The Intermediate Filament Synemin Regulates Non-Homologous End Joining in an ATM-Dependent Manner

Abstract

<jats:p>The treatment resistance of cancer cells is a multifaceted process in which DNA repair emerged as a potential therapeutic target. DNA repair is predominantly conducted by nuclear events; yet, how extra-nuclear cues impact the DNA damage response is largely unknown. Here, using a high-throughput RNAi-based screen in three-dimensionally-grown cell cultures of head and neck squamous cell carcinoma (HNSCC), we identified novel focal adhesion proteins controlling DNA repair, including the intermediate filament protein, synemin. We demonstrate that synemin critically regulates the DNA damage response by non-homologous end joining repair. Mechanistically, synemin forms a protein complex with DNA-PKcs through its C-terminal tail domain for determining DNA repair processes upstream of this enzyme in an ATM-dependent manner. Our study discovers a critical function of the intermediate filament protein, synemin in the DNA damage response, fundamentally supporting the concept of cytoarchitectural elements as co-regulators of nuclear events.</jats:p>

c-Abl Tyrosine Kinase Is Regulated Downstream of the Cytoskeletal Protein Synemin in Head and Neck Squamous Cell Carcinoma Radioresistance and DNA Repair

“…Intriguingly, these findings about synemin/c-Abl interactions are also consistent with a previous report demonstrating interactions of synemin and DNA-PK to co-control DSB repair [ 23 ]. Several publications document a complex signaling network between c-Abl and different DNA repair proteins.…”

“…Previously, we reported that the intermediate filament synemin is involved in the response to X-ray irradiation in dependence on DNA-PKcs [ 23 ]. To further unravel the complex involvement of synemin in the regulation of radiation survival, we performed synemin knockdowns using three different siRNAs and one esiRNA (endoribonuclease-prepared siRNA) in two 3D lrECM grown HNSCC cell lines, i.e., Cal33 and SAS ( Figure 1 A–F and Figure S1A,B ).…”

“…Extra- and intracellular players orchestrate radio- and chemoresistance of cancer cells through complex and yet not fully understood mechanisms. The intermediate filament synemin, also defined as focal adhesion protein, has been shown to confer radioresistance by co-regulating DNA-PKcs-dependent DNA repair processes [ 23 ]. Here, we further elucidated the involvement of synemin in radioresistance and DNA repair and add additional facets.…”

“…To address c-Abl´s interrelation with other DNA repair factors, we focused on ATM as putative candidate. In a recent study, synemin has been shown to functionally interconnect with DNA-PK via ATM [ 23 ]. Interestingly, our data support the notion that ATM is associated with synemin and c-Abl as ATM inhibition does affect their protein-protein interaction.…”

“…NHEJ repair is error-prone and is active during the whole cell cycle. Recently, we were able to demonstrate that FAP/cytoskeletal components such as the large type IV intermediate filament protein synemin influence radioresistance and DNA-PK regulated NHEJ in an ATM-dependent manner in head and neck cancer cells [ 23 ].…”