Biomedical subjects

M Stacey Ricci

Publications and source records attributed to M Stacey Ricci.

5 recordsLinked to original sources

PubMed2006

Chemotherapeutic approaches for targeting cell death pathways.

For several decades, apoptosis has taken center stage as the principal mechanism of programmed cell death in mammalian tissues. It also has been increasingly noted that conventional chemotherapeutic agents not only elicit apoptosis but other forms of nonapoptotic death such as necrosis, autophagy, mitotic catastrophe, and senescence. This review presents background on the signaling pathways involved in the different cell death outcomes. A re-examination of what we know about chemotherapy-induced death is vitally important in light of new understanding of nonapoptotic cell death signaling pathways. If we can precisely activate or inhibit molecules that mediate the diversity of cell death outcomes, perhaps we can succeed in more effective and less toxic chemotherapeutic regimens.

Animals↗

PubMed2005

Mxi1 is induced by hypoxia in a HIF-1-dependent manner and protects cells from c-Myc-induced apoptosis.

HIF-1, a hypoxia inducible transcription factor, plays a pivotal role in the cellular response to hypoxia by activating genes involved in glucose metabolism, vascular remodeling, and erythropoiesis. We identified Mxi1, a c-Myc antagonist, as a novel target gene induced in hypoxia. Mxi1 was not induced in cells deficient in ARNT (HIF-1beta), suggesting that Mxi1 is a transcriptional target of the HIF-1 complex. Notably, c-Myc protein levels decreased during hypoxia but were stabilized by a proteasome inhibitor. Analysis of downstream transcriptional targets of c-Myc during hypoxia revealed that genes regulated by c-Myc, such as ornithine decarboxylase (ODC), were downregulated during hypoxia. In contrast, genes that are regulated by c-Myc and HIF-1, such as LDH-A, were upregulated. Mxi1 protects against c-Myc-dependent sensitization to hypoxia-induced apoptosis. The results suggest a coordinated mechanism for opposing c-Myc signaling during hypoxia that is mediated by a reduction in c-Myc levels, the induction of Mxi1, and a dominant effect of HIF-1 transcriptional activity.

Animals↗

PubMed2005

Modulation of TRAIL-induced tumor cell apoptosis in a hypoxic environment.

Hypoxia induces Hif-1alpha and selects for loss of wild-type p53 function, both of which can promote tumor cell survival. We evaluated the ability of TRAIL to induce apoptosis of human tumor cell lines exposed to hypoxia. H460 lung cancer cells express low levels of Hif-1alpha, stabilize wild-type p53 during hypoxia, and undergo TRAIL-induced apoptosis. In U2OS osteosarcoma or PA1 ovarian teratocarcinoma cells, high levels of Hif-1alpha and low levels of stable p53 are detected during hypoxia, and cells undergo low levels of TRAIL-induced apoptosis as compared to H460 cells. H460 cells are sensitized to TRAIL-induced apoptosis, whereas U2OS are protected, and little apoptosis is observed in relatively TRAIL-resistant PA1 during hypoxia. Forced expression of Hif-1alpha is also surprisingly a potent inducer of apoptosis in wild-type p53 expressing H460 cells and further promotes TRAIL-induced apoptosis. TRAIL-sensitive wild-type p53-expressing HCT116 colon carcinoma cells modestly elevate Hif-1alpha levels and are equally or slightly more sensitive to TRAIL during hypoxia. In contrast, p53-null HCT116 have higher levels of Hif-1alpha during normoxia and are extremely sensitive to TRAIL, but are protected from TRAIL-induced apoptosis during hypoxia. We hypothesize that a hypoxic tumor microenvironment may alter sensitivity to TRAIL, which may be impacted by Hif-1alpha levels and p53 status. These findings suggest that particular attention to hypoxic regions of tumors and sensitizers to hypoxia-induced cell death may be required to optimize therapeutic combinations using TRAIL.

Apoptosis↗

PubMed2004

Direct repression of FLIP expression by c-myc is a major determinant of TRAIL sensitivity.

Tumor necrosis factor alpha (TNF-alpha)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF-alpha family of death receptor ligands and holds great therapeutic potential as a tumor cell-specific cytotoxic agent. Using a panel of established tumor cell lines and normal cells, we found a significant difference between the number of TRAIL-sensitive cells expressing high levels of c-myc and TRAIL-resistant cells expressing low levels of c-myc (P < 0.05, n = 19). We also found a direct linear correlation between c-myc levels and TRAIL sensitivity in TRAIL-sensitive cell lines (r = 0.94, n = 6). Overexpression of c-myc or activation of a myc-estrogen receptor (ER) fusion sensitized TRAIL-resistant cells to TRAIL. Conversely, small interfering RNA (siRNA)-mediated knockdown of c-myc significantly reduced both c-myc expression and TRAIL-induced apoptosis. The gene encoding the inhibitor of caspase activation, FLICE inhibitory protein (FLIP), appears to be a direct target of c-myc-mediated transcriptional repression. Overexpression of c-myc or activation of myc-estrogen receptor (ER) decreased FLIP levels both in cell culture and in mouse models of c-myc-induced tumorigenesis, while knocking down c-myc using siRNA increased FLIP expression. Chromatin immunoprecipitation and luciferase reporter analyses showed that c-myc binds and represses the human FLIP promoter. c-myc expression enhanced TRAIL-induced caspase 8 cleavage and FLIP cleavage at the death-inducing signaling complex. Combined siRNA-mediated knockdown of FLIP and c-myc resensitized cells to TRAIL. Therefore, c-myc down-regulation of FLIP expression provides a universal mechanism to explain the ability of c-myc to sensitize cells to death receptor stimuli. In addition, identification of c-myc as a major determinant of TRAIL sensitivity provides a potentially important screening tool for identification of TRAIL-sensitive tumors.

Animals↗

PubMed2003

DNA footprinting.

Explore the source record for details and available documents.

Cloning, Molecular↗