The Role of Polyamines in Supporting Growth of Mammalian Cells Is Mediated through Their Requirement for Translation Initiation and Elongation

Guy Landau,Zippi Bercovich,Myung Hee Park,Chaim Kahana

doi:10.1074/jbc.m110.106419

Abstract

Polyamines are essential cell constituents whose depletion results in growth cessation. Here we have investigated potential mechanisms of action of polyamines in supporting mammalian cell proliferation. We demonstrate that polyamines regulate translation both at the initiation and at the elongation steps. L-alpha-difluoromethylornithine treatment resulting in polyamine depletion reduces protein synthesis via inhibition of translation initiation. N1-guanyl-diaminoheptane (GC7), a spermidine analogue that inhibits eukaryotic initiation factor 5A (eIF5A) hypusination, also caused inhibition of translation initiation. In contrast, depletion of eIF5A by short hairpin RNA inhibits translation elongation as was recently demonstrated in yeast and Drosophila. These results suggest that in addition to competing with spermidine in the hypusination reaction, GC7 also competes with spermidine at yet undefined sites required for translation initiation. Finally, we show that either polyamine depletion or GC7 treatment induced eIF2alpha phosphorylation and reduced phosphorylation of 4E-BP, thus setting the molecular basis for the observed inhibition of translation initiation.

Highlights

The polyamines are small organic polycations that are essential for the process of cellular proliferation as their depletion leads to growth inhibition [1, 2]
The requirement of eukaryotic initiation factor 5A (eIF5A) hypusination for cell growth raised the possibility that eIF5A hypusination may represent the major or even the entire requirement of polyamines for cellular proliferation [7, 15, 16]. eIF5A, which was originally suggested to function as a translation initiation factor [17], was recently demonstrated to function in regulating translation elongation in yeast and Drosophila [18,19,20]
We show here that polyamines are required for the translation process in mammalian cells both at the initiation and at the elongation steps and that as suggested before [16, 38, 39], the requirement of polyamines in these translational processes is likely to account for their essentiality in the process of cellular proliferation

Summary

Introduction

The polyamines are small organic polycations that are essential for the process of cellular proliferation as their depletion leads to growth inhibition [1, 2]. Their exact mode of action is far from being resolved, they are suggested to play important roles in regulating fundamental cellular processes such as signaling, replication, transcription, and translation [2]. We show that in addition to regulating translation elongation through eIF5A hypusination, polyamines regulate translation initiation through an eIF5Aindependent mechanism by modulating phosphorylation of eIF2␣ and 4E-BP1, two key regulators of the process of translation initiation

Methods

Results

Conclusion