A Protective Role for the Human SMG-1 Kinase against Tumor Necrosis Factor-α-induced Apoptosis

Vasco Oliveira,William J Romanow,Christoph Geisen,Diane M Otterness,Frank Mercurio,Hong Gang Wang,William S Dalton,Robert T Abraham

doi:10.1074/jbc.m708008200

Abstract

The human suppressor of morphogenesis in genitalia-1 (hSMG-1) protein kinase plays dual roles in mRNA surveillance and genotoxic stress response pathways in human cells. Here, we report that small interfering RNA-mediated depletion of hSMG-1, but not ATM, ATR, hUpf1, or hUpf2, in human U2OS osteosarcoma cells markedly increases the magnitude and accelerates the rate of apoptosis induced by tumor necrosis factor-alpha (TNFalpha) stimulation. The increase in TNFalpha-mediated cell killing observed in hSMG-1-depleted cells is not related to the suppression of nonsense-mediated mRNA decay or to the inhibition of TNFalpha-induced NF-kappaB activation. Rather, we observed that loss of hSMG-1 accelerates the degradation of the long form of the FLICE-inhibitory protein (FLIP(L)), an inhibitor of death-inducing signaling complex-mediated caspase-8 activation, in TNFalpha-treated cells. These results suggest that hSMG-1 plays an important role in cell survival during TNFalpha-induced stress.

Highlights

Members of the phosphoinositide 3-kinase-related kinase (PIKK)3 family play central roles in cell growth and stress response pathways [1]
HSMG-1 Protects U2OS Cells against TNF␣-induced Apoptosis—Preliminary studies aimed at defining the subcellular localization of human suppressor of morphogenesis in genitalia-1 (hSMG-1) revealed that this PIKK is predominantly expressed in the cytoplasm, as reported previously [13]
Based on the central role of mitochondria in apoptotic cell death, we examined the effects of several apoptosis-inducing stimuli in U2OS cells depleted of hSMG-1 by transfection with multiple specific siRNAs

Summary

Introduction

Members of the phosphoinositide 3-kinase-related kinase (PIKK)3 family play central roles in cell growth and stress response pathways [1]. Based on the central role of mitochondria in apoptotic cell death, we examined the effects of several apoptosis-inducing stimuli in U2OS cells depleted of hSMG-1 by transfection with multiple specific siRNAs. In preliminary experiments, we observed that hSMG-1 depletion dramatically accelerated and magnified the apoptotic response induced by the combination of TNF␣ plus the protein synthesis inhibitor, CHX (results not shown).

Results

Conclusion