CONICET | Buscador de Institutos y Recursos Humanos

Cytoplasmic c-Fos activates phospholipid synthesis by its association with particular lipid synthesizing enzymes at the endoplasmic reticulum (ER) which induces an increase in their catalytic activity. This activity of c-Fos is associated with the molecular mechanisms that allow the higher rate of membrane genesis required for the complex events that take place during neuronal differentiation, such as sprouting and branching. Studying this role, we found c-Fos strongly co-localizing with ER markers in particular unidentified structures located at branching sites of growing neuronal processes. Blocking either c-Fos expression or its activity promotes an impairment in differentiation with no observable development of axonal processes. In addition, the expression of N-terminal deletion mutants of c-Fos that are capable of blocking only its cytoplasmic activity produces a similar effect. CTP:phosphocholine cytidylyltransferase-β2 (CCTβ2), the key regulatory enzyme responsible for CDP-choline formation in the brain, associates to the ER membranes and plays an important role in the formation of axon branches. To determine if this enzyme is activated by c-Fos, and taking into consideration that this activation mechanism implies an interaction between both proteins, we initially studied this possibility. We found co-immunoprecipitation of c-Fos with the enzyme and positive FRET values between the tagged proteins both in the soma and in the axon, mainly at the branching points of developing neurons, thus evidencing an interaction between these proteins. These results support the participation of CCTβ2 in the regulation of branching formation and sustain the notion that c-Fos-mediated activation of phospholipid synthesis is of importance during neuronal differentiation.