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


CONCLUSIONS
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.
Galvez
Thierry
T
Department of Chemical and Systems Biology and Bio-X Program, Stanford University School of Medicine, Stanford, CA 94305, USA. galvez@mpi-cbg.de
Teruel
Mary N
MN
Heo
Won Do
WD
Jones
Joshua T
JT
Kim
Man Lyang
ML
Liou
Jen
J
Myers
Jason W
JW
Meyer
Tobias
T
D004705:Endocytosis / Q000187:drug effects; D006801:Humans; D018129:Phosphatidylinositol Phosphates / Q000502:physiology*; D011494:Protein Kinases / Q000235:genetics / Q000502:physiology*; D021381:Protein Transport / Q000187:drug effects; D020543:Proteome / Q000235:genetics / Q000502:physiology*; D040901:Proteomics / Q000379:methods*; D034622:RNA Interference; D034741:RNA, Small Interfering / Q000235:genetics / Q000494:pharmacology; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D014162:Transfection; D014168:Transferrin / Q000378:metabolism*
D018129:Phosphatidylinositol Phosphates; D020543:Proteome; D034741:RNA, Small Interfering; D014168:Transferrin; C060974:phosphatidylinositol 3,4,5-triphosphate; D011494:Protein Kinases; C546842:MTOR protein, human; D058570:TOR Serine-Threonine Kinases