Longstanding ulcerative and Crohn's colitis increases the risk of colorectal cancer (CRC) compared to the general population. Elevated IGF-II mRNA and protein have been found in tumour tissue in sporadic CRC. The association of IGF-II in colitis-related-CRC is unknown.
Objectives: To determine whether pro-inflammatory cytokines associated with colitis, namely IL-5, TNF-alpha and IL-1beta, alter the proliferative effect of IGF-II on the colorectal cancer cell line, Caco-2.
Design: Caco-2 cells were cultured with IGF-II and IL-5, TNF-alpha or IL-1beta. At 24 h intervals cell proliferation was assessed. The mechanism of action of any synergistic affect was investigated by RT-PCR to determine change in mRNA expression of IGF-II, IGF-1R or IGF-2R.
Results: After 72 h, IGF-II increased absorption (corresponding to cell density) compared to controls by 25% (p < 0.02). Co-incubation with IGF-II and IL-5 increased absorption by 42% (p < 0.001) compared to controls and 18% (p < 0.03) compared to IGF-II alone. Enhanced growth response was also seen with TNF-alpha and IL-1beta, but less so than IL-5. The IL-5 receptor was not expressed by Caco-2 cells and mRNA expression of the IGF-1R or IGF-2R was unchanged by incubation with cytokines.
Conclusions: IGF-II promotes Caco-2 growth, an effect enhanced with IL-5, TNF-alpha and IL-1beta. The greatest response was with IL-5. This was IL-5 receptor-independent. Possible mechanisms include IL-5 interaction on an un-identified receptor or interference with IGF-binding proteins, as occurs with IL-1beta and IL-6. The enhanced growth response of Caco-2 cells to pro-inflammatory cytokines and IGF-II may have implications for the pathogenesis of CRC formation in colitis.