The expression and purification of the N-terminal activation domain of the transcription factor c-Myc: a model substrate for exploring ERK2 docking interactions

Cell surface marker phenotypes and gene expression profiles of murine radiation-induced acute myeloid leukemia stem cells are similar to those of common myeloid progenitors

Radiation exposure induces acute myeloid leukemia (AML) in humans and mice. Recent studies postulated that AML stem cells of spontaneous human AML arise from hematopoietic stem cells. However, other studies support the possibility that short-lived committed progenitors transform into AML stem cells, accompanied by a particular gene mutation. It remains unclear whether AML stem cells are present in radiation-induced AML, and information regarding AML-initiating cells is lacking. In this study, we identified and analyzed AML stem cells of mice with radiation-induced AML. The AML stem cells were identified by transplanting 100 bone marrow cells from mice with radiation-induced AML. We injected 100 cells of each of seven cell populations corresponding to different stages of hematopoietic cell differentiation and compared the latencies of AMLs induced in recipient mice. The identified radiation-induced AML stem cells frequently displayed similarities in both CD antigen and gene expression profiles with normal common myeloid progenitors. The number of common myeloid progenitor-like AML stem cells was significantly increased in mice with radiation-induced AML, but the progeny of common myeloid progenitors was decreased. In addition, analysis of radiation effects on the hematopoietic system showed that common myeloid progenitor cells were extremely radiosensitive and that their numbers remained at low levels for more than 2 months after radiation exposure. Our results suggest that murine radiation-induced AML stem cells arise from radiosensitive cells at a common myeloid progenitor stage.

Flow cytometric analysis of genetic FRET detectors containing variable substrate sequences

A genetic Fluorescence Resonance Energy Transfer (FRET) detector undergoes a post-translational modification (PTM)-induced conformational change that results in increased FRET. To test if the PTM-dependent FRET change can be quantified by flow cytometry, we purified and immobilized a genetic detector on microbeads and used flow cytometry to measure its FRET efficiency before and after Erk-2-mediated phosphorylation. The fluorescence ratio R between the acceptor and donor fluorescence, which was obtained by fitting a straight line through the data points in linear space, increases following phosphorylation, thus demonstrating that flow cytometry is capable of detecting a PTM-dependent FRET response. Furthermore, when Erk-2 and a genetic detector are coexpressed in bacteria, the measured R value changes with the substrate sequence with near single residue resolution. Similarly, the cells coexpressing the glycosylating enzyme O-GlcNAc transferase (OGT) and a genetic detector specific for OGT exhibit a PTM-induced change in FRET efficiency. Therefore, the combination of flow cytometry and a genetic detector may be useful to characterize the substrate specificity of a PTM enzyme and identify the sequences that are preferentially targeted for PTM in vivo.

Crystallization of the focal adhesion kinase targeting (FAT) domain in a primitive orthorhombic space group

X-ray diffraction data from the targeting (FAT) domain of focal adhesion kinase (FAK) were collected from a single crystal that diffracted to 1.99 A resolution and reduced to the primitive orthorhombic lattice. A single molecule was predicted to be present in the asymmetric unit based on the Matthews coefficient. The data were phased using molecular-replacement methods using an existing model of the FAK FAT domain. All structures of human focal adhesion kinase FAT domains solved to date have been solved in a C-centered orthorhombic space group.