The VHL gene is epigenetically inactivated in pheochromocytomas and abdominal paragangliomas

Area of Science:

• Endocrinology
• Oncology
• Epigenetics

Background:

• Pheochromocytoma (PCC) and paraganglioma (PGL) are neuroendocrine tumors linked to catecholamine excess.
• Genetic mutations in predisposing genes occur in about a third of PCC/PGL cases.
• Epigenetic alterations, particularly promoter methylation, in these genes are poorly understood.

Purpose of the Study:

• To investigate the role of promoter methylation in 11 key PCC/PGL disease genes.
• To assess the correlation between gene methylation and expression levels in PCC and PGL tumors.
• To identify potential epigenetic drivers in the pathogenesis of PCC and PGL.

Main Methods:

• Bisulphite pyrosequencing was used to analyze the methylation density of 11 PCC/PGL genes in 96 tumors and 34 normal adrenal tissues.
• Quantitative RT-PCR was employed to determine gene expression levels.
• Statistical analyses were performed to compare methylation and expression between tumor types and normal tissues.

Main Results:

• Most investigated genes (EGLN1, MAX, MEN1, NF1, SDHB, SDHC, SDHD, SDHAF2, TMEM127, RET) showed low promoter methylation in tumors and normal samples.
• The VHL gene promoter exhibited significantly increased methylation in PCC/PGL tumors compared to normal adrenals (57% vs. 27%).
• VHL promoter methylation was higher in malignant vs. benign tumors and in PGL vs. PCC, with decreased VHL gene expression inversely correlated with methylation (R = -0.359).

Conclusions:

• The VHL gene promoter is aberrantly methylated in approximately 75% of PCC and PGL tumors.
• Increased VHL promoter methylation and decreased VHL gene expression suggest a significant role for VHL epigenetic dysregulation in PCC/PGL development.
• These findings highlight VHL as a potential therapeutic target in PCC and PGL.