Epigallocatechin gallate (EGCG) inhibits type II phosphatidylinositol 4-kinases: a key component in pathways of phosphoinositide turnover

Research progress on phosphatidylinositol 4-kinase inhibitors

Phosphatidylinositol 4-kinases (PI4Ks) could phosphorylate phosphatidylinositol (PI) to produce phosphatidylinositol 4-phosphate (PI4P) and maintain its metabolic balance and location. PI4P, the most abundant monophosphate inositol in eukaryotic cells, is a precursor of higher phosphoinositols and an essential substrate for the PLC/PKC and PI3K/Akt signaling pathways. PI4Ks regulate vesicle transport, signal transduction, cytokinesis, and cell unity, and are involved in various physiological and pathological processes, including infection and growth of parasites such as Plasmodium and Cryptosporidium, replication and survival of RNA viruses, and the development of tumors and nervous system diseases. The development of novel drugs targeting PI4Ks and PI4P has been the focus of the research and clinical application of drugs, especially in recent years. In particular, PI4K inhibitors have made great progress in the treatment of malaria and cryptosporidiosis. We describe the biological characteristics of PI4Ks; summarize the physiological functions and effector proteins of PI4P; and analyze the structural basis of selective PI4K inhibitors for the treatment of human diseases in this review. Herein, this review mainly summarizes the developments in the structure and enzyme activity of PI4K inhibitors.

Purine analogs as phosphatidylinositol 4-kinase IIIβ inhibitors

We report on an extensive structure–activity relationship study of novel PI4K IIIβ inhibitors. The purine derivative of the potent screening hit T-00127-HEV1 has served as a suitable starting point for a thorough investigation of positions 8 and 2. While position 8 of the purine scaffold can only bear a small substituent to maintain the inhibitory activity, position 2 is opened for extensive modification and can accommodate even substituted phenyl rings without the loss of PI4K IIIβ inhibitory activity. These empirical observations nicely correlate with the results of our docking study, which suggests that position 2 directs towards solution and can provide the necessary space for the interaction with remote residues of the enzyme, whereas the cavity around position 8 is strictly limited. The obtained compounds have also been subjected to antiviral screening against a panel of (+)ssRNA viruses.

Expression patterns of immune-associated genes in external genital and perianal warts treated with sinecatechins

The role of human papillomavirus (HPV) in human disease includes external genital and perianal warts (EGW), with some HPV genotypes having oncogenic potential (i.e., HPV-16 and -18). While green-tea extracts have antitumor and antiproliferative effects in vitro, the mechanism of action of sinecatechins in the treatment of EGW is not well understood. To investigate the role of immune-regulated genes further, an open-label, single institution, prospective study was conducted enrolling patients with clinically diagnosed EGW. Thirty subjects were enrolled, and 18 completed the trial. All patients applied sinecatechins 15% ointment to target lesions in the study. RNA expression microarrays were obtained from treated EGW lesions and analyzed for differential gene expression of immune-regulated genes. HPV types were analyzed and, based on copy number, were stratified into virological responders (VR) or nonresponders (VNR). Gene expression analysis of RNA samples was performed using TaqMan arrays for human T cell receptor and CD3 complex (TCR), Toll-like receptors (TLR) pathway, interferon (IFN) pathway, and antigen processing pathway. A total of 256 genes were analyzed across the four arrays. Genes that were significantly regulated between VRs and VNRs were CREB3L4, HIST1H3A, HIST1H3H, IFNA1, IFNA4, IFNA5, IFNA6, IFNA8, IFNA14, IFNG, IFNAR1, IL6, IRF9, MAPK4, MAPK5, MAPK14, NET1, and PIK3C2A in the IFN array. In the TCR array, HLA_B was found to be statistically significantly upregulated in both the VR and VNR groups; concomitantly, CD8A was found to be statistically significantly downregulated only in VRs. In the TLR array, only LBP and MAPK8 were found to be differentially regulated. In the antigen processing array, HLA-A, HLA-C, HLA-DMA, HLA-DMB, HLA-F, PSMA5, PSMB8, and PSMB9 were differentially downregulated. Based on these findings, it was determined that sinecatechins treatment modulates and downregulates genes involved in the pro-inflammatory response to HPV infection.

