Purpose: To investigate the promoter methylation status of
Interferon regulatory factor 8 (IRF8) and its relation with
IRF8 transcriptional silencing or downregulation in renal cell
carcinoma (RCC), which further clarifies the effects of IRF8 on
RCC tumorigenesis and identifies a new epigenetics biomarker
for early diagnosis of RCC.
Materials and Methods: IRF8 expression and methylation was
detected by semi-quantitative RT-PCR and methylation specific
PCR (MSP) in multiple RCC cell lines and primary tumors.
We examined the cell cycle of IRF8-transfected RCC cell lines
by flow cytometry method, and assessed the colony formation
ability of IRF8 by colony formation assay. We also tested the
target genes of IRF8 by quantitative PCR.
Results: IRF8 was highly expressed in normal human adult tissues,
but was greatly down-regulated or transcriptional silenced in
RCC cell lines. The methylation specific PCR revealed that IRF8
promoter was methylated in 50% RCC cell lines, and in 31.25%
renal primary tumors. The silencing of IRF8 in RCC, due to
aberrant DNA methylation, could be reversed by pharmacologic
demethylation reagent AZA. Ecotopic expression of IRF8 inhibited
RCC cell lines (786-O, A498) colony formation, and caused G2/M
arrest, suggesting its tumor-suppressive function in RCC cell lines.
In addition, Caspase8, a target gene of IRF8, was up-regulated 3
times in IRF8-transfected RCC cell lines.
Conclusions: IRF8 exerts tumor-suppressive function in RCC, and
its promoter methylation could lead to its transcriptional silencing
or downregulation. Our results indicated that IRF8 may serve as a
biomarker for early detection and prognosis prediction of RCC.