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Articles by S. K Ye
Total Records ( 3 ) for S. K Ye
  S. H Lee , K. H Koo , J. W Park , H. J Kim , S. K Ye , J. B Park , B. K Park and Y. N. Kim

The plasma membrane microdomains, lipid rafts, are involved in regulation of cellular functions such as cell survival and adhesion. Cholesterol is a critical component of lipid rafts in terms of their integrity and functions and rafts disruption by cholesterol depletion can induce detachment-induced cell death. Hypoxia inducible factor-1 (HIF-1) is stabilized in hypoxia and transactivates numerous genes required for cellular adaptation to hypoxia. It is also induced by non-hypoxic stimuli and contributes to cell survival. Because hypoxia inhibits cholesterol synthesis and HIF-1 plays a role in this process, we here explored a possible connection between lipid rafts and HIF-1. We investigated whether HIF-1 is regulated during cholesterol depletion/rafts disruption in A431 cells in normoxic conditions. Methyl-beta cyclodextrin (MβCD), which induces cholesterol depletion, upregulated HIF-1 even under normoxic conditions and this upregulation required epidermal growth factor receptor (EGFR) and extracellular signal-regulated kinase 1 and 2 activation, but not Akt activation. MβCD treatment induced HIF-1 upregulation at both the transcriptional and translational levels but not at the posttranslational levels. In addition, MβCD robustly induced vascular endothelial growth factor production and stimulated an hypoxia response element-driven luciferase reporter activity under normoxic conditions, indicating that MβCD-induced HIF-1 is functionally activated. Both EGFR activity and HIF-1 expression were higher in the attached cells than in the detached cells after MβCD treatment. Furthermore, inhibition of HIF-1 by RNA interference accelerated cell detachment, thus increasing cell death, indicating that HIF-1 expression attenuates MβCD-induced anoikis-like cell death. These data suggest that, depending on cholesterol levels, lipid rafts or membrane fluidity are probably to regulate HIF-1 expression in normoxia by modulating rafts protein activities such as EGFR, and this connection between lipid rafts and HIF-1 regulation may provide cell survival under membrane-disturbing stress.

  S Tani ichi , H. C Lee , S. K Ye and K. Ikuta

The signal of the IL-7R and signal transducers and activators of transcription (STAT) 5 plays an essential role in T-cell development by inducing V–J recombination in the TCR locus. Previously, we have shown that STAT5 binds to the J promoters and controls chromatin accessibility by histone acetylation. However, little is known on control mechanism of V region by the IL-7R. To elucidate the regulation by STAT5, we first analyzed the chromatin status of V region in primary thymocytes. The levels of histone H3 acetylation are high at V5, HsA element and V2 in Rag2–/– thymocytes but low in IL-7R -chain (IL-7R)-deficient early thymocytes, suggesting that IL-7R signaling controls the accessibility of the V region. In addition, high levels of histone H3 acetylation and germ line transcription were induced at V5 and HsA by cytokine and STAT5 in cytokine-dependent Ba/F3 and other hematopoietic cell lines. Importantly, the chromatin accessibility of V5 gene is increased by cytokine signal. Furthermore, STAT5 was not recruited to a non-canonical STAT-binding motif in the endogenous chromatin of the V5 promoter by cytokine stimulation, while STAT5 binds to a consensus motif in the HsA element. In accordance with this result, STAT5 does not directly activate the V5 promoter by reporter assay. These results suggested that while STAT5 directly binds to HsA element and induces its histone acetylation, STAT5 indirectly activates the V5 promoter. Thus, this study implies a potential role of STAT5 in accessibility control of V region, especially at V5 and HsA.

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