Figure 5

Involvement of ABCA1 in Curcumin induced resistance. The effect of Curcumin on p65 (A), the apoptosis related factors bcl2 (B) and surviving (C) and cell death (increase of free nucleosomes, D) was analyzed in a series of double modulation experiments. Silencing of the multidrug resistance gene ABCA1 led to a reduction of p65 expression down to 50% of the original level already after 15 h (panel A, M14ABCA1si (triangle down)). The simultaneous treatment with 25 μM Curcumin further reduced p65 expression down to about 15% of the initial value after 24 h treatment (panel A, M14ABCA1si Cur (diamond)). Expression of the NFκB regulated anti-apoptotic factors bcl2 and survivin was reduced after ABCA1 silencing: bcl2 expression was reduced 10% in ABCA1-silenced cells 24 h after transfection with siRNA (panel B, M14ABCA1si (triangle down)). Treatment of M14 cells carrying the ABCA1 knock-downs with 25 μM Curcumin led to a significant reduction of bcl2 expression of about 35% with (panel B, M14ABCA1si Cur (diamond)). Hence Curcumin reduces bcl2 expression in M14 cells transfected with ABCA1 siRNAs by about 25%. Expression of survivin was diminished upon silencing of ABCA1 in M14 cells to about 50% of the basic value 24 h after transfection with siRNAs (panel C, M14ABCA1si (triangle down)). The addition of 25 μM Curcumin to ABCA1 silenced cells further reduced survivin expression significantly in M14 cells down to about 40% of initial expression levels (figure 5C, M14ABCA1si Cur (diamond)). Accordingly Curcumin treatment diminishes survivin expression in ABCA1 silenced M14 cells to 10%. Apoptosis as measured by means of increased numbers of free nucleosomes in cell lysates was induced in ABCA1 silenced M14 cells 24 h after transfection with siRNAs (panel D, M14ABCA1si (triangle down)). Curcumin treatment of the ABCA1 silenced M14 cells dramatically induced apoptosis already after 2 h with increasing effect up to 24 h (panel D, M14ABCA1si Cur (diamond)). Transfection of an unspecific nonsilencing siRNA control alone (M14nonsi) or in combination with 25 μM Curcumin (M14nonsi Cur) did neither alter the expression of p65, bcl2 and survivin nor induce apoptosis in M14 cells (panels A, B, C, D, M14nonsi (triangle up), M14nonsi Cur (square))