Abstract
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.
Publication types
-
Research Support, N.I.H., Extramural
-
Research Support, Non-U.S. Gov't
MeSH terms
-
Apoptosis / drug effects
-
Blotting, Western
-
Breast / cytology
-
Breast / metabolism
-
Breast Neoplasms / genetics
-
Breast Neoplasms / metabolism*
-
Breast Neoplasms / pathology*
-
Cell Cycle / drug effects
-
Cell Transformation, Neoplastic
-
Cells, Cultured
-
Culture Media, Serum-Free / pharmacology
-
Cyclic GMP / metabolism
-
Enzyme Activation / drug effects
-
Eukaryotic Initiation Factor-2 / antagonists & inhibitors
-
Eukaryotic Initiation Factor-2 / genetics
-
Eukaryotic Initiation Factor-2 / metabolism*
-
Female
-
Free Radical Scavengers / pharmacology
-
Genes, ras / physiology
-
Heme / chemistry
-
Humans
-
Hydrogen Peroxide / pharmacology
-
Immunoprecipitation
-
Mitogen-Activated Protein Kinase 1 / metabolism
-
Mitogen-Activated Protein Kinase 3 / metabolism
-
Nitric Oxide / pharmacology*
-
Oxidants / pharmacology
-
Oxidative Stress*
-
Phosphorylation / drug effects
-
Protein Biosynthesis / physiology*
-
RNA, Small Interfering / pharmacology
-
eIF-2 Kinase / antagonists & inhibitors
-
eIF-2 Kinase / metabolism
Substances
-
Culture Media, Serum-Free
-
Eukaryotic Initiation Factor-2
-
Free Radical Scavengers
-
Oxidants
-
RNA, Small Interfering
-
Nitric Oxide
-
Heme
-
Hydrogen Peroxide
-
eIF-2 Kinase
-
Mitogen-Activated Protein Kinase 1
-
Mitogen-Activated Protein Kinase 3
-
Cyclic GMP