Poliovirus proteinase 3C converts an active form of transcription factor IIIC to an inactive form: a mechanism for inhibition of host cell polymerase III transcription by poliovirus.

Abstract

In HeLa cells, RNA polymerase III (pol III)‐mediated transcription is severely inhibited by poliovirus infection. This is due primarily to a reduction in the transcriptional activity of TFIIIC, a transcription factor which binds in a sequence specific manner to the internal promoter of pol III genes. Using gel retardation assays, we have shown previously that inhibition of pol III transcription by poliovirus is correlated with disappearance of a transcriptionally active form of TFIIIC (complex I) concomitant with the appearance of a faster mobility, transcriptionally inactive form of TFIIIC (complex III). We show here that a poliovirus with a point mutation in the proteinase 3C (3Cpro) region failed to produce complex III and is limited in its ability to inhibit pol III transcription compared with the wild‐type virus. Incubation of purified 3Cpro, expressed in Escherichia coli, with transcriptionally active TFIIIC (complex I) in vitro resulted in generation of the transcriptionally inactive complex III form of TFIIIC. In an in vitro transcription assay, treatment of the complex I form of TFIIIC with 3Cpro almost completely inhibited pol III transcription. Finally expression of the 3Cpro gene in transfected HeLa cells resulted in significant inhibition of pol III‐mediated transcription. The results presented here suggest that proteolysis of the transcriptionally active form of TFIIIC by poliovirus 3Cpro is a mechanism by which poliovirus inhibits host cell RNA pol III transcription.

Cleavage site analysis in picornaviral polyproteins: Discovering cellular targets by neural networks

“…Studies by Clark and colleagues (Clark & Dasgupta, 1990;Clark et al, 1991Clark et al, , 1993 neural network method suggest that human TFIIIC (TFC3-HUM) may be cleaved between Q732-G (see Table 4), with a cleavage score of 0.644. This prediction supports the results presented in a recent report (Shen et al, 1996).…”

Stable Formation of Compositionally Unique Stress Granules in Virus-Infected Cells

“…In addition to reducing translation of cellular mRNAs, cleavage of host factors by 2A pro and 3C pro is also responsible for disrupting a number of cellular processes. For example, cleavage of nuclear pore complex proteins by 2A pro is thought to be responsible for inhibition of nucleo-cytoplasmic transport (2,38), while cleavage of TFIIIC and TBP by 3C pro contributes to the inhibition of transcription that occurs in infected cells (7,8,51). Numerous other targets for these proteases have been identified, including PABP (21), poly(rC) binding proteins 1 and 2 (41), the La autoantigen (46), the p65 subunit of NF-B (35), and polypyrimidine tract binding protein (1).…”

Mutational Analysis of Poliovirus 2Apro

“…Likewise, cleavage of transcription factor IIC subunit by poliovirus 3C pro leading to the shut-off of RNA polymerase III transcription in vitro has been documented (21,22). However, the relevance of these cleavages for the inhibition of cellular transcription by poliovirus infection remains to be established.…”