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1 Indiana Center for Biological Microscopy, Division of Nephrology, Department of Medicine, Indiana University School of Medicine and Roudebush Veterans Affairs Medical Center, Indianapolis, Indiana 46202; and 2 Division of Nephrology, Department of Medicine, University Hospital Essen, Essen, Germany
Disruption of the actin cytoskeleton in proximal tubule cells is a key pathophysiological factor in acute renal failure. To investigate dynamic alterations of the actin cytoskeleton in live proximal tubule cells, LLC-PK10 cells were transfected with an enhanced yellow fluorescence protein (EYFP)-actin construct, and a clone with stable EYFP-actin expression was established. Confluent live cells were studied by confocal microscopy under physiological conditions or during ATP depletion of up to 60 min. Immunoblots of stable transfected LLC-PK10 cells confirmed the presence of EYFP-actin, accounting for 5% of total actin. EYFP-actin predominantly incorporated in stress fibers, i.e., cortical and microvillar actin as shown by excellent colocalization with Texas red phalloidin. Homogenous cytosolic distribution of EYFP-actin indicated colocalization with G-actin as well. Beyond previous findings, we observed differential subcellular disassembly of F-actin structures: stress fibers tagged with EYFP-actin underwent rapid and complete disruption, whereas cortical and microvillar actin disassembled at slower rates. In parallel, ATP depletion induced the formation of perinuclear EYFP-actin aggregates that colocalized with F-actin. During ATP depletion the G-actin fraction of EYFP-actin substantially decreased while endogenous and EYFP-F-actin increased. During intracellular ATP repletion, after 30 min of ATP depletion, there was a high degree of agreement between F-actin formation from EYFP-actin and endogenous actin. Our data indicate that EYFP-actin did not alter the characteristics of the endogenous actin cytoskeleton or the morphology of LLC-PK10 cells. Furthermore, EYFP-actin is a suitable probe to study the spatial and temporal dynamics of actin cytoskeleton alterations in live proximal tubule cells during ATP depletion and ATP repletion.
actin cytoskeleton; green fluorescent protein; live imaging; renal proximal tubule cell; enhanced yellow fluorescent protein
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