Consequences of the Hsp110DE9 mutation in tumorigenesis and the 5-fluorouracil-based chemotherapy response in Msh2-deficient mice.

Heat shock proteins (HSPs) play oncogenic roles in human tumours. We reported a somatic inactivating mutation of HSP110 (HSP110DE9) in mismatch repair-deficient (dMMR) cancers displaying microsatellite instability (MSI) but did not assess its impact. We evaluated the impact of the Hsp110DE9 mutation on tumour development and the chemotherapy response in a dMMR knock-in mouse model (Hsp110DE9 KI Msh2 KO mice). The effect of the Hsp110DE9 mutation on tumorigenesis and survival was evaluated in Msh2 KO mice that were null (Hsp110 wt ), heterozygous (Hsp110DE9 KI/+ ), or homozygous (Hsp110DE9 KI/KI ) for the Hsp110DE9 mutation by assessing tumoral syndrome (organomegaly index, tumour staging) and survival (Kaplan-Meier curves). 5-Fluorouracil (5-FU), which is the backbone of chemotherapy regimens in gastrointestinal cancers and is commonly used in other tumour types but is not effective against dMMR cells in vivo, was administered to Hsp110DE9 KI/KI , Hsp110DE9 KI/+ , and Hsp110 wt Msh2 KO mice. Hsp110, Ki67 (proliferation marker) and activated caspase-3 (apoptosis marker) expression were assessed in normal and tumour tissue samples by western blotting, immunophenotyping and cell sorting. Hsp110 wt expression was drastically reduced or totally lost in tumours from Msh2 KO Hsp110DE9 KI/+ and Msh2 KO Hsp110DE9 KI/KI mice. The Hsp110DE9 mutation did not affect overall survival or tumoral syndrome in Msh2 KO Hsp110DE9 KI/+ and Msh2 KO Hsp110DE9 KI/KI mice but drastically improved the 5-FU response in all cohorts (Msh2 KO Hsp110DE9 KI/KI : P 5fu  = 0.001; Msh2 KO Hsp110DE9 KI/+ : P 5fu  = 0.005; Msh2 KO Hsp110 wt : P 5fu  = 0.335). Histopathological examination and cell sorting analyses confirmed major hypersensitization to 5-FU-induced death of both Hsp110DE9 KI/KI and Hsp110DE9 KI/+ dMMR cancer cells. This study highlights how dMMR tumour cells adapt to HSP110 inactivation but become hypersensitive to 5-FU, suggesting Hsp110DE9 as a predictive factor of 5-FU efficacy.