HTT and cancer: While Gsk3β phosphorylates HSF1 S303 and drives HSF1 degradation in cancer cells36, 41, a GSK3 inhibitor or GSK3 RNAi knockdown moderately stimulated Hsp70 expression (Supplementary Fig. 4E,H) and did not impact Htt-Q74 aggregation (Supplementary Fig. 4E).