TLS Inhibits RNA Polymerase III Transcription

Abstract

RNA transcription by all the three RNA polymerases (RNAPs) is tightly controlled, and loss of regulation can lead to, for example, cellular transformation and cancer. While most transcription factors act specifically with one polymerase, a small number have been shown to affect more than one polymerase to coordinate overall levels of transcription in cells. Here we show that TLS (translocated in liposarcoma), a protein originally identified as the product of a chromosomal translocation and which associates with both RNAP II and the spliceosome, also represses transcription by RNAP III. TLS was found to repress transcription from all three classes of RNAP III promoters in vitro and to associate with RNAP III genes in vivo, perhaps via a direct interaction with the pan-specific transcription factor TATA-binding protein (TBP). Depletion of TLS by small interfering RNA (siRNA) in HeLa cells resulted in increased steady-state levels of RNAP III transcripts as well as increased RNAP III and TBP occupancy at RNAP III-transcribed genes. Conversely, overexpression of TLS decreased accumulation of RNAP III transcripts. These unexpected findings indicate that TLS regulates both RNAPs II and III and supports the possibility that cross-regulation between RNA polymerases is important in maintaining normal cell growth.

We thank N. Rao for HeLa nuclear extract; P. Richard and E. Rosonina for assistance with ChIP; C. David and Y. Feng for purified proteins; V. Vethantham, S. Bush, C. Wachtel, and other members of the Manley lab for helpful discussions; R. Beckerman and L. Biderman for assistance with quantitative PCR; and R. Prywes for pET11d-hTBP. We are grateful for antibodies from R. Roeder (Rockefeller University) and R. White (University of Glasgow).

A.Y.T. was partially funded by a Postgraduate Scholarship from the Natural Sciences and Engineering Research Council of Canada, and this work was supported by grants from the National Institutes of Health to J.L.M.