Epigenetic silencing of LPP/miR-28 in multiple myeloma

Area of Science:

• Oncology
• Epigenetics
• Molecular Biology

Background:

• MicroRNA-28-5p (miR-28-5p) functions as a tumor suppressor in various cancers.
• The host gene for miR-28-5p, LIM domain containing preferred translocation partner in lipoma (LPP), lacks a CpG island, unlike miR-28-5p's intronic location.

Purpose of the Study:

• To investigate the hypothesis that miR-28-5p is epigenetically silenced by promoter DNA methylation of its host gene, LPP, in multiple myeloma.
• To explore the relationship between LPP/miR-28 methylation, miR-28-5p expression, and the expression of its target gene CCND1.

Main Methods:

• Methylation-specific PCR and quantitative bisulfite pyrosequencing were used to assess LPP/miR-28 methylation in healthy controls, human myeloma cell lines (HMCLs), and primary myeloma samples.
• Quantitative reverse transcription PCR was employed to measure the expression levels of miR-28-5p, LPP, and CCND1.

Main Results:

• LPP/miR-28 was unmethylated in healthy controls but showed partial methylation in 20% of HMCLs, correlating with decreased miR-28-5p and LPP expression.
• Demethylation using 5-AzadC in RPMI-8226R cells restored miR-28-5p and LPP expression, while methylation was re-established upon drug withdrawal.
• Higher CCND1 expression was observed in HMCLs with LPP/miR-28 methylation, supporting miR-28-5p's tumor suppressor function. Methylation was infrequent in primary myeloma samples at diagnosis and absent at relapse.

Conclusions:

• This study provides the first evidence of epigenetic regulation of intronic miR-28-5p expression through promoter DNA methylation of its host gene, LPP.
• The findings suggest that epigenetic silencing of miR-28-5p by LPP promoter methylation is a mechanism in multiple myeloma, warranting further investigation in other cancers.