Double-strand breaks (DSBs) occur frequently in
the genome during genome replication or by DNA
damaging agents. DNA lesions affect fundamental
DNA-dependent nuclear processes, such as
replication and transcription. We have developed
an experimental system where DSBs are induced
at coding regions of RNA polymerase II transcribing
genes. We have started to study the kinetics of RNA
polymerase II transcription inhibition in the presence
of DNA breaks. We observed that induction of the
break led to transcription inhibition and the restoration
of transcription closely followed the dynamics of
the repair of breaks. We confirmed by chromatinimmunoprecipitation
that the break induction led to
displacement of RNA polymerase II affecting both
the elongation and the initiation of transcription. Our
results show that this is dependent on one of the
major kinase in DNA damage repair called DNAPKcs.
We also investigated the downstream steps of RNA
polymerase II removal and we claimed that it was
a multistep process involving additional kinases and
ubiquitin ligases NEDD4 and CUL3. At the last step
of break dependent transcriptional silencing the RNA
polymerase II is targeted for proteasome dependent
degradation. These data demonstrate that the DNA
damage repair complexes and proteasomal system
have a synergistic and active role in transcriptional
silencing during the DSB repair by removing the RNA
pol II from the transcribing region. We show here
that DNA lesions occurring at transcribed regions
cause a transient repression until the lesion is
repaired. This is probably a cell defense mechanism
to avoid production of truncated or mutated
transcripts in essential genes whose alterations in
their gene expression would endanger cell viability.
Understudying the role of DNAPKcs, in preventing
RNA pol II bypassing a DSB might be a key in
avoiding the production of mutated transcripts that
could lead to cancerous phenotypes
