The four receptors of the Notch family are widely expressed transmembrane proteins that function as key conduits through which mammalian cells communicate to regulate cell fate and growth. Ligand binding triggers a conformational change in the receptor negative regulatory region (NRR) that enables ADAM protease cleavage at a juxtamembrane site that otherwise lies buried within the quiescent NRR. Subsequent intramembrane proteolysis catalysed by the gamma-secretase complex liberates the intracellular domain (ICD) to initiate the downstream Notch transcriptional program. Aberrant signalling through each receptor has been linked to numerous diseases, particularly cancer, making the Notch pathway a compelling target for new drugs. Although gamma-secretase inhibitors (GSIs) have progressed into the clinic, GSIs fail to distinguish individual Notch receptors, inhibit other signalling pathways and cause intestinal toxicity, attributed to dual inhibition of Notch1 and 2 (ref. 11). To elucidate the discrete functions of Notch1 and Notch2 and develop clinically relevant inhibitors that reduce intestinal toxicity, we used phage display technology to generate highly specialized antibodies that specifically antagonize each receptor paralogue and yet cross-react with the human and mouse sequences, enabling the discrimination of Notch1 versus Notch2 function in human patients and rodent models. Our co-crystal structure shows that the inhibitory mechanism relies on stabilizing NRR quiescence. Selective blocking of Notch1 inhibits tumour growth in pre-clinical models through two mechanisms: inhibition of cancer cell growth and deregulation of angiogenesis. Whereas inhibition of Notch1 plus Notch2 causes severe intestinal toxicity, inhibition of either receptor alone reduces or avoids this effect, demonstrating a clear advantage over pan-Notch inhibitors. Our studies emphasize the value of paralogue-specific antagonists in dissecting the contributions of distinct Notch receptors to differentiation and disease and reveal the therapeutic promise in targeting Notch1 and Notch2 independently.
We have established a rapid and sensitive transient expression system for Dictyostelium discoideum. We constructed a gene fusion containing the promoter from the Dictyostelium Actin 15 gene fused to the firefly luciferase gene. The enzymatic activity of this gene fusion, expressed at very high levels in stable transformants, was measured to determine optimum conditions for transient expression using electroporation to introduce the DNA into cells. With these conditions, we show that a luciferase gene fusion driven by a prestalk, cell-type specific promoter from the pst-cathepsin gene expresses luciferase at the appropriate developmental stage. In addition, we present results suggesting that the system will be useful for expressing genes in non-axenic cell lines. Finally, we observe that electroporation is more efficient for obtaining stable transformations than the standard calcium phosphate procedure using extrachromosomally replicating shuttle vectors but less efficient for vectors that integrate into the Dictyostelium chromosomes.
Maturation of human natural killer cells (NK cells) as defined by accumulation of cell surface expression of CD57 is associated with increased cytotoxic character and TNF and IFN-γ production upon target cell recognition. Notably, multiple studies point to a unique role for CD57+ NK cells in cancer immunosurveillance, yet there is scant information about how they mature. In this study, we show that pharmacological inhibition of GSK3 kinase in peripheral blood NK cells expanded ex vivo with IL-15 greatly enhances CD57 upregulation and late-stage maturation. GSK3 inhibition elevated the expression of several transcription factors associated with late-stage NK cell maturation including T-BET, ZEB2 and BLIMP-1 without affecting viability or proliferation. When exposed to human cancer cells, NK cell expanded ex vivo in the presence of a GSK3 inhibitor exhibited significantly higher production of TNF and IFN-γ, elevated natural cytotoxicity, and increased antibody-dependent cellular cytotoxicity (ADCC). In an established mouse xenograft model of ovarian cancer, adoptive transfer of NK cells conditioned in the same way also displayed more robust and durable tumor control. Our findings show how GSK3 kinase inhibition can greatly enhance the mature character of NK cells most desired for effective cancer immunotherapy.
When Dictyostelium cells that have initiated their developmental program upon starvation are returned to growth medium, there is a rapid and transient de novo tyrosine phosphorylation of a 43-kilodalton protein. This protein was found to be actin. Most of the phosphorylation occurred in a single, minor acidic isoform of actin. Developing cells that had been returned to growth medium lost their pseudopod extensions, became round, and had reduced adhesion to the substratum. These effects occurred with kinetics that matched the increase in tyrosine phosphorylation of actin. In mutant cell lines in which the gene for the phosphotyrosine phosphatase PTP1 had been disrupted, tyrosine phosphorylation of actin was rapid and more prolonged. These cells responded with proportionally accelerated kinetics of cell rounding. Cell lines overexpressing PTP1 had diminished amplitude and duration of actin tyrosine phosphorylation and exhibited diminished cell-shape change and an accelerated return to the extended cell-shape morphology seen in starved cells.
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