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J. Biol. Chem., Vol. 282, Issue 51, 37276-37284, December 21, 2007

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BAG-1 Associates with Hsc70·Tau Complex and Regulates the Proteasomal Degradation of Tau Protein^*

Evan Elliott, Peter Tsvetkov, and Irith Ginzburg¹

From the Departments of Neurobiology and Biological Regulation, Weizmann Insitute of Science, Rehovot, Israel 76100

Intraneuronal accumulation of phosphorylated Tau protein is a molecular pathology found in many forms of dementia, including Alzheimer disease. Research into possible mechanisms leading to the accumulation of modified Tau protein and the possibility of removing Tau protein from the system have revealed that the chaperone protein system can interact with Tau and mediate its degradation. Hsp70/Hsc70, a member of the chaperone protein family, interacts with Tau protein and mediates proper folding of Tau and can promote degradation of Tau protein under certain circumstances. However, because Hsp70/Hsc70 has many binding partners that can mediate its activity, there is still much to discover about how Hsp70 acts in vivo to regulate Tau protein. BAG-1, an Hsp70/Hsc70 binding partner, has been implicated as a mediator of neuronal function. In this work we show that BAG-1 associates with Tau protein in an Hsc70-dependent manner. Overexpression of BAG-1 induced an increase in Tau levels, which is shown to be due to an inhibition of protein degradation. We further show that BAG-1 can inhibit the degradation of Tau protein by the 20 S proteasome but does not affect the ubiquitination of Tau protein. RNA-mediated interference depletion of BAG-1 leads to a decrease in total Tau protein levels as well as promoting hyperphosphorylation of the remaining protein. Induction of Hsp70 by heat shock enhanced the increase of Tau levels in cells overexpressing BAG-1 but induced a decrease of Tau levels in cells that were depleted of BAG-1. Finally, BAG-1 is highly expressed in neurons bearing Tau tangles in a mouse model of Alzheimer disease. This data suggests a molecular mechanism through which Tau protein levels are regulated in the cell and possible consequences for the pathology and treatment of Alzheimer disease.

Received for publication, August 2, 2007 , and in revised form, September 25, 2007.

^* This work was supported in part by Israel Science Foundation Grant 03454, by the Benoziyo Center for Neurological Diseases, and by the R. Solis Foundation, Weizmann Institute of Science grants (to I. G.). 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.

¹ Holds the Sophie and Richard S. Richards Professorial Chair in Cancer Research. To whom correspondence should be addressed. Tel.: 972-8-934-2799; Fax: 972-8-934-4131; E-mail: irith.ginzburg{at}weizmann.ac.il.

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