TIAR and TIA-1 mRNA-binding proteins co-aggregate under conditions of rapid oxygen decline and extreme hypoxia and suppress the HIF-1α pathway.
T-cell intracellular antigen (TIA)-1 and TIA-1-related protein (TIAR) are mRNA-binding proteins that can aggregate within granules under specific stress conditions. In this study, we analyzed TIAR/TIA-1 aggregation under different hypoxic conditions, and studied the effects on the hypoxia-inducible factor (HIF)-1α in different cancer cell lines. Under acute and pronounced hypoxic conditions TIAR/TIA-1 co-aggregated to granules and positive co-staining with eIF3η marker suggested these to represent stress granules. In parallel, HIF-1α expression was blocked in cells displaying TIAR/TIA-1 granules. Silencing of TIAR and TIA-1 caused upregulation of HIF-1α expression, as demonstrated by western blot, immunocytochemistry and HIF-1-dependent reporter gene expression. Additionally, a critical region of the 3' end of the untranslated HIF-1α mRNA with possible adenosine-uridine-rich elements (AREs) was coupled to the luciferase reporter gene, causing downregulation of expression. Employing this reporter construct, inhibition of TIAR by siRNA attenuated the inhibitory cis-effect of this ARE-sequence. Furthermore, immunohistochemical analysis of A549 cell tumor xenografts revealed a nearly complementary expression of HIF-1α and TIAR reflecting the control of HIF-1α expression by TIAR as revealed in the cell culture studies. In sum, rapid and severe hypoxia caused co-aggregation of TIAR/TIA-1 and these proteins suppressed HIF-1α expression.
Gottschald
Oana R
OR
Department of Internal Medicine II, Justus-Liebig-University, D-35392 Giessen, Germany.
Malec
Viktor
V
Krasteva
Gabriela
G
Hasan
Diya
D
Kamlah
Florentine
F
Herold
Susanne
S
Rose
Frank
F
Seeger
Werner
W
Hänze
Jörg
J
D000818:Animals; D015687:Cell Hypoxia; D045744:Cell Line, Tumor; D039621:Eukaryotic Initiation Factor-3 / Q000378:metabolism; D006801:Humans; D051795:Hypoxia-Inducible Factor 1, alpha Subunit / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D010100:Oxygen / Q000378:metabolism*; D039102:Poly(A)-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D012333:RNA, Messenger / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D000074019:T-Cell Intracellular Antigen-1; D014183:Transplantation, Heterologous
D039621:Eukaryotic Initiation Factor-3; D051795:Hypoxia-Inducible Factor 1, alpha Subunit; D039102:Poly(A)-Binding Proteins; D012333:RNA, Messenger; D034741:RNA, Small Interfering; D016601:RNA-Binding Proteins; D000074019:T-Cell Intracellular Antigen-1; C071558:TIA1 protein, human; C076751:TIAL1 protein, human; D010100:Oxygen