Silencing of a death associated protein kinase as a pro-survival factor in colon cancer cells

Aims: Cyclooxygenase-2 (COX-2) regulates apoptosis in colorectal cancer. We previously identified DRAK2, a pro-apoptotic 'death associated' kinase, as negatively regulated by COX-2 both in-vitro and in-vivo. We aimed to characterise the role of DRAK2 at a cellular level in regulating survival and death in colon cancer cells. Methods: To mirror the effects of COX-2 expression on DRAK2 transcription in cancer cells, we used small interfering RNAs (siRNAs) to silence DRAK2 expression and look for changes in susceptibility to cell death in HT-29 cells. To overcome problems associated with low transfection efficiency, a green fluorescent protein (GFP) tag was co-transfected to select out positively transfected cells. Results: Significant reductions in DRAK2 expression were achieved with the use of siRNAs (mean reduction of 70% as assessed by qRT-PCR, ANOVA p=0.02). The GFP tagged 'DRAK2 silenced' cells maintained cell viability and showed a reduced susceptibility to apoptosis induced by COX-2 inhibitors compared with either wild-type or mock transfected cells (n=3). Conclusions: Silencing of DRAK2 expression in colon cancer cells, mirroring the effect of COX-2 expression, improves cell survival and reduces susceptibility to apoptosis. This may in part explain the anti-neoplastic effects of COX-2 inhibitors.