Yeast Stress Responses PDF Download

Proper stress responses are pivotal for cells to survive and adapt to new environments. Stressed cells coordinate a multi-faceted response spanning many levels of physiology involving growth and cell cycle arrest, metabolites changes, translation arrest and a large fraction of transcriptomic change, which includes the common environmental stress response (ESR). Yet knowledge of the complete stress-activated regulatory network, principles for signal integration as well as the rationale of ESR activation upon stress remains elusive. To decipher complicated signaling networks, we developed an experimental and computational approach to integrate available protein interaction data with gene fitness contributions, mutant transcriptome profiles, and phospho-proteome changes in cells responding to salt stress, to infer the salt-responsive signaling network in yeast. The inferred subnetwork presented many novel predictions by implicating new regulators, uncovering unrecognized crosstalk between known pathways, and pointing to previously unknown 'hubs' of signal integration. We exploited these predictions to show that Cdc14 phosphatase is a central hub in the network and that modification of RNA polymerase II coordinates ESR activation: induction of stress-defense genes with reduction of growth-related transcripts. Additionally, we show that the yeast ESR cannot be simply explained as a byproduct of altered cell-cycle distribution or arrested growth upon stress, given that arrest of growth and cell cycle progression did not trigger strong ESR activation. Furthermore, ESR transcripts did not fluctuate with cell cycle phase in dividing cells and did not respond to arrest points as proposed previously. We also show that activation of the ESR is an active response to stress as arrested cells show robust, dose-dependent ESR activation in response to stress. We propose that ESR activation helps reallocate transcription and translation capacity to stress defense genes upon stresses.