Distinct Roles of Thioredoxin in the Cytoplasm and in the Nucleus

Abstract

Oxidative stresses such as UV irradiation to mammalian cells triggers a variety of oxistress responses including activation of transcription factors. Recently, activation of nuclear factor-B (NF-B) has been shown to be under oxidoreduction (redox) regulation controlled by thioredoxin (TRX), which is one of major endogenous redox-regulating molecules with thiol reducing activity. In order to elucidate where in the cellular compartment TRX participates in NF-B regulation, we investigated the intracellular localization of TRX. UVB irradiation induced translocation of TRX from the cytoplasm into the nucleus. In our in vitro diamide-induced cross-linking study, we showed that TRX can associate directly with NF-B p50. Overexpression of wild-type TRX suppressed induction of luciferase activity under NF-Bbinding sites in response to UV irradiation compared with the mock transfectant. In contrast, overexpression of nuclear-targeted TRX enhanced the luciferase activity. Thus, TRX seems to play dual and opposing roles in the regulation of NF-B. In the cytoplasm, it interferes with the signals to IB kinases and blocks the degradation of IB. In the nucleus, however, TRX enhances NF-B transcriptional activities by enhancing its ability to bind DNA. This two-step TRX-dependent regulation of the NF-B complex may be a novel activation mechanism of redox-sensitive transcription factors.

Thioredoxin reductase regulates AP-1 activity as well as thioredoxin nuclear localization via active cysteines in response to ionizing radiation

“…The role of TRX in the regulation of AP-1 DNAbinding activity following IR, as well as other environmental stress inducing agents (Hirota et al, 1999(Hirota et al, , 2000a, has been well established. However, the role of the critical cysteines in IR-induced induction of the AP-1 complex has not been investigated.…”

“…It has been previously shown that following exposure to IR (Wei et al, 2000) or other oxidants (Hirota et al, 1999(Hirota et al, , 2000a, TRX translocates into the nucleus, where it interacts with another redox-sensitive signaling protein, redox factor-1, and appears to regulate the nuclear transcription factor complex, AP-1. The current study demonstrates the essential role of TR as a redox-sensitive signaling factor functioning upstream of TRX in the regulation of AP-1 activity and demonstrates that the active site cysteine residues are essential in mediating IR-induced activation as well as the regulation of stress-induced TRX nuclear translocation.…”

“…There are two confirmed forms of mammalian TRs, TR1 and TR2, both of which share in common a conserved -Cys-ValAsn-Val-Gly-Cys-redox catalytic motif thought to play a central role in the redox function of TR (Mustacich and Powis, 2000;Powis et al, 1998). Interestingly, one major downstream target of TR, TRX, also contains a redox-active disulfide/dithiol motif within the conserved active site-Cys-Gly-Pro-Cys- (Hirota et al, 1999;Williams et al, 2000).…”

“…One intracellular function of TRX is to activate protein-nucleic acid interactions of nuclear transcription factors via redox regulation (Hirota et al, 1999(Hirota et al, , 2000aWei et al, 2000). It has been previously shown that following exposure to IR (Wei et al, 2000) or other oxidants (Hirota et al, 1999(Hirota et al, , 2000a, TRX translocates into the nucleus, where it interacts with another redox-sensitive signaling protein, redox factor-1, and appears to regulate the nuclear transcription factor complex, AP-1.…”

Thioredoxin, a regulator of gene expression

“…During oxidative stress conditions IkBa becomes ubiquitinylated and subsequently degraded by the 26S proteasome complex. It was shown that Trx inhibits the degradation of IkBa (Hirota et al, 1999). We demonstrate here that Trx also induces the expression of IkBa/MAD-3.…”