Person:

Bunch, Heeyoun

TRIM28 is a multidomain protein with versatile functions in transcription and DNA repair. Recently it was shown that this factor plays unanticipated roles in transcriptional elongation. TRIM28 was shown to stabilize the pausing of RNA polymerase II (Pol II) close to the transcriptional start site in many unactivated genes, permitting Pol II accumulation and readying genes for induction. In addition, the factor was shown to respond rapidly to signals accompanying transcriptional activation permitting the productive elongation of RNA by previously paused Pol II. We discuss here critical regulatory mechanisms of TRIM28 in transcriptional control and DNA repair that may illuminate the novel roles of this factor in pausing and elongation of Pol II.

Summary Promoter proximal pausing of RNA polymerase II (Pol II) is a major checkpoint in transcription. An unbiased search for novel human proteins that could regulate paused Pol II at the HSPA1B gene identified TRIM28. In vitro analyses indicated HSF1-dependent attenuation of Pol II pausing upon TRIM28 depletion, whereas in vivo data revealed de novo expression of HSPA1B and other known genes regulated by paused Pol II upon TRIM28 knockdown. These results were supported by genome-wide ChIP-sequencing analyses of Pol II occupancy that revealed a global role for TRIM28 in regulating Pol II pausing and pause release. Furthermore, in vivo and in vitro mechanistic studies suggest that transcription-coupled phosphorylation regulates Pol II pause release by TRIM28. Collectively, our findings identify TRIM28 as a novel factor that modulates Pol II pausing and transcriptional elongation at a large number of mammalian genes.

We have previously shown that RNA polymerase II (Pol II) pause release and transcriptional elongation involve phosphorylation of the factor TRIM28 by the DNA damage response (DDR) kinases ATM and DNA-PK. Here we report a significant role for DNA breaks and DDR signalling in the mechanisms of transcriptional elongation in stimulus-inducible genes in humans. Our data show the enrichment of TRIM28 and γH2AX on serum-induced genes and the important function of DNA-PK for Pol II pause release and transcriptional activation-coupled DDR signalling on these genes. γH2AX accumulation decreases when P-TEFb is inhibited, confirming that DDR signalling results from transcriptional elongation. In addition, transcriptional elongation-coupled DDR signalling involves topoisomerase II because inhibiting this enzyme interferes with Pol II pause release and γH2AX accumulation. Our findings propose that DDR signalling is required for effective Pol II pause release and transcriptional elongation through a novel mechanism involving TRIM28, DNA-PK and topoisomerase II.