Translocation between membranes and cytosol of p42(IP4), a specific inositol 1,3,4,5-tetrakisphosphate/phosphatidylinositol 3,4,5-trisphosphate- receptor protein from brain, is induced by inositol 1,3,4,5-tetrakisphosphate and regulated by a membrane-associated 5-phosphatase

Abstract

The highly conserved 42-kDa protein, p42(IP4) was identified recently from porcine brain. It has also been identified similarly in bovine, rat and human brain as a protein with two pleckstrin homology domains that binds Ins(1,3,4,5)P4 and PtdIns(3,4,5)P3 with high affinity and selectivity. The brain-specific p42(IP4) occurs both as membrane-associated and cytosolic protein. Here, we investigate whether p42(IP4) can be translocated from membranes by ligand interaction, p42(IP4) is released from cerebellar membranes by incubation with Ins(1,3,4,5)P4. This dissociation is concentration-dependent (> 100 nM), occurs within a few minutes and and is ligand-specific, p42(IP4) specifically associates with PtdIns(3,4,5)P3- containing lipid vesicles and can dissociate from these vesicles by addition of Ins(1,3,4,5)P4. p42(IP4) is only transiently translocated from the membranes as Ins(1,3,4,5)P4 can be degraded by a membrane-associated 5- phosphatase to Ins(1,3,4)P3. Then, p42(IP4) re-binds to the membranes from which it can be re-released by re-addition of Ins(1,3,4,5)P4. Thus, Ins(1,3,4,5)P4 specifically induces the dissociation from membranes of a PtdIns(3,4,5)P3 binding protein that can reversibly re-associate with the membranes. Quantitative analysis of the inositol phosphates in rat brain tissue revealed a concentration of Ins(1,3,4,5)P4 comparable to that required for p42(IP4) translocation. Thus, in vivo p42(IP4) might interact with membranes in a ligand-controlled manner and be involved in physiological processes induced by the two second messengers Ins(1,3,4,5)P4 and PtdIns(3,4,5)P3.