Journal of Korean Endocrine Society 2004;19(5):501-510.
Published online October 1, 2004.
The Abundance and Nuclear Distribution of TonEBP in Response to Changes of Tonicity in Hyperglycemic Cells .
Won Kun Park
Department of Internal Medicine, Samsung Cheil Hospital & Women's Healthcare Center, Sungkyunkwan University School of Medicine, Seoul, Korea.
Abstract
BACKGROUND
TonEBP (Tonicity-responsive enhancer binding protein) regulates the transcription of tonicity responsive genes, such as sodium-myo-inositol and the sodium- chloride-betaine co- transporters (SMIT & BGT1), heat shock protein 70 (HSP70) and aldose reductase (AR). To characterize the signals that activate TonEBP in hyperglycemic human retinal pigment epithelial (hRPE) cells, the abundance and nuclear distribution of TonEBP were studied in response to changes of tonicity in culture media. METHODS: After the cultures reached confluence, the hRPE cells were exposed for 3 days to 25 mM glucose and 100 mM NaCl, both with and without 20 M tolrestat. The expressions of AR, SMIT and HSP 70 were determined by northern blot, and the abundances of TonEBP by western blot. The nuclear distributions of TonEBP were observed by fluorescence microscopy, after immuno staining. RESULTS: The AR and SMIT mRNA levels in hyperglycemic and hypertonic media were decreased compared to those in hypertonic media alone. These decreased AR and SMIT mRNA expressions were also observed to be significantly prevented in those cells incubated with tolrestat. Stimulation of TonEBP in hypertonic medium occurs due to a combination of an increased abundance of TonEBP and an increased distribution into the nucleus from the cytoplasm. However, the expressions and nuclear distributions of TonEBP in hyperglycemic and hypertonic media were not different from those in hypertonic media alone. CONCLUSION: The expressions of AR and SMIT genes that may influence the development of diabetic complication were down-regulated by the intracellular accumulation of sorbitol in sustained hyperglycemia. TonEBP does not play a key role in the hypertonicity-induced transcriptional regulation of AR and SMIT in hyperglycemic cells, due to the intracellular accumulation of sorbitol and depletion of myo-inositol
Key Words: TonEBP, AR, SMIT, Hyperglycemia, Hypertonicity
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