Interferon action
This is an Open Access Thesis
Abstract
This thesis is divided into two parts: the first deals with studies that focus on the effect of interferons on the expression of foreign genetic material. The second part deals with the interferon-regulated (2$\sp\prime$-5$\sp\prime$)oligoadenylate system. This system is most probably an effector arm of the anti-viral anti-mitogenic actions of interferons.I show here that interferons inhibit the expression of both early SV40 RNA and SV40 Tag, and SV40 DNA replication in SV40 infected cells. Interferons selectively inhibit the expression of the Tag encoded by superinfecting SV40 virions in SV40-transformed cells superinfected with SV40. The effect of interferon was seen when cells were transfected with SV40 DNA or infected with SV40 virions.Data shown indicates that interferons inhibit the expression of bacterial genes driven by the SV40 early promoter-enhancer elements. Moreover, interferon treatment inhibits the expression of a bacterial gene driven by cellular promoter-enhancer elements, when newly transfected into cells. Thus, it seems that interferons can distinguish between stably integrated genes and newly arriving genes.The (2$\sp\prime$-5$\sp\prime$)oligoadenylate system is composed of the (2$\sp\prime$-5$\sp\prime$)oligoadenylate synthetases, the RNase L, a (2$\sp\prime$-5$\sp\prime$)phosphodiesterase, and the (2$\sp\prime$-5$\sp\prime$)oligoadenylates. In the presence of double stranded RNA the (2$\sp\prime$-5$\sp\prime$)oligoadenylate synthetases convert ATP into (2$\sp\prime$-5$\sp\prime$)oligoadenylates. The RNase L is a latent endonuclease that when activated by binding a (2$\sp\prime$-5$\sp\prime$)oligoadenylate cleaves on single stranded regions of RNA. A scheme for the partial purification of the RNase L from calf spleens is presented. Furthermore, the discovery of a (2$\sp\prime$-5$\sp\prime$)oligoadenylate binding protein in wheat is described.Growth conditions profoundly affect the (2$\sp\prime$-5$\sp\prime$)oligoadenylate system. I show here that Platelet-derived growth factor increases the levels of (2$\sp\prime$-5$\sp\prime$)oligoadenylate synthetase transcripts and of (2$\sp\prime$-5$\sp\prime$)oligoadenylate synthetases in Balb/c-3T3 cells. Moreover, Platelet-derived growth factor decreases the levels of RNase L in these cells. Interferon treatment inhibits the mitogenic action of Platelet-derived growth factor without inhibiting the expression of c-myc RNA.Finally I present a hypothesis implicating endogenous double stranded RNAs in the control of cell growth.