EGF signalling and rapamycin-mediated mTOR inhibition in glioblastoma multiforme evaluated by phospho-specific flow cytometry

Shedding Light on Intracellular Proteins using Flow Cytometry

Intracellular protein abundance is routinely measured in mammalian cells using population-based techniques such as western blotting which fail to capture single cell protein levels or using fluorescence microscopy which is although suitable for single cell protein detection but not for rapid analysis of large no. of cells. Flow cytometry offers rapid, high-throughput, multiparameter-based analysis of intracellular protein expression in statistically significant no. of cells at single cell resolution. In past few decades, customized assays have been developed for flow cytometric detection of specific intracellular proteins. This review discusses the scope of flow cytometry for intracellular protein detection in mammalian cells along with specific applications. Technological advancements to overcome the limitations of traditional flow cytometry for the same are also discussed.

Flow cytometry: principles, applications and recent advances

Flow cytometry (FCM) is a sophisticated technique that works on the principle of light scattering and fluorescence emission by the specific fluorescent probe-labeled cells as they pass through a laser beam. It offers several unique advantages as it allows fast, relatively quantitative, multiparametric analysis of cell populations at the single cell level. In addition, it also enables physical sorting of the cells to separate the subpopulations based on different parameters. In this constantly evolving field, innovative technologies such as imaging FCM, mass cytometry and Raman FCM are being developed in order to address limitations of traditional FCM. This review explains the general principles, main applications and recent advances in the field of FCM.

JAK Inhibition Impairs NK Cell Function in Myeloproliferative Neoplasms

Ruxolitinib is a small-molecule inhibitor of the JAK kinases, which has been approved for the treatment of myelofibrosis, a rare myeloproliferative neoplasm (MPN), but clinical trials are also being conducted in inflammatory-driven solid tumors. Increased infection rates have been reported in ruxolitinib-treated patients, and natural killer (NK) cells are immune effector cells known to eliminate both virus-infected and malignant cells. On this basis, we sought to compare the effects of JAK inhibition on human NK cells in a cohort of 28 MPN patients with or without ruxolitinib treatment and 24 healthy individuals. NK cell analyses included cell frequency, receptor expression, proliferation, immune synapse formation, and cytokine signaling. We found a reduction in NK cell numbers in ruxolitinib-treated patients that was linked to the appearance of clinically relevant infections. This reduction was likely due to impaired maturation of NK cells, as reflected by an increased ratio in immature to mature NK cells. Notably, the endogenous functional defect of NK cells in MPN was further aggravated by ruxolitinib treatment. In vitro data paralleled these in vivo results, showing a reduction in cytokine-induced NK cell activation. Further, reduced killing activity was associated with an impaired capacity to form lytic synapses with NK target cells. Taken together, our findings offer compelling evidence that ruxolitinib impairs NK cell function in MPN patients, offering an explanation for increased infection rates and possible long-term side effects associated with ruxolitinib treatment.

Ginsenoside Rh2 inhibits growth of glioblastoma multiforme through mTor

Being the most malignant primary brain tumor in humans, glioblastoma multiforme (GBM) has a fairly poor patient survival after current combined treatment with chemotherapy, radiation, and surgery. Ginsenoside Rh2 (GRh2) has been reported to have a therapeutic effect on some tumors, and we recently reported its inhibitory effect on GBM growth in vitro and in vivo, possibly through an epidermal growth factor receptor (EGFR) signaling pathway. Here, using specific inhibitors, we found that the activation of EGFR signaling promoted GBM growth through PI3k/Akt/mTor signaling pathways. Moreover, GRh2 efficiently inhibited activation of this pathway at the receptor level. Together with our previous findings, these data suggest that GRh2 may suppress GBM growth through its competition with EGFR ligands for binding to the EGFR, and binding to EGFR by GRh2 does not lead to receptor phosphorylation. Thus, our data highlight a previous unappreciated role for GRh2 to inhibit EGFR signaling. GRh2 thus appears to be a promising therapy for cancers that require EGFR signaling to growth.

