Delving deeper into RNAPII degradation upon UV-induced DNA damage

BECKERMAN, INÉS; MUÑOZ, JUAN C.; REBOTTARO, MARÍA LUZ; ALVAREZ, GONZALO G.; ETCHEPAREBORDA, JOAQUÍN A.; BOUVIER, LEÓN A.; MUÑOZ, MANUEL J.

Rosario

Congreso; LIX Annual Meeting of the Argentine Society for Biochemistry and Molecular Biology Research (SAIB); 2023

Argentine Society for Biochemistry and Molecular Biology Research (SAIB)

Among the numerous responses that occur in the event of DNA damage by ultraviolet (UV) light, RPB1, the major and catalytic subunit of human RNA Polymerase II (RNAPII), is specifically degraded by the ubiquitin-proteasome system. However, the mechanisms that control RPB1 degradation are not yet fully understood. The “last resort” model proposes that RPB1 is degraded at the damage site, or in cis, in order to facilitate access to the repair machinery. However, RPB1 degradation might not necessarily occur only as a last resort. In this sense, unpublished results from our group indicate that RNAPII degradation is controlled by a DNA damage-recognition system which does not rely on the stalling of RNAPII in front of a lesion. Here, we show that, accordingly with an in trans mechanism, UV-induced RNAPII degradation is not restricted to active RNAPII molecules. Indeed, the carboxy-terminal domain (CTD) of RPB1, which serves as a platform for post-translational modifications that regulate gene expression, is not required for RNAPII degradation. In this sense, two mutant versions of RPB1, one lacking the entire CTD and another one incapable of being phosphorylated on residues which are relevant for transcription, are both degraded upon UV-induced DNA damage. On another hand, we have studied the relationship between chromatin structure and RNAPII degradation. Unlike exposure of cells with UV light, transfection of in-vitro damaged DNA did not trigger RNAPII degradation, suggesting that chromatin structure might be involved in the signaling pathway controlling RPB1 levels. With this in mind, treatment with trichostatin A, a histone deacetylase inhibitor, partially inhibited RNAPII degradation. Altogether, these results indicate that RNAPII degradation is not restricted to RPB1 molecules that are engaged in transcription, and that the chromatin structure modulates the signaling pathway involved in the control of RPB1 levels in response to DNA damage.