Regulation of Inositol 1,4,5-Trisphosphate 3-Kinases by Calcium and Localization in Cells

Abstract

We also compared the effects of the these IP 3 Ks with other enzymes that metabolize Ins(1,4,5)P 3 , including the Type I Ins(1,4,5)P 3 5-phosphatase, in both membrane-targeted and soluble forms, the human inositol polyphosphate multikinase, and the two isoforms of IP 3 K found in Drosophila. All reduce the Ca 2؉ signal but to varying degrees. We demonstrate that the activity of only one of two IP 3 K isoforms from Drosophila is positively regulated by calmodulin and that neither isoform associates with the cytoskeleton. Together the data suggest that IP 3 Ks evolved to regulate kinetic and spatial aspects of Ins (1,4,5)P 3 signals in increasingly complex ways in vertebrates, consistent with their probable roles in the regulation of higher brain and immune function.The metabolism of the calcium-mobilizing second messenger inositol 1,4,5-trisphosphate (Ins(1,4,5)P 3 ) 5 proceeds via two biochemical pathways. Type I Ins(1,4,5)P 3 5-phosphatase catalyzes the dephosphorylation of Ins(1,4,5)P 3 , producing the inactive (1, 2) metabolite Ins(1,4)P 2 (3). Alternatively, Ins(1,4,5)P 3 can be further phosphorylated to Ins(1,3,4,5)P 4 , in a reaction catalyzed by Ins(1,4,5)P 3 3-kinase (IP 3 K) (4). Ins(1,3,4,5)P 4 does not mobilize Ca 2ϩ , but is suggested to have a number of second messenger functions, most notably in the immune system (5, 6) and in neurons (7, 8) (reviewed in Ref. 9). Furthermore, IP 3 Ks may initiate a chain of reactions responsible for the production of higher inositol phosphates, having diverse intracellular roles (10), although this view has been challenged (11, 12).The human genome encodes three differentially expressed isoforms of IP 3 K, denoted IP 3 KA, -B, and -C (13, 14). In addition, inositol polyphosphate multikinase (IPMK; also described as IPK2, and Arg82 in yeast) harbors a range of inositol phosphate kinase activities, including Ins (1,4,5)P 3 3-kinase activity (15, 16). Two IP 3 Ks occur in Drosophila melanogaster, denoted dmIP 3 K␣ (17) and dmIP 3 K␤ (11). One IP 3 K gene occurs in Caenorhabditis elegans, and genetic evidence from both worms and flies strongly argues that IP 3 Ks function as negative regulators of Ins(1,4,5)P 3 Ca 2ϩ signals through their ability to remove Ins(1,4,5)P 3 (17, 18). Expression studies in mammalian cells further support the consensus view that IP 3 Ks negatively regulate Ins(1,4,5)P 3 Ca 2ϩ signals by their ability to remove Ins(1,4,5)P 3 (19 -25). The product of these enzymes, Ins(1,3,4,5)P 4 , may further regulate Ca 2ϩ homeostasis, although exactly how it may do that remains controversial (10).From the first studies of the IP 3 Ks, it has been assumed that because they are enzymes with a higher affinity for Ins(1,4,5)P 3 than the Type I Ins(1,4,5)P 3 5-phosphatase (26) and differ from the 5-phosphatase in that they are positively regulated by CaM and CaM kinase (see Refs. 13,14,27, and 28 for reviews), they must play a preferential role in regulating the pools of Ins (1,4,5)P 3 involved in signaling. However, the exact nature of this contribution is st...

Inositol trisphosphate 3-kinases: focus on immune and neuronal signaling

“…, all three human isoforms bind calmodulin (CaM) in a Ca 2? -dependent manner, via a conserved domain [45]. The three human isoforms of ITPK show diversity in their N-termini [8].…”

“…The L34P mutation destroys F-actin binding in ITPKA [133], while L139P and L159P reduce F-actin binding in ITPKB [77]. The W167R mutation destroys CaM binding in ITPKA; analogous mutations behave similarly for ITPKB and C [45]. Arrowheads in the blue and gray areas point to two of the many mutations in the active site that destroy catalytic activity [21].…”

“…Arrowheads in the blue and gray areas point to two of the many mutations in the active site that destroy catalytic activity [21]. The fruit fly Drosophila melanogaster possesses two isoforms [42], one of which is positively regulated by calmodulin [45]. The nematode Caenorhabditis elegans posesses one ITPK gene, which is not regulated by CaM and shows diversity generated by alternative splicing at the 5 0 end [39] possess one ITPK gene, which exhibits alternative splicing at the N-terminus [39] (Fig 2b, bottom).…”

“…The two ITPK isoforms in fruit flies can be distinguished by their differential regulation by Ca 2? /CaM [45]. Like the worm ITPK, ITPKa is not regulated by CaM (and lacks a CaM-binding domain).…”

Headpiece Domain of Dematin Regulates Calcium Mobilization and Signaling in Platelets

“…Like dematin, IP3KB is ubiquitously expressed and was recently shown to be enriched within the cortical actin filaments (53). It has been suggested that the localization of IP3KB may offer a means to regulate IP 3 levels in the cells (36,54). However, the precise mechanism of IP3KB localization at the membrane sites via cortical actin structures is not known (53).…”