Inhibitory effect of retinoids on Epstein-Barr virus induction in Raji cells

Getting the message direct manipulation of host mRNA accumulation during gammaherpesvirus lytic infection

The Gammaherpesvirinae subfamily of herpesviruses comprises lymphotropic viruses, including the oncogenic human pathogens Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus. During lytic infection, gammaherpesviruses manipulate host gene expression to optimize the cellular environment for viral replication and to evade the immune response. Additionally, although a lytically infected cell will itself be killed in the process of viral replication, lytic infection can contribute to pathogenesis by inducing the secretion of paracrine factors with functions in cell survival and proliferation, and angiogenesis. The mechanisms by which these viruses manipulate host gene expression are varied and target the accumulation of cellular mRNAs and their translation, signaling pathways, and protein stability. Here, we discuss how gammaherpesviral proteins directly influence host mRNA biogenesis and stability, either selectively or globally, in order to fine-tune the cellular environment to the advantage of the virus. Appreciation of the mechanisms by which these viruses interface with and adapt normal cellular processes continues to inform our understanding of gammaherpesviral biology and the regulation of mRNA accumulation and turnover in our own cells.

Inhibitory effects of triptogelin A-1 on 12-O-tetradecanoylphorbol-13- acetate-induced skin tumor promotion

Dihydroagarofuran sesquiterpenes, which were isolated from Tripterygium wilfordii Hook fil. var. regelii Makino and Euonymus sieboldianus Blume, showed inhibitory effects on Epstein-Barr virus early antigen (EBV-EA) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA). Triptogelin A-1, one of the active dihydroagarofuran sesquiterpenes, exhibited remarkable inhibitory effects on mouse skin tumor promotion in an in vivo two-stage carcinogenesis test. Interestingly, triptogelin A-1 was more effective when applied after TPA-treatment (post-treatment) than before TPA-treatment (pretreatment). The findings indicate that these dihydroagarofuran sesquiterpenes might be valuable antitumor promoters.

Inhibitory effects of ursolic and oleanolic acid on skin tumor promotion by 12-O-tetradecanoylphorbol-13-acetate

Ursolic acid (UA) and oleanolic acid (OA), which had been isolated from Glechoma hederacea as inhibitors of Epstein-Barr virus (EBV) activation induced by 12-O-tetradecanoylphorbol-13-acetate (TPA), were tested against inhibitory effect on tumor promotion by TPA in vivo. They inhibited effectively the tumor promotion in mouse skin and the activities were comparable to that of a known inhibitor of tumor promotion, retinoic acid (RA). Interestingly, UA was more effective on a single application before initial TPA-treatment than on a continuous application before each TPA-treatment, while OA and RA were ineffective in the same treatment. These data suggest that the role of UA for inhibitory action on tumor promotion differs slightly from those of RA and OA.

Ultrastructural studies on human lymphoblastoid cells treated with n-butyrate and 12-O-tetradecanoylphorbol-13-acetate

The effects of n-butyrate and/or 12-O-tetradecanoylphorbol-13-acetate (TPA) on Raji and P3HR-1 cells were examined using electron microscopy. n-Butyrate treatment caused a decrease in the number and elongation of surface microvilli. In addition, well-developed rough endoplasmic reticulum and a marked decrease in condensed chromatin clumps were observed in the nucleus. The filamentous structures and nuclear membrane-like structures, which were not reported previously, appeared occasionally in the nucleus. On the other hand, in the cells treated with TPA no marked morphological changes were observed except the higher cytoplasmic:nuclear ratio. n-Butyrate-induced morphological changes were not inhibited when combined with TPA or retinoic acid. Electron microscopic studies showed remarkable differences in morphological change in these cells treated with n-butyrate and/or TPA.