IL-32γ Enhances TNF-α-Induced Cell Death in Colon Cancer

Interleukin (IL)-32 is a recently discovered cytokine that appears to play an important role in human colon cancer growth. We investigated that IL-32 in combination with TNF- remarkably inhibited cell growth of human colon cancer cells (HCT116 and SW620) and tumor growth in xenograft-bearing nude mice. The transient enforced overexpression of IL-32 potentiated the inhibitory effect of TNF- on DNA synthesis, cell number and protein content, and enhanced apoptosis in colon cancer cells. We also found that knockdown of IL-32 by siRNA showed the abolishment of cell growth inhibitory effect of TNF-. The IL-32-overexpressing colon cancer cells further increased TNF--mediated expression of p38 MAPK as well as that of Bax, cleaved caspase-3 and -9, but decreased that of antiapoptotic proteins such as Bcl-2, cellular inhibitor of apoptosis protein (IAP) and X chromosome IAP. In xenograft model, the lipopolysaccharide (LPS)-injected (1.25mg/kg) mice inoculated with IL-32-transfected HCT116 colon cancer cells were more decrease tumor volume and weight than inoculated with vector. Tumor tissues isolated from LPS-injected mice inoculated with IL-32-overexpressing colon cancer cells potentiated the expression levels of pro-apoptotic proteins such as cleaved caspase-3, 9 and Bax, but decreased that of Bcl-2. Furthermore, the mice increased IL-10 production, but decreased IL-6 levels in serum. In conclusion, our results suggest that IL-32 may potentiate TNF--induced cell growth inhibition through activation of p38 MAPK pathways.