Research

siRNA screen of the human signaling proteome identifies the PtdIns(3,4,5)P₃-mTOR signaling pathway as a primary regulator of transferrin uptake

Thierry Galvez , Mary N Teruel , Won Do Heo , Joshua T Jones , Man Lyang Kim , Jen Liou , Jason W Myers and Tobias Meyer

Department of Chemical and Systems Biology and Bio-X Program, Stanford University School of Medicine, Stanford, CA 94305, USA

author email corresponding author email

Genome Biology 2007, 8:R142doi:10.1186/gb-2007-8-7-r142

Published:	19 July 2007

Subject areas: Cell biology, Drug discovery, Genetics, Genome studies

Abstract

Background

Iron uptake via endocytosis of iron-transferrin-transferrin receptor complexes is a rate-limiting step for cell growth, viability and proliferation in tumor cells as well as non-transformed cells such as activated lymphocytes. Signaling pathways that regulate transferrin uptake have not yet been identified.

Results

We surveyed the human signaling proteome for regulators that increase or decrease transferrin uptake by screening 1,804 dicer-generated signaling small interfering RNAs using automated quantitative imaging. In addition to known transport proteins, we identified 11 signaling proteins that included a striking signature set for the phosphatidylinositol-3,4,5-trisphosphate (PtdIns(3,4,5)P3)-target of rapamycin (mTOR) signaling pathway. We show that the PI3K-mTOR signaling pathway is a positive regulator of transferrin uptake that increases the number of transferrin receptors per endocytic vesicle without affecting endocytosis or recycling rates.

Conclusion

Our study identifies the PtdIns(3,4,5)P3-mTOR signaling pathway as a new regulator of iron-transferrin uptake and serves as a proof-of-concept that targeted RNA interference screens of the signaling proteome provide a powerful and unbiased approach to discover or rank signaling pathways that regulate a particular cell function.