Phosphatidylinositol-3-phosphate 5-kinase type III (PIKfyve)

Phosphatidylinositol‑3‑phosphate 5‑kinase type III (PIKfyve) is a large multi-domain enzyme encoded by the *PIKFYVE* gene. It catalyzes the phosphorylation of phosphatidylinositol‑3‑phosphate to generate phosphatidylinositol-(3,5)-bisphosphate [PtdIns(3,5)P₂], as well as producing phosphatidylinositol 5-phosphate [PtdIns5P]. These lipids are critical regulators of membrane trafficking events within the endosomal system. The FYVE finger domain targets the protein to endosomes. Loss or inhibition of PIKfyve disrupts lysosome fission/homostasis and leads to cytoplasmic vacuolation due to defective vesicle dynamics. Biologically, it is essential for processes such as cell migration/polarization through integrin recycling pathways, platelet granule biogenesis in megakaryocytes, Th17 T-cell differentiation via mTORC1/STAT3 activation (implicating it in autoimmunity), insulin-regulated glucose uptake in muscle tissue (linking it with metabolic disease), viral entry by endocytosis (Ebola/SARS-CoV‑2), and tumor progression/autophagy dependence in certain cancers. Mutations cause corneal fleck dystrophy; pharmacological inhibitors like apilimod are under investigation for cancer immunotherapy due to their ability to enhance anti-tumor immunity by increasing MHC-I surface expression on tumor cells.

Other names

PIKFYVEFYV1PIPKIII1-phosphatidylinositol 3-phosphate 5-kinase

Inhibition of lipid kinase activity impairs endosomal trafficking, lysosome fission/homostasis, autophagy; upregulates MHC-I surface expression in cancer cells; modulates immune response by affecting Th17 differentiation and mTORC1/STAT3 pathways.