James J. Greene

To identify genes mediating the antiproliferative action of interferon (IFN), two cDNA libraries were constructed with mRNA from IFN-treated and untreated human fibrosarcoma (HT1080) cells previously shown to be highly sensitive to the antiproliferative effects of IFN. Differential screening of these two libraries identified cloned sequences whose expression was either induced or repressed with IFN treatment. Rescreening of these sequences with cDNA probes constructed from proliferating or quiescent cells led to the identification of one IFN-induced and three IFN-repressed sequences whose expressions also appeared to be modulated by cell proliferation. Blot-hybridization analysis revealed that RNA levels corresponding to the three repressed genes decreased when HT1080 cells were treated with IFN or when proliferation of normal CUA foreskin fibroblast cells became naturally arrested by contact inhibition. Levels of RNA corresponding to the induced gene increased in HT1080 cells within 24 hr after IFN-treatment but declined below basal levels by 48 hr. Expression of these genes was unaffected or only slightly affected by IFN treatment in variant cells resistant to the antiproliferative effects of IFN. Collectively, these results suggest that the identified cDNAs correspond to genes that are involved in the antiproliferative action of IFN. Moreover, these results also suggest that IFN's antiproliferative action may be exerted through genes that contribute to arresting cell proliferation during contact inhibition.

Abstract Several interferon (IF) inducers, including polyinosinicrpolycytidylic acid (rIn•rCn), have previously been found to augment murine natural killer (NK) cell activity and to increase resistance to tumor growth. Our studies were undertaken to determine i) whether rIn•rCn could augment human NK cell activity, ii) whether there is a correlation between the ability of structurally different analogues of rIn•rCn to augment NK activity with their known ability to induce IF, and iii) whether analogues of rIn•rCn that do not induce the toxic effects ascribed to rIn•rCn would augment human NK activity. Treatment of human mononuclear cells with rIn•rCn resulted in marked augmentation of human NK cell activity against K562 leukemia cells. Depletion of lymphocytes expressing receptors for the Fc portion of IgG ablated the ability of rIn•rCn to augment cytotoxic activity, an observation consistent with previous findings that native NK cells and IF-activated NK cells express receptors for the Fc portion of IgG. Lymphocytes exposed to rIn•rCn for as few as 30 min developed augmented NK activity if followed by at least four additional hours of incubation, indicating parallels with the temporal requirements of double-stranded RNAs for cell triggering and resultant IF biosynthesis. Specific mismatched nontoxic analogues of rIn•rCn including rIn•rCn(Cl2,U)„ and rIn•rCn(C29,G)n, which preserve the function of IF inducibility, also augment NK activity, whereas a methylated analogue, rIn•rCn which fails to induce IF, does not augment NK cell activity. It is proposed, therefore, that augmentation of NK cell activity is an integral component of the double-stranded RNA interferon system rather than a secondary biologic property of certain RNA molecules.