Proteasome assembly chaperone translation upon stress requires Ede1 phase separation at the plasma membrane

Distinct TORC1 signalling branches regulate Adc17 proteasome assembly chaperone expression

When stressed, cells need to adapt their proteome to maintain protein homeostasis. This requires increased proteasome assembly. Increased proteasome assembly is dependent on increased production of proteasome assembly chaperones. In Saccharomyces cerevisiae, inhibition of the growth-promoting kinase complex TORC1 causes increased proteasome assembly chaperone translation, including that of Adc17. This is dependent upon activation of the mitogen-activated protein kinase (MAPK) Mpk1 and relocalisation of assembly chaperone mRNA to patches of dense actin. We show here that TORC1 inhibition alters cell wall properties to induce these changes by activating the cell wall integrity pathway through the Wsc1, Wsc3 and Wsc4 sensor proteins. We demonstrate that, in isolation, these signals are insufficient to drive protein expression. We identify that the TORC1-activated S6 kinase Sch9 must be inhibited as well. This work expands our knowledge on the signalling pathways that regulate proteasome assembly chaperone production.

Translation regulation in response to stress

Cell stresses occur in a wide variety of settings: in disease, during industrial processes, and as part of normal day-to-day rhythms. Adaptation to these stresses requires cells to alter their proteome. Cells modify the proteins they synthesize to aid proteome adaptation. Changes in both mRNA transcription and translation contribute to altered protein synthesis. Here, we discuss the changes in translational mechanisms that occur following the onset of stress, and the impact these have on stress adaptation.