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Molecular and Cellular Biology, May 2009, p. 2359-2371, Vol. 29, No. 9
0270-7306/09/$08.00+0 doi:10.1128/MCB.01259-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Dulbecco Telethon Institute at Dibit-San Raffaele, Milan, Italy,1 Whitehead Institute for Biomedical Research, Cambridge, Massachusetts,2 The Johns Hopkins University School of Medicine, Baltimore, Maryland,3 Harvard Medical School, Boston, Massachusetts,4 Beth Israel Deaconess Medical Center, Boston, Massachusetts5
Received 8 August 2008/ Returned for modification 12 August 2008/ Accepted 6 February 2009
Autosomal dominant polycystic kidney disease (ADPKD) is a common genetic disease characterized by bilateral renal cyst formation. Both hyperproliferation and hypertrophy have been previously observed in ADPKD kidneys. Polycystin-1 (PC-1), a large orphan receptor encoded by the PKD1 gene and mutated in 85% of all cases, is able to inhibit proliferation and apoptosis. Here we show that overexpression of PC-1 in renal epithelial cells inhibits cell growth (size) in a cell cycle-independent manner due to the downregulation of mTOR, S6K1, and 4EBP1. Upregulation of the same pathway leads to increased cell size, as found in mouse embryonic fibroblasts derived from Pkd1–/– mice. We show that PC-1 controls the mTOR pathway in a Tsc2-dependent manner, by inhibiting the extracellular signal-regulated kinase (ERK)-mediated phosphorylation of tuberin in Ser664. We provide a detailed molecular mechanism by which PC-1 can inhibit the mTOR pathway and regulate cell size.
Published ahead of print on 2 March 2009.
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