OCT4 (octamer-binding protein 4) is a transcription factor that binds to the octamer motif (5'-ATTTGCAT-3') and generates a trimeric complex with SOX2 on DNA for controlling the expression of several genes (YES1, FGF4, UTF1, ZFP206 etc.) involved in embryonic development. Expressed mainly in the nucleus, OCT4 interacts with UBE2I, ZSCAN10, PKM, WWP2 etc. and OCT4-PKM interaction positively regulate OCT4's transcriptional activity. Once translated, its modifications such as sumoylation enhances the protein stability, DNA binding and transactivation activity and is required for enhanced YES1 expression. OCT4 undergoes 'Lys-63'-linked polyubiquitination by WWP2 leading to proteasomal degradation. OCT4 is found in oocytes and is zygotically expressed in pluripotent cells of pre-gastrulation embryos, and has been observed to be essential for early embryogenesis as well as for embryonic stem cell pluripotency. OCT4 is expressed in developing brain with highest levels in specific cell layers of the cortex, the olfactory bulb, hippocampus and cerebellum. Its expression decreases gradually after embryoid body formation, however, improper re-activation of OCT4 contributes to oncogenic processes and it has been implicated in certain malignancies such as breast and ovarian cancer.