Heat shock induces assembly of a protein complex that activates yeast SAPKs Mpk1 and Hog1.

Abstract

Stress-activated protein kinases (SAPKs) respond to a wide variety of stressors. The Saccharomyces cerevisiae SAPK Mpk1 (Slt2) is a well-characterized component of the cell wall integrity (CWI) signaling pathway, which responds to physical and chemical challenges to the cell wall. We find here that Mpk1 is activated by heat shock (HS) through both a "top-down" pathway that activates its MEK and a "lateral" pathway that does not require regulation of the MEK by a MEKK, and which appear to be additive. The lateral pathway requires active SAPK Hog1 and the formation of a protein complex, named here the CWI HS complex. Hog1 is transiently recruited to the complex and is activated therein. Release of Hog1 from the complex requires its catalytic activity, suggesting that it phosphorylates one or more targets while associated with the complex resulting in the activation of Mpk1 and release of Hog1. These results add to the diversity of intracellular mechanisms by which SAPKs are activated.

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