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Mark Thornton

Publications and source records attributed to Mark Thornton.

6 recordsLinked to original sources
PubMed2006

GM2 expression in renal cell carcinoma: potential role in tumor-induced T-cell dysfunction.

Multiple mechanisms have been proposed to account for immune escape by tumors. Although gangliosides have long been known to suppress T-cell immunity, few studies have examined the effect of human tumor-derived gangliosides on immune responses. Here, we show that gangliosides isolated from renal cell carcinoma (RCC) cell lines and clear cell tumor tissue can induce apoptosis in peripheral blood T cells. The RCC tissue-derived gangliosides also suppressed IFN-gamma and, in many cases, interleukin-4 production by CD4+ T cells at concentrations (1 ng/mL-100 pg/mL) well below those that induce any detectable T-cell death (4-20 microg/mL). Additional findings show that GM2 expressed by RCC plays a significant role in promoting T-cell dysfunction. This is supported by the demonstration that all RCC cell lines examined (n = 5) expressed GM2 as did the majority of tumors (15 of 18) derived from patients with clear cell RCC. Furthermore, an antibody specific for GM2 (DMF10.167.4) partially blocked (50-60%) T-cell apoptosis induced by coculturing lymphocytes with RCC cell lines or with RCC tissue-derived gangliosides. DMF10.167.4 also partially blocked the suppression of IFN-gamma production induced by RCC tissue-derived gangliosides, suggesting that GM2 plays a role in down-regulating cytokine production by CD4+ T cells.

Apoptosis↗
PubMed2003

The Bcl-2 transgene protects T cells from renal cell carcinoma-mediated apoptosis.

PURPOSE: Tumors induce T-cell apoptosis as a mechanism of inhibiting antitumor immunity. Using coculture experiments, it has been shown that tumor lines stimulate T-cell apoptosis by a pathway involving a mitochondrial permeability transition and cytochrome c release. Activated T cells express abundant levels of Bcl-2, an antiapoptotic molecule that would be expected to confer resistance to such tumor-mediated killing. We examined the mechanism by which Bcl-2 is dysregulated in T cells exposed to the renal tumor line SK-RC-45, and we determined whether overexpressing Bcl-2 protects T cells from tumor-mediated apoptosis. EXPERIMENTAL DESIGN: Activated T lymphocytes and Jurkat cells transfected or not transfected with Bcl-2 were exposed to SK-RC-45 for 48-72 h. After coculture, lymphocytes were analyzed for Bcl-2 expression using Western analysis and for tumor-induced apoptosis by terminal deoxynucleotidyl transferase-mediated nick end labeling. The role of SK-RC-45-stimulated caspase activation in degrading T-cell Bcl-2 was assessed using a pan-caspase inhibitor, as well as a specific inhibitor of caspase-9. RESULTS: The renal cell carcinoma cell line SK-RC-45 sensitizes peripheral blood activated T lymphocytes and Jurkat cells to apoptosis by a mechanism that involves degradation of the antiapoptotic protein Bcl-2. The SK-RC-45-induced modulation of lymphocyte Bcl-2 levels was largely caspase independent because pretreatment of T cells with pan-caspase inhibitor III or an inhibitor of caspase-9 had minimal or no effect on stabilizing the protein, although it did provide protection against apoptosis. Overexpression of Bcl-2 protected Jurkat cells from tumor-mediated killing. CONCLUSIONS: Bcl-2 inhibition is a mechanism by which tumors may render lymphocytes sensitive to other tumor-derived, proapoptotic stimuli.

Apoptosis↗
PubMed2003

Gangliosides expressed by the renal cell carcinoma cell line SK-RC-45 are involved in tumor-induced apoptosis of T cells.

