Dynamic regulation of murine RNA Polymerase III transcription during heat shock stress
Cells respond to many different types of stresses by overhauling gene expression patterns, both at the transcriptional and translational level. Under heat stress, global transcription and translation are inhibited, while the expression of chaperone proteins are preferentially favored. As the direct link between mRNA transcription and protein translation, tRNA expression is intricately regulated during the stress response. Despite extensive research into the heat shock response (HSR), the regulation of tRNA expression by RNA Polymerase III (Pol III) transcription has yet to be fully elucidated in mammalian cells. Here, we examine the regulation of Pol III transcription during different stages of heat shock stress in mouse embryonic stem cells (mESCs). We observe that global transcription of tRNAs is downregulated after 30 minutes of heat shock, followed by an overall increase in tRNA transcription after 60 minutes of heat shock. This effect is more evident in tRNAs, though other RNA Pol III gene targets are also similarly affected. Notably, we show that the down-regulation at 30 minutes of heat shock is independent of HSF1, the master transcription factor of the HSR, but that the subsequent increase in expression at 60 minutes requires HSF1. Taken together, these results demonstrate an adaptive RNA Pol III response to heat stress, and an intricate relationship between the canonical HSR and tRNA expression. Overall design: CUT&Tag of RNA Polymerase III subunit RPC7 in wildtype and HSF1 knockout mouse embryonic stem cells (mESCs) subjected to varying lengths of heat shock treatment at 42C, either unconditioned (unCond) or preconditioned (preCond) with a prior heat shock.