Alexander Metz

"SETD2 loss in renal carcinoma cells induces the unfolded protein response"

Introduction
SETD2 encodes a histone H3-K36 methyltransferase which is frequently inactivated in clear cell renal carcinomas (ccRCCs) and papillary RCCs via 3p deletion/LOH and deleterious mutations. Histone H3-K36 trimethylation is facilitated by SETD2, which is necessary for proper pre-mRNA intron splicing. Improperly spliced mature mRNA may lead to aberrant translation of retained introns (ATaRI), which represents potential therapeutic vulnerabilities. We explored this hypothesis using real world data and RCC models.

Methods and Results
Gene set enrichment analysis comparing SETD2-mutant to WT tumors using samples from the TCGA KIRC data set revealed that the untranslated protein response (UPR) was strongly enriched, as were several immunotherapy-relevant pathways. This suggested that peptides arising from ATaRI may be present, since they would not be expected to fold properly and thus need to be addressed by the UPR pathway to maintain homeostasis. To investigate this further, we generated Setd2-isogenic RENCA cells using CRISPR. Knockout was confirmed by sequencing and immunoblot. H3K36 trimethylation was decreased or eliminated in monoclonal knockout cell lines, confirming a functional effect. Markers of UPR activation, including cleaved Atf6 and increased Atf4, were found to be upregulated in Setd2-null RENCA cells compared to controls as measured by immunoblot. Cleaved ATF6 is known to translocate to the nucleus to take part in a UPR transcriptional program. Consistent with this, ATF6 was found to preferentially localize to the nucleus in Setd2-knockout cells using immunofluorescence. Interestingly, CHOP, another downstream effector of the UPR pathway which predominantly regulates cell death, did not become upregulated in Setd2-knockout cells, suggesting activation of a compensatory cell survival pathway. 

Conclusions
We identify activation of the UPR upon Setd2 loss and suggest that activation of part of the UPR pathway may represent a new therapeutic vulnerability for exploitation as a rationale for personalized medicine, potentially in therapeutic cancer vaccines. We continue to evaluate the generation of peptides arising from ATaRI in Setd2-mutant contexts.