Cancer research
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The estrogen-receptor-related receptors (ERRs) alpha, beta, and gamma are orphan nuclear hormone receptors that share significant homology with the estrogen receptors (ERs) but are not activated by natural estrogens. In contrast, the ERRs display constitutive transcriptional activity in the absence of exogenously added ligand. However, the ERRs bind to the estrogen response element and to the extended half-sites of which a subset can also be recognized by ERalpha, suggesting that ERRs and ERs may control overlapping regulatory pathways. ⋯ We show that ERR transcriptional activity on the pS2 promoter is considerably enhanced in the presence of all three members of the steroid receptor coactivator family but is completely abolished on treatment with the synthetic estrogen diethylstilbestrol, a recently described inhibitor of ERR function. Finally, we demonstrate that ERRalpha is the major isoform expressed in human breast cancer cell lines and that diethylstilbestrol can inhibit the growth of both ER-positive and -negative cell lines. Taken together, these results demonstrate that estrogen-inducible genes such as pS2 can be ERR targets and suggest that pharmacological modulation of ERRalpha activity may have therapeutic value in the treatment of breast cancer.
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It is well established that ErbB1 and ErbB2 can cooperate in mammary epithelial cell transformation. Therefore, to understand how ErbB1/ErbB2 signaling contributes to this process, we used the ErbB kinase inhibitor AG1478in ErbB2-dependent BT-474 and SKBR-3 human breast cancer cells. These cells overexpress ErbB2 and also display moderate levels of ErbB1. ⋯ Antisense p27 oligonucleotides decreased p27 levels and abrogated the G(1) arrest induced by AG1478. Similarly, infection with an adenovirus encoding inducible cyclin D1 also counteracted the antiproliferative effect of AG1478. These data imply that: (a) modulation of both p27 and cyclin D1 are required for the growth arrest that results from blockade of the ErbB2 kinase; and (b) ErbB2 overexpressing cells use both MAPK and PI3K/Akt to modulate p27 and cyclin D1 and, hence, subvert the G(1)-to-S transition.
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N(1),N(11)-Diethylnorspermine (DENSPM) is a polyamine analogue with clinicalrelevance as an experimental anticancer agent and the ability to elicit a profound apoptotic response in certain cell types. Here, we characterize the polyamine effects and apoptotic signaling events initiated by treatment of SK-MEL-28 human melanoma with 10 microM DENSPM. Maximal induction of the polyamine catabolic enzyme spermidine/spermine N(1)-acetyltransferase (SSAT) and polyamine pool depletion were seen by 16 h, whereas early apoptosis was first apparent at 36 h. ⋯ Three DENSPM analogues that differentially induced SSAT activity but similarly depleted polyamine pools revealed a close correlation between enzyme induction and cytochrome c release, caspase activation, and apoptosis. Dose-dependent inhibition of polyamine oxidase, an enzyme that oxidizes acetylated polyamines generated by SSAT and releases toxic by-products such as H(2)O(2) and aldehydes, prevented cytochrome c release, caspase activation, and apoptosis. Taken together, the findings indicate that DENSPM-induced apoptosis is at least partially initiated via massive induction of SSAT and related oxidative events and subsequently mediated by the mitochondrial apoptotic signaling pathway as indicated by cytochrome c release and caspase activation.
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RRR-alpha-tocopherol succinate (vitamin E succinate, VES) is a potent, selective apoptotic agent for cancer cells but not normal cells. VES has been shown to inhibit the growth of a wide variety of tumor cells in cell culture and animal models. Studies addressing mechanisms of action of VES-induced apoptosis have identified transforming growth factor-beta, Fas/CD95-APO-1, and mitogen-activated protein kinase (MAPK) signaling pathway involvement. ⋯ Expression of dominant negative mutants of ERK1, MAPK/ERK activator-1, or JNK1 but not p38 blocked phosphorylation of the substrate glutathione S-transferase-c-Jun and inhibited VES-induced apoptosis. Increased phosphorylation and transactivation activity of nuclear transcription factors c-Jun, ATF-2, and Elk-1 are observed after VES treatments; however, only c-Jun and ATF-2 appear to be involved in VES-induced apoptosis based on antisense blockage experiments. Collectively, these results imply a critical role for ERK1 and JNK1 but not p38 in VES-induced apoptosis of human MDA-MB-435 breast cancer cells.
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MAGE-encoded antigens, which are expressed by tumors of many histological types but not in normal tissues, are suitable candidates for vaccine-based immunotherapy of cancers. Thus far, however, T-cell responses to MAGE antigens have been detected only occasionally in cancer patients. In contrast, by using HLA/peptide fluorescent tetramers, we have observed recently that CD8(+) T cells specific for peptide MAGE-A10(254-262) can be detected frequently in peptide-stimulated peripheral blood mononuclear cells from HLA-A2-expressing melanoma patients and healthy donors. ⋯ Importantly, only CD8(+) T cells able to recognize the antigenic peptide with high efficiency are able to lyse MAGE-A10-expressing tumor cells. Under defined experimental conditions, the tetramer staining intensity exhibited by MAGE-A10(254-262)-specific CD8(+) T cells correlates with efficiency of peptide recognition so that "high" and "low" avidity cells can be separated by FACS. Altogether, the data reported here provide evidence for functional diversity of MAGE-A10(254-262)-specific T cells and will be instrumental for the monitoring of peptide MAGE-A10(254-262)-based clinical trials.