In the nucleus, phosphatidylinositol 5-phosphate (PI5P) is phosphorylated to phosphatidylinositol 4,5-bisphosphate (PI(4,5)P2) mainly by phosphatidylinositol-5-phosphate 4-kinase type-2 beta (PIP4K2B). In the nucleus, PIP4K2B predominantly functions as a homodimer or a heterodimer with PIP4K2A. A low level of PIP4K2A homodimers can also be found in the nucleus. Nuclear localization of PIP4K2C has not been examined but is assumed to be possible, at least through formation of heterodimers with PIP4K2B (Ciruela et al. 2000, Jones et al. 2006, Bultsma et al. 2010). Under conditions of cellular stress, nuclear PIP4K2B can be phosphorylated by p38 MAP kinases, resulting in PIP4K2B inactivation. The putative p38 target site, serine residue S326 of PIP4K2B, is conserved in PIP4K2A, but the role and mechanism of p38-mediated regulation of PIP4K2 isoforms has not been studied in detail (Jones et al. 2006).