AJP - Renal Physiology, Vol 266, Issue 4 612-F619, Copyright © 1994 by American Physiological Society
Glyceraldehyde-3-phosphate dehydrogenase modifier protein is associated with microtubules in kidney epithelial cells
N. H. Aithal, M. M. Walsh-Reitz, S. Kartha, M. P. Janulis, T. E. Martin and F. G. Toback
Department of Medicine, University of Chicago, Illinois 60637.
After exposure of monkey kidney epithelial cells to a reduced concentration
of K, a known mitogenic signal, the glycolytic enzyme
glyceraldehyde-3-phosphate dehydrogenase (G3PD) is activated by a cytosolic
protein whose function appears to be novel. A monospecific antibody was
used as an immunoprobe to study the contribution of this G3PD modifier
protein (MP) to signal transduction. Raising the extracellular Na
concentration as well as lowering the K concentration of the medium
increased the amount of MP in cytosol and also activated G3PD. Metabolic
labeling of cells followed by preparation of detergent-soluble (cytosolic)
and detergent-resistant (cytoskeletal) fractions, immunoprecipitation, and
sodium dodecyl sulfate-polyacrylamide gel electrophoresis of radiolabeled
immune precipitates suggested that the protein was also associated with
cytoskeleton. Depolymerization of the microtubules with colchicine or
nocodazole increased cytosolic immunoreactive MP, whereas cytochalasin D
had no effect. Taxol, which stabilizes microtubules, blocked the effects of
colchicine or nocodazole. When tubulin, actin, and intermediate filament
fractions of the cytoskeleton were prepared, blotted, and probed with
specific antibodies, MP was found in the tubulin fraction. These
observations suggest that MP is associated with the microtubules and can be
displaced into the cytosol, wherein it could activate G3PD and thereby
stimulate glycolytic production of ATP during mitogenic signal
transduction.
