Reciprocal modulation of tumor necrosis factor and gamma interferon receptors in human carcinoma cells: Biological significance and mechanisms of action.

Abstract

Human recombinant cytokines may have a role in the clinical treatment of pancreatic and colorectal cancers. In the present studies, the growth inhibitory actions of recombinant human tumor necrosis factor (rhTNF) and recombinant human gamma interferon (rhIFN-γ) were examined in several human pancreatic and colorectal carcinoma cell lines in vitro in relation to the expression TNF and IFN-γ receptors. rhTNF and rhIFN-γ exerted significant, but differential, growth inhibitory effects in five of six cell lines examined. All six cell lines exhibited high affinity binding sites for both ¹²⁵I-labeled rhTNF and ¹²⁵I-labeled rhIFN-γ. However, the basal number of binding sites in general did not correlate with the relative growth inhibitory effects induced by either rhTNF or rhIFN-γ. In contrast, in three cell lines in which the cytokines exerted synergistic effects, rhTNF increased by 2-3 fold the number of ¹²⁵I-rhIFN-γ binding sites. Further, in two of these cell lines, rhIFN-γ also upregulated ¹²⁵I-rhTNF binding. As demonstrated by anti-IFN-γ receptor antibody labeling and the use of transcriptional and translational inhibitors, the increase in ¹²⁵I-rhIFN-γ binding by rhTNF was due to enhanced synthesis and expression of IFN-γ receptor protein. Recombinant human lymphotoxin (rhLT), which binds to the TNF receptor, and recombinant human interleukin-1 alpha (rhIL-1), which binds to a distinct receptor and mimicks many of the biological actions of TNF, also increased the expression of IFN-γ receptors. Further, rhIL-1 exerted synergistic growth inhibitory effects with rhIFN-γ. Taken together, these results suggest that the synergistic effects of either TNF/LT or IL-1 and IFN-γ may involve the upregulation of IFN-γ receptors. The mechanisms by which rhTNF and rhIL-1 upregulate IFN-γ receptors are unclear. However, the upregulatory effects of both rhTNF and rhIL-1 were attenuated by the Ca²⁺ ionophore A23187 and the phorbol ester 12-O-tetradecanoyl phorbol-13-acetate, suggesting that the mechanisms involved in IFN-γ receptor upregulation by TNF and IL-1 are negatively modulated by Ca²⁺ and protein kinase C activation. The results of this dissertation suggest that immunotherapy with recombinant cytokines may be useful in that treatment of pancreatic and colorectal cancer in vivo.