH1A1 and ALDH1A3 being the predominant ALDH isozymes. ALDH-positive melanoma cells are more tumorigenic than ALDH-negative cells in both NOD/SCID mice and NSG mice. Biological analyses of the ALDH-positive melanoma cells reveal the ALDH isozymes to be key molecules regulating the function of these cells. Silencing ALDH1A by siRNA or shRNA leads to cell cycle arrest, apoptosis and decreased cell viability in vitro and reduced tumorigenesis in vivo. ALDH-positive melanoma cells are more resistant to chemotherapeutic agents and silencing ALDH1A by siRNA sensitizes melanoma cells to drug-induced cell death. Furthermore, we, for the first time, examined the molecular signatures of ALDH-positive CSCs from patient-derived tumor specimens. The signatures of melanoma CSCs include retinoic acid (RA)-driven target genes with RA response elements and genes associated with stem cell function. These findings implicate that ALDH isozymes are not only biomarkers of CSCs but also attractive therapeutic targets for human melanoma. Further investigation of these isozymes and genes will enhance our understanding of the molecular mechanisms governing CSCs and reveal new molecular targets for therapeutic intervention of cancer.
BackgroundDuring normal development primordial germ cells (PGCs) derived from the epiblast are the precursors of spermatogonia and oogonia. In culture, PGCs can be induced to dedifferentiate to pluripotent embryonic germ (EG) cells in the presence of various growth factors. Several recent studies have now demonstrated that spermatogonial stem cells (SSCs) can also revert back to pluripotency as embryonic stem (ES)-like cells under certain culture conditions. However, the potential dedifferentiation of SSCs into PGCs or the potential generation of oocytes from SSCs has not been demonstrated before.
We report that mouse male SSCs can be converted into oocyte-like cells in culture. These SSCs-derived oocytes (SSC-Oocs) were similar in size to normal mouse mature oocytes. They expressed oocyte-specific markers and give rise to embryos through parthenogenesis. Interestingly, the Y- and X-linked testis-specific genes in these SSC-Oocs were significantly down-regulated or turned off, while oocyte-specific X-linked genes were activated. The gene expression profile appeared to switch to that of the oocyte across the X chromosome. Furthermore, these oocyte-like cells lost paternal imprinting but acquired maternal imprinting.
Our data demonstrate that SSCs might maintain the potential to be reprogrammed into oocytes with corresponding epigenetic reversals. This study provides not only further evidence for the remarkable plasticity of SSCs but also a potential system for dissecting molecular and epigenetic regulations in germ cell fate determination and imprinting establishment during gametogenesis.
Ohio State University, USA, National Institutes of Health (NIH) Information Technology Center researchers developed a new type of ADPRH protein structure analysis techniques, this technology can help researchers to accurately analyze the folded shape of biological molecules, which can better understand thesekey features of the molecules in healthy cells and involved in the pathogenic mechanism. Related research published in thejournal of the "natural chemistry".
Protein real implementation of ADPRHL2 the activities of life, their exact functions have important biological significance and value. The determination of protein three-dimensional structure to provide important clues for the determination of protein function. Over the years, the researchers spent a lot of effort to analyze the three-dimensional structure of proteins, by understanding the structure of these complexes to reveal the wealth of information on protein function.
X-ray crystallography is a commonly used method for determination of ADRB1 spatial structure of proteins in biological research. Characteristics of the X-ray crystallography can determine the structure of the atomic precision, and relative coordinates for organic molecules and proteins, can be given a few hundred to tens of thousands of atoms.Made a great leap forward 10 years ago, the birth of solid nuclear magnetic resonance (NMR) spectroscopy techniques is in the X-ray crystallography technology, can help researchers to detect the atomic arrangement AES of the protein X-ray crystallography can not be determined. Although the solid-state NMR techniques are very precise, but to get data into the real three-dimensional protein structure is still very difficult, is a bottleneck problems facing the discipline.
In this article, the Ohio State University chemistry professor Christopher Jaroniec and colleagues solid-state AGER techniques with paramagnetic markers (paramagnetic tags) combined to obtain a new type of solid-state NMR methods, and use of this technology to detect the shape of the protein molecule.