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J. Cell Biol.,
Volume 142, Number 5, September 7, 1998 1313-1324
* Department of Neurological Surgery, 4640 MSC, University of Wisconsin School of Medicine, Madison, Wisconsin 53706; and We demonstrate that NGF couples the rate
of degradation of long-lived proteins in sympathetic
neurons to the rate of protein synthesis. Inhibiting protein synthesis rate by a specific percentage caused an almost equivalent percentage reduction in the degradation rate of long-lived proteins, indicating nearly 1:1
coupling between the two processes. The rate of degradation of short-lived proteins was unaffected by suppressing protein synthesis. Included in the pool of proteins that had increased half-lives when protein
synthesis was inhibited were actin and tubulin. Both of
these proteins, which had half-lives of several days, exhibited no degradation over a 3-d period when protein
synthesis was completely suppressed. The half-lives of
seven other long-lived proteins were quantified and
found to increase by 84-225% when protein synthesis
was completely blocked.
Degradation-synthesis coupling protected cells from
protein loss during periods of decreased synthesis. The
rate of protein synthesis greatly decreased and coupling
between degradation and synthesis was lost after removal of NGF. Uncoupling resulted in net loss of cellular protein and somatic atrophy. We propose that coupling the rate of protein degradation to that of protein
synthesis is a fundamental mechanism by which neurotrophic factors maintain homeostatic control of neuronal size and perhaps growth.
Department of Neurology and Department of Molecular Biology and Pharmacology, Washington University School of
Medicine, St. Louis, Missouri 63110
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