Hisactophilin is involved in osmoprotection in Dictyostelium.
BACKGROUND
Dictyostelium cells exhibit an unusual stress response as they protect themselves against hyperosmotic stress. Cytoskeletal proteins are recruited from the cytosolic pool to the cell cortex, thereby reinforcing it. In order to gain more insight into the osmoprotective mechanisms of this amoeba, we used 1-D and 2-D gel electrophoresis to identify new proteins that are translocated during osmotic shock.


RESULTS
We identified hisactophilin as one of the proteins that are enriched in the cytoskeletal fraction during osmotic shock. In mutants lacking hisactophilin, viability is reduced under hyperosmotic stress conditions. In wild type cells, serine phosphorylation of hisactophilin was specifically induced by hypertonicity, but not when other stress conditions were imposed on cells. The phosphorylation kinetics reveals a slow accumulation of phosphorylated hisactophilin from 20-60 min after onset of the hyperosmotic shock condition.


CONCLUSIONS
In the present study, we identified hisactophilin as an essential protein for the osmoprotection of Dictyostelium cells. The observed phosphorylation kinetics suggest that hisactophilin regulation is involved in long-term osmoprotection and that phosphorylation occurs in parallel with inactivation of the dynamic actin cytoskeleton.
Pintsch
Tanja
T
Max-Planck-Institute for Biochemistry, 82152 Martinsried, Germany. pintsch@switch-biotech.com
Zischka
Hans
H
Schuster
Stephan C
SC
D000818:Animals; D002352:Carrier Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D002455:Cell Division / Q000187:drug effects / Q000235:genetics; D003599:Cytoskeleton / Q000187:drug effects / Q000378:metabolism; D004023:Dictyostelium / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D015180:Electrophoresis, Gel, Two-Dimensional; D006982:Hypertonic Solutions / Q000494:pharmacology; D008840:Microfilament Proteins; D009154:Mutation; D009997:Osmotic Pressure; D010766:Phosphorylation / Q000187:drug effects; D015800:Protozoan Proteins / Q000187:drug effects / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D013012:Sorbitol / Q000494:pharmacology*
D002352:Carrier Proteins; D006982:Hypertonic Solutions; D008840:Microfilament Proteins; D015800:Protozoan Proteins; C058561:hisactophilin protein, Protozoan; D012694:Serine; D013012:Sorbitol