High Glucose Levels Increase Major Histocompatibility Complex Class I Gene Expression in Thyroid Cells and Amplify Interferon-γ Action

Abstract

Increased major histocompatibility complex (MHC) class I gene expression in target tissues may be relevant to the pathogenesis of autoimmune diseases. In this study, we questioned whether high glucose levels might increase MHC class I levels and thereby contribute to autoimmune complications. We used thyrocytes in continuous culture, because there is an increased incidence of autoimmune thyroiditis in type 2 diabetics and because transcriptional regulation of MHC class I is well studied in these cells. Northern analysis and flow cytometry showed that 20 and 30 mM D-glucose up-regulated MHC class I expression and that the glucose effect was additive to and independent of interferon-gamma. The effect was specific, because L-glucose did not modify class I expression. The glucose acted transcriptionally, requiring both enhancer A and a cAMP-response element-like element located in the hormone-sensitive region of the MHC class I 5'flanking region. These elements are different from those activated by interferon-gamma. High glucose levels increase formation of the MOD-1 complex with enhancer A; MOD-1 is a heterodimer of fra-2 and the p50 subunit of NF-kappaB. Both TSH and insulin are required for full expression of the glucose activity in thyrocytes. The glucose effect is partially blocked by wortmannin, suggesting involvement of the PI3K signal system. The data support the possibility that high serum glucose levels in type 2 diabetic patients may increase MHC class I levels in target tissues and contribute to autoimmune complications of the disease.

The Flavonoid Quercetin Induces AP-1 Activation in FRTL-5 Thyroid Cells

“…The pSV0-CAT vector was obtained from the pSV2-CAT vector by removing the SV40 (Simian virus 40) early promoter sequences [17]. The reporter vectors were transiently transfected into the FRTL-5 cells using the diethylaminoethyl (DEAE)-dextran procedure [18,19]. The cells were grown to 60% confluency, maintained in 5H5% medium for 6 days, and then returned to 6H5% medium 12 h before transfection.…”

Hormonal Regulation of the MHC Class I Gene in Thyroid Cells: Role of the Promoter “Tissue-Specific” Region

“…Conversely, cellular extracts from cells treated with compounds that cause an increase of MHC class I expression, as thymosin-a1 1 mg/mL or glucose 30 mM, showed a decrease of the silencer complex (Figure 3B 3). The choice of treatment conditions is based on our previous experiments (17,18,20) and are detailed in the Materials and Methods section. Figure 3D shows the effect of these treatments on the MHC class I RNA level, which confirm our previous studies Cell extracts from FRTL-5 cells maintained in 6H5% medium were then preincubated with antibodies against the p65 subunit of NF-kB and c-jun.…”

“…In more details, those studies have shown that some compounds such as TSH, MMI and C10 act inducing the formation of two protein-DNA complexes on a region that includes the constitutive 38 bp silencer of the MHC class-I promoter, which contains a CRE-like sequence (11,15). Other compounds as hydrocortisone, insulin/IGF-1, TGF-b1, thym and glucose act regulating the binding of the Mod-1 complex with the enhancer A element (12,(16)(17)(18)22). In most cases, an increase in Mod-1 binding stimulates the gene transcription, while a decrease inhibits it.…”

“…Regarding the thyroid, previous studies have demonstrated that hormones and growth factors that regulate thyroid cell growth and function, such as thyroid stimulating hormone (TSH), hydrocortisone, insulin and insulin-like growth factor-I (IGF-I) decrease MHC class I expression in a coordinate and specific way (7,13,14). Of note is that MHC class I expression is also decreased by iodide, phorbol esters, transforming growth factor (TGF)-b1, and methimazole (MMI), whereas it is increased by a-and g-interferons (IFNs), thymosin-a1, and high levels of glucose (15)(16)(17)(18)(19)(20)(21). The specific regulation of MHC class I gene by these substances is particularly intriguing since the level of expression of MHC class I molecules differs between tissues, with the highest expression in lymphoid tissues and lower expression in some tissues as endocrine glands, skeletal muscle, myocardium, or gastric mucosa (22,23).…”

“…The functional relationship between these two regulatory regions has been confirmed by the observation that insulin and IGF-1 lose their inhibitory effect on the activity of a full length MHC class I promoter that lacks the enhancer A element. Furthermore, electrophoretic mobility shift assays (EMSAs) have shown that both the "tissue-specific" region and the "hormone/cytokinessensitive" region (particularly the enhancer A and the interferon response elements) interact with different members of the same family of transcription factors, nuclear factor-kB (NF-kB) and activator protein-1 (AP-1) (13)(14)(15)(16)(17)(18)(19)(20)30). In detail, the silencer element of the "tissue-specific" region interacts with the p65 subunit of NF-kB and c-jun, whereas the enhancer A element binds a protein complex named Mod-1 consisting of the p50 subunit of NF-kB and fra-2.…”