Suppression of BCRP expression and restoration of sensitivity to chemotherapy in multidrug-resistant HCC cell line HEPG2/ADM by RNA interference.

BACKGROUND/AIMS: Breast cancer resistance protein (BCRP) is an ATP-binding cassette multidrug transporter that confers resistance to various anticancer drugs like Adriamycin. Overexpression of BCRP confers multidrug resistance (MDR) in hepatocellular carcinoma cells and is a frequent impediment to successful chemotherapy. METHODOLOGY: We evaluated a new approach using RNA interference for the specific knockdown of BCRP in hepatocellular carcinoma cells. To overcome the BCRP-mediated atypical multidrug drug resistance, one small interfering RNA construct (RNAi) targeting one special region of BCRP gene were designed to inhibit the atypical MDR expression by transfecting them into HepG2/ADM cell lines. RESULTS: We found that the overexpression of BCRP gene was suppressed efficiently by the introduction of small interfering RNA, which caused sequence specific gene silence. The level of BCRP mRNA reduced to 22.55% after transfected by pSUPER-BCRPs compared with those of the controls. Similarly, the level of BCRP decreased too. Furthermore, the sensitivity to Adriamycin of pSUPER-BCRPs-treated HEPG2/ADM cells is increased 3.55-fold compared to their control (p<0.05). The relative reverse rate of HepG2/ADM cell to Adriamycin is 72.2%. CONCLUSIONS: These data indicated that pSUPER-BCRPs could modulate MDR and may present a new approach to overcome BCRP-mediated drug resistance in HEPG2/ADM cells. It may reverse multidrug resistance phenotype and therefore provide promising therapeutic modalities in the treatment of hepatocellular carcinoma.

Down-regulation of Dicer in hepatocellular carcinoma.

Dicer, the key enzyme in the RNAi pathway, is misregulated in tumor tissues. The altered expression of Dicer is associated with clinical characteristics in patients with cancer. Liver carcinoma and adjacent non-neoplastic tissues were obtained from 36 patients with hepatocellular carcinoma (HCC) undergoing surgery. Expressions of Dicer mRNA were evaluated using the Real-time reverse transcription-PCR in 36 liver carcinoma tissues and 36 adjacent histologically non-cancerous liver tissues. Dicer mRNA levels were evaluated in relation to age, sex, tumor number, tumor size, tumor stage, and distant metastasis. Dicer mRNA level was significantly lower in malignant tissues than in the corresponding non-neoplastic tissues in 34 of the 36 patients with HCC (94.4%). The Dicer expression level was not associated with clinical characteristics, including age, sex, tumor number, tumor size, tumor stage, or distant metastasis in HCC cases. These results demonstrate that Dicer is significantly down-regulated in HCC, suggesting that reduced expression of Dicer may play an important role during the process of hepatocarcinogenesis.

[Intercellular transfer of P-glycoprotein in hepatocellular cell line HepG2].

OBJECTIVE: To investigate whether there is intercellular transfer of functional P-glycoprotein(P-gp) from P-gp-positive cells to P-gp-negative cells in vitro. METHODS: HepG2/GFP cells, a HepG2 cell line stably expressing GFP, were co-cultured with HepG2/ADM cells, an adriamycin-resistant cell line derived from HepG2 cells. The distribution of P-gp in hepatocellular carcinoma cell was observed under laser scanning confocal microscope (LSCM). Immunomagnetic beads were used to separate HepG2/GFP cells from the mixed culture. The abundance of P-gp was analyzed by western blot, and the expression of mdr1 mRNA was detected by qRT-PCR. RESULTS: Yellow fluorescence was detected in HepG2/aqMDR cells, green fluorescence was detected in HepG2/GFP cells, red fluorescence was detected in HepG2/ADM cells by LSCM. The level of P-gp protein in HepG2/aqMDR cells was lower than that in HepG2/ADM cells, but higher than that in HepG2/GFP cells (q = 35.07, P < 0.05) and HepG2 cells (q = 36.87, P < 0.05). The expression of mdr1 mRNA in HepG2/ADM cells was higher than that in HepG2/aqMDR, HepG2 and HepG2/GFP cells, but there was no significant difference in mdr1 mRNA among HepG2/aqMDR, HepG2 and HepG2/GFP cells (F = 2.30, P > 0.05). CONCLUSIONS: P-gp can transfer from drug resistant hepatocellular cells to sensitive hepatocellular carcinoma cells. This study suggests a novel mechanism of multidrug resistance in hepatocellular carcinoma.

