TIAR and TIA-1 mRNA-Binding Proteins Co-aggregate under Conditions of Rapid Oxygen Decline and Extreme Hypoxia and Suppress the HIF-1  Pathway

Abstract

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.

Downregulation of BRCA1 protein in BCR-ABL1 leukemia cells depends on stress-triggered TIAR-mediated suppression of translation

“…Selective inhibition of translation by formation of TIAR-containing granule aggregates was shown under different stress conditions such as rapid oxygen decline and hypoxia. 33 Our observation was additionally supported by findings that TIAR is translocated to the cytoplasm after eIF2a phosphorylation, where it acts as a translational suppressor. 11 As our recent work showed that BCR-ABL1 expression leads to activation of the eIF2a phosphorylation-dependent pathway, 10 this can explain why TIAR is involved in the regulation of translation in CML cells.…”

Low-Level Light in Combination with Metabolic Modulators for Effective Therapy of Injured Brain

“…Although Oxyrase consumed oxygen rapidly and effectively inside and outside the cells, CoCl 2 must enter cells to be effective, which proved to be difficult and insufficient in tissues, in marked contrast to cells, and thus Oxyrase was selected for subsequent studies. 19 As shown in Figure 3B, hypoxia was uniformly and specifically detected in hypoxic cultures as early as 20 minutes of Oxyrase incubation. For in vivo study, Oxyrase was applied topically to the cortex at the injured site of the brain by dropping artificial cerebrospinal fluid comprised of Oxyrase.…”

The Histone Deacetylase Inhibitor, Vorinostat, Represses Hypoxia Inducible Factor 1 Alpha Expression through Translational Inhibition

“…Stress granules contain non-translating mRNAs, translation initiation components, and many additional proteins affecting mRNA translation [52]. To explore the possible role of stress granules in the observed effect of SAHA on HIF-1α, we performed an immunofluorescence analysis of the stress granule associated proteins, TIA-1 (T-cell intracellular antigen-1) and TIAR (TIA-1 related protein) [53]. Neither SAHA (Figure S4E) nor SAHA+MG132 (data not shown) treatments induced the formation of stress granules (Figure S4E), a phenomenon that was observed in response to Tunicamycin treatment (positive control) (Figure S4E).…”