Abstract
BackgroundThe yeast ribosomal protein Asc1 is a WD-protein family member. Its mammalian ortholog, RACK1 was initially discovered as a receptor for activated protein C kinase (PKC) that functions to maintain the active conformation of PKC and to support its movement to target sites. In the budding yeast though, a connection between Asc1p and the PKC signaling pathway has never been reported.Methodology/Principal FindingsIn the present study we found that asc1-deletion mutant (asc1Δ) presents some of the hallmarks of PKC signaling mutants. These include an increased sensitivity to staurosporine, a specific Pkc1p inhibitor, and susceptibility to cell-wall perturbing treatments such as hypotonic- and heat shock conditions and zymolase treatment. Microscopic analysis of asc1Δ cells revealed cell-wall invaginations near bud sites after exposure to hypotonic conditions, and the dynamic of cells' survival after this stress further supports the involvement of Asc1p in maintaining the cell-wall integrity during the mid-to late stages of bud formation. Genetic interactions between asc1 and pkc1 reveal synergistic sensitivities of a double-knock out mutant (asc1Δ/pkc1Δ) to cell-wall stress conditions, and high basal level of PKC signaling in asc1Δ. Furthermore, Asc1p has no effect on the cellular distribution or redistribution of Pkc1p at optimal or at cell-wall stress conditions.Conclusions/SignificanceTaken together, our data support the idea that unlike its mammalian orthologs, Asc1p acts remotely from Pkc1p, to regulate the integrity of the cell-wall. We speculate that its role is exerted through translation regulation of bud-site related mRNAs during cells' growth.
Highlights
Asc1p is a member of the WD-40 repeat protein family that adopts a seven-bladed b-propeller structure [1,2]
In mammalian cells RACK1 serves as a scaffold protein for numerous components of diverse signal transduction pathways, of which PKCbII is the most recognized [40]
The dynamics of asc1-deletion mutant (asc1D) loss of viability, whereby more than half of asc1D cells were damaged within the first minute of exposure to hypotonic conditions, is highly similar to the response of PKC1-deleted cells (pkc1D) strain (Fig. 3)
Summary
Asc1p is a member of the WD-40 repeat protein family that adopts a seven-bladed b-propeller structure [1,2]. Later studies positioned RACK1 at a central point for multiple cellular functions, as it was found to serve as a scaffold protein for many component from diverse signaling cascades [11,12,13,14,15,16,17,18,19,20], with some of them able to interact simultaneously with RACK1, and allow it to integrate inputs from distinct signaling pathways [21] Based on these observations, it was suggested that RACK1, as a part of the 40 S ribosomal subunit, serves as a docking site for signaling molecules that regulate the activity of translation initiation factors or recruit mRNA-binding proteins to the ribosome [22]. We point Asc1p as a factor required for the integrity of the cell-wall near the bud site, and suggest that this function is independent of Pkc1p
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call