There is increasing evidence that an augmented state of cellular oxidative stress modulates the expression of stress genes implicated in diseases associated with health disparities such as certain cancers and diabetes. Lens epithelium -derived growth factor p75 (LEDGF/ p75), also known as DFS70 autoantigen, is emerging as a survival oncoprotein that promotes resistance to oxidative stress -induced cell death and chemotherapy. We previously showed that LEDGF/p75 is targeted by autoantibodies in prostate cancer patients and is overexpressed in prostate tumors, and that its stress survival activity is abrogated during apoptosis. LEDGF/ p75 has a COOH-terminally truncated splice variant, p52, whose role in stress survival and apoptosis has not been thoroughly investigated. We observed unbalanced expression of these proteins in a panel of tumor cell lines, with LEDGF/p75 generally expressed at higher levels. During apoptosis, caspase-3 cleaved p52 to generate a p38 fragment that lacked the NH 2 -terminal PWWP domain and failed to transactivate the Hsp27 promoter in reporter assays. However, p38 retained chromatin association properties and repressed the transactivation potential of LEDGF/p75. Overexpression of p52 or its variants with truncated PWWP domains in several tumor cell lines induced apoptosis, an activity that was linked to the presence of an intron-derived COOH-terminal sequence. These results implicate the PWWP domain of p52 in transcription function but not in chromatin association and proapoptotic activities. Consistent with their unbalanced expression in tumor cells, LEDGF/p75 and p52 seem to play antagonistic roles in the cellular stress response and could serve as targets for novel antitumor therapies.

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TGFβ mediates cell cycle arrest in late G 1 phase of the cell cycle with a simultaneous peak in the levels of the cyclin-dependent kinase inhibitor, p27 kip1 (p27). In this report, we show that whereas p27 resides in the cytoplasm in the endometrial carcinoma (ECA) cell line HEC-1A, TGFβ increases the total levels and translocation of p27 into the nucleus. Concomitantly, TGFβ activates the transcription factors Smad2 and Smad3, inhibits proliferation, and blocks Cdk2 activity; all these events are blocked by an inhibitor of TβRI serine kinase activity (SD208). In addition, we show that inhibiting p27 transcription with a specific siRNA completely blocks TGFβ-mediated growth inhibition in these cells. These data suggest that TGFβ inhibits cellular proliferation by increasing p27 levels through Smad2/3 signaling in HEC-1A cells. We further show that TGFβ decreases the levels of components of the SCF Skp2 targeting complex for ubiquitin-mediated degradation of p27 in proteasomes, at the protein but not the mRNA level. Therefore, TGFβ accumulates nuclear p27 by preventing its degradation to enable G 1 arrest in HEC-1A cells. Importantly, these data suggest a novel mechanism for TGFβ/Smad mediated growth inhibition that might be inoperable in the numerous human cancers demonstrating early dysregulated TGFβ signaling and loss of growth inhibition. The TGFβ/p27 axis might provide novel therapeutic targets for cancer.

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Prostaglandins (PG) are released during tissue injury and inflammation, and inhibit immune responses at many points. PG may be one of several factors that protect not only against injury-induced, but also spontaneous, organ-specific autoimmune disease. Here we show that the production of PGE(2), normally produced at a very low rate in islets of Langerhans, is significantly increased in inflamed islets of non-obese diabetic (NOD) mice. We investigated a possible role of PGE(2) in controlling TCR-dependent release of IFN-gamma from islet-reactive NOD CD8(+) T cells. PGE(2) inhibited anti-TCR antibody-triggered release of IFN-gamma from CD8(+) T cell clone 8D8 and from polyclonal cytotoxic T lymphocytes (CTL). Using receptor subtype selective agonists, we present evidence that the effect of PGE(2) is mediated by EP(2) and EP(4) receptors, both of which are coupled to an increase in intracellular cAMP production. The cAMP analogs 8-Br-cAMP and Sp-cAMPS mimic the effect of EP(2)/EP(4) receptor agonists, inhibiting TCR-triggered IFN-gamma release from NOD CD8(+) T cells in a dose-dependent manner. The inhibitory effect of PGE(2) was largely reversed by IL-2 added at the time of culture initiation and decreased with increasing strength of stimulation through the TCR. Resting CTL were more sensitive to PGE(2) than recently expanded CTL and NOD CD8(+) T cells remained insensitive to PGE(2) for a longer time than BALB/c cells. Our study suggests that PGE(2) may be part of a regulatory network that controls local activation of T cells and may play a role in the balance between the development of islet autoimmunity or maintenance of tolerance.