SCF and G-CSF lead to the synergistic induction of proliferation and gene expression through complementary signaling pathways

Reparative Effects of Stem Cell Factor and Granulocyte Colony-Stimulating Factor in Aged APP/PS1 Mice

Alzheimer's disease (AD), characterized by the accumulation of β-amyloid (Aβ) plaques and tau neurofibrillary tangles in the brain, neuroinflammation and neurodegeneration, is the most common form of neurodegenerative disease among the elderly. No effective treatment is available now in restricting the pathological progression of AD. The aim of this study is to determine the therapeutic efficacy of stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF) (SCF+G-CSF) in aged APPswe/PS1dE9 (APP/PS1) mice. SCF+G-CSF was subcutaneously injected for 12 days to 25-month-old male APP/PS1 mice. We observed that SCF+G-CSF treatment reduced the Aβ plaques in both the cortex and hippocampus. SCF+G-CSF treatment increased the association of TREM2+/Iba1+ cells with Aβ plaques and enhanced Aβ uptake by Iba1+ and CD68+cells in the brains of aged APP/PS1 mice. Importantly, cerebral expression area of P2RY12+and TMEM119+ homeostatic microglia and the branches of P2RY12+ homeostatic microglia were increased in the SCF+G-CSF-treated aged APP/PS1 mice. SCF+G-CSF treatment also decreased NOS-2 and increased IL-4 in the brains of aged APP/PS1 mice. Moreover, the loss of MAP2+dendrites and PSD-95+post-synapses and the accumulation of aggregated tau in the brains of aged APP/PS1 mice were ameliorated by SCF+G-CSF treatment. Furthermore, the density of P2RY12+ microglia was negatively correlated with Aβ deposits, but positively correlated with the densities of MAP2+ dendrites and PSD-95+ puncta in the brains of aged APP/PS1 mice. These findings reveal the therapeutic potential of SCF+G-CSF treatment in ameliorating AD pathology at the late stage.

Mitogenic signals initiated via interleukin-6 receptor complexes in cooperation with other transmembrane molecules in myelomas

Cytokines exert multiple biological functions through binding to their specific receptors that triggers activation of intracellular signaling cascades. The cytokine-mediated signals may produce variable and even opposing effects on different cell types, depending on cellular context that is also dictated by the differentiation stage of the cell. Multiple myeloma (MM) is a monoclonal proliferative disorder of human plasma cells. Myeloma cells appear to include mixed subpopulations in accordance with the expression of their surface antigens, such as CD45. Although interleukin-6 (IL-6) is widely accepted as the most relevant growth factor for myeloma cells, only a few subpopulations of tumor cells, such as CD45(+) immature cells, proliferate in response to IL-6. The activation of both signal transducer and activator of transcription (STAT) 3 and extracellular signal-regulated kinase (ERK) 1/2 is not sufficient for IL-6-induced proliferation of myeloma cells that requires the src family kinase activation associated with a rapid translocation of CD45 to lipid rafts. The CD45 expression renders myeloma cells competent for not only mitogenic but also apoptotic stimuli, resulting in either proliferation or apoptosis of CD45(+) myeloma cells dependently upon the circumstantial stimuli. In contrast, in CD45(-) myeloma cells highly expressing IL-6 receptor alpha chain (IL-6Ralpha), IL-6Ralpha and insulin-like growth factor (IGF)-I receptors exist on plasma membrane in close proximity, facilitating efficient assembly of two receptors in response to IL-6. The synergistic effects of IL-6Ralpha on IGF-I receptor-mediated signals provide a novel insight into a Jak-independent IL-6 signaling mechanism of receptor cross talk in human myeloma cells. Furthermore, the signaling cross talk between the cytokine receptor, IL-6Ralpha/gp130 and the growth factor receptor tyrosine kinase, fibroblast growth factor receptor (FGFR) 3 appears in myeloma cells carrying t(4;14)(p16.3;q32). In this review we propose several mechanisms of the IL-6-induced cell proliferation that is strictly dependent upon the cellular context in myelomas.

Mad2 is required for optimal hematopoiesis: Mad2 associates with c-Kit in MO7e cells

Mitotic arrest deficiency 2 (Mad2) is a component of mitotic spindle checkpoint proteins and is essential for accurate chromosome segregation. We investigated a role for Mad2 in hematopoiesis using Mad2-haploinsufficient (Mad2+/-) mice. Mad2+/- bone marrow (BM) and spleen manifested decreased absolute numbers and cycling status of immature, but not mature, hematopoietic progenitor cells. Mad2+/- BM granulocyte-macrophage colony-forming units (CFU-GMs) did not manifest synergistic proliferation in response to stem cell factor (SCF) plus GM-CSF. The percentage of annexin V+ cells was higher in Mad2+/- than Mad2+/+c-Kit+lin- BM after culture with SCF and GM-CSF. However, no significant difference in phosphorylation of extracellular signal-related kinase (Erk1/2) at Thr202/Tyr204 and Akt at Ser473 between Mad2+/- and Mad2+/+BM c-Kit+lin- cells was observed. Immunoprecipitation assays performed in human MO7e cells demonstrated physical association of c-Kit with Mad2. Moreover, stimulation with SCF plus GM-CSF led to dissociation of Mad2 from c-Kit. Confocal microscopy demonstrated that Mad2 colocalized with c-Kit in the cytoplasm of MO7e cells. These results suggest that Mad2 is involved in synergistic growth of immature hematopoietic progenitor cells in response to SCF plus GM-CSF, effects that may be mediated via physical association of Mad2 with c-Kit.

Signal transducer and activator of transcription 3 is required for the oncogenic effects of non-small-cell lung cancer-associated mutations of the epidermal growth factor receptor

Somatic mutations in the epidermal growth factor receptor (EGFR) occur frequently in lung cancer and confer sensitivity to EGFR kinase inhibitors gefitinib and erlotinib. These mutations, which occur in the kinase domain of the protein, also render EGFR constitutively active and transforming. Signal transducers and activators of transcription 3 (STAT3) transduces signals from a number of oncogenic tyrosine kinases and contributes to a wide spectrum of human malignancies. Here, we show that STAT3 is activated by mutant EGFRs and is necessary for its downstream phenotypic effects. Inhibiting STAT3 function in fibroblasts abrogates transformation by mutant EGFR. In non-small-cell lung cancer cells, STAT3 activity is regulated by EGFR through modulation of STAT3 serine phosphorylation. Inhibiting STAT3 function increases apoptosis of these cells, suggesting that STAT3 is necessary for their survival. Finally, a group of genes constituting a STAT3 signature is enriched in lung tumors with EGFR mutations. Thus, STAT3 is a critical mediator of the oncogenic effects of somatic EGFR mutations and targeting STAT3 may be an effective strategy for treating tumors characterized by these mutations.