Abstract

Purpose: Epigenetic dysregulation plays a role in pituitary tumor pathogenesis. Some differences in DNA methylation were observed between invasive and noninvasive nonfunctioning gonadotroph tumors. This study sought to determine the role of DNA methylation changes in repetitive LINE-1 elements in nonfunctioning gonadotroph pituitary tumors. Methods: We investigated LINE-1 methylation levels in 80 tumors and normal pituitary glands with bisulfite-pyrosequencing. Expression of two LINE-1 open reading frames (L1-ORF1 and L1-ORF2) was analyzed with qRT-PCR in tumor samples and mouse gonadotroph pituitary cells treated with DNA methyltransferase inhibitor. Immunohistochemical staining against L1-ORF1p was also performed in normal pituitary glands and tumors. Results: Hypomethylation of LINE-1 was observed in pituitary tumors. Tumors characterized by invasive growth revealed lower LINE-1 methylation level than noninvasive ones. LINE-1 methylation correlated with overall DNA methylation assessed with HM450K arrays and negatively correlated with L1-ORF1 and L1-ORF2 expression. Treatment of αT3-1 gonadotroph cells with 5-Azacytidine clearly increased the level of L1-ORF1 and L1-ORF2 mRNA; however, its effect on LβT2 cells was less pronounced. Immunoreactivity against L1-ORF1p was higher in tumors than normal tissue. No difference in L1-ORF1p expression was observed in invasive and noninvasive tumors. Conclusion: Hypomethylation of LINE-1 is related to invasive growth and influences transcriptional activity of transposable elements.

Highlights

  • ConclusionHypomethylation of LINE-1 is related to invasive growth and influences transcriptional activity of transposable elements

  • Pituitary neuroendocrine tumors (PitNETs) are frequently diagnosed intracranial tumors originating from different functional pituitary cells

  • LINE-1 DNA methylation levels were determined in five samples of normalpituitary pituitary gland and 80

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Summary

Conclusion

Hypomethylation of LINE-1 is related to invasive growth and influences transcriptional activity of transposable elements.

Introduction
Patients and Samples
Analysis of LINE-1 DNA Methylation Level
Analysis of Genome-Wide Methylation
Reverse Transcription and Quantitative PCR
Cell Culture and Treatment
Immunohistochemical Staining
Statistical Analysis
LINE-1
LINE-1 DNA Methylation and Expression of LINE-1 Open Reading Frame
L1-ORF1p Expression in Nonfunctioning Gonadotroph Tumor Tissue and Normal
L1-ORF1p expression in nonfunctioning gonadotroph
Discussion
Conclusions
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