Critical role for c‐FLIP L on Fas resistance in colon carcinoma cell line HT‐29

The cellular Fas‐associated death domain‐like interleukin‐1β‐converting enzyme inhibitory protein‐long form (c‐FLIP L ) is a key regulator of Fas signaling, although owing a dominant‐negative homologue of caspase‐8, the role of c‐FLIP L remains controversial. In the present study, two pairs of small interfering RNA (siRNA) directed against c‐FLIP L were used to assess the effect of c‐FLIP L on Fas‐mediated apoptosis of colon carcinoma in vitro . HT‐29 cell line was selected for overexpression of c‐FLIP L and Fas with RT—PCR and flow cytometry analyses. After electroporation, the mRNA level of c‐FLIP L was significantly decreased (control siRNA versus c‐FLIP L siRNA, 77.97 ± 5.61% versus 26.22 ± 3.79%) and the maximum interfering efficiency was around 66.49% using semi‐quantitative RT—PCR analysis. Knockdown of c‐FLIP L with the specific siRNA sensitized colon carcinoma cells to Fas‐mediated apoptosis (control siRNA versus c‐FLIP L siRNA, 5.68 ± 2.11% versus 29.50 ± 2.27%) using DNA content analysis and Annexin V—FITC analysis. In conclusion, our study indicated that c‐FLIP L might be a suppressor of Fas‐mediated apoptosis in Fas antigen expressing colon carcinoma and therefore a potential target for novel anticancer therapies.