Integration of human ERKs and DUSPs into the yeast cell wall integrity pathway.

The Saccharomyces cerevisiae Cell Wall Integrity (CWI) pathway responds to cell wall stress and is composed of MAP3K Bck1, MAP2Ks Mkk1 and Mkk2 and MAPK Slt2. Although human ERK5 has been considered the functional orthologue of Slt2, our results indicate that human ERK1 and ERK2 exhibit a much greater ability than ERK5 to replace Slt2 under various cell wall stresses. ERK5 is only able to slightly complement an slt2Δ mutant phenotype in the presence of tunicamycin, and the constitutively active truncated version ERK5ΔCt did not improve this complementation ability. Like Slt2, ERK1, ERK2 and ERK5ΔCt are concentrated in the nucleus, and show higher phosphorylation than ERK5 upon CWI pathway stimulation. Expression of a hyperactive version of the human MAP2K MEK5 leads to specific ERK5 and ERK5ΔCt phosphorylation, leading to a partial replacement of the Mkk1/2-Slt2 function under cell wall stress. Expressed in yeast, the human Dual Specificity Phosphatases DUSP3 and DUSP6 reduce the level of ERK5 phosphorylation to a similar extent, whereas DUSP6 shows higher activity than DUSP3 on ERK1 or ERK2. Our results show the different degree of integration of human ERKs and DUSPs into the yeast CWI signalling circuit, which can be exploited for functional analysis or pharmacological screenings.