Dynamic regulation of RNA Polymerase III transcription in mouse embryonic stem cells during heat shock stress

Abstract

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 Pol III transcription is downregulated after 30 minutes of heat shock, followed by an overall increase in transcription after 60 minutes of heat shock. This effect is more evident in tRNAs, though other Pol III gene targets are also similarly affected. Notably, we show that the downregulation 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.