Hepatocellular carcinoma (HCC) is the most common type of liver cancer. Most cases of HCC are secondary to either a viral hepatitis infection (hepatitis B or C) or cirrhosis (alcoholism being the most common cause of hepatic cirrhosis)
. Although much is known about both the cellular changes that lead to HCC and the etiological agents responsible for the majority of HCC cases (hepatitis B virus, hepatitis C virus, alcohol), the molecule pathogenesis of HCC is still not well understood
Myc (c-Myc) is a regulator gene that encodes for a transcription factor. A mutated version of Myc is found in many cancers, which causes Myc to be constitutively (persistently) expressed. This further induces an unregulated expression of several genes, some of which are involved in cell proliferation
. A frequent genetic abnormality seen in HCC is the overexpression of c-Myc
[5, 6]. The importance of c-Myc expression in HCC is demonstrated both by studies of transgenic mice
[7, 8] and clinical research which has indicated that overexpression of c-Myc is found in most HCC patients and correlated with poor prognosis
A recent study demonstrates that temporary inhibition of Myc selectively kills mouse lung cancer cells or induces apoptosis, making it a potential cancer drug target
[10, 11]. In the human genome, Myc is located on chromosome 8 and is believed to regulate expression of 15% of all genes
 through binding on Enhancer Box sequences (E-boxes) and recruiting histone acetyltransferases (HATs). This means that in addition to its role as a classical transcription factor, Myc also functions to regulate global chromatin structure by regulating histone acetylation both in gene-rich regions and at sites far from any known genes
. In this study, we aimed to investigate whether specific down-regulating the protein level of c-Myc in a HepG2 cell line might result in the inhibition of cell growth.
RNA interference (RNAi) is a process in which activation of an intracellular pathway modulated by small-interfering RNA (siRNA) composed of 21–23 nucleotides (nt) leads to degradation of a specific, targeted mRNA
. The selective and robust effect of RNAi on gene expression makes it a valuable research tool, both in cell culture and in living organisms because synthetic dsRNA introduced into cells can induce suppression of specific genes of interest
[15, 16]. RNAi has been used to inhibit diseases induced by virus (for instance, HIV
 and influenza
), tumorigenesis caused by oncogenic K-ras, and H-ras
[19, 20], activation of oncogenes resulting from chromosomal translocations (for example bcr/abl in chromic myeloid leukemia
), cancers caused by viral infections, and others. Recently, retroviral-based approaches to deliver siRNA into tissue cultured mammalian cells have been proved to be powerful, and doxycycline-regulated inducible gene expression by RNAi has been shown to be particularly useful for the analysis of genes that are necessary for cellular survival (22,23). These studies have established a new area in the genetic manipulation of human cancer development by allowing oncogenes to be down regulated by RNAi. For this purpose, RNAi directed against c-Myc was used here.
In this study, HepG2 cell was transfected with a plasmid which was under the control of the U6 promoter to deliver and express siRNA targeting c-Myc to determine whether this technique could be used for the specific inhibition of oncogene overexpression and whether this inhibition resulted in antitumor effects. Our results showed that specific down-regulation of c-Myc by RNAi was sufficient to inhibit the proliferative, invasive, and migrative capabilities of HepG2 cell, and that c-Myc might serve as a therapeutic target for HCC.