Involvement of Rho and Rac small G proteins and Rho GDI in Ca2+-dependent exocytosis from PC12 cells.
BACKGROUND
The Rho small G protein family, which includes the Rho, Rac and Cdc42 subfamilies, is implicated in various cell functions such as cell shape change, cell motility and cytokinesis, through the reorganization of actin filaments. Rho GDI is an inhibitory regulator of the Rho small G protein family and inhibits the Rho family dependent cell functions. Reorganization of actin filaments is also known to regulate Ca2+-dependent exocytosis.


RESULTS
We have examined here whether the Rho family members are also involved in Ca2+-dependent exocytosis. We have found, by the use of the human growth hormone (GH) co-expression assay system on PC12 cells, that overexpression of Rho GDI inhibits high K+-induced, Ca2+-dependent GH release. This inhibitory action of Rho GDI is restored by co-expression of a dominant active mutant of RhoA or Rac1, but not of a dominant active mutant of Cdc42. C3 transferase, known to ADP-ribosylate Rho and to inhibit its function, also inhibits this GH release. Overexpression of a dominant active mutant of RhoA or Rac1 alone shows only a small effect on GH release. Moreover, immunocytochemical studies show that the overexpression of Rho GDI prevents a partial disruption of the cortical actin network which accompanies exocytosis.


CONCLUSIONS
These results suggest that RhoA, Rac1 and Rho GDI are involved in Ca2+-dependent exocytosis at least partly through the reorganization of actin filaments, and that the activation of RhoA or Rac1 alone is not sufficient for this reaction.
Komuro
R
R
Department of Molecular Biology and Biochemistry, Osaka University Medical School, Suita, Japan.
Sasaki
T
T
Takaishi
K
K
Orita
S
S
Takai
Y
Y
D036002:ADP Ribose Transferases; D008841:Actin Cytoskeleton / Q000648:ultrastructure; D000199:Actins; D000818:Animals; D001905:Botulinum Toxins; D002118:Calcium / Q000502:physiology*; D018797:Cell Cycle Proteins / Q000502:physiology; D005089:Exocytosis / Q000502:physiology*; D019204:GTP-Binding Proteins / Q000502:physiology*; D013006:Growth Hormone / Q000378:metabolism; D020730:Guanine Nucleotide Dissociation Inhibitors; D009154:Mutation; D016716:PC12 Cells; D011188:Potassium / Q000502:physiology; D051381:Rats; D011994:Recombinant Proteins / Q000378:metabolism; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D020742:rhoA GTP-Binding Protein
D000199:Actins; D018797:Cell Cycle Proteins; D020730:Guanine Nucleotide Dissociation Inhibitors; D011994:Recombinant Proteins; D062947:rho-Specific Guanine Nucleotide Dissociation Inhibitors; D013006:Growth Hormone; D036002:ADP Ribose Transferases; C063007:exoenzyme C3, Clostridium botulinum; D001905:Botulinum Toxins; D019204:GTP-Binding Proteins; D020764:cdc42 GTP-Binding Protein; D020744:rac GTP-Binding Proteins; D020741:rho GTP-Binding Proteins; D020742:rhoA GTP-Binding Protein; D011188:Potassium; D002118:Calcium