Phospholipids are main cell constituents required for the assembly of biological membranes. In addition to their structural role, phospholipids participate in the regulation of cellular processes as signaling molecules and secondary messengers. Large scale lipid synthesis is an essential requirement for the delivery of new membrane during normal or tumoral cell proliferation. We have described for the first time a protein that activates the enzymatic machinery of phospholipids biosynthesis. This protein is c-Fos and it activates phospholipid synthesis by a mechanism independent of its genomic AP-1 activity. Recent results reveal a dual function of c-Fos: to release the genomic program for differentiation and to activate the synthesis of phospholipids via association to the endoplasmic reticulum. Main aim of this project is to study if exacerbated growth of tumors depends of the activation of the phospholipids synthesis mediated by c-Fos, and to further characterize the molecular mechanism involved in this activation. In addition shed light on a fundamental problem of cell biology, it is expected that this information will allow the rational design of drugs that by inhibiting the stimulatory effect of c-Fos on phospholipid synthesis, can control membrane provision and hence cell proliferation.