Activation of the murine monocyte/macrophage cell line, J774A1 by poly(A).poly(U): I. Binding of poly(A).poly(U) and induction of oligo-2',5'-adenylate synthetase

Ultrastructural nucleolar alterations induced by an ametantrone--poly r(A-U) complex

The current study has documented changes in the ultrastructure as well as in the intranucleolar distribution of rDNA and rRNA in RT4 (human transitional cell bladder carcinoma) cell nucleoli following a 3-h exposure to toxic doses of 50 microM ametantrone (AMT), 200 microM poly (adenylate-uridylate) (poly r(A-U) or an AMT/poly r(A-U) combination with an AMT/polyribonucleotide ratio of 1:4 and a poly r(A-U) concentration of 200 microM. While the main nucleolar components (fibrillar center (F), dense fibrillar component (D), granular component (G) and interstices (I) can be discerned following all treatments, the nucleoli exhibit: compaction, segregation, a decrease in the number of F, an increase in the size of remaining F, margination of intranucleolar chromatin and retention of intranucleolar pre-rRNA and rRNA. The relative abilities of the test agents to induce nucleolar compaction are AMT/poly r(A-U) > poly r(A-U) > AMT > sham-treated, while the abilities of the test agents to induce the remaining nucleolar changes are AMT/poly r(A-U) > or = AMT > poly r(A-U) > sham-treated cells. Poly r(A-U) and the induced interferon induce nucleolar compaction, while AMT produces nucleolar segregation. These results are consistent with a model in which the poly r(A-U) and/or the AMT inhibit DNA transcription and rRNA processing as well as the release of nascent preribosomes from the nucleolus.

Ultrastructural nucleolar alterations induced by an ametantrone/polyr(A-U) complex

In the present study we examined the ultrastructural modifications as well as the precise distribution of DNA and RNA in RT4 cell nucleoli following a 3-h exposure to nontoxic or toxic doses of ametantrone (AMT), poly(adenylate-uridylate) (polyr(A-U), or an AMT/polyr(A-U) combination. While distribution of nucleic acids within the various nucleolar components is not modified following all treatments, the nucleoli exhibit several ultrastructural changes: redistribution of the nucleolar components, decrease in the number of fibrillar centers, and increase in the size of the fibrillar centers. The relative frequencies of the test agents to induce the apparition of nucleoli of compact type are AMT/polyr(A-U) > AMT approximately polyr(A-U) > sham-treated, while the abilities of the test agents to induce the nucleolar segregation are AMT/polyr(A-U) approximately AMT > polyr(A-U) > sham-treated cells. These ultrastructural changes are characteristics of drugs that intercalate into DNA and inhibit rDNA transcription as well as rRNA processing and release of nascent preribosomes from the nucleolus.

Involvement of interleukin-6 and interferon-alpha in the poly(A).Poly(U)-induced 2',5'-oligoadenylate synthetase activity in the mouse monocyte-macrophage cell line, J774A1

The synthetic polyribonucleotide poly(A).poly(U) induces 2',5'-oligoadenylate synthetase activity in the murine macrophage cell line J774A1. The possible role of several cytokines involved in macrophage activation (i.e., IL-1, IL-6, TNF, and IFN) was examined in the present study. It was first demonstrated that among the anticytokine antibodies, only monoclonal antibodies directed against IL-6 inhibited the induction of 2',5'-oligoadenylate synthetase by poly(A).poly(U) in a dose-dependent manner. Moreover, it was established that poly(A).poly(U) elicited IL-6 production in J774A1 cells in a time-and dose-dependent manner. Consequently, the effect of IL-6 on 2',5'-oligoadenylate synthetase activity was studied. IL-6 either alone or in combination with IL-1 and TNF did not induce 2',5'-oligoadenylate synthetase activity. IL-6 did not potentiate IFN-gamma-induced 2'-5'-oligoadenylate synthetase activity. In contrast, addition of IL-6 to the incubation medium potentiated the stimulation of 2'-5'-oligoadenylate synthetase activity by IFN-alpha. These results suggest that IL-6 is a necessary but not sufficient factor in the induction of 2'-5'-oligoadenylate synthetase activity in the J774A1 cell line by poly(A).poly(U).