Phosphatidylinositol-4-phosphate kinase from rat brain. Activation by polyamines and inhibition by phosphatidylinositol 4,5-bisphosphate

Abstract

Phosphatidylinositol-4-phosphate (PtdIns-P) kinase was purified approximately 30-fold from rat brain cytosol. No contaminating activity of PtdIns kinase or of phosphomonoesterase and phospholipase C using PtdIns-P or PtdIns-P2 as substrate could be detected in the enzyme preparation. The PtdIns-P kinase activity was severalfold higher when PtdIns-PIPtdEtn vesicles rather than PtdIns-P alone were used as substrate. This might be due to increased accessibility of the enzyme for the vesicular substrate, further indicated by the lower activity obtained when PtdCho or PtdIns, phospholipids with bulky head groups, was also present in the vesicles. The product PtdIns-P2 was a competitive inhibitor with respect to PtdIns-P and 50% inhibition of enzyme activity was observed at the same product concentration regardless of whether the substrate-product mixture was presented in vesicular or micellar form, or the substrate and product were added in separate vesicles.The polyamines spermine and spennidine enhanced PtdIns-P kinase activity severalfold. Spermine also caused a shift in the MgClz saturation curve from sigmoidal to hyperbolic, lowering the MgZ + concentration required for optimum kinase activity to the physiological range. Myelin basic protein enhanced the enzyme activity when PtdIns-PIPtdEtn vesicles were used as substrate, whereas it was inhibitory when PtdIns-P was added alone. The possible role of polyamines and the product PtdIns-P2 in the regulation of PtdIns-P kinase activity is discussed.According to recent hypotheses, PtdIns-Pz constitutes the substrate for a receptor-controlled phospholipase C reaction which generates diacylglycerol and inositol trisphosphate. These products then act as intracellular messengers for the activation of a protein kinase (kinase C) and for the mobilization of intracellular CaZ+, respectively [I, 21. In addition, PtdIns-P2 in the plasma membrane might play other functional roles, such as in the regulation of actin polymerization [3].

Integrin α9β1 in airway smooth muscle suppresses exaggerated airway narrowing

“…The 2 best-characterized cytosolic effects of spermidine and spermine that are not shared by putrescine are inward rectification of inwardly rectifying potassium (Kir) channels (49,50) and dramatic enhancement of PIP5K1γ activity (31,51). We have previously shown that integrin α 9 β 1 -mediated enhancement of cell migration is caused by altered rectification of a specific Kir channel, Kir4.2 (25), and have found that Kir4.2 is also the major Kir channel expressed in airway smooth muscle (our unpublished observations).…”

Influence of polyamines on membrane functions

“…The reasons for this discrepancy are unknown, but here again caution should be exercised since several types of this kinase can occur in a tissue (see, e.g., Endemann et al, 1987). The formation of Ptdlns(4,5)P2, catalysed by the Ptdlns(4)P 5-kinase, is also activated several-fold by polyamines in rat brain or liver plasma membranes (Lundberg et al, 1986(Lundberg et al, , 1987. Interestingly, work with a partially purified rat brain kinase indicated that maximal stimulation by spermine was observed at the approximate intracellular concentration of Mg2+ (Lundberg et al, 1986;Cochet & Chambaz, 1986).…”

“…The formation of Ptdlns(4,5)P2, catalysed by the Ptdlns(4)P 5-kinase, is also activated several-fold by polyamines in rat brain or liver plasma membranes (Lundberg et al, 1986(Lundberg et al, , 1987. Interestingly, work with a partially purified rat brain kinase indicated that maximal stimulation by spermine was observed at the approximate intracellular concentration of Mg2+ (Lundberg et al, 1986;Cochet & Chambaz, 1986). The mechanisms of these polyamine effects and their relevance to situations in vivo remain to be established.…”

Excitatory Amino Acid‐Induced Phosphoinositide Turnover in Guinea Pig Cerebral Cortical Slices: Selective Enhancement by Spermine of the Response to DL‐1‐Aminocyclopentane‐ trans‐1, 3‐Dicarboxylate

“…In particular, polyamine inhibition of phosphoinositidase C activity has been described in permeabilized GH, cells (Wojcikiewicz and Fain, 1988), although other authors have observed enhancements of soluble phosphoinositidase activity by polyamines (Eichberg et al, 1981). Other reported effects of polyamines on the phosphoinositide system include the activation of MODULA TION OF PHOSPffOINOSITIDE HYDROLYSIS 611 phosphoinositide kinases, thereby increasing the radiolabelling of phosphatidylinositol mono-and bisphosphates (Lundberg et al, 1986;Vogel and Hoppe, 1986;Smith and Snyderman, 1988;Wojcikiewicz and Fain, 1988), the inhibition of phosphatidylinosi-to1 bisphosphate phosphatase (Smith and Snyderman, 1988), the activation of inositol 1,4,5-trisphosphate phosphatase (Seyfred et al, 1984), and the inhibition of phorbol ester activation of protein kinase C (Thams et al, 1986).…”