Hematopoietic stem cell (HSC) differentiation is regulated by cell-intrinsic and extrinsic cues. In addition to transcriptional regulation, post-translational regulation may also control HSC differentiation. To test this hypothesis, we visualized ubiquitin-regulated protein stability of a single transcription factor, c-Myc. The stability of c-Myc protein was instructive of HSC quiescence and c-Myc protein abundance was controlled by the ubiquitin ligase Fbw7. Fine changes in stability of c-Myc protein regulated the HSC “gene expression signature”. Using whole genome genomic approaches, we identified specific regulators of HSC function that are directly controlled by c-Myc binding, however adult HSCs and embryonic stem cells sense and interpret distinctly c-Myc regulated gene expression. These studies show a ubiquitin ligase substrate pair can orchestrate the molecular program of HSC differentiation.
The ubiquitin-proteasome system (UPS) is a multi-subunit pathway that allows for ubiquitin modification of proteins and leads to either degradation or other non-proteolytic processes such as trafficking or transcriptional activation. Given its role as a regulator of cellular homeostasis it is not surprising that members of the UPS are frequently aberrantly expressed in a number of disease states including cancer. This review will focus on one member of the UPS, the F-box protein, Fbw7 (also known as Sel-10, Ago, hCDC4) and mechanisms by which Fbw7 interacts with its substrates in the context of development and tumorigenesis will be discussed. In addition, antagonists of this pathway as well as current and future therapeutics for the UPS will be examined.
On their entry into the thymus, developing lymphocyte progenitors depend on signaling from the pre-T cell receptor (pre-TCR), which orchestrates differentiation, cell proliferation, and survival. The exact mechanism of pre-TCR-mediated suppression of T cell death remains unclear and controversial. Here, we identify Bim and Bid, 2 members of the BH3-only group of the BCL2 family, as important regulators of pre-T cell death. Both factors are highly expressed in proapoptotic thymocytes and their expression is suppressed on signaling through the pre-TCR. Their expression is directly regulated by the transcription factors FoxO3a and p53. Bid expression and p53 activity are related to the ongoing rearrangement of the TCR loci and induced DNA damage responses. Bim expression and FoxO3a nuclear translocation are directly controlled by the pre-TCR by means of its downstream kinase Akt/PKB. Interestingly, deletion of either gene on a pre-TCR ؊/؊ background rescues survival, but fails to induce further progenitor differentiation uncoupling the 2 processes.BCL2 family ͉ cell death ͉ pre-TCR signaling ͉ T cell development
The ssRNA+ family Coronaviridae includes two subfamilies prototyped by coronaviruses and toroviruses that cause respiratory and enteric infections. To facilitate the identification of new distantly related members of the family Coronaviridae, we have developed a molecular assay with broad specificity. The consensus-degenerated hybrid oligonucleotide primer (CODEHOP) strategy was modified to design primers targeting the most conserved motifs in the RNA-dependent RNA polymerase locus. They were evaluated initially on RNA templates from virus-infected cells using a two-step RT-PCR protocol that was further advanced to a one-step assay. The sensitivity of the assay ranged from 10(2) to 10(6) and from 10(5) to 10(9) RNA copy numbers for individual corona-/torovirus templates when tested, respectively, with and without an excess of RNA from human cells. This primer set compared to that designed according to the original CODEHOP rules showed 10-10(3) folds greater sensitivity for 5 of the 6 evaluated corona-/torovirus templates. It detected 57% (32 of 56) of the respiratory specimens positive for 4 human coronaviruses, as well as stool specimens positive for a bovine torovirus. The high sensitivity and broad virus range of this assay makes it suitable for screening biological specimens in search for new viruses of the family Coronaviridae.
Novel viruses might be responsible for numerous disease cases with unknown etiology. In this study, we screened 1800 nasopharyngeal samples from adult outpatients with respiratory disease symptoms and healthy individuals. We employed a reverse transcription (RT)-PCR assay and CODEHOP-based primers (CT12-mCODEHOP) previously developed to recognize known and unknown corona- and toroviruses. The CT12-mCODEHOP assay detected 42.0 % (29/69) of samples positive for human coronaviruses (HCoV), including HCoV-229 (1/16), HCoV-NL63 (9/17), and HCoV-OC43 (19/36), and additionally HCoV-HKU1 (3), which was not targeted by the diagnostic real-time PCR assays. No other coronaviruses were identified in the analyzed samples.
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