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.
Human thioredoxin (hTrx) is a cellular redox-active protein that catalyzes dithiol/disulfide exchange reactions, thus controlling multiple biological functions, including cell growth-promoting activity. Here we show that the expression of hTrx protein and messenger RNA was up-regulated by incubation with 17beta-estradiol (E2) in primary culture of stromal cells isolated from human endometrium. Maximal enhancement of hTrx protein and messenger RNA was observed after 6-12 h of incubation with 10-100 nM E2, and the enhancing effect was suppressed by tamoxifen, an estrogen antagonist. Release of hTrx into the culture medium was markedly augmented after 5-day exposure of E2 plus progesterone (P) accompanied by in vitro differentiation of endometrial stromal cells (decidualization). Immunocytochemical studies showed that hTrx was localized in the nucleus, nucleolus, and cytosol in the stromal cells. Strongly enhanced immunoreactivity for hTrx was observed in the E2-treated cells, whereas there was no apparent difference in the pattern of subcellular localization among the untreated and E2- and/or P-treated cells. Although 1-50 microg/ml recombinant hTrx alone did not promote endometrial stromal cell growth, epidermal growth factor-dependent mitogenesis was additively enhanced by hTrx. Our results indicate that hTrx modulates endometrial cell growth, acting as a comitogenic factor for epidermal growth factor, which is known to be a mediator of estrogen action. It is also suggested that hTrx is deeply involved in the hormonal control of the endometrium by E2 and P, playing a regulatory role in endometrial cell growth and differentiation.
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