It is now understood that the genetic plasticity of cancer cells can lead to alterations that confer selective growth advantages to the tumor, some of which play a role in immune escape. A number of mutations veiling tumor cells from host immune defenses have been well characterized but more recent studies suggest that a variety of tumors can also express products that are actually toxic for the immune effectors. A component of this tumor-induced T-cell death has been attributed to receptor-mediated apoptosis. Some tumors, however, synthesize soluble factors that mediate similar effects. In this regard, we previously showed that supernatants from explanted renal cell carcinoma (RCC) tumors sensitized normal T cells to activation induced cell death, and the responsible products had the features of gangliosides. We have also shown that renal tumor lines, including SK-RC-45, induce apoptosis of both Jurkat cells and normal T lymphocytes. Here, we used the ganglioside synthesis inhibitor PPPP to define the role of gangliosides in RCC cell line (SK-RC-45)-mediated T cell and Jurkat cell apoptosis and to elucidate the proapoptotic molecular events by which the glycosphingolipids produce their effects. The ganglioside-synthesizing SK-RC-45 line stimulated the TUNEL (terminal deoxynucleotidyl transferase-mediated nick end labeling) positivity of cocultured T cells by a mechanism that involved decreasing lymphocyte expression levels of Bcl-2 and Bcl-(XL), inducing cytochrome c release from their mitochondria and activating caspases 9 and 3. These proapoptotic events were partially or completely abrogated when tumor cells were pretreated with PPPP for 5 days before the SK-RC-45/T lymphocyte coincubation, a regimen that reduced tumor-associated ganglioside levels by 70-80%. Our results suggest that gangliosides may be key mediators of RCC-induced T-cell apoptosis and imply that they contribute to the T-cell dysfunction in the tumor microenvironment.

Apoptosis↗
PubMed2003

Optimisation of the degree of sulfation of a polymer based construct to block the entry of HIV-1 into cells.

Blocking the entry of HIV-1 into CD4+ cells is an important new therapeutic target for the development of novel vaginal microbicides. In this study, sulfated derivatives of the linear polysaccharide dextrin were synthesised whose percentage sulphation increased incrementally from 7.4 to 48.3%. Their anti-HIV-1 activity in C8166 cells was first seen when percentage sulfation reached 33.2%, but it was only seen in peripheral blood mononuclear cells when it reached 36.3%. It did not increase further when sulfation reached 40.2%. Primary viruses with a V3 loop charge of greater than +5 were blocked by 80 microg/ml of dextrin 2 sulfate but primary viruses with a V3 loop charge of less than +3 required 1,600 microg/ml to block viral entry effectively. Our results identify the relative contribution of the percentage sulfation of a polymer based construct for optimising its anti-HIV-1 activity whilst minimising its toxicity. A better understanding of these structure-function relationships will inform the design and development of novel vaginal microbicides to effectively block the sexual transmission of all primary viral isolates of HIV-1.

Anti-HIV Agents↗
PubMed2002

Expression of hypothalamic-pituitary-thyroid axis related genes in the human skin.

The skin is commonly affected in thyroid diseases, but the mechanism for this association is still unclear. As the skin expresses numerous neuroendocrine elements, we tested the additional cutaneous expression of mediators operating in the hypothalamic-pituitary-thyroid axis. We found significant expression of the thyroid-stimulating hormone receptor mRNA in cultured keratinocytes, epidermal melanocytes, and melanoma cells. The presence of thyroid-stimulating hormone receptor was confirmed by northern analyses and the thyroid-stimulating hormone receptor was found to be functionally active in cyclic adenosine monophosphate signal assays. Thyroid-stimulating hormone receptor expressing cells also expressed the sodium iodide symporter and thyroglobulin genes. We also found expression of deiodinases 2 and 3 (mainly deiodinase 2) in whole skin biopsy specimens, and in the majority of epidermal and dermal cells by reverse transcription-polymerase chain reaction followed by sequencing of the amplified gene segments. There was selective expression of the gene for thyroid-stimulating hormone beta; detection of the thyroid-releasing hormone gene was minimal and thyroid-releasing hormone receptor mRNA was not detected in most of the samples. Expression of functional thyroid-stimulating hormone receptor in the skin may have significant physiologic and pathologic consequences, particularly in autoimmune conditions associated with production of stimulating antibodies against the thyroid-stimulating hormone receptor. We conclude that the expanding list of neuroendocrine elements expressed in the skin supports a strong role for this system in cutaneous biology.

Animals↗