Inositol phosphates are a large and diverse family of signalling molecules. While genetic studies have discovered important functions for them, the biochemistry behind these roles is often not fully characterized. A key obstacle in inositol phosphate research in mammalian cells has been the lack of straightforward techniques for their purification and analysis. Here we describe the ability of titanium dioxide (TiO2) beads to bind inositol phosphates. This discovery allowed the development of a new purification protocol that, coupled with gel analysis, permitted easy identification and quantification of InsP6 (phytate), its pyrophosphate derivatives InsP7 and InsP8, and the nucleotides ATP and GTP from cell or tissue extracts. Using this approach, InsP6, InsP7 and InsP8 were visualized in Dictyostelium extracts and a variety of mammalian cell lines and tissues, and the effects of metabolic perturbation on these were explored. TiO2 bead purification also enabled us to quantify InsP6 in human plasma and urine, which led to two distinct but related observations. Firstly, there is an active InsP6 phosphatase in human plasma, and secondly, InsP6 is undetectable in either fluid. These observations seriously question reports that InsP6 is present in human biofluids and the advisability of using InsP6 as a dietary supplement.

The family of phosphatidylinositol 5-phosphate 4-kinases (PI5P4Ks) is emerging from a comparative backwater in inositide signalling into the mainstream, as is their substrate, phosphatidylinositol 5-phosphate (PI5P). Here we review some of the key questions about the PI5P4Ks, their localisation, interaction, and regulation and also we summarise our current understanding of how PI5P is synthesised and what its cellular functions might be. Finally, some of the evidence for the involvement of PI5P4Ks in pathology is discussed.

Phosphatidylinositol 5-phosphate 4-kinases (PI5P4Ks) are enigmatic lipid kinases with physiological functions that are incompletely understood, not the least because genetic deletion and cell transfection have led to contradictory data. Here, we used the genetic tractability of DT40 cells to create cell lines in which endogenous PI5P4Kα was removed, either stably by genetic deletion or transiently (within 1 h) by tagging the endogenous protein genomically with the auxin degron. In both cases, removal impacted Akt phosphorylation, and by leaving one PI5P4Kα allele present but mutating it to be kinase-dead or have PI4P 5-kinase activity, we show that all of the effects on Akt phosphorylation were dependent on the ability of PI5P4Kα to synthesize phosphatidylinositol (4,5)-bisphosphate [PI(4,5) P 2 ] rather than to remove PI5P. Although stable removal of PI5P4Kα resulted in a pronounced decrease in Akt phosphorylation at Thr308 and Ser473, in part because of reduced plasma membrane PIP 3 , its acute removal led to an increase in Akt phosphorylation only at Ser473. This process invokes activation primarily of mammalian target of rapamycin complex 2 (mTORC2), which was confirmed by increased phosphorylation of other mTORC2 substrates. These findings establish PI5P4Kα as a kinase that synthesizes a physiologically relevant pool of PI(4,5)P 2 and as a regulator of mTORC2, and show a phenomenon similar to the "butterfly effect" described for phosphatidylinositol 3-kinase Iα [Hart JR, et al. (2015) Proc Natl Acad Sci USA 112(4):1131-1136], whereby through apparently the same underlying mechanism, the removal of a protein's activity from a cell can have widely divergent effects depending on the time course of that removal.phosphatidylinositol 5-phosphate 4-kinase | phosphatidylinositol 5-phosphate | phosphatidylinositol (4,5)-bisphosphate | Akt | mTOR T he phosphatidylinositol 5-phosphate 4-kinases (PI5P4Ks) are an enigmatic family of three (PI5P4Kα, -β, and -γ) with cellular functions that remain poorly understood (1-3). In general, their principal activity is believed to be to remove and thus, regulate the levels of their substrate phosphatidylinositol 5-phosphate (PI5P). Phenotypes from knockout mice have highlighted that PI5P4Ks have important roles to play in physiology and pathology, including links between PI5P4Ks and the Akt signaling pathway, and other studies have pointed to roles in the generation of cancer (3). A number of key questions, however, remain unanswered. Knocking proteins out or down (by RNAi) is a long-term strategy that may lead to indirect changes, such as, for example, those highlighted in the recent study by Hart et al. (4) concerning the indirect long-term consequences of a point mutation in phosphatidylinositol 3-kinase-α (PI3Kα). Another issue still unresolved for PI5P4Ks is whether removal of PI5P is their only function or whether their ability to synthesize phosphatidylinositol (4,5)-bisphosphate [PI(4,5)P 2 ] may also be important (5, 6).We have recently used the high homologous recombi...

