RNAPII DEGRADATION IN RESPONSE TO UV-INDUCED DNA DAMAGE

MUÑOZ, JUAN C.; BECKERMAN, INÉS; BOUVIER, LEÓN A.; MUÑOZ, MANUEL J.

Congreso; CONGRESO CONJUNTO SAIB-SAMIGE 2021-LVII Reunión Anual de SAIB; 2021

Our skin is regularly exposed to ultraviolet (UV) radiation that reaches Earth's surface and damages cellular components. Since DNA is the only biopolymer that is neither disposable nor recyclable, it must be repaired when damaged. Among the various repair systems that human cells have, the nucleotide excision repair (NER) system is the most relevant for repair of UV light-induced lesions. Damage detection by NER system occurs by two different DNA-sensing mechanisms that then converge on the same machinery that repairs the damage: transcription-coupled repair (TC-NER) and global genome repair (GG-NER). At the same time, it is well known that UV-induced DNA lesions favour the degradation of RNA Polymerase II (RNAPII). The residue responsible for the ubiquitination and degradation of the RNAPII major subunit was recently identified and it was shown that RNAPII levels are essential for the gene expression response and cell survival upon UV-induced DNA damage. However, the mechanisms that lead to the degradation of RNAPII have not yet been elucidated. One hypothesis, known as the "last resort" theory, states that RNAPII degradation is dependent on TC-NER. According to this theory, the arrest of RNAPII in DNA - given its inability to transcribe the lesions - would lead to its degradation, thus allowing access to the repair machinery. However, different evidences suggest that the scenario could be different. On the one hand, most of the repair of lesions in template strands in transcriptionally active genes, the only lesions repaired by TC-NER, occurs in the first hours post UV, while the degradation of RNAPII is observed hours later. On the other hand, preliminary results from our group show that RNAPII degradation is mainly controlled by the GG-NER system. Using the CRISPR/Cas9 editing system, we generated human keratinocytes unable to recognize lesions through the GG-NER system (GG-NER KO / TC-NER WT cells) and observed a marked inhibition in the degradation of RNAPII and an increase in cell viability in response to UV light. Consequently, we propose that RNAPII levels determine cell viability and are mainly controlled by an unexplored GG-NER-dependent mechanism. It is only very recently that we began to understand the impact of RNAPII levels on gene expression and cell survival. Thus, understanding the mechanisms that governs RNAPII degradation in response to UV irradiation is of vital importance.