PIP4P1 (also known as TMEM55B) is a phosphatidylinositol-4,5-bisphosphate 4-phosphatase that catalyzes hydrolysis of PtdIns(4,5)P2 to PtdIns(4)P with high substrate specificity 1. The enzyme plays multiple critical roles in lysosomal homeostasis and cellular metabolism. PIP4P1 regulates lysosomal positioning by recruiting the adaptor protein JIP4 to lysosomal membranes, thereby inducing retrograde transport toward the cell center via dynein motor proteins 2. Additionally, PIP4P1 assembles the V-ATPase complex within lysosomal membrane lipid rafts, facilitating amino acid-dependent mTORC1 activation essential for nutrient sensing 3. PIP4P1 phosphorylation by Erk/MAPK regulates this lysosomal positioning in response to external stimuli 4. In cholesterol metabolism, PIP4P1 modulates PtdIns(4,5)P2 levels to regulate low-density lipoprotein receptor degradation in lysosomes, thereby controlling plasma cholesterol homeostasis 5. Conversely, PIP4P2 (another phosphatidylinositol-4,5-bisphosphate 4-phosphatase) positively regulates basal autophagy 6. PIP4P1 dysfunction may contribute to cleft lip/palate pathogenesis 7. These coordinated functions position PIP4P1 as a master regulator of lysosomal dynamics and metabolic signaling.