Overexpression of REIC/Dkk-3 suppresses the expression of CD147 and inhibits the proliferation of human bladder cancer cells

Abstract

Our group previously developed an adenoviral vector encoding the REIC/Dkk-3 gene (Ad-REIC), a tumor suppressor, for cancer gene therapy. The Ad-REIC agent induces apoptosis and inhibits invasion in a number of cancer cell lines; however, the molecular mechanisms underlying its effects remain unclear. Cluster of differentiation 147 (CD147), also known as extracellular matrix metalloproteinase inducer (EMMPRIN), is a key molecule that promotes cancer proliferation and invasion. In order to elucidate the therapeutic mechanism of Ad-REIC, its effect on the expression of CD147 in human bladder cancer KK47 cells was investigated. Treatment with Ad-REIC markedly downregulated the expression of CD147 and significantly inhibited cellular proliferation. Since the expression of CD147 is reported to be under the positive control of mitogen-activated protein kinase (MAPK) signaling and the c-Myc protein, the correlations between the expression of CD147 and the activation of MAPKs or the expression of c-Myc were examined. Unexpectedly, no positive correlation was observed between the level of CD147 and the potential regulators that were assessed, indicating that another signaling pathway is responsible for the downregulation of CD147. The results from the present study demonstrate that Ad-REIC treatment can significantly downregulate the expression of CD147 in bladder cancer cells. Downregulation of the cancer-progression factor CD147 may be a novel mechanism that underlies the therapeutic effects of Ad-REIC treatment.

Keywords: CD147; EMMPRIN; REIC/Dkk-3; bladder cancer; cell proliferation.

Figure 1.

Expression of CD147 in human urothelial cancer cell lines. (A) Western blot analysis of CD147 expression in human and mouse urothelial cell lines. Human normal bladder urothelial cells (HUC) and various bladder cancer cell lines were examined. β-actin was used as a loading control (B) Correlation analysis between the expression of CD147 and the hTERT promoter-driving activity in human urothelial cells. The band density in was determined by a densitometric analysis. The hTERT promoter-driving activity was measured as an index of malignancy using an hTERT promoter-dependent expression system. CD147, cluster of differentiation 147; hTERT, human telomerase reverse transcriptase; a.u., arbitrary unit.

Figure 2.

Ad-REIC treatment downregulates the expression of CD147 in human bladder cancer KK47 cells. The overexpression of REIC/Dkk-3 was induced by the Ad-REIC agent at 100 MOI and the expression level of the indicated proteins was analyzed by western blotting. β-actin was used as a loading control. REIC/Dkk3, reduced expression in immortalized cells/Dickkopf-3; CD147, cluster of differentiation 147; Ad-REIC, adenoviral vector encoding the human REIC/Dkk3 gene.

Figure 3.

Inhibition of cell proliferation in KK47 human bladder cancer cells following Ad-REIC treatment. (A) The appearance of the cells after the indicated treatment is shown by phase contrast microscopy. (B) Bar graph of the number of cells following the treatment. Five experiments were performed. A significant difference was observed (*P<0.05) between the Ad-REIC and the control Ad-LacZ treatments. REIC/Dkk3, reduced expression in immortalized cells/Dickkopf-3; Ad-REIC, adenoviral vector encoding the human REIC/Dkk3 gene.

Figure 4.

Expression levels of the possible factors regulating the expression of CD147 in KK47 cells following Ad-REIC treatment. Since the expression of CD147 is reported to be under the positive control of p38-, Erk1/2- and JNK-dependent MAPK signaling and the expression of c-Myc, these proteins were analyzed by western blotting. β-actin was used as a loading control. CD147, cluster of differentiation 147; REIC/Dkk3, reduced expression in immortalized cells/Dickkopf-3; Ad-REIC, adenoviral vector encoding the human REIC/Dkk3 gene; p38, p38 MAPK; Erk1/2, extracellular signal-regulated kinase 1/2; JNK, c-Jun N-terminal kinase; MAPK, mitogen-activated protein kinase.