Chemotherapy causes a reversible decrease in VMP1/MIR21 DNA methylation in granulocytes from breast cancer survivors

Abstract

BackgroundDNA methylation alterations within the VMP1/MIR21 gene region, a potential epigenetic biomarker of systemic inflammation, have been demonstrated in mononuclear blood cells from early breast cancer (BC) patients after chemotherapy. Whether these changes are present in granulocytes, persist in the years after treatment, and affect VMP1 or MIR21 gene expression, remains unknown. AimWe aimed to investigate whether adjuvant chemotherapy alters the DNA methylation and gene expression of VMP1/MIR21 in granulocytes from postmenopausal BC patients and, if so, whether these treatment-induced changes are reversible in the first two years after completed chemotherapy. MethodsWhole blood samples were obtained from 30 postmenopausal BC patients before chemotherapy and every six months for two years, and from 10 healthy age- and BMI-matched controls. DNA and RNA was extracted from isolated granulocytes, and DNA methylation of four CpG sites located in the gene body of VMP1, which is situated in the promoter region of MIR21, was assessed through bisulfite pyrosequencing. qPCR was used for assessment of VMP1 and MIR21 expression. ResultsVMP1/MIR21 was significantly demethylated in granulocytes from BC patients shortly after completed chemotherapy compared to before (10 percentage points decrease, p<0.0001). Six months thereafter, DNA methylation values were significantly increased (6 percentage points, p = 0.002), and they were further increased to pre-chemotherapy levels 12, 18 and 24 months post chemotherapy. Chemotherapy did not cause significant changes in the expression of VMP1 or MIR21. ConclusionThe unique follow-up samples in this study demonstrated that chemotherapy induced a transient reduction in DNA methylation of the VMP1/MIR21 region in granulocytes from postmenopausal BC patients. Although transient, chemotherapy-induced epigenetic changes in blood cells may contribute to the increased risk of inflammatory-related comorbidities in BC survivors.