H. Alex Brown
Principle Investigator; Professor of Pharmacology, Chemistry, and Biochemistry; Associate Director, VICB;
Last active: 2/12/2015

PLD1 regulates mTOR signaling and mediates Cdc42 activation of S6K1.

Fang Y, Park IH, Wu AL, Du G, Huang P, Frohman MA, Walker SJ, Brown HA, Chen J
Curr Biol. 2003 13 (23): 2037-44

PMID: 14653992 · DOI:10.1016/j.cub.2003.11.021

BACKGROUND - The mammalian target of rapamycin (mTOR) regulates cell growth and proliferation via the downstream targets ribosomal S6 kinase 1 (S6K1) and eukaryotic translation initiation factor 4E binding protein 1 (4E-BP1). We have identified phosphatidic acid (PA) as a mediator of mitogenic activation of mTOR signaling. In this study, we set out to test the hypotheses that phospholipase D 1 (PLD1) is an upstream regulator of mTOR and that the previously reported S6K1 activation by Cdc42 is mediated by PLD1.

RESULTS - Overexpression of wild-type PLD1 increased S6K1 activity in serum-stimulated cells, whereas a catalytically inactive PLD1 exerted a dominant-negative effect on S6K1. More importantly, eliminating endogenous PLD1 by RNAi led to drastic inhibition of serum-stimulated S6K1 activation and 4E-BP1 hyperphosphorylation in both HEK293 and COS-7 cells. Knockdown of PLD1 also resulted in reduced cell size, suggesting a critical role for PLD1 in cell growth control. Using a rapamycin-resistant S6K1 mutant, Cdc42's action was demonstrated to be through the mTOR pathway. When Cdc42 was mutated in a region specifically required for PLD1 activation, its ability to activate S6K1 in the presence of serum was hindered. However, when exogenous PA was used as a stimulus, the PLD1-inactive Cdc42 mutant behaved similarly to the wild-type protein.

CONCLUSIONS - Our observations reveal the involvement of PLD1 in mTOR signaling and cell size control, and provide a molecular mechanism for Cdc42 activation of S6K1. A new cascade is proposed to connect mitogenic signals to mTOR through Cdc42, PLD1, and PA.

MeSH Terms (14)

Animals Blotting, Western Carrier Proteins cdc42 GTP-Binding Protein COS Cells Gene Expression Models, Biological Phospholipase D Phosphoproteins Precipitin Tests Protein Kinases Ribosomal Protein S6 Kinases, 90-kDa Signal Transduction TOR Serine-Threonine Kinases

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