Increased susceptibility of breast cancer cells to stress mediated inhibition of protein synthesis.
Protein synthesis is a tightly controlled process, and its deregulation plays an important role in tumorigenesis. Protein synthesis remains poorly understood with very few well-identified validated targets for therapeutic purposes. In this study, we use nitric oxide (NO), which suppresses protein synthesis by inactivating eukaryotic initiation factor 2-alpha (eIF2-alpha), to examine the mechanism by which low and high oxidative stress inhibits protein synthesis. In breast cancer cells, low NO stress induced heme-regulated inhibitor (HRI) activation, which facilitated gradual decline in short half-life proteins. High NO stress induced HRI and protein kinase R (PKR) activation, leading to a sharp decline in protein synthesis as accessed by a decline in short and long half-life proteins and dramatic morphologic changes. In contrast, human mammary epithelial (HME) and Ras transfected untransformed HME (MCF-10A1 neo N) cells were less susceptible to NO-induced inhibition of protein synthesis and cytostasis. Our results suggest that NO-induced cytostasis in breast cancer cells was due to PKR activation and increased phosphorylation of eIF2-alpha, whereas the reduced susceptibility of normal mammary epithelial cells to NO could be due to the inaccessibility of PKR, which is bound to inhibitor p58.
Department of Obstetrics and Gynecology, David Geffen School of Medicine at University of California, Los Angeles, USA. spervin@mednet.ucla.edu
Shehla
S
Pervin
An H
AH
Tran
Shaghayegh
S
Zekavati
Jon M
JM
Fukuto
Rajan
R
Singh
Gautam
G
Chaudhuri
D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D001940:Breast / Q000166:cytology / Q000378:metabolism; D001943:Breast Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology*; D002453:Cell Cycle / Q000187:drug effects; D002471:Cell Transformation, Neoplastic; D002478:Cells, Cultured; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D006152:Cyclic GMP / Q000378:metabolism; D004789:Enzyme Activation / Q000187:drug effects; D015852:Eukaryotic Initiation Factor-2 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005260:Female; D016166:Free Radical Scavengers / Q000494:pharmacology; D011905:Genes, ras / Q000502:physiology; D006418:Heme / Q000737:chemistry; D006801:Humans; D006861:Hydrogen Peroxide / Q000494:pharmacology; D047468:Immunoprecipitation; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009569:Nitric Oxide / Q000494:pharmacology*; D016877:Oxidants / Q000494:pharmacology; D018384:Oxidative Stress; D010766:Phosphorylation / Q000187:drug effects; D014176:Protein Biosynthesis / Q000502:physiology*; D034741:RNA, Small Interfering / Q000494:pharmacology; D019892:eIF-2 Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism
D016895:Culture Media, Serum-Free; D015852:Eukaryotic Initiation Factor-2; D016166:Free Radical Scavengers; D016877:Oxidants; D034741:RNA, Small Interfering; D009569:Nitric Oxide; D006418:Heme; D006861:Hydrogen Peroxide; D019892:eIF-2 Kinase; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D006152:Cyclic GMP