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,Jen Liou,Jason W Myers,Joshua T Jones,Won Heo,Man Kim,Tobias Meyer

doi:10.1186/gb-2007-8-7-r142

Abstract

A survey of 1,804 human dicer-generated signaling siRNAs using automated quantitative imaging identified the phosphatidylinositol-3,4,5-trisphosphate-mTOR signaling pathway as a primary regulator of iron-transferrin uptake.

Highlights

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 nontransformed cells such as activated lymphocytes
This quantification was sufficiently sensitive to measure the time-course of transferrin uptake and recycling (Figure 1d), as well as to detect expected decreases in transferrin uptake when we knocked down elements of the endocytic machinery, μ2 subunit of the AP2 adaptor (AP2M1) or clathrin heavy chain (CLTC), using diced pools of small interfering RNA (siRNA) (Figure 1e)
Our study identifies the PtdIns(3,4,5)P3-mTOR signaling pathway as an important regulator of transferrin uptake, adding a new function to this important regulatory system for cell growth

Summary

Introduction

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 nontransformed cells such as activated lymphocytes. Intracellular iron deficiency leads to cell cycle arrest in G1 phase and apoptosis [3,4], whereas an excess of cytosolic iron causes oxidative stress and necrosis through the production of reactive oxygen species [5]. Since neither iron deficiency nor excess are tolerated by cells, iron uptake and consumption must be tightly coordinated. Most extracellular iron is bound to transferrin and uptake of ironloaded transferrin is mediated primarily by the transferrin receptor ( named TfR1 or TFRC), which is internalized by clathrin-mediated endocytosis [6]. Iron is released from transferrin in the acidic endosomal environment and reaches the cytosol via divalent metal transporter 1 [2,7]. Transferrin and its receptor recycle back to the cell surface where

Methods

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Conclusion