DEAH-BOX HELICASE 8 IS A REGULATOR OF HEAT SHOCK FACTOR 1
Heat Shock Factor 1 (HSF1) is a key transcription factor mediating the cellular stress response and promoting cancer cell survival. We identify DEAH-box helicase 8 (DHX8) as a crucial regulator of HSF1 pre-mRNA processing. Silencing DHX8 leads to the accumulation of HSF1 transcripts with retained introns and reduced HSF1 protein. Intron retention is also detected in canonical heat shock and cancer-signature gene sets regulated by HSF1, and in mitosis, G2M checkpoint, cMYC and E2F-associated gene sets. Consistent with intron retention and the role DHX8 in the later stages of splicing, eCLIP analysis finds significant enrichment of DHX8 binding between the lariat branch site and 3' splice junction. DHX8 silencing induces apoptosis in cancer cells to a greater extent than in non-tumorigenic cells. We show that the ATPase activity of DHX8 is essential for function, and propose DHX8 as a therapeutic target on pathways that protect cancer cells from oncogene-induced stress. Overall design: H1299 non-small cell lung cancer cells DHX8-dTAG cells were treated for 6 hours with 250 nM dTAG-V1 heterobifunctional small molecule to induce degradation of the DHX8-dTAG fusion protein.  H1299 cells were also treated with 10nM siTOOLs DHX8 or scramble control pooled siRNA for 72 hours.  HCT116 colorectal cancer cells were transduced with a lentiviral construct encoding doxycyline-inducible human DHX8 (DHX8 wild-type, DHX8-K549 ATPase-dead or DHX8-R647G/F648G RNA binding mutant). Cells were treated with DHX8 siRNA to remove endogenous DHX8 or scramble control siRNA or mock transfection conditions. Treatments were run in the absence or presence of doxycycline to assess the impact of inducing the exogenous wild-type or mutant DHX8. Four independent biological repeats were run for each condition