Phosphatidylinositol 4,5-bisphosphate (PIP2) is a critical phospholipid component of the inner leaflet of the plasma membrane that plays a pivotal role in cell signaling by serving as a substrate for various enzymes, including phospholipase C, which generates second messengers like inositol trisphosphate and diacylglycerol. It also regulates the activity of ion channels and other proteins, influencing processes such as cytoskeletal organization, membrane trafficking, and cellular responses to external stimuli.