Inhibition of FoxO1 nuclear exclusion prevents metastasis of glioblastoma

Glioblastoma is the most aggressive malignant primary brain tumor in humans, with extremely poor patient survival. Although previous studies have demonstrated that expression of matrix metalloproteinase-9 (MMP9) in glioblastoma promotes cancer metastasis, the upstream molecular signaling cascades that control activation of MMP9 remain largely unknown. Here, we used a human glioblastoma line, A-172, to examine molecular signaling to activate MMP9. We found that epidermal growth factor (EGF)-induced activation of epidermal growth factor receptor (EGFR) in A-172 cells activated MMP9, resulting in an increase in cancer invasiveness. A specific inhibitor for EGFR efficiently blocked EGF-induced activation of MMP9 and then cancer invasiveness. Moreover, an inhibitor for phosphatidylinositol 3-kinase (PI-3 K)/protein kinase B (Akt) significantly inhibited the EGF-induced activation of MMP9. Furthermore, nuclear exclusion of a major Akt downstream target, Forkhead box protein O1 (FoxO1), was induced by Akt activation, which could be inhibited by either an EGFR inhibitor or by PI-3 K/Akt inhibitor. An expression of a constitutive nuclear form of FoxO1 significantly inhibited MMP9 activation induced by EGF. Taken together, these findings suggest that EGF/EGFR signaling activates downstream PI-3 K/Akt to induce FoxO1 nuclear exclusion, which activates MMP9 to promote glioblastoma invasiveness. Thus, FoxO1 appears to be a novel therapeutic target for inhibiting metastasis of glioblastoma.

EGFR signaling-dependent inhibition of glioblastoma growth by ginsenoside Rh2

Glioblastoma is the most common and most aggressive malignant primary brain tumor in humans, accounting for 52 % of all functional tissue brain tumor cases and 20 % of all intracranial tumors. The typical treatment involves a combination of chemotherapy, radiation, and surgery, whereas it still achieves fairly poor patient survival. Ginsenoside Rh2 has been reported to have a therapeutic effect on some tumors, but its effect on glioblastoma has not been extensively evaluated. Here, we show that ginsenoside Rh2 can substantially inhibit the growth of glioblastoma in vitro and in vivo in a mouse model. Moreover, the inhibition of the tumor growth appears to result from combined effects on decreased tumor cell proliferation and increased tumor cell apoptosis. Further analyses suggest that ginsenoside Rh2 may have its antiglioblastoma effect through inhibition of the epidermal growth factor receptor (EGFR) signaling pathway in tumor cells. In a lose-of-function experiment, recombinant EGFR was given together with ginsenoside Rh2 to the tumor cells in vitro and in vivo, which completely blocked the antitumor effects of ginsenoside Rh2. Thus, our data not only reveal an anti-glioblastoma effect of ginsenoside Rh2 but also demonstrate that this effect may function via inhibition of EGFR signaling in glioblastoma cells.

Cell signalling analyses in the functional genomics era

The advancements in proteomics over the past decade have brought tremendous increases in sensitivity of mass spectrometry (MS) analyses and new technologies such as methods for quantitative MS and phosphoproteomics. The development of antibodies targeting a large fraction of the human proteome as well as specific antibodies that detect phosphorylations and other post-translational modifications now allows detection of a great variety of signalling marks. Combined with medium and high throughput methods for detecting many parallel signalling events such as phospho-flow cytometry analyses and MS-based analyses to identify signalling complexes, the available tools now allows analysis of whole signalling networks facilitating systems level understanding of cellular signalling. The even more recent advances in chemical biology and chemical proteomics are further enhancing the development in this area by providing a cache of small molecule compounds allowing perturbations of signal pathways further advancing our global understanding of the signal transduction dynamics at the single cell level as well as in cellular system, tissue and whole organs. This review highlights the recent advances of quantitative MS, phosphoflow cytometry and chemical biology with focus on the dynamic spatiotemporal phosphorylation events, and examples of their application.