The intermediate filament
synemin has been previously identified as novel regulator of
cancer cell therapy resistance and
DNA double strand break (
DSB) repair. c-Abl
tyrosine kinase is involved in both of these processes. Using PamGene technology, we performed a broad-spectrum
kinase activity profiling in three-dimensionally, extracellular matrix grown
head and neck cancer cell cultures. Upon
synemin silencing, we identified 86 deactivated
tyrosine kinases, including c-Abl, in irradiated
HNSCC cells. Upon irradiation and
synemin inhibition, c-Abl hyperphosphorylation on
tyrosine (Y) 412 and
threonine (T) 735 was significantly reduced, prompting us to hypothesize that c-Abl
tyrosine kinase is an important signaling component of the
synemin-mediated radioresistance pathway. Simultaneous targeting of
synemin and c-Abl resulted in similar radiosensitization and
DSB repair compared with single
synemin depletion, suggesting
synemin as an upstream regulator of c-Abl. Immunoprecipitation assays revealed a
protein complex formation between
synemin and c-Abl pre- and post-irradiation. Upon pharmacological inhibition of ATM,
synemin/c-Abl
protein-
protein interactions were disrupted implying
synemin function to depend on ATM
kinase activity. Moreover, deletion of the SH2 domain of c-Abl demonstrated a decrease in interaction, indicating the dependency of the
protein-
protein interaction on this domain. Mechanistically, radiosensitization upon
synemin knockdown seems to be associated with an impairment of DNA repair via regulation of non-homologous end joining independent of c-Abl function. Our data generated in more physiological 3D
cancer cell culture models suggest c-Abl as further key determinant of radioresistance downstream of
synemin.