Background: Treatment free remission (TFR) is now a realistic goal of treatment for CML. Approximately 50% of patients (pts) who discontinue tyrosine kinase inhibitors (TKI) after achieving deep molecular responses (DMR) are able to remain off treatment without losing major molecular response (MR3). Data from the largest available TKI stopping trial, EURO-SKI, showed that the most important variable associated with prolonged TFR is the duration of DMR. However, to date no clinical tool exists to guide clinicians and patients in predicting the likelihood of success of TFR attempt. Methods: We performed a retrospective analysis of clinical data from 172 pts with CML in whom treatment was discontinued in 6 hospital centres in order to identify factors associated with TFR. Data analysis started with a training set (TS) derived from pts treated at a single centre which was then validated on a validation set (VS) derived from the 5 other centres. Eligibility criteria included diagnosis of CML in chronic phase, a minimum duration of treatment with TKI of 3 years and discontinuation of TKI after achievement of confirmed ≥MR4. Patients diagnosed in accelerated phase CML and/or who underwent prior allogeneic stem cell transplant were excluded. Kaplan-Meier method was used for univariate analysis, with log-rank test for group comparison. A Cox proportional hazards model was employed with the purpose of choosing the most influential prognostic predictors on the probability of TFR in MR3 (pTFR3) and TFR in MR4 (pTFR4) on the TS. Variables with a p-value ≤0.1 entered in the multivariate analysis (MVA). Proportional hazard assumptions were tested for the final model. A prognostic TFR score was built from the combination of the predictors identified by the Cox model and validated on the VS. Results: The TS included 118 pts, while the VS 54 pts (Table 1). In the TS, the 2-year pTFR3 was 67.4% (95% CI 66.5-68.3%) and the 2-y pTFR4 was 56.8% (95% CI, 55.9-57.7%). The median time to MR3 loss was 3.8 months (range 1-31), and for MR4 loss was 3.2 months (range 0.8-24.5). After loss of MR4, the 1-year probability of MR3 loss was 77% (95% CI, 70.8-73.2%). However, 10 pts (8.5%) resumed TKI after MR4 loss and were not evaluable for time to loss of MR3. In univariate analysis, the variables most significantly associated with higher pTFR3 and pTFR4 were age at diagnosis >40 years (p=0.029 and p=0.002), absence of previous TKI resistance (p=0.003 and p= 0.068), longer duration of MR4 (p=0.003 and p<0.0001) and ≥MR4.5 at stopping (p=0.026 and p= 0.004). Variables entered into the MVA were age at diagnosis, BCR-ABL1 transcript type, Sokal score, dose of TKI at stopping, previous TKI resistance, duration of MR4 at stopping, depth of response at stopping. The Cox model suggested the inclusion of the following variables, for both pTFR3 and pTFR4: duration of MR4, previous TKI resistance, age at diagnosis and transcript type. Using these variables we developed a predictive score (Figure 1a), which was able to identify a good risk population (2-y pTFR3 81.8%, 2-y pTFR4 80%); intermediate (66.6% and 61.5%) and poor risk (42.3% and 30.8%) (overall log-rank test p=0.00092 and p <0.0001 for pTFR3 and pTFR4, respectively)(Figure 1b). The score was tested on the VS of 54 pts. In this population, the overall 2-y pTFR3 and pTFR4 were 61.3% (95% CI, 59.8-62.7%) and 42.6% (95% CI, 41.2-44%), respectively. Despite the small sample size, our score was still able to predict different 2-y TFR probabilities (Figure 1c) in the three risk groups. Of the pts who lost MR3 in the TS (n=39), 37 regained ≥MR3 after resuming TKI; 1 patient did not restart TKI and died from an unrelated cause; 1 patient had only 2 months follow-up after TKI resumption. In the VS, 15 of 21 pts losing MR3 achieved ≥MR3 again after TKI resumption; 3 pts had a follow-up <3 months after MR3 loss, 2 were lost to follow-up and 1 had not yet re-gained MR3 6 months after restarting TKI. In both cohorts no case of disease progression had occurred at last follow-up. Conclusions:This retrospective study confirms the safety of TFR attempt and identifies variables strongly associated with prolonged TFR. The resulting predictive score presented here, if validated in larger patient cohorts, might help in tailoring the choice of TKI discontinuation to the individual patient. Also, most pts who lose MR4 inevitably lose MR3, suggesting the importance of a more intense monitoring strategy in this subgroup. Disclosures Claudiani: Pfizer: Honoraria; Incyte: Honoraria. Byrne:Ariad/Incyte: Honoraria, Speakers Bureau. Rothwell:Incyte: Speakers Bureau; Novartis: Honoraria, Other: advisory board; Pfizer: Speakers Bureau. Copland:Incyte: Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Astellas: Honoraria, Speakers Bureau; Cyclacel: Research Funding; Bristol-Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Clark:Ariad/Incyte: Honoraria; Pfizer: Honoraria, Research Funding; BMS: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. Milojkovic:BMS: Honoraria, Speakers Bureau; Pfizer: Honoraria, Speakers Bureau; Incyte: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau. Apperley:Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Incyte: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Bristol Myers Squibb: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau.