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Abstract: Background: The transcription factor NF-AT plays a key role in the activation of many early immune response genes and is regulated by subcellular localization. NF-AT translocates from the cytoplasm to the nucleus then returns in response to the intracellular calcium level. Methods: We have investigated NF-AT nucleocytoplasmic shuttling in real-time in living cells using NF-ATc1 tagged with the reversibly photoswitchable fluorescence protein, Dronpa. We monitored both nuclear import and export rate of Dronpa-tagged NF-AT in live cells upon stimulation with ionomycin plus calcium (I+Ca2+) or cyclosporin A (CsA). Results: The results show that NF-AT moved into the nucleus within 3–9 min after stimulation and moved back out into the cytoplasm within 15–50 min after CsA addition. In the absence of stimulation, NF-AT stayed in the cytoplasm as in the cells overexpressing GSK-3β, a calcineurin-opposing regulator. General Significance: This semi-quantitative imaging with constant fluorescence provides the basis to detect the real-time effect by several regulators on NF-AT family proteins. [Copyright &y& Elsevier]

Abstract: We constructed a new cell line which stably expressed Cav3.1 and Kir2.1 subunits in HEK293 cells (HEK293/Cav3.1/Kir2.1) in order to investigate the unknown cellular signaling pathways of T-type voltage-dependent calcium channels. The new cell line has a stable resting membrane potential and can activate T-type Ca2+ channels by KCl-mediated depolarization. We showed that Cav3.1 activation resulted in the level of p21ras-GTP in the cells being rapidly decreased during the first 2 min, and then recovering between 2 min and 15 min. The kinetics of ERK activation following Cav3.1 stimulation was also investigated. ERK activation was decreased from 2 min to 5 min after KCl stimulation, which means that Cav3.1 activation reduced ERK activity in the very early stages of activation. In addition, similar results for Cav3.1 activation were also shown in the case of Sos1, Grb2, and Shc, which means that Cav3.1 activation triggers p21ras and that this signal is transferred to ERK by Sos1, Grb2, and Shc. [Copyright &y& Elsevier]