Exactly how hepatitis B virus causes liver cancer has been a mystery for a long time. It is clear that the X protein (HBx) has something to do with it, but exactly what mechanisms are involved? These are very different to other cancer-causing viruses.
Some recent studies have demonstrated that viruses alter the expression of microRNAs, non-coding RNA molecules that can block the expression of target genes. Researchers have just reported that miR-148a is repressed by HBx to promote growth and metastasis of liver cancer. In normal liver cells, miR-148a represses the expression of the oncogenic protein HPIP, but the hepatitis B virus prevents expression of miR-148a, leading to increased levels of HPIP and subsequent oncogenic transformation. This study demonstrates that a cancer-associated virus promotes carcinogenesis through direct manipulation of a microRNA.
Hepatitis B virus X protein represses miRNA-148a to enhance tumorigenesis: http://goo.gl/2HkK7
Abstract: MicroRNAs (miRNAs) have been shown to be dysregulated in virus-related cancers; however, miRNA regulation of virus-related cancer development and progression remains poorly understood. Here, we report that miR-148a is repressed by hepatitis B virus (HBV) X protein (HBx) to promote cancer growth and metastasis in a mouse model of hepatocellular carcinoma (HCC). Hematopoietic pre–B cell leukemia transcription factor–interacting protein (HPIP) is an important regulator of cancer cell growth. We used miRNA target prediction programs to identify miR-148a as a regulator of HPIP. Expression of miR-148a in hepatoma cells reduced HPIP expression, leading to repression of AKT and ERK and subsequent inhibition of mTOR through the AKT/ERK/FOXO4/ATF5 pathway. HBx has been shown to play a critical role in the molecular pathogenesis of HBV-related HCC. We found that HBx suppressed p53-mediated activation of miR-148a. Moreover, expression of miR-148a was downregulated in patients with HBV-related liver cancer and negatively correlated with HPIP, which was upregulated in patients with liver cancer. In cultured cells and a mouse xenograft model, miR-148a reduced the growth, epithelial-to-mesenchymal transition, invasion, and metastasis of HBx-expressing hepatocarcinoma cells through inhibition of HPIP-mediated mTOR signaling. Thus, miR-148a activation or HPIP inhibition may be a useful strategy for cancer treatment.