Role of G proteins and ERK activation in hemin-induced erythroid differentiation of K562 cells.
ABSTRACT Heterotrimeric G proteins which couple extracellular signals to intracellular effectors play a central role in cell growth and differentiation. The pluripotent erythroleukemic cell line K562 that acquires the capability to synthesize hemoglobin in response to a variety of agents can be used as a model system for erythroid differentiation. Using Western blot analysis and RT-PCR, we studied alterations in G protein expression accompanying hemin-induced differentiation of K562 cells. We demonstrated the presence of G(alpha s), G(alpha i2) and G(alpha q) and the absence of G(alpha i1), G(alpha o) and G(alpha 16) in K562 cells. We observed the short form of G(alpha s) to be expressed predominantly in these cells. Treatment of K562 cells with hemin resulted in an increase in the levels of G(alpha s) and G(alpha q). On the other hand, the level of G(alpha i2) was found to increase on the third day after induction with hemin, followed by a decrease to levels lower of those of uninduced cells. The mitogen-activated protein kinase ERK1/2 pathway is crucial in the control of cell proliferation and differentiation. Both Gi- and Gq-coupled receptors stimulate MAPK activation. We therefore examined the phosphorylation of ERK1/2 during hemin-induced differentiation of K562 cells. Using anti-ERK1/2 antibodies, we observed that ERK2 was primarily phosphorylated in K562 cells. ERK2 phosphorylation increased gradually until 48 h and returned to basal values by 96 h following hemin treatment. Our results suggest that changes in G protein expression and ERK2 activity are involved in hemin-induced differentiation of K562 cells.
Conference Paper: Soon: self organising oscillator networks for use in clustering problems[Show abstract] [Hide abstract]
ABSTRACT: The self-organising oscillator network (SOON) is a comparatively new clustering algorithm [H.F.M.B.H. Rhouma, February 2001], that has received relatively little attention so far. The SOON is distance based, meaning that clustering behaviour is different in a number of ways that can be beneficial. This paper examines the effect of adjusting the control parameters of the SOON with two widely different datasets which represent two different types of real-world data; the first is a communications signal dataset representing one modulation scheme under a variety of noise conditions. The second is a biological dataset taken from microarray experiments on the cell-cycle of yeast. The modulation scheme data is relatively easy to cluster at high SNR, however at lower SNR, the clustering problem becomes much more difficult as the separation between the cluster reduces. The paper demonstrates that the SOON is a viable tool to analyse these problems, and can add many useful insights to the data, that may not always be available using other clustering methodsMachine Learning for Signal Processing, 2004. Proceedings of the 2004 14th IEEE Signal Processing Society Workshop; 01/2004
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ABSTRACT: Diallyl disulfide (DADS) is a major constituent of garlic. Previously, we found that DADS both inhibited proliferation in human gastric cancer cells in vitro and in vivo, and induced G2/M arrest. In this study, we investigated whether this differentiation effect was induced by DADS in human gastric cancer MGC803 cells, and whether it was related to an alteration in ERK activity. The results showed that the growth of MGC803 cells was inhibited by DADS. Cells treated with DADS displayed a lower nucleocytoplasmic ratio and tended to form gland and intercellular conjunction structures. The ConA-mediated cell agglutination ratio and cells' ALP specific activity decreased. In MGC803 cells, dye transfer was limited to a few cells neighbouring the dye-injected cell and to a depth of 1-2 layers beneath the scrape site. However, after treatment with DADS, the LY (Lucifer Yellow) was transferred to several cells immediately neighbouring the microinjected cell and to a depth of 2-4 cell layers from the scrape site. This indicated that DADS induced differentiation in MGC803 cells. Western blot analysis revealed that although DADS did not influence the quantity of ERK1/2 protein expressed, it did decrease its phosphorylation in a concentration-dependent manner, compared with the controls. At 30 mg x L(-1), DADS inhibited the activation of ERK1/2 in 15-30 min. These results suggested that the DADS-induced differentiation of MGC803 cells involved an alteration of the ERK1/2 signaling pathway.Cellular & Molecular Biology Letters 02/2006; 11(3):408-23. · 1.95 Impact Factor
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ABSTRACT: HIV-1 triggers infection through interaction with the CD4 receptor and the chemokine receptors, CCR5 or CXCR4, on host cells. The involvement of signaling via the chemokine receptors in viral infection remains an issue of debate. We have previously reported that Galphai1 is involved in the signaling triggered by R5 HIV-1 strains through CCR5 binding to facilitate viral replication in unstimulated peripheral blood mononuclear cells. In this study, we pursued the identification of the downstream signaling molecules in CCR5-mediated infection. We also questioned whether CXCR4 using HIV-1 strains induce the same signaling mechanism. We analyzed by western blotting the coreceptor-mediated activation of various mitogen-acitvated protein kinases, including extracellular signal-regulated kinase (ERK)1/2, p38 and c-jun N-terminal kinase in non-stimulated human peripheral blood mononuclear cells. The involvement of Galphai protein in ERK1/2 activation was tested using pertussis toxin. Using real-time PCR, we studied the role of ERK1/2 in the life cycle of HIV-1. We found that pertussis toxin inhibited the replication of X4 as well as R5 strains. Furthermore, both strains activated a pertussis toxin-sensitive mitogen-activated protein kinase pathway involving mitogen-activated protein kinase kinases-1/2 and ERK1/2. The inhibition of ERK1/2 activation by U0126 and PD98059 blocked both R5 and X4 HIV-1 replication. Furthermore, ERK1/2 activity was required for the completion of HIV-1 reverse transcription. Our results show that R5 and X4 HIV-1 strains induce the same Galphai-dependent ERK pathway that facilitates reverse transcription. The identification of the signaling pathway required for optimal viral replication sheds a new light on HIV physiopathology and opens new therapeutic possibilities.AIDS (London, England) 09/2008; 22(13):1569-76. · 4.91 Impact Factor