c-FOS, also named as Proto-oncogene c-Fos and G0/G1 switch regulatory protein 7, is a 380 amino acid protein, which contains 1 bZIP (basic-leucine zipper) domain and belongs to the bZIP family. FOS is expressed at very low levels in quiescent cells. When cells are stimulated to reenter growth, FOS undergo 2 waves of expression, the first one peaks 7.5 minutes following FBS induction. At this stage, the FOS protein is localized endoplasmic reticulum. The second wave of expression occurs at about 20 minutes after induction and peaks at 1 hour. At this stage, the FOS protein becomes nuclear. The calculated molecular weight of FOS is 40 kDa, but Phosphorylated FOS protein is about 60-65 kDa. It is involved in important cellular events, including cell proliferation, differentiation and survival; genes associated with hypoxia; and angiogenesis; which makes its dysregulation an important factor for cancer development. It can also induce a loss of cell polarity and epithelial-mesenchymal transition, leading to invasive and metastatic growth in mammary epithelial cells. Expression of c-fos is an indirect marker of neuronal activity because c-fos is often expressed when neurons fire action potentials. Upregulation of c-fos mRNA in a neuron indicates recent activity