BAG-1 is up-regulated in colorectal tumour progression and promotes colorectal tumour cell survival through increased NF-kappa B activity

Although expression of the anti-apoptotic protein Bcl-2-associated athanogene-1 (BAG-1) has been reported as up-regulated in a number of malignancies, we show for the first time that BAG-1 is over-expressed in medium/large-sized colorectal adenomas and carcinomas compared with normal epithelium. To investigate whether expression of BAG-1 is important for colorectal tumour cell survival, microarray analysis was carried out on the HCT116 colorectal carcinoma cell line following transfection with BAG-1 small interfering RNA (siRNA). Analysis identified altered expression of a subset of potential nuclear factor-kappa B (NF-kappa B)-regulated genes. Furthermore, knock down of BAG-1 was shown to inhibit NF-kappa B transcriptional activity. Inhibition of NF-kappa B activity using BAG-1 siRNA or the NF-kappa B inhibitor BAY-117082 suppressed HCT116 cell yield and induced apoptosis; combined treatment had no additive effect, suggesting that the decrease in cell yield associated with knock down of BAG-1 expression is mediated via inhibition of NF-kappa B. Of clinical relevance, BAG-1 siRNA sensitized colorectal carcinoma cells to apoptosis induced by potential therapeutic agent TRAIL as well as tumour necrosis factor-alpha, both inducers of NF-kappa B activity. In summary, knock down of BAG-1 leads to inhibition of NF-kappa B, identifying BAG-1 as a novel regulator of NF-kappa B. It is proposed that, by inhibiting NF-kappa B, suppression of BAG-1 could represent a novel strategy to impede colorectal cancer cell survival and as an adjuvant increase sensitivity to current therapeutic regimes