Expression of the Transcription Factor STAT-1α in Insulinoma Cells Protects against Cytotoxic Effects of Multiple Cytokines

Abstract

Destruction of pancreatic islet ␤-cells in type 1 diabetes appears to result from direct contact with infiltrating T-cells and macrophages and exposure to inflammatory cytokines such as interferon (IFN)-␥, interleukin (IL)-Type 1 diabetes is caused by autoimmune destruction of pancreatic islet ␤-cells. Destruction of ␤-cells appears to result from direct contact with infiltrating T-cells and macrophages and exposure to inflammatory cytokines such as IFN-␥, 1 IL-1␤, and TNF-␣ that such cells produce (1-5). Insulin replacement by injection, the current treatment, fails to replicate the precise control of fuel homeostasis afforded by normal regulation of insulin secretion in response to glucose and other physiological cues. Islet transplantation has therefore been investigated as an alternative to insulin injection therapy for more than 3 decades (6, 7). Success in this area had been very limited until a recent trial in Edmonton, Alberta, Canada, in which a combination of mild immunosuppressive agents were used in conjunction with freshly isolated islet tissue to achieve insulin independence in seven successive patients studied for up to 14.9 months post-transplant (8).Unfortunately, enthusiasm for this important finding is tempered by the fact that the number of human pancreata available for islet transplantation in the United States is on the order of several thousand per year (6, 7), which does not approach the number of patients that could benefit from this new form of therapy. To deal with this problem, we and others have been attempting to develop a replenishable source of cells that could serve as islet surrogates for cell-based insulin replacement in diabetes (9 -13). One working concept is that immortalized cell lines engineered for robust glucose-stimulated insulin secretion can be transplanted in the context of a cellimpermeant macroencapsulation device, preventing contact of cellular elements of the immune system with the transplanted cells (11). However, because such devices are envisioned to allow rapid exit of insulin, as well as highly efficient equilibration of nutrients, oxygen, and waste products, it is anticipated that soluble mediators of immunological damage such as cytokines or reactive oxygen species will readily gain access to the cells within the device. Thus, development of methods to protect transplanted cells against diffusable, noncellular mediators of immunological destruction may be important for the eventual success of cell-based insulin replacement strategies.Recently, we described a method for selection of cell lines with resistance to the cytotoxic effects of exposure to a mixture of IL-1␤ and IFN-␥, known mediators of ␤-cell destruction in type 1 diabetes (14). This involved growth of INS-1 insulinoma cells in progressively elevated concentrations of the two cytokines over an 8-week period and selection of surviving cells. The resultant cell line, termed INS-1 res , was 80% viable after 5 days of exposure to the combination of 10 ng/ml IL-1␤ and 100 units/ml IFN-␥, while less th...

Requirement of Histone Deacetylase Activity for Signaling by STAT1

“…We showed that inhibitors of HDAC activity sensitize cells to IFN␥-induced apoptosis, demonstrating that STAT1-dependent signaling protects cells from IFN␥-induced apoptosis. This is consistent with reports that STAT1 can protect against cytotoxic effects of multiple cytokines, including IFN␥ and IFN␣ (78,79). Enhanced apoptosis of cells treated with IFN␥ and butyrate suggests that IFN␥ in the absence of STAT1 signaling induces the expression of genes that promote apoptosis or inhibits the expression of antiapoptotic genes.…”

Inflammatory mechanisms in diabetes: lessons from the β-cell

“…However, STAT-1a expression was dramatically increased in response to the selection procedure. 25 That the increase in STAT-1a levels might be relevant to the IFN-g resistance induced by the selection procedure was supported by the finding that the increase in expression was observed only in cells that were grown in the continual presence of cytokines, and not in cells subjected to the selection procedure and grown in the absence of cytokines. Recall that cells grown under the latter conditions lose their IFN-g resistance.…”

“…We concluded that induction of STAT-1a makes an important contribution to the IFN-g resistance conferred by our selection procedure. 25 Combined effects of an antiapoptotic gene and cytokine selection…”

γ-Interferon Signaling in Pancreatic β-Cells Is Persistent but Can Be Terminated by Overexpression of Suppressor of Cytokine Signaling-1

“…Resistance was found to be associated with increased expression of STAT1␣ and could be reproduced by overexpression of STAT1␣ in nonresistant cells, although the biochemical mechanism remains unclear (30). The continual expression of STAT1 in response to IFN-␥ appears to be at odds with the idea of transient IFN-␥-receptor signaling.…”