Kinase that can phosphorylate various inositol polyphosphate such as Ins(3;4;5;6)P4 or Ins(1;3;4)P3. Phosphorylates Ins(3;4;5;6)P4 at position 1 to form Ins(1;3;4;5;6)P5. This reaction is thought to have regulatory importance; since Ins(3;4;5;6)P4 is an inhibitor of plasma membrane Ca2+-activated Cl-?channels; while Ins(1;3;4;5;6)P5 is not. Also phosphorylates Ins(1;3;4)P3 on O-5 and O-6 to form Ins(1;3;4;6)P4; an essential molecule in the hexakisphosphate (InsP6) pathway. Also acts as an inositol polyphosphate phosphatase that dephosphorylate Ins(1;3;4;5)P4 and Ins(1;3;4;6)P4 to Ins(1;3;4)P3; and Ins(1;3;4;5;6)P5 to Ins(3;4;5;6)P4. May also act as an isomerase that interconverts the inositol tetrakisphosphate isomers Ins(1;3;4;5)P4 and Ins(1;3;4;6)P4 in the presence of ADP and magnesium. Probably acts as the rate-limiting enzyme of the InsP6 pathway. Modifies TNF-alpha-induced apoptosis by interfering with the activation of TNFRSF1A-associated death domain. Plays an important role in MLKL-mediated necroptosis. Produces highly phosphorylated inositol phosphates such as inositolhexakisphosphate (InsP6) which bind to MLKL mediating the release of an N-terminal auto-inhibitory region leading to its activation. Essential for activated phospho-MLKL to oligomerize and localize to the cell membrane during necroptosis.