c-fos activates the synthesis of proteins in differentiating PC12 cells and in vitro endoplasmic reticulum translation

DURAND E.S.; CAPUTTO B.L

Búzios

Congreso; I Congresso IBRO/LARC de Neurociências da América Latina, Caribe e Península Ibérica; 2008

International Brain Research Organization (IBRO)/Latin American Regional Committee (LARC)

We have found that c-Fos, in addition to its activity as a member of the AP-1 family of transcription factors, associates to endoplasmic reticulum (ER) and activates the synthesis of phospholipids in events that require membrane biogenesis. However, membrane biogenesis not only requires lipids, it also requires other components such as proteins. Consequently, we examined if c-Fos also activates protein synthesis by an AP-1 independent mechanism. Cultured PC12 cells induced to differentiate by feeding with nerve growth factor (NGF) showed an increased labelling of proteins with 35S-methionine; this activation was abolished upon blocking of c-Fos expression; culturing cells with a peptide that specifically blocks th e nuclear import of AP-1-c-Fos shows that AP-1 is required to trigger neuronal differentiation whereas cytoplasmic c-Fos is necessary for differentiation to continue. Neuronal differentiation positively correlates with protein synthesis activation. To establish if the activation of protein synthesis by c-Fos is a direct effect of this protein on the ER we performed in vitro translation. Increasing concentrations of recombinant c-Fos were incubated with the rabbit reticulocyte system in the presence of canine pancreatic microsomal membranes and a signal sequence mRNA. These results show activated protein biosynthesis in the ER that is dependent on the concentration of c-Fos. To analyse if c-Fos associates to the ER membranes to activate protein synthesis, membranes were pre-incubated with c-Fos, washed and translation measured in vitro in the pelleted fraction. The results show that c-Fos associates to ER and activates protein synthesis. Similar results were found with a synthetic peptide of the basic domain of c-Fos (aa 139-160). This is the first evidence that c-Fos can activate, in addition to the metabolism of lipids, protein metabolism. Since c-Fos protein is highly regulated, the regulation of its expression can result in an interesting mechanism for controlling the genesis of the components that the cell requires according to its physiological status that is, during growth, proliferation, differentiation, etc.