Role of isoprenoids in cytoskeleton integrity and albumin endocytosis by opossum kidney cells.
BACKGROUND
The actin cytoskeleton has been increasingly implicated in endocytic events that are involved in the reabsorption of filtered protein by the proximal tubule. Isoprenylated small G proteins have emerged as key regulators of the actin cytoskeleton. This study examines the role of isoprenoid intermediates in organization of the cytoskeleton, and the effect of modification of the cytoskeleton on albumin endocytosis.


METHODS
The effect of lovastatin on cytoskeleton morphology of opossum kidney cells (OK cells) was determined by staining with fluorescent isothiocyanate (FITC)-phalloidin followed by examination using confocal microscopy. Quantitative effects on albumin binding and uptake were determined using a well-established method.


RESULTS
Inhibition of isoprenoid synthesis by lovastatin led to morphological disruption of the cytoskeleton with a concentration-dependent decrease in albumin uptake into OK cells. Addition of mevalonate, but not cholesterol, ameliorated the effects of lovastatin on the cytoskeleton and albumin uptake. Selective inhibition of isoprenoid intermediates with a farnesyltransferase inhibitor suggests that geranylgeranylated proteins mediate cytoskeleton organization.


CONCLUSIONS
These results confirm the importance of cytoskeleton integrity in albumin endocytosis in renal proximal tubules. While the present data suggest that synthesis of isoprenoids via the mevalonate pathway is a critical step in maintenance of the cytoskeleton, the role of individual small G proteins in control of the cytoskeleton and other endocytic events is yet to be defined.
Victorian Paediatric Renal Service, Royal Children's Hospital, University of Melbourne, Parkville, Vic., Australia. steven_mctaggart@health.qld.gov.au
Steven J
SJ
McTaggart
Eveline
E
Eitle
Peter J
PJ
Harris
Colin L
CL
Jones
D000418:Albumins / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D002784:Cholesterol / Q000096:biosynthesis; D003599:Cytoskeleton / Q000737:chemistry*; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors / Q000494:pharmacology; D007668:Kidney / Q000166:cytology / Q000502:physiology*; D009893:Opossums; D013729:Terpenes / Q000378:metabolism*
D000418:Albumins; D019161:Hydroxymethylglutaryl-CoA Reductase Inhibitors; D013729:Terpenes; D002784:Cholesterol