Effect of dominant negative transforming growth factor-β receptor type II on cytotoxic activity of RAW 264.7, a murine macrophage cell line

Transforming growth factor-beta (TGF-beta) is a potent suppressor of the immune system. In the present study, we investigated the effect of TGF-beta resistance on a murine macrophage cell line. RAW 264.7, by overexpressing a dominant negative TGF-beta receptor type II (T beta RIIDN) construct. As expected, T beta IIDN-expressing RAW cells, designated as RAW-T beta RIIDN, were resistant to TGF-beta signaling. When these cells were cocultured with the murine renal cell carcinoma cell line, Renca, a dramatic increase in apoptosis of Renca cells was observed. Simultaneously, elevated levels of inducible nitric oxide synthase (iNOS) and tumor necrosis factor-alpha, (TNF-alpha) in association with IFN-gamma were detected in RAW-T beta RIIDN cells. When the effects of TNF-alpha and iNOS were neutralized through the use of neutralizing antibody and N-G-methyl-L-arginine, respectively, the enhanced cytotoxicity of T beta RIIDN-RAW cells was partially reversed. Taken together, these results show that TGF-beta-resistant RAW 264.7 murine macrophage cells have increased cytotoxic activity that is in part mediated by iNOS and TNF-alpha.