Does cytoplasmic c-Fos activate protein synthesis?

DURAND E.S.; CAPUTTO B.L

Valle Hermoso

Workshop; Tango Lessons for brain cancer research. Understanding cellular intricacy, improvising new therapies.; 2007

James S. McDonnell Foundation

We have found that c-Fos, in addition to being a member of the AP-1 family of transcription factors, associates to the endoplasmic reticulum and activates the machinery for phospholipid synthesis in events related to: sensorial stimulation (ganglion and retina photoreceptor cells), neural differentiation (PC12 cells) and normal (NIH3T3 fibroblasts induced to re-enter the cellular cycle), and exacerbated (tumor cell) growth. These events share the characteristic of requiring membrane biogenesis to occur. Membrane biogenesis is a complex process that in addition to lipids, requires other components such as proteins. This study is directed towards establishing if c-Fos, in addition to activating phospholipid synthesis in PC12 cells induced to differentiate, also activates protein synthesis by an AP-1 independent mechanism. 35S-methionine was added to the medium of PC12 cells at 4 days of culture and the cells were harvested one hour later. We have found an increase in the 35S-labeling of protein in cells cultured +NGF with respect to the those cultured -NGF; these differences were no longer observed if an antisense oligonucleotide for the c-fos mRNA was added to the cultures together with NGF whereas the sense oligonucleotide did not modify these differences. In cells cultured +NGF, +NLSP, a peptide that specifically blocks the nuclear import of AP-1-c-Fos, levels of protein synthesis at 4 days in culture were reduced to that of sister cells cultured -NGF indicating the need of AP-1 transcription factor to trigger PC12 cell differentiation. However, cells cultured 2 days +NGF followed by 2 days +NGF, +NLSP, showed protein synthesis levels similar to cells cultured 4 days +NGF indicating the need of cytoplasmic c-Fos to continue the neuritogenesis process. It is postulate that cytoplasmic c-Fos participates in the activation of protein synthesis required for neuronal differentiation.