A role for transportin in deposition of TTP to cytoplasmic RNA granules and mRNA decay

Abstract

Importin-β family members, which shuttle between the nucleus and the cytoplasm, are essential for nucleocytoplasmic transport of macromolecules. We attempted to explore whether importin-β family proteins change their cellular localization in response to environmental change. In this report, we show that transportin (TRN) was minimally detected in cytoplasmic processing bodies (P-bodies) under normal cell conditions but largely translocated to stress granules (SGs) in stressed cells. Fluorescence recovery after photobleaching analysis indicated that TRN moves rapidly in and out of cytoplasmic granules. Depletion of TRN greatly enhanced P-body formation but did not affect the number or size of SGs, suggesting that TRN or its cargo(es) participates in cellular function of P-bodies. Accordingly, TRN associated with tristetraprolin (TTP) and its AU-rich element (ARE)-containing mRNA substrates. Depletion of TRN increased the number of P-bodies and stabilized ARE-containing mRNAs, as observed with knockdown of the 5′–3′ exonuclease Xrn1. Moreover, depletion of TRN retained TTP in P-bodies and meanwhile reduced the fraction of mobile TTP to SGs. Therefore, our data together suggest that TRN plays a role in trafficking of TTP between the cytoplasmic granules and whereby modulates the stability of ARE-containing mRNAs.

AU-Rich-Element-Dependent Translation Repression Requires the Cooperation of Tristetraprolin and RCK/P54

“…Previous studies showed that TTP localizes to P bodies and associates with multiple P-body components (5,17,23,(25)(26)(27)45). We confirmed that localization of TTP overlaps with P-body markers Dcp1a and Ago2 (a functional partner for TTP in ARE-mRNA decay), suggesting their interactions (Fig.…”

Importin β3 mediates the nuclear import of human ribosomal protein L7 through its interaction with the multifaceted basic clusters of L7

“…This indicates that importin b3 interacted multifacetedly with L7 basic cluster, and allowed proteins to undergo nuclear entry as reported previously [2]. A RanGTP release experiment [12] revealed that the binding between importin b3 and the basic cluster is RanGTP dependent. This was evident from the fact that the binding of importin b3 to GST-N54 was uncoupled by the presence of RanGTP, but not by that of RanGDP in a competition affinity chromatography experiment (Fig.…”

“…The RanGTP release experiments were carried out using the procedure of Chang and Tarn [12] with the Q69L mutant form of Ran protein (a kind gift from Dr. W.-Y. Tarn, Academia Sinica, Taiwan).…”

Stability of the LATS2 Tumor Suppressor Gene Is Regulated by Tristetraprolin

“…They achieve sequence-and cell type-specific regulation by using several strategies: cell typespecific expression of these proteins or other factors and grouping of factors at clusters of RNA motifs (44). One recent study suggested the possibility of association between TTP and hnRNP by demonstrating that transportin, which recognizes hnRNP A1, interacts with TTP and modulates TTP-mediated decay of ARE-containing mRNAs (45). Further characterizing the other factors (especially hnRNPs) involved in TTP-mediated mRNA decay will elucidate the molecular mechanisms of gene and cell type specificity of mRNA decay.…”