[Up-regulation of major histocompatibility complex class I-related molecules A (MICA) induced by 5-aza-2'-deoxycytidine].

OBJECTIVE: Major histocompatibility complex class I C-related molecules A and B (MICA and MICB) are innate immune system ligands for the NKG2D receptor expressed by natural killer cells and activated CD8(+)T cells. Our previous study showed that 5-aza-2'-deoxycytidine (5-aza-dC), a DNA methyltransferase inhibitor, can induce the expression of MICB and sensitized cells to NKL-cell-mediated cytolysis. The aim of this study was to determine the expression level of MICA in HepG2 cells (an HCC cell line) and L02 cells ( a normal liver cell), and to investigate the effect of 5-aza-dC on MICA expression in HepG2 cells. METHODS: Cells were treated with 5-aza-dC, caffeine and ATM-specific siRNA. The cell surface MICA protein on HepG2 cells and L02 cells was determined using flow cytometry. The mRNA level was detected using real time RT-PCR. RESULTS: MICA was undetectable on the surface of L02 cells, but was highly expressed on HepG2 cells. MICA expression was upregulated in response to 5-aza-dC treatment (P less than 0.05), and the upregulation of MICA was partially prevented by pharmacological or genetic inhibition of ataxia telangiectasia mutated (ATM) kinase (P less than 0.05). CONCLUSION: Our data suggest that 5-aza-dC induces the expression of MICA by a DNA damage-dependent mechanism.

Decreased Dicer expression elicits DNA damage and up-regulation of MICA and MICB.

RNA interference (RNAi) acts constitutively to silence the innate immune response, and innate immunity genes are misregulated in Dicer-deficient Caenorhabditis elegans. Here, we show that inhibition of Dicer expression by RNAi in human cells up-regulates major histocompatibility complex class I-related molecules A and B (MICA and MICB). MICA and MICB are innate immune system ligands for the NKG2D receptor expressed by natural killer cells and activated CD8(+)T cells. We reveal that knockdown of Dicer elicits DNA damage. Up-regulation of MICA and MICB by Dicer knockdown is prevented by pharmacologic or genetic inhibition of DNA damage pathway components, including ataxia telangiectasia mutated (ATM) kinase, ATM- and Rad3-related kinase, or checkpoint kinase 1. Therefore we conclude that up-regulation of MICA and MICB is the result of DNA damage response activation caused by Dicer knockdown. Our results suggest that RNAi is indirectly linked to the human innate immune system via the DNA damage pathway.

Induction of MHC class I-related chain B (MICB) by 5-aza-2'-deoxycytidine.

5-Aza-2'-deoxycytidine (5-aza-dC), a DNA methyltransferase inhibitor, exerts antitumor activity through induction of cell cycle arrest, apoptosis and DNA damage. In this study, we showed that MHC class I-related chain B (MICB), a ligand of the NKG2D receptor expressed by natural killer cells and activated CD8(+) T cells, was upregulated following 5-aza-dC treatment. The upregulation of MICB was accompanied by promoter DNA demethylation and DNA damage. Furthermore, the upregulation of MICB was partially prevented by pharmacological or genetic inhibition of ataxia telangiectasia mutated (ATM) kinase. Our results suggest that promoter DNA demethylation, in combination with DNA damage, contribute to the upregulation of MICB induced by 5-aza-dC.