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J. Biol. Chem., Vol. 280, Issue 27, 25864-25870, July 8, 2005
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From the Department of Molecular and Cellular Physiology, Tufts University School of Medicine, Boston, Massachusetts 02111
Chaperone-mediated autophagy (CMA) is a selective lysosomal protein
degradative process that is activated in higher organisms under conditions of
prolonged starvation and in cell culture by the removal of serum. Ketone
bodies are comprised of three compounds (
-hydroxybutyrate, acetoacetate,
and acetone) that circulate during starvation, especially during prolonged
starvation. Here we have investigated the hypothesis that ketone bodies induce
CMA. We found that physiological concentrations of
-hydroxybutyrate
(BOH) induced proteolysis in cells maintained in media with serum and without
serum; however, acetoacetate only induced proteolysis in cells maintained in
media with serum. Lysosomes isolated from BOH-treated cells displayed an
increased ability to degrade both glyceraldehyde-3-phosphate dehydrogenase and
ribonuclease A, substrates for CMA. Isolated lysosomes from cells maintained
in media without serum also demonstrated an increased ability to degrade
glyceraldehyde-3-phosphate dehydrogenase and ribonuclease A when the reaction
was supplemented with BOH. Such treatment did not affect the levels of
lysosome-associated membrane protein 2a or lysosomal heat shock cognate
protein of 70 kDa, two rate-limiting proteins in CMA. However, pretreatment of
glyceraldehyde-3-phosphate and ribonuclease A with BOH increased their rate of
degradation by isolated lysosomes. Lysosomes pretreated with BOH showed no
increase in proteolysis, suggesting that BOH acts on the substrates to
increase their rates of proteolysis. Using OxyBlotTM analysis to detect
carbonyl formation on proteins, one common marker of protein oxidation, we
showed that treatment of substrates with BOH increased their oxidation.
Neither glycerol, another compound that increases in circulation during
prolonged starvation, nor butanol or butanone, compounds closely related to
BOH, had an effect on CMA. The induction of CMA by ketone bodies may provide
an important physiological mechanism for the activation of CMA during
prolonged starvation.
Received for publication, March 4, 2005 , and in revised form, April 22, 2005.
* The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
To whom correspondence should be addressed: Dept. of Molecular and Cellular
Physiology, Tufts University School of Medicine, Arnold 809, 136 Harrison
Ave., Boston, MA 02111. Tel.: 617-636-0408; Fax: 617-636-0445; E-mail:
Patrick.Finn{at}tufts.edu.
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