The Methylation Analysis of the Glucose-Dependent Insulinotropic Polypeptide Receptor (GIPR) Locus in GH-Secreting Pituitary Adenomas

The glucose-dependent insulinotropic polypeptide receptor (GIPR) is aberrantly expressed in about one-third of GH-secreting pituitary adenomas (GH-PAs) and has been associated with a paradoxical increase of GH after a glucose load. The reason for such an overexpression has not yet been clarified. In this work, we aimed to evaluate whether locus-specific changes in DNA methylation patterns could contribute to this phenomenon. By cloning bisulfite-sequencing PCR, we compared the methylation pattern of the GIPR locus in GIPR-positive (GIPR(+)) and GIPR-negative (GIPR) GH-PAs. Then, to assess the correlation between Gipr expression and locus methylation, we induced global DNA methylation changes by treating the lactosomatotroph GH3 cells with 5-aza-2 '-deoxycytidine. Differences in methylation levels were observed between GIPR+ and GIPR GH-PAs, both within the promoter (31.9% vs. 68.2%, p < 0.05) and at two gene body regions (GB_1 20.7% vs. 9.1%; GB_2 51.2% vs. 65.8%, p < 0.05). GH3 cells treated with 5-aza-2 '-deoxycytidine showed a similar to 75% reduction in Gipr steady-state level, possibly associated with the observed decrease in CpGs methylation. These results indicate that epigenetic regulation affects GIPR expression in GH-PAs, even though this possibly represents only a part of a much more complex regulatory mechanism.

Automated summary

It has been found that aberrant expression of glucose-dependent insulinotropic polypeptide receptor (GIPR) in GH-secreting pituitary adenomas (GH-PAs) can lead to an increase in GH levels after glucose load. This study aimed to investigate if DNA methylation changes in the GIPR locus could contribute to this phenomenon. The results showed differences in methylation levels between GIPR-positive and GIPR-negative GH-PAs, indicating that epigenetic regulation affects GIPR expression. Treatment with 5-aza-2'-deoxycytidine resulted in a reduction in Gipr expression, suggesting a correlation between DNA methylation and Gipr expression.