The heparanase gene is located on human chromosome 4q 21.3, which contains a CpG island at the 5′ end of the promoter region, indicating that expression of heparanase is regulated by epigenetic mechanisms such as methylation[
1]. High levels of heparanase have been reported for hepatic carcinoma, breast cancer, colorectal cancer, lung cancer and lymphoma[
2‐
4], and are involved in tumor metastasis and invasion[
5‐
7]. On the other hand, inhibition of expression of heparanase has been reported to have an inhibitory effect on cancer invasion and metastasis. Zheng
et al. reported that small RNA interference-mediated gene silencing of heparanase could inhibit the invasion, metastasis and angiogenesis of gastric cancer cells[
8]. RNA interference (RNAi), a new technology in molecular biology, has become one of the most commonly used methods in research into gene function[
9], including transcriptional gene silencing (TGS) and post-transcriptional gene silencing (PTGS)[
10]. In PTGS, a small molecule RNA (siRNA) is designed for the coding region of a gene and targets the corresponding mRNA sequence-specific binding and degradation of the target sequence, inducing gene silencing[
9]. Continuous activation of upstream gene transcription leads to synthesis of a large amount of mRNA, which makes it difficult to maintain the silencing of a gene for a long time. Therefore, the interference efficiency of PTGS is not high. Previous studies have found that TGS has a high efficiency in plant cells, acting through permanent gene silencing by DNA methylation or histone deacetylation of the 5′ end of the promoter region of DNA. This is called siRNA-direct DNA methylation or histone modification[
11‐
13]. Kawasaki
et al.[
14] have found that this effect of TGS also occurs in human cells. Theoretically, interfering with a gene using an siRNA targeting the 5′ end of the promoter region can produce a long-lasting silence. Therefore, TGS seems more effective than PTGS with respect to the costs and prospects for clinical application.
In the present study, siRNA was transfected into hepatoma SMCC-7721 cells using TGS and PTGS to interfere with the expression of heparanase. Differences in the effect and the length of gene silencing were determined to evaluate the impact of silenced heparanase on the migration and invasion of SMCC-7721 cells.