High impact information on PIKfyve

• GTP-bound recombinant Rho stimulated PIP 5-kinase activity, whereas GDP-Rho was much less potent and GTP-bound Rac was ineffective [1].
• In the rodent malaria agent P. yoelii yoelii, a multigene family codes for merozoite rhoptry proteins of relative molecular mass 235,000 (p235 proteins); these proteins are thought to determine the subset of erythrocytes that the parasites invade [2].
• We report here that this Rac1-dependent pathway involves recruitment of phosphoinositol-4-phosphate-5-kinase (PIP5K) to form phosphoinositol-4,5-bisphosphate (PIP2) at the phagocytic cup [3].
• This reduction in PIP2 occurred in spite of fact that PIP5K appeared to be recruited efficiently to the site of bacterial binding, indicating a role for Arf6 in activation of the kinase [3].
• A differential display screen for fat- and muscle-specific transcripts led to identification and cloning of the full-length cDNA of a novel mammalian 2,052-amino-acid protein (p235) from a mouse adipocyte cDNA library [4].

Biological context of PIKfyve

• The phosphorylation and activation of PIKfyve by PKB provides a novel signalling paradigm that may link plasma membrane-localised PtdIns(3,4,5)P3 signals via a protein kinase cascade to regulated PtdIns(3,5)P2 production, and thereby to the control of trafficking of other membrane cargos [5].
• We have isolated a novel mammalian PI kinase, p235, whose exact substrate specificity remained to be determined (Shisheva, A., Sbrissa, D., and Ikonomov, O. (1999) Mol. Cell. Biol. 19, 623-634) [6].
• By analyzing deletion mutants in a heterologous cell system, we determined that in addition to the predicted catalytic domain other regions of the molecule are critical for the p235 enzymatic activity [6].
• PIKfyve lipid kinase is a protein kinase: downregulation of 5'-phosphoinositide product formation by autophosphorylation [7].
• Up-regulation of PIKfyve protein expression was documented in the early stages of differentiation of cultured 3T3-L1 fibroblasts into adipocytes and a kinase-dead mutant, PIKfyveDeltaK, introduced into the preadipocyte stage profoundly delayed the hormone-induced adipogenesis [8].

Anatomical context of PIKfyve

• Here we report that recombinant p235 expressed in COS cells, like the authentic p235 in adipocytes, displays striking specificity for PtdIns over PI substrates and generates two products identified as PtdIns 5-P and PtdIns 3,5-P(2) by HPLC analyses [6].
• In preadipocytes (fibroblasts) PIP5K expression promoted actin polymerization on membrane-bound vesicles to form motile actin comets [9].
• Surprisingly, PtdIns 4-kinase was found exclusively in the peripheral nuclear matrix, whereas PtdIns(4)P 5-kinase was found to be associated to internal matrix structures [10].
• While the presence of a FYVE finger in PIKfyve predicts early endosome targeting, density gradient sedimentation, immunoadsorption, and fluorescence microscopy analyses segregated the LDM-associated PIKfyve from the membranes of the recycling endosomes and GLUT4 [11].
• PIKfyve's role in acute insulin action has been suggested on the basis of its association with the insulin stimulatable phosphatidylinositol-3-kinase and the ability of acute insulin to recruit and phosphorylate PIKfyve on intracellular membranes of 3T3-L1 adipocytes [8].

Associations of PIKfyve with chemical compounds

• In conclusion, the mouse p235 protein determines an important novel class of phosphoinositide kinases that seems to be targeted to specific intracellular loci by a Zn-dependent mechanism [4].
• In cell lysates, GTP gamma S stimulated PIP 5-kinase activity, and this effect was blocked by botulinum C3 exoenzyme, suggesting that Rho was responsible [1].
• Type I phosphatidylinositol 4-phosphate (PtdIns(4)P) 5-kinases (PIP5K) catalyze the synthesis of phosphatidylinositol 4, 5-bisphosphate, an essential lipid molecule in various cellular processes [12].
• ADP-ribosylation of Rho with C3 exoenzyme enhanced PIP5K binding by approximately eightfold, consistent with the ADP-ribosylated Rho functioning as a dominant negative inhibitor [13].
• Important properties of the p235 PI 5-kinase include high sensitivity to nonionic detergents and relative resistance to wortmannin and adenosine [6].

Other interactions of PIKfyve

• PIKfyve fluorescence staining largely coincided with trans-Golgi network/multivesicular body markers, indicating PIKfyve's role in the late endocytic/biosynthetic pathways [11].
• PIKfyve autophosphorylation or transphosphorylation engaged Ser but not Thr or Tyr residues [7].

Analytical, diagnostic and therapeutic context of PIKfyve

• Immunofluorescence microscopy analysis of endogenous p235 localization in 3T3-L1 adipocytes with affinity-purified anti-p235 antibodies documented a punctate peripheral pattern [4].
• HPLC resolution of monophosphoinositide products, generated by p235 immune complexes derived from lysates of 3T3-L1 adipocytes acutely stimulated with insulin, revealed essentially the same PtdIns 5-P levels as the corresponding p235 immune complexes of resting cells [6].
• However, RT-PCR analysis revealed that this similarity is not evident at the level of transcription, with the lethal line not transcribing a whole subset of its p235 gene repetoire [14].

References