The Hsp40 Molecular Chaperone Ydj1p, Along With the Protein Kinase C Pathway, Affects Cell-Wall Integrity in the YeastSaccharomyces cerevisiae

Abstract

Molecular chaperones, such as Hsp40, regulate cellular processes by aiding in the folding, localization, and activation of multi-protein machines. To identify new targets of chaperone action, we performed a multi-copy suppressor screen for genes that improved the slow-growth defect of yeast lacking the YDJ1 chromosomal locus and expressing a defective Hsp40 chimera. Among the genes identified were MID2, which regulates cell-wall integrity, and PKC1, which encodes protein kinase C and is linked to cell-wall biogenesis. We found that ydj1D yeast exhibit phenotypes consistent with cell-wall defects and that these phenotypes were improved by Mid2p or Pkc1p overexpression or by overexpression of activated downstream components in the PKC pathway. Yeast containing a thermosensitive allele in the gene encoding Hsp90 also exhibited cell-wall defects, and Mid2p or Pkc1p overexpression improved the growth of these cells at elevated temperatures. To determine the physiological basis for suppression of the ydj1D growth defect, wild-type and ydj1D yeast were examined by electron microscopy and we found that Mid2p overexpression thickened the mutant's cell wall. Together, these data provide the first direct link between cytoplasmic chaperone function and cell-wall integrity and suggest that chaperones orchestrate the complex biogenesis of this structure.

The Mammalian Hsp40 ERdj3 Requires Its Hsp70 Interaction and Substrate-binding Properties to Complement Various Yeast Hsp40-dependent Functions

“…6). These data further support our hypothesis that the role of Ydj1 in the maintenance of cell wall integrity is not reliant upon its interaction with Ssa1 (29).…”

“…5 and 6), and that hlj1⌬ yeast do not exhibit slow growth and cell wall phenotypes (data not shown) but ydj1⌬ do (29,44), we surmise that cell wall function and robust growth at elevated temperature are linked to the ability of Ydj1 to bind to specific substrates. Formally, the cell wall phenotypes may also arise from the ability of Ydj1 to partner with Hsp82, the cytosolic Hsp90 that plays a role in high osmotic stress response in yeast (29,56,57) and acts in conjunction with Ydj1 in the folding and maturation of certain client proteins (54,58,59). The cell wall phenotype may additionally arise from altered association with Sse1, the cytosolic Hsp110 (56), which has previously been shown to genetically interact with YDJ1 (60).…”

“…Cell wall integrity, which is essential during growth, cell division, and stress, is maintained by the coordinated action of several signaling pathways (52). Recently, we demonstrated that Ydj1 also plays a role in the maintenance of cell wall integrity (29). For example, the slow growth phenotype of ydj1⌬ mutant yeast was rescued by osmostabilizing agents such as sodium chloride and sorbitol.…”

The Hsp110 protein chaperone Sse1 is required for yeast cell wall integrity and morphogenesis

“…An important conclusion that can be drawn from our findings is that many temperaturesensitive growth phenotypes of Hsp90 and cochaperone mutants [HSF(1-583), sse1Δ, sti1Δ, ydj1Δ] are not simply due to indiscriminate destabilization or aggregation of cellular proteins (Truman et al 2007;Wright et al 2007). Instead, these phenotypes are due to improper signaling through Slt2 resulting in weakened cell walls leading to cell lysis.…”

“…Unlike many other protein kinase clients of Hsp90, stability and phosphorylation of Slt2 is not impaired in the absence of chaperone function, suggesting a specific chaperone requirement for interaction with the downstream effectors Rlm1 and SBF (Truman et al 2007). With the exception of Cdc37 and Ydj1, the role of other Hsp90 cochaperones in cell integrity signaling has not been investigated (Hawle et al 2007;Wright et al 2007).…”