Cell-type specific concentration regulation of the basal transcription factor TFIIH

Abstract

The basal transcription/repair factor TFIIH is a ten sub-unit complex essential for RNA polymerase II (RNAP2) transcription initiation and DNA repair. In both these processes TFIIH acts as a DNA helix opener (by the enzymatic activity of the XPB and XPD helicases), required for promoter escape of RNAP2 in transcription initiation, and to set the stage for strand incision within the Nucleotide Excision Repair (NER) pathway. We generated a knock-in mouse model that endogenously expresses a fluorescent version of XPB. Here we demonstrate, via confocal imaging of ex vivo tissues and cells derived from this mouse model, that TFIIH steady state levels are tightly regulated at the single cell level, thus keeping nuclear TFIIH concentrations remarkably constant in a cell type dependent manner. Moreover, we show that individual cellular TFIIH levels are proportional to the speed of mRNA production, hence to a cells transcriptional activity, which we can correlate to proliferation status. Importantly, cancer tissue presents a higher TFIIH than normal healthy tissues. Taken together, these results show that TFIIH cellular concentration might be used as a bona-fide marker of transcriptional activity and proliferation.\n\nSignificanceUsing a mouse model expressing a fluorescently version of TFIIH, we showed that TFIIH concentration is tightly controlled and that this concentration is proportional to the cellular transcriptional activity and proliferation capacity.