Type II PtdIns 4-kinase β associates with CD4-p56lck complex and is involved in CD4 receptor signaling

Type II phosphatidylinositol (PtdIns) 4-kinases are involved in the synthesis of PtdIns 4-phosphates and modulate various cell functions like, intracellular signaling, cytoskeletal rearrangements, vesicular trafficking, and pathogen invasion. In CD3 receptor activated T cells, a type II PtdIns 4-kinase β is recruited to CD3 receptor zeta and plays a role in intracellular calcium release and probably in actin cytoskeleton reorganization. T cell receptor mediated activation is supported by CD4 receptor. The role of type II PtdIns 4-kinase β in CD4 receptor-mediated signaling was addressed in the present manuscript. Crosslinking of CD4 receptors with monoclonal antibodies showed an increase in CD4-associated PtdIns 4-kinase activity and requires p56(lck) activity. Biochemical characterization suggests that it belongs to type II PtdIns 4-kinase family. shRNA mediated knockdown of type II PtdIns 4-kinase β showed abrogation of CD4 receptor induced intracellular calcium release. These results suggest that type II PtdIns 4-kinase β plays an integral part in CD4 receptor-mediated signaling.

Type II phosphatidylinositol 4-kinases interact with FcεRIγ subunit in RBL-2H3 cells

Ligation of high-affinity IgE receptor I (FcεRI) on RBL-2H3 cells leads to recruitment of FcεRI and type II phosphatidylinositol 4-kinases (PtdIns 4-kinases) into lipid rafts. Lipid raft integrity is required for the activation of type II PtdIns 4-kinases and signal transduction through FcεRIγ during RBL-2H3 cell activation. However, the molecular mechanism by which PtdIns 4-kinases are coupled to FcεRI signaling is elusive. Here, we report association of type II PtdIns 4-kinase activity with FcεRIγ subunit in anti-FcεRIγ immunoprecipitates. FcεRIγ-associated PtdIns 4-kinase activity increases threefold upon FcεRI ligation in anti-FcεRIγ immunoprecipitates. Biochemical characterization of PtdIns 4-kinase activity associated with FcεRIγ reveals that it is a type II PtdIns 4-kinases. Canonical tyrosine residues mutation in FcεRIγ ITAM (Y65 and Y76) reveals that these two tyrosine residues in γ subunit are required for its interaction with type II PtdIns 4-kinases.

Fyn kinase regulates type II PtdIns 4-kinases in RBL 2H3 cells

Type II phosphatidylinositol 4-kinases are implicated in FcεRI-mediated signaling cascades leading to release of inflammatory molecules. Cross-linking of FcεRI on RBL 2H3 cells results in protein tyrosine phosphorylation and activation of type II PtdIns 4-kinase activity. Protein tyrosine kinase(s) that phosphorylate type II PtdIns 4-kinase(s) in RBL 2H3 cells remains elusive and is being addressed in this manuscript. Anti-Fyn kinase antibodies co-immunoprecipitated type II PtdIns 4-kinase activity from FcεRI cross-linked RBL 2H3 cells. In reciprocal assays, His-tagged types II PtdIns 4-kinases were shown to pull down Fyn kinase. Further, anti-Fyn immunoprecipitates were shown to phosphorylate type II PtdIns 4-kinase α and β in in vitro assays. Pull down studies with GST-Fyn-SH2 and GST-Fyn-SH3 domains showed that type II PtdIns 4-kinases associate with Fyn-SH2 domain. Knockdown of Fyn kinase in RBL 2H3 cells abrogated activation of type II PtdIns 4-kinase activity in response to FcεRI cross-linking and type II PtdIns 4-kinase activity in anti-phosphotyrosine immunoprecipitates. Knockdown of Fyn kinase was also strongly correlated with a reduction in β-hexosaminidase release in response to FcεRI cross-linking. These results suggest that type II PtdIns 4-kinases act downstream of Fyn kinase in FcεRI signaling cascades and are regulated by Fyn kinase.

Mammalian phosphatidylinositol 4-kinases as modulators of membrane trafficking and lipid signaling networks

The four mammalian phosphatidylinositol 4-kinases modulate inter-organelle lipid trafficking, phosphoinositide signalling and intracellular vesicle trafficking. In addition to catalytic domains required for the synthesis of PI4P, the phosphatidylinositol 4-kinases also contain isoform-specific structural motifs that mediate interactions with proteins such as AP-3 and the E3 ubiquitin ligase Itch, and such structural differences determine isoform-specific roles in membrane trafficking. Moreover, different permutations of phosphatidylinositol 4-kinase isozymes may be required for a single cellular function such as occurs during distinct stages of GPCR signalling and in Golgi to lysosome trafficking. Phosphatidylinositol 4-kinases have recently been implicated in human disease. Emerging paradigms include increased phosphatidylinositol 4-kinase expression in some cancers, impaired functioning associated with neurological pathologies, the subversion of PI4P trafficking functions in bacterial infection and the activation of lipid kinase activity in viral disease. We discuss how the diverse and sometimes overlapping functions of the phosphatidylinositol 4-kinases present challenges for the design of isoform-specific inhibitors in a therapeutic context.