BCL-3 expression promotes colorectal tumorigenesis through activation of AKT signalling.

OBJECTIVE: Colorectal cancer remains the fourth most common cause of cancer-related mortality worldwide. Here we investigate the role of nuclear factor-κB (NF-κB) co-factor B-cell CLL/lymphoma 3 (BCL-3) in promoting colorectal tumour cell survival. DESIGN: Immunohistochemistry was carried out on 47 tumour samples and normal tissue from resection margins. The role of BCL-3/NF-κB complexes on cell growth was studied in vivo and in vitro using an siRNA approach and exogenous BCL-3 expression in colorectal adenoma and carcinoma cells. The question whether BCL-3 activated the AKT/protein kinase B (PKB) pathway in colorectal tumour cells was addressed by western blotting and confocal microscopy, and the ability of 5-aminosalicylic acid (5-ASA) to suppress BCL-3 expression was also investigated. RESULTS: We report increased BCL-3 expression in human colorectal cancers and demonstrate that BCL-3 expression promotes tumour cell survival in vitro and tumour growth in mouse xenografts in vivo, dependent on interaction with NF-κB p50 or p52 homodimers. We show that BCL-3 promotes cell survival under conditions relevant to the tumour microenvironment, protecting both colorectal adenoma and carcinoma cells from apoptosis via activation of the AKT survival pathway: AKT activation is mediated via both PI3K and mammalian target of rapamycin (mTOR) pathways, leading to phosphorylation of downstream targets GSK-3ß and FoxO1/3a. Treatment with 5-ASA suppressed BCL-3 expression in colorectal cancer cells. CONCLUSIONS: Our study helps to unravel the mechanism by which BCL-3 is linked to poor prognosis in colorectal cancer; we suggest that targeting BCL-3 activity represents an exciting therapeutic opportunity potentially increasing the sensitivity of tumour cells to conventional therapy.

BAG-1 is up-regulated in colorectal tumour progression and promotes colorectal tumour cell survival through increased NF-kappaB 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-kappaB (NF-kappaB)-regulated genes. Furthermore, knock down of BAG-1 was shown to inhibit NF-kappaB transcriptional activity. Inhibition of NF-kappaB activity using BAG-1 siRNA or the NF-kappaB 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-kappaB. 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-kappaB activity. In summary, knock down of BAG-1 leads to inhibition of NF-kappaB, identifying BAG-1 as a novel regulator of NF-kappaB. It is proposed that, by inhibiting NF-kappaB, 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.