The involvement of mRNA processing factors TIA-1, TIAR, and PABP-1 during mammalian hibernation

Abstract

Mammalian hibernators survive low body temperatures, ischemia-reperfusion, and restricted nutritional resources via global reductions in energy-expensive cellular processes and selective increases in stress pathways. Consequently, studies that analyze hibernation uncover mechanisms which balance metabolism and support survival by enhancing stress tolerance. We hypothesized processing factors that influence messenger ribonucleic acid (mRNA) maturation and translation may play significant roles in hibernation. We characterized the amino acid sequences of three RNA processing proteins (T cell intracellular antigen 1 (TIA-1), TIA1-related (TIAR), and poly(A)-binding proteins (PABP-1)) from thirteen-lined ground squirrels (Ictidomys tridecemlineatus), which all displayed a high degree of sequence identity with other mammals. Alternate Tia-1 and TiaR gene variants were found in the liver with higher expression of isoform b versus a in both cases. The localization of RNA-binding proteins to subnuclear structures was assessed by immunohistochemistry and confirmed by subcellular fractionation; TIA-1 was identified as a major component of subnuclear structures with up to a sevenfold increase in relative protein levels in the nucleus during hibernation. By contrast, there was no significant difference in the relative protein levels of TIARa/ TIARb in the nucleus, and a decrease was observed for TIAR isoforms in cytoplasmic fractions of torpid animals. Finally, we used solubility tests to analyze the formation of reversible aggregates that are associated with TIA-1/R function during stress; a shift towards the soluble fraction (TIA-1a, TIA-1b) was observed during hibernation suggesting enhanced protein aggregation was not present during torpor. The present study identifies novel posttranscriptional regulatory mechanisms that may play a role in reducing translational rates and/or mRNA processing under unfavorable environmental conditions.

To be or not to be: the regulation of mRNA fate as a survival strategy during mammalian hibernation

“…Further to this, when the distribution of poly(A) tail lengths were plotted as a function of torpor bout progression, the distribution pattern was consistent with the binding of poly(A)-binding protein (PABP), indicating a possible role of PABP in mRNA stability, as has been shown in other studies (Bernstein et al 1989;Korner and Wahle 1997). While the interaction between mRNA and PABP-1 has not been fully described, we have also recently suggested a role for PABP-1 as an mRNA stabilizer in hepatocytes of thirteen-lined ground squirrels during deep torpor (Tessier et al 2014). Our data showed that despite no observed changes in the relative expression levels of PABP-1 in nuclear fractions from euthermic versus torpid ground squirrels, RNA binding proteins including PABP-1 and TIA-1/R localized to subnuclear structures during torpor.…”

“…The presence of these nuclear structures is correlated with reduced metabolic rate and their reversal occurs within a few minutes of arousal, providing a mechanism for the rapid resumption of protein synthesis (Malatesta et al 2001). We have also identified a novel subcellular body during hibernation in thirteen-lined ground squirrels (Tessier et al 2014). This subnuclear body consists of RNA-binding proteins such as TIA-1, TIAR, and PABP-1 which are also markers of cytoplasmic stress granules.…”

“…Western blotting was used to assess the presence of TIA-1 and PABP-1 in the polysome profiles of kidney extracts from euthermic versus hibernating ground squirrels (Hittel and Storey 2002). TIA-1 was restricted to the monosome fractions in both situations, suggesting TIA-1 may mediate translational suppression of mRNA pools during hibernation, a hypothesis which has also been proposed in the liver of thirteen-lined ground squirrels (Tessier et al 2014). In contrast, PABP-1 was found in monosome fractions (fractions 8-10) in extracts from euthermic animals whereas, in extracts from hibernating individuals, PABP-1 was also detected in fractions 4, 5, and 7.…”

“…Evidence for the importance of mRNA processing factors in hibernation has been accumulated for several species including hazel and edible dormice (Malatesta et al 2008), greater horseshoe bats (Chen et al 2008), arctic ground squirrels , and thirteen-lined ground squirrels (Tessier et al 2014). A study in hazel dormice (Muscardinus avellanarius) analyzed the role of transcriptional (RNA polymerase II), splicing (hnRNPs, snRNPs, and SC35), and cleavage factors (CStF and CFIm68) in liver and brown adipose tissue from euthermic, hibernating, and aroused animals (Malatesta et al 2008).…”

“…During hibernation, the level of the active PPARα1wt did not vary significantly but PPARα2tr nearly disappeared so that the wt:tr ratio rose by 3.74-fold as compared with liver of active jerboas. Most recently, we described data whereby alternative TIA-1 and TIAR gene variants were detected in the liver of thirteenlined ground squirrels (Tessier et al 2014). T cell intracellular antigen 1 (TIA-1) and TIA1-related (TIAR) are RNA-binding proteins that play a role in pre-mRNA splicing (MinvielleSebastia et al 1997;Suswam et al 2005), translation (Sachs and Davis 1989;Kedersha and Anderson 2007), mRNA stabilization (Decker and Parker 1993), and decay (Caponigro and Parker 1995).…”