c-FOS TYR PHOSPHORYLATION REGULATES c-FOS/ ER ASSOCIATION AND c-FOS DEPENDENT PHOSPHOLIPID SYNTHESIS ACTIVATION

MAXIMILIANO MOISES PORTAL; GABRIEL ORLANDO FERRERO; BEATRIZ LEONOR CAPUTTO

PInamar, Bs.As.,Argentina

Simposio; Reunión de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB); 2005

Reunión de la Sociedad Argentina de Investigación Bioquímica y Biología Molecular (SAIB)

c-Fos, a component of the AP-1 transcription factor family, participates in a variety of cellular processes ranging from gene transactivation in the nucleus to phospholipid synthesis activation in the cytoplasm. For this latter activity, c-Fos associates with ER membranes. Herein, the regulation of c-Fos/ER association and consequently c-Fos dependent phospholipid synthesis activation were examined in T98G cells. The small amounts of c-Fos present in quiescent cells were found phosphorylated on tyrosine (Y) residues, whereas re entry of cells to cell cycle results in Y-dephosphorylation. Y-dephosphorylated-c-Fos is now capable of associating to the ER and activating phospholipid synthesis. If Y-dephosphorylation is impaired by a phosphatase inhibitor, no c-Fos/ER association is observed and no phospholipid synthesis activation takes place. Furthermore, purified Y-phosphorylated-c-Fos failed to activate phospholipid synthesis in vitro. Bioinformatic analysis showed 4 Y residues in c-Fos predicted as phosphorylatable. Single point mutation over Y residues (Y/F) was performed to determine which phosphorylated Y participates in regulating c-Fos/ER association. Only phosphorylation over Y10 and Y30 impaired c-Fos/ER dissociation whereas that on Y106 and Y337 had no effect. We postulate c-Fos Y phosphorylation as a regulatory mechanism to determine the rate of synthesis of phospholipids by regulating c-Fos/ER interaction.