Activation of B‐Myb by E2F1 in hepatocellular carcinoma

Abstract

Deregulation of E2F1 transcriptional activity is observed in a variety of cancers, including hepatocellular carcinoma (HCC). The aim of the present study is to identify transcriptional target genes of E2F1 in HCC. We determined expression levels for E2F1 and ten candidate genes thought to be targets of E2F1 in primary HCCs using a real-time quantitative reverse transcription-PCR assay. Following small interfering RNA (siRNA)-mediated knockdown of E2F1 in HCC cell lines, we quantified mRNA levels of the candidate E2F1 target genes. E2F1 was significantly over-expressed in 41 primary HCCs as compared to non-tumorous liver tissues. Among the candidates, MYBL2, whose product is the transcriptional factor B-Myb, which is involved in controlling cell-cycle progression and apoptosis, was significantly over-expressed in primary HCCs. Additionally, expression levels of MYBL2 correlated with those of E2F1. Knockdown of E2F1 resulted in a decrease in expression of MYBL2. A copy-number gain for MYBL2 was observed in 36 of 66 primary HCCs, suggesting that MYBL2 expression is up-regulated by amplification in addition to being regulated by E2F1. Moreover, siRNA-mediated knockdown of MYBL2 led to reduced expression of CDC2 (which encodes CDC2), cyclin A2 (CCNA2), and topoisomerase II alpha (TOP2A), implicating these genes in the cell cycle and suggesting that they may be downstream targets of B-Myb. MYBL2 is a probable transcriptional target of E2F1 in HCC and may therefore be a useful biomarker for diagnosis and an attractive target for molecular therapies useful to treat HCC.