Phosphatidylinositol 5 phosphate 4 kinases, or type II PIPKs, represent a family of enzymes able to phosphorylate PI5P in order to produce PI(4,5)P
2 [23]. PIP4Ks are conserved in different species spanning from flies and worms to mice and humans. Mammalians are characterized by the presence of three different isoforms, namely, PIP4K2A, PIP4K2B, and PIP4K2C
[4][8][60][61][62]. They share dimerization and lipid kinase domains and carry main differences in amino acid sequences found at -N and -C termini, which confer each isoform specific characteristics
[4][8][61][62][63]. PIP4K2A is considered the most active isozyme if compared to PIP4K2B, while PIP4K2C possesses a limited capacity to phosphorylate PI5P
[4][8][60][61][62]. Interestingly, PIP4K2B preferentially uses GTP instead of ATP for its kinase function
[64][65]. PIP4K isozymes also differ from each other for their intracellular localization: 2A is mostly located in the cytoplasm/membrane, 2B can also be found in the nucleus, and 2C is found in not well defined membraneless compartments. As already indicated, this class of enzymes was first discovered in 1997 by members of Cantley’s lab, who were able to overcome an issue related to the mix between PI4P and PI5P in bovine brain preparations
[23]. This finding rendered the study of PIP4K substrate specificity possible and described those proteins as different from their related family of PIP5K
[66]. In any case, the capacity of PIP4K to produce PI(4,5)P
2 is considered minor with respect to PIP5K, so they are suggested as being involved in the regulation of PI5P levels in cells
[4][8][61][62] (). Indeed, knockdown/inhibition of PIP4Ks in mammalian cells or knockout in drosophila leads to increased levels of PI5P, with almost no effects on the pool of PI(4,5)P
2 [61][67][68]. These proteins have been recently connected with many cellular functions, including DNA damage, cell proliferation, and chromatin remodeling, and have been proposed as possible targets for treatment of cancer or autoimmune diseases
[69][70][71][72